Sbv annals vol 3 iss 2 jul dec 2014

SRI BALAJI VIDYAPEETH ACADEMY OF HEALTH PROFESSIONS EDUCATION AND ACADEMIC DEVELOPMENT

ANNALS OF SBV Volume 3 - Issue 2 July - dec 2014

Theme

Recent advances in dental biomaterialS

Annals of SBV Editorial Advisor

Editor-in-Chief

K R. Sethuraman

N.Ananthakrishnan Core Committee

K.A. Narayan

V.N. Mahalakshmi

M. Ravishankar

Karthiga Jayakumar

Seetesh Ghose

R. Jagan Mohan R. Pajanivel Issue Editor Usha Carounanidy

Editorial and Production Consultant A.N. Uma Technical Assistance George Fernandez Published, Produced and Distributed by

Sri Balaji Vidyapeeth

Editorial correspondence to Editorial and Production Consultant

Annals of SBV Sri Balaji Vidyapeeth

(Deemed to be University, Declared Under Section 3 of the UGC Act, 1956) Mahatma Gandhi Medical College & Research Institute Campus Pillaiyarkupam, Puduchery - 607 402 INDIA E.mail:annals@sbvu.ac.in | Phone : +91 413 2615449 to 58 | Fax : +91 413 2615457 Visit Annals of SBV Online at http://www.annals.sbvu.ac.in

Annals of SBV

Annals of SBV

Index 1.

From the Editor’s Desk

From the editor’s desk The Inseparable Duo- The Dentist and the Dental Biomaterials.

The Inseparable Duo- Dentist And Dental Biomaterials 05

- Carounanidy Usha

2.

Guided Tissue Regeneration Membranes

07

- Pratebha B, Jananni M, Arvind Raaj V, Karthikeyan I, Vineela KR, Saravanakumar R

3.

Platelet Rich Fibrin (PRF) in Periodontal Regeneration

14

- Jananni.M, Sivaramakrishnan.M, Pratebha. B, Vineela KR, Saravanakumar

4. Dental Biomaterials in Non-Operative Management of Dental Caries

21

- Carounanidy Usha

5.

The “Physics and Chemistry” Behind the “Biology” of Pulpal Regeneration

27

- Sathyanaryanan R

6.

Advances in Prosthodontic Biomaterials

31

- P. S. Manoharan

7.

Biomaterial Advances in Orthodontics

40

- AraniNandakumar, Dr. Anoop

8.

Nano Technology In Adhesive Restorative Biomaterials

46

- Carounanidy Usha, Bindu Meera John

Dr. Carounanidy Usha

In the days of yore, tooth extraction had been the main service of dental profession. Subsequent to extraction, replacement was done with artificial materials. Later, the non-extraction group, intending to preserve the tooth structure, resorted to partly restoring the diseased defects. These two trends can be considered as the nuclei to the evolution of dental material science. Wood, metal and ivory, under the creative skills of the dentist, transformed to dental prosthesis and restorations. Only in 1900s scientifically well-controlled experiments on the materials were started. Since then, this field has evolved as a separate science called as Dental material science.

Dental materials are expected to perform and sustain in the dynamic, harsh oral environment, may it be for a short span or long span of time. Therefore they are expected to possess appreciable physical, chemical and mechanical properties.Exhaustive efforts have always gone into making these attributes of the artificial materials as compatible as possible to the natural tooth structures.

Biocompatibility is yet another important attribute of the dental materials. They should not be irritating to the hard and the soft tissue structures in the oral cavity and should also resist degradation over a period time in the salivary environment. In order to emphasize the three dimensional role of the materials in satisfying the mechanical, physical and biological needs and also as they are intended to replace the natural biological tissues, they were rechristened as Dental Biomaterials, Biomaterial is any material, natural or man-made, that comprises whole or part of a living structure or biomedical device which performs, augments, or replaces a natural function. As they are designed

to mimic the natural tissues, they are called as biomimetic materials. Certain dental biomaterials possess antibacterial activity or regenerative capability, thus they are also called as bio active materials. These materials can also act as scaffolds for further tissue regeneration.

Dental biomaterials are used profusely in all fields of dentistry, such as, in the replacement of the lost tooth, in the correction of misaligned teeth and in the prevention and management of diseases affecting the tooth structure, the pulp and the periodontium.

Metals, polymers, ceramics and semiconductors form the group of synthetic dental biomaterials. Adhesive Dentistry is a major breakthrough in dentistry that has resulted in materials that bond and interact very intimately with the tooth structure. With advancements in this field, it became possible to introduce more bioactive materials Though bioactivity and biocompatibility of the synthetic biomaterials are receiving their due attention, attempts in identifying a natural biological material for replacement or restoration, a true dental biomaterial, is in a very infantile stage. The current thinking toward this idea, has begun with the decoding of the human genome and revelation of biological engineering of tissues. Stem cells from the dental tissues have opened up promising avenues in tissue engineering for dentistry; yet to go a long way to be translated into patient service.

However, evidence on the longevity of the new biomaterials is not robust enough. With the rapid advancements in the material technology and proliferation of the new materials, possibility for long term clinical trials is declining.

* Principal, Indira Gandhi Institute of Dental Sciences, Sri Balaji Vidyapeeth, Puducherry 607402, India.

Page 4

Ann. SBV, July - Dec 2014;3(2)

Ann. SBV, July - Dec 2014;3(2)

Page 5

Annals of SBV

A minimal survival rate of a restoration, for example, should be 10 years. Certain traditional restorations have shown a longevity of maximum 40 years. But the duration of clinical trial in the current literature for the newer materials is rarely for 10 years. The claims and promises of the trade that release the materials to the market with very short term trials or only laboratory studies should be recieved with caution. To critically evaluate a new introduction, it is imperative that a dental professional is equipped with the basic knowledge of the material science and also keep abreast with the latest developments.

It should be remebered that materials that can fail within a short span, will necessitate the replacement and such repeated replacments can

Annals of SBV

result in progressive loss of natural tooth structure.

Thus in the interest of the patient service, it is imperative that the profession does not overlook the long-term clinical performance and safety of these newer generation materials. Wisdom lies in expertly balancing the collateral damages of such revolutionary paradigm shifts.

A dentist is what the material he uses! This is one common science by which the multiple specilaities of dentistry are linked together. Therefore in this issue, attempts have been made to throw light on certain recent advances in dental biomaterials used in different fields such as periodontology, orthodontia, prosthodontia, restorative dentistry and endodontics.

Guided Tissue Regeneration Membrane Pratebha B, Jananni M, Arvind Raaj V, Karthikeyan I, Vineela KR, Saravanakumar R

Abstract

Periodontal therapy is aimed at achieving restoration of tissues lost due to periodontal disease. The ultimate goal is regeneration of cementum, periodontal ligament, and alveolar bone. There has been a constant effort to improve predictability by introduction of newer techniques. Guided tissue regeneration (GTR) is a promising method to achieve predictable periodontal regeneration. GTR allows and provides space for repopulation of certain cells on denuded root surface to enhance new attachment. One of the limitations of all regenerative procedures is low predictability but selection of cases and operator’s skill yields better regeneration. This review discusses the principle, material science and applications of GTR

Key Words : periodontal therapy, guided tissue regeneration, periodontal regeneration Introduction

Principle & Concept

Periodontitis causes substantial changes on affected tooth root surfaces. The normal cementum is rich in collagen with intrinsic and extrinsic fibers. Inflammation of periodontium brings about destruction of these fibers allowing apical proliferation of junctional epithelium. The cemental surface becomes hypermineralised; bacteria and endotoxins from plaque and calculus penetrate into cemental surface as far as dentin. [1]

The principle of GTR is to impede apical migration of epithelium by placing a membrane between the flap and root surface (preventing contact of the connective tissue with the root surface); cells derived from the periodontal membrane are induced on the root surface selectively and periodontal tissue is regenerated.

The surface changes on cementum during periodontitis renders the tooth root unsuitable for new connective tissue attachment and regeneration.

It is therefore imperative to alter the affected root surface to improve predictability of regenerative procedures. Procedures like scaling and root planing removes the altered cementum and provides a substrate that is more suitable for regenerative procedures. Root bio modification removes smear layer off root surfaces. Finally when GTR membranes are appropriately used in such an environment the predictability of new attachment and regeneration increases manifold. [2, 3]

The concept of guided tissue regeneration was first developed by Melcher in 1970. He postulated that four types of connective tissue compete for populating root surfaces: a) Lamina propria of the gingiva b) PDL c) Cementum d) Alveolar bone.

The cell phenotype which succeeds in repopulating the root surface determines the nature of periodontal regeneration. [4, 5] The barrier membrane creates a space and facilitates the proliferation of angiogenic & osteogenic cells from the marrow space into that defect without interferences by fibroblasts [6, 7]

Dr. B. Pratebha, Professor; Dr. M. Jananni, Senior lecturer; Dr. Arvind Raaj V, Post graduate; Dr.Karthikeyan I, Senior lecturer; Dr.K. R.Vineela, Reader; Dr. R. Saravanakumar, Prof. & Head; Dept of Periodontology, Indira Gandhi Intitute Dental Science, Sri Balaji Vidyapeeth, Puducherry 607402, India. .

Page 6

Ann. SBV, July - Dec 2014;3(2)

Ann. SBV, July - Dec 2014;3(2)

Page 7

Annals of SBV

Guided Tissue Regeneration Membrane

Definition [3]

Knitted nylon fabric

The 1996 World Workshop in periodontics defined GTR as “procedure attempting to regenerate lost periodontal structures through differential tissue responses�.

Another non resorbable membrane is Knitted nylon fabric which is mechanically bonded onto a semi permeable silicone membrane and coated with collagen peptides [11]

Classification [8]

Resorbable membrane

Gottlow (1993) classified the membranes into 3 groups

To overcome the need for surgery and risk of early membrane exposure, resorbable membranes were developed. Ideal resorbable membrane should have the following properties: Biocompatibility Biodegradable Biologically inert Non-reactive breakdown products Should not induce foreign body or allergic reactions Completely resorbable (resorption rate 100%)

1.First generation (Non resorbable)

a. Ethyl cellulose (Millipore filter)

b. Expanded Polytetra-fluoro ethylene (e PTFE) membrane (Goretex)

c. Nucleopore membrane

d. Rubber dam 2.Second Generation (resorbable)

a. Collagen membrane.

b. Polylactic acid membrane. (GUIDOR)

c. Vicrylmesh (polyglactin 910)

d. Cargile membrane.

e. Oxidized cellulose.

f. Hydrolysable polyester.

3.Third Generation

Bio resorbable matrices with growth factors.

Material Science Non-resorbable membrane The advantage of non- resorbable membrane is that they retain their build and form. But they require a second surgical procedure for its removal.

This adds to the tissue trauma during surgery and increases patient discomfort, cost and duration of therapy.

Polytetrafluoroethylene TEFLON is the first non-resorbable membrane made of polytetrafluoroethylene (ePTFE, Gore-Tex) manufactured when the polymer is subjected to high tensile stress, forming porous microstructure of solid nodes and fibrils [9]. PTFE is a fluorocarbon polymer with exceptional inertness and biocompatibility. It prevents tissue in growth and does not elicit foreign body response after implantation. Gore-Tex, ePTFE membrane consists of 2 parts (Fig 1) Page 8

Figure 1: Gore tex, ePTFE membrane a. An open microstructure collar which promotes connective tissue ingrowth, positioned coronally and prevents apical epithelial migration and ensures wound stability. This part of the membrane is 1mm thick & 90% porous. b. Other part is occlusive membrane 0.15 mm thick and 30% porous, serving as a space provides for regeneration, which possess structural ability and serves as a barrier towards the gingival flap [10] Modifications such as incorporation of titanium reinforcements (Fig 2) between the two layers leading to increased mechanical strength and space maintenance have been incorporated. Excellent space maintenance and cell occlusivity are the advantages.

The requirement of a second surgical technique to retrieve the membrane is the only disadvantage.

Figure 2:Titanium reinforcements Ann. SBV, July - Dec 2014;3(2)

combination of type I and II. Collagen is derived from calf skin, porcine dermis, tendon etc. Collagen membrane exhibit properties such as hemostasis, chemotaxis for fibroblasts, easy manipulation, and ability to augment tissue thickness [14,15] Examples of collagen membrane are Biogide which resorbs in 8 weeks and another membrane derived from rat tail collagen which resorbs in 4 weeks. (Fig 3) Studies have reported that both membranes resulted in periodontal regeneration.

Biomend (Fig 4,5) This is a semi occlusive membrane derived from Achilles tendon with a pore size of 0.004 microns and resorbs in 4-6 weeks[11] Avitene and collistat are examples of haemostatic collagen membrane derived from bovine corium . Histologic evaluation of the membranes for disintegration revealed that resorption was complete in 7days. Paroguide, another collagen

Synthetic aliphatic polyester and collagen derived from animal sources are two materials currently used to manufacture resorbable membranes.

The disintegration of resorbable membranes are inherently difficult to control and the process of resorption starts immediately after placement of membrane in the surgical site. The speed and extent of resorption varies from individual to individual especially for those membranes requiring enzymatic degradation [12, 13]

Natural Materials Collagen A predominant component of collagen membranes commercially available is Type I or sometimes a

Figure 3: Collagen Membrane Ann. SBV, July - Dec 2014;3(2)

Figure 4:Commercially available collagen membrane- Bio Mend

Figure 5: Trimming of membrane to adapt to defects Page 9

Annals of SBV

Guided Tissue Regeneration Membrane

membrane enriched with chondroitin sulphate was developed and this membrane showed limited value in GTR because of inadequate toughness and low space maintenance. Other natural products tested for GTR without success were Durameter, Oxidized cellulose & laminae bone [11]

Polylactic acid

Synthetic Materials Synthetic resorbable materials are usually organic aliphatic thermoplastic polymers. The materials most commonly used are Poly β- hydroxy acids, which include polyglycolic acid and their copolymers which on hydrolysis gives water and carbon dioxide.

Degradation time can be lengthened through the addition of lactides and glycols. Resolute (Fig 6) is an example of an occlusive membrane composed of glycolide-lactic copolymer and porous polyglycolide fiber. [11]

Figure 7(b): Vicryl periodontal mesh Periodontal Mesh. (Fig 7a,7b) It is reported that the membrane loses its structure after 2 weeks and complete resorption takes place in 4 or more weeks.

[16]

Figure 6: Resolute membrane Vicryl periodontal mesh Fibres of polyglactin 910, copolymers of glycolide & 1-lactide form a tightly woven mesh called Vicryl

Page 10

Defect morphology plays a major role in the healing response of guided tissue regeneration therapy in intrabony defects. It has been demonstrated that greater amounts of clinical attachment and bone can be gained in deeper defects.

Oxidized cellulose

In Furcation Defect [34,35]

Oxidized cellulose mesh is a commercially available resorbable haemostatic dressing that converts to a gelatinous mass upon incorporating blood. In vivo and in vitro studies have demonstrated that the material resorbed without harmful effects and may possess antibacterial properties. [21]

The risk of periodontitis progression in the furcation lesions increases with the severity of the furcation involvement [34] and therefore Grade I furcation have generally been well managed with routine periodontal surgical procedures aimed to thoroughly debride the lesion, reduce pockets and expose the furcation entrance for adequate plaque control. [35]

Natural eggshell membrane (ESM)

It is the only GTR membrane with Polylactic polymer manufactured chairside in flowable form and dissolved in N-methyl 2 – pyrolidone. [11]

ESM is a non-calcifying bi-layered membrane between the egg albumin and the inner surface of the eggshell. It is composed of water-insoluble interwoven protein fibbers that highly cross-linked by a large amount of disulphide bridges [22, 23]. It has been discovered to contain types I, V, and X collagens, osteopontin, sialoprotein, sialic acid, lysozyme, ovotransferrin, uronic acid, clusterin, etc [24, 25] . It exhibits antibacterial activity by decreasing the heat resistance of bacterial pathogens. This whole eggshell bio mineralization only takes less than 24 hours and is among the most rapid mineralization processes ever known. [25, 26, 27] Bone marrow stromal cells (BMSCs) could grow and proliferate well on natural ESM and then concluded that ESM had the potential to be used as a bone tissue engineering scaffold [28] These studies indicated that ESM has great biocompatibility and the ability to enhance the healing of damaged tissues, thus suggested that it can be a suitable candidate for GTR membrane [25, 26]

This membrane has three layers and is composed of Polylactic acid polymers to exclude epithelial cells and fibroblasts. It resorbs in 6-12 months and maintains its structure for 20 weeks Experimental mempol It is manufactured from polydioxanon (PDs), a dioxanon polymer and is bilayered. The first layer is completely impermeable covered with PDs loop 200Âľm long on the gingival side intended for integration with connective tissue [11]. It is a completely impermeable bilayered membrane on the gingival side and manufactured from polydioxanon polymer.

Cargile membrane

Figure 7 (a): Vicryl periodontal mesh

It is a biodegradable ester polymer & was originally used in orthopedic surgery in various configurations and Polylactic acid barriers inhibit epithelial migration. [18, 19] The Polylactic acid was designed to degrade in 3-4 months. By using a thinner membrane or a material with uniform and relatively low molecular weight, [20] degradation time of 1-2 months would be sufficient and achieved.

Atrisorb membrane

Epi-guide

It is derived from the cecum of ox and is processed and chromatized in a similar manner as that of suture material. It is supposed to resorb in 30-60 days. The Cargile membranes degraded within 4-8 weeks, adding support to the concept that critical events in new attachment formation occur during the first month of healing. [17] Ann. SBV, July - Dec 2014;3(2)

Applications of Guided Tissue Regeneration

Soluble Eggshell Membrane Proteins (SEP) This is manufactured from natural hen ESM by the process of reductive cleavage with aqueous mecaptoproionic acid in the presence of acetic acid.

Cell culture tests have reported biocompatibility comparable to that of collagen type 1 and superior to raw ESM [29, 30, 31]

Ann. SBV, July - Dec 2014;3(2)

In Intrabony Defects [32, 33]

Grade II furcations however require various regenerative such as open flap debridement, bone replacement grafts, coronally repositioned flaps and guided tissue regeneration barriers [34] [35] In Gingival Recessions [36, 37, 38, 39] The applicability of the treatment of gingival recessions with barrier membranes has also been clinically demonstrated in humans [40].

Two major surgical problems that are to be resolved to increase the possibility of obtaining satisfactory clinical results have been identified: 1. Difficulty in providing enough space for regeneration between the prominent root surface and the membrane 2. Difficulty in providing and maintaining an adequate biological coverage of the membrane with the flap in sites where the gingival tissues had receded [37] Ideally, the membrane should cover all of the denuded root surface up to the cementoenamel junction and maintain a space between its inner surface and the root surface. [37] Solutions to these problems have been proposed in a series of clinical trials and case reports with the aim of obtaining Page 11

Annals of SBV

the best results in terms of root coverage, clinical attachment gain and pocket depth reduction [37] For bone augmentation around implants [41, 42] GTR has been successfully used in the placemnt of dental implants in immediate extraction sockets sites and is also used for regeneration ofbony defects around the implants.

Future Trends in GTR To enhance regenerative properties while using GTR, numerous modifications have been attempted in the membrane properties. To ensure cell specificity during repopulation, adhesion molecules have been incorporated.

Recent advances include infusion of antibiotics in GTR membranes. This antibacterial nature of membrane is thought to be of great benefit during early wound healing phases and thus improve regenerative outcome. Addition of growth factors have also been investigated. These factors are expected to aid in cell differentiation and migration to the wound space. An example is development of combined polylactide and alginate membranes, with controlled TGF-� release.

Conclusion It is important to understand that Guided tissue regeneration is not a procedure aimed at treating periodontitis. It is rather a promising approach for attempting regeneration of tissues lost due to periodontitis and therefore appropriate periodontal treatment should precede before GTR is attempted.

The future of periodontal reconstruction depends on emergence of such techniques in tissue regeneration which when used diligently for appropriate periodontal defects will yield predictable results

References 1. Polson AM, Caton J. Factors influencing periodontal repair and regeneration. J Periodontol 1982;53:617-29.

2. Garrett JS, Crigger M, Egelberg J. Effects of citric acid on diseased root surfaces. J Periodont Res 1978;13:155-63.

3. Jack G.Caton and Gary Greenstein: Factors related to periodontal regeneration. Periodontology 2000 1993;1:9-15.

4. Laurell L, Gottlow J. Guided tissue regeneration update. Int Dent Journal 1998;48:386-98.

5. Darby I. Periodontal materials. Aust Dent J 2011;56:107-11.

6. Caffesse .G, Becker.W. Principles and techniques of guided

Page 12

Guided Tissue Regeneration Membrane tissue regeneration. Dent clin of N Am1991;35(3):479-93.

7. Listgarten MA. Periodontal probing: what does it mean? J Clin Periodontol 1980;7:165-76.

8. Minabe M: Critical review of the biologic rationale for guided tissue regeneration. J Periodontol 1991;62:171-79.

9. Hanel KC, McCabe C, Abbott WM, Fallon J, Megerman J. Current PTFE grafts: a biomechanical, scanning electron, and light microscopic evaluation. Ann Surg. 1982;195(4):456–63.

10. Daniel Buser. Guided bone regeneration :2nd edition :2-50 11. Aurer, A Jorgic–Srdjak K. Membranes for periodontal regeneration: Acta Stomat Goat 2005;107-112 12. Greenstein G, Jack G. Biodegradable barriers and guided tissue regeneration: Periodontol 2000 1993;1:36-45 13. Bunyaratavej P, Wang HL : Collagen Membranes . A review: J periodontal 2001;72:215-29 14. Pitaru S, Tal H, Soldinger, Noff M. Collagen membranes prevent apical migration of epithelium and support new connective tissue attachment during periodontal wound healing in dogs. J Periodontal Res 1989 ;24:247-53.

15. Pitaru S, Noff M, Grosskopf A. Heparin sulfate and fibronectin improve the capacity of collagen barriers to prevent apical migration of the junctional epithelium. J Periodontol 1991;628:598-601 16. Quinones CR, Caton JG, Polson AM. Evaluation of synthetic biodegradable barriers to facilitate guided tissue regeneration. J Periodont Res 1990;69:275 17. Card SJ, Caffesse RC, Smith B, Nasjleti C. New attachment following the use of a resorbable membrane in treating periodontitis in beagle dogs. Int J Periodont Restorative Dent 1989;9:59-69 18. Kulkarni RK, Pani KC, Neuman C, Leonard F. Polylactic acid for surgical implants. Arch Surg 1966;93:839-43.

19. Magnusson 1, Stenberg WV, Batich C, Egelberg J. Connective tissue repair in circumferential periodontal defects in dogs following use of a biodegradable membrane.

J Clin Periodontol 1990;17:243-48.

20. Magnusson I, Batich C, Collins BR. New attachment formation following controlled tissue regeneration using biodegradable membranes. J Periodontol 1988;59:1-7.

21. Galgut PN. Oxidized cellulose mesh used as a biodegradable barrier membrane in the technique of guided tissue regeneration. A case report. J Periodontol 1990;61:766-68.

22. Tsai WT, Yang JM, Lai CW, Cheng YH, Lin CC, Yeh CW. Characterization and adsorption properties of eggshells and eggshell membrane. Bioresour Technol 2006;97:488-93.

23. Nakano T, Ikawa NI, Ozimek L. Chemical composition of chicken eggshell and shell membranes. Poult Sci 2003;82:510-14.

24. Wong M, Hendrix MJ, Von der Mark K, Little C, Stern R. Collagen in the egg shell membranes of the hen. Dev Biol 1984;104:28-36 25. Jun Jia, Zhaoxia Guo, Jian Yu and Yuanyuan Duan :A New Candidate for Guided Tissue Regeneration: Biomimetic Eggshell Membrane. Irn J Med Hypotheses Ideas 2011;5:20 26. Zadik Y. Self-treatment of full-thickness traumatic lip laceration with chicken egg shell membrane. Wilderness Environ Med 2007;18:230-31.

27. Croll M, Croll L. Egg membrane for chemical injuries of the eye; a new adjuvant treatment. Am J Ophthalmol 1952;35:1585-96.

28. Zhao H, Zhang X, Li R, Xie H, Chen X. Experimental study on bone marrow mesenchymal stem cells cultured with Ann. SBV, July - Dec 2014;3(2)

eggshell membrane scaffold. Biomedical Engineering and Clinical Medicine 2006;10:206-9 29. Yi F, Yu J, Guo Z, Zhang L, Li Q. Natural Bioactive Material: A Preparation of Soluble Eggshell Membrane Protein.

Macromol Biosci 2003;3:234-37 30. Yi F, Guo ZX, Zhang LX, Yu J, Li Q. Soluble eggshell membrane protein: preparation, characterization and biocom-patibility. Biomaterials 2004;25:4591-99.

31. Jia J, Duan YY, Yu J, Lu JW. Preparation and immobilization of soluble eggshell membrane protein on the electrospun nanofibers to enhance cell adhesion and growth. J Biomed Mater Res A 2008;86:364-73.

32. Cortellini P, Carnevale G, Sanz M, Tonetti MS. Treatment of deep and shallow intrabony defects. A multicenter randomized controlled clinical trial. J Clin Periodontol 1998;25:981–87.

33. Cortellini P, Tonett MS. Focus on Intrabony Defects :Guided Tissue regeneration. Periodontal 2000 2000;22:104-32 34. Carnevale G, Pontoriero R, Lindhe J. Treatment of furcationinvolved teeth. In: Lindhe J, Clinical Periodontology and implant dentistry. Copenhagen: Munksgaard, 1997: 683– 710.

35. Sanz M, Giovannoli JL. Focus on furcation defects :Guided tissue regeneration. Periodontal 2000 2000;22:169-89.

Ann. SBV, July - Dec 2014;3(2)

36. Cortellini P, De Sanctis M, Pini Prato G, Baldi C, Clauser C: Guided tissue regeneration procedure using a fibrinfibronectin system in surgically induced recessions in dogs. Int J Periodontics Restorative Dent 1991; 11:151- 63.

37. Pin Prato G, Clauser C, Tonetti MS, Cortellini P. Guided tissue regeneration in Ginigival Recessions . Periodontol 2000 1996;11:49-57 38. Caffesse RG, Kon S, Castelli WA, Nasjleti C. Revascularisation following the lateral sliding flap procedure.

J Periodontol l984;55:352-58 39. Gottlow J , Nyman S, Karring T, Lindhe J. Treatment of localized gingival recessions with coronally displaced flaps and citric acid. An experimental study in the dog. J Clin Periodontol 1986;13:57-63.

40. Cortellini I, De Sanctis M, Pini Prato GP, Baldi C, Clauser C. Guided tissue regeneration procedure in the treatment of a bone dehiscence associated with a gingival recession: a case report. Int J Periodontics Restorative Dent 1991;11:472-79.

41. Celletti R, Davarpanah M, Etienne D, Pecora G, Tecucianu JF, Djukanovic D, Donath K. Guided tissue regeneration around dental implants in immediate extraction sockets: comparison of E-PTFE and a new titanium membrane. Int J Periodontics Restorative Dent. 1994;14(3):242-53.

42. Hermann JS, Buser D. Guided bone regeneration for dental implants Curr Opin Periodontol 1996;3:168-77.

Page 13

Annals of SBV

PLATELET RICH FIBRIN (PRF) IN PERIODONTAL REGENERATION

These proteins, initiate tissue healing responses, starting with the initiation, differentiation and chemotaxix of the desired cells, angiogenesis, formation of extracellular matrix and remodelling to the desired tissue. [10] Studies have also found a dose– response relationship between platelet concentration and the proliferation of human adult mesenchymal stem cells, fibroblasts, and production of collagen by them.[11]

PLATELET RICH FIBRIN (PRF) IN PERIODONTAL REGENERATION Jananni.M, Sivaramakrishnan.M, Pratebha. B, Vineela KR, Saravanakumar.R

Abstract

The ultimate goal of periodontal therapy is to restore the periodontal health by complete regeneration of the attachment apparatus. Though numerous methods of regeneration are available, researches are directed towards search for autologous materials considering the safety and availability issues. Among the various autologous material options, use of platelet concentrates have found to be more promising due to ease of procurement, handling and biochemical properties. This article throws limelight on the role of platelets on wound healing, preparation, mechanical properties, biochemical properties and clinical application of PRF in periodontal regeneration.

Key Words : periodontal regeneration, platelet rich fibrin, platelet rich plasma, tissue engineering

Introduction Periodontitis is an inflammatory disease of bacterial origin, affecting the periodontal tissues, resulting in loss of attachment apparatus.[1] The goal of periodontal therapy is to improve periodontal health and thereby to satisfy the patient’s esthetic and functional demands.To achieve this complete reestablishment of the lost attachment is necessary. [2] Histological analysis of periodontal new attachment procedures revealed that periodontal healing occurs with process of repair rather than regeneration.[3] Over the years numerous periodontal regenerative therapies have been developed from simple periodontal debridement to use of various biomaterials like guided tissue regeneration membranes, enamel matrix proteins and bone graft materials. Studies have shown that combination therapies resulted in better results as compared to stand-alone treatment modalities.[4,5] But the availability and cost are other important factors to be considered. Studies have also shown substantial variation in clinical predictability, degree of efficacy, and histological outcomes.

Use of autologous materials is considered a promising alternative. Autologous soft tissue grafts, buccal pad of fat,[6] periosteum,[7] and bone grafts have been tried, but again they were technique sensitive and required a second surgical site. So with the advent of platelet concentrates, the direction of periodontal regenerative therapies took a turn as they were simple to procure and easy to use.

Why Platelet Concentrates?

Platelet concentrates are blood derived products obtained by centrifugation of autologous blood and are widely used as surgical additive biomaterial to aid tissue healing. [8,9] The intracellular and extracellular events mediated by various signalling proteins during tissue healing are a complex cascade of events that still needs complete understanding. Platelets play a dominant role in every phase of healing of hard and soft tissues. Immediately following tissue injury, platelets are activated and start a sequence of events that result in formation of platelet plug and fibrin clot. This causes hemostasis and secretion of biologically active proteins.[9]

* Dr. M. Jananni, Senior lecturer; Dr. B. Pratebha, Professor; Dr.KR.Vineela, Reader; Dr. R. Saravana kumar, Prof. & Head, Dept of Periodontology; ** Dr. M. Sivaramakrishnan, Senior lecturer, Dept of Oral Pathology & Microbiology, Indira Gandhi Institute of Dental Sciences, Sri Balaji Vidyapeeth, Puducherry 607 402, India.

Page 14

Ann. SBV, July - Dec 2014;3(2)

Platelets contain numerous growth factors within α granules that has a strong influence on the wound healing events. Among them growth factors of periodontal importance are platelet-derived growth factor (PDGF), transforming growth factor (TGF β), platelet-derived angiogenesis factor (PDAF), vascular endothelial growth factor (VEGF), plateletderived endothelial growth factor (PDEGF), epidermal growth factor (EGF), insulin-like growth factor (IGF), osteocalcin, osteonectin, fibrinogen, vitronectin, fibronectin, and thrombospondin (TSP).

[12] The role of individual growth factors in stages of wound healing is summarized in Table 1.

Classification of Platelet Concentrates Dohan et al in 2009 classified platelet concentrates according to the composition of the centrifuged product. Based on this the platelet concentrates were classified into four categories [13] P-PRP - Pure Platelet Rich Plasma L-PRP - Leucocyte and Platelet Rich Plasma P-PRF - Pure Platelet Rich Fibrin L-PRF - Leucocyte and Platelet RichFibrin

Platelet Rich Pasma Platelet rich plasma (PRP) is considered as the first generation platelet concentrate preparation.

It is obtained by double step centrifugation of autologous blood thereby concentrating platelets in a gel. Hence they are also termed as ‘platelet pellet’ or ‘platelet gel’.[14] But the disadvantages associated with PRP is additional use of calcium chloride and bovine thrombin. The use of bovine thrombin is found to be associated with risk of development of coagulopathies.[15]

TABLE 1 – Role of individual growth factors in periodontal regeneration S.no

Growth factor growth

Role in wound healing

1

Transforming (TGF-β)

factor-β Stimulates proliferation and chemotaxix of osteoblasts thereby enhancing the woven bone formation.

2

Platelet-derived growth factor (PDGF

3

Vascular endothelial growth factor Initiates angiogenesis (VEGF)

Stimulates migration and proliferation of mesenchymal lineage cells

4

Insulin growth factor-1 (IGF-1)

Acts in synergy with the TGF. Stimulates osteoblast proliferation. Stimulates proliferation and chemotaxix of osteoblasts thereby enhancing the woven bone formation.

5

Fibroblast growth factor (FGF)

Enhances fibroblast proliferation, migration and differentiation.

6

Epidermal growth factor (EGF)

Stimulation of cell proliferation and extracellular matrix turnover

Ann. SBV, July - Dec 2014;3(2)

Page 15

Annals of SBV

PLATELET RICH FIBRIN (PRF) IN PERIODONTAL REGENERATION

Platelet Rich Fibrin It is a second generation autologous platelet concentrate biomaterial harvested from a simple blood sample. The main component is a fibrin matrix which incorporates leucocytes, platelets and growth factors in it. PRF was first developed in France in 2000 by Choukroun et al. This protocol proposed by him eliminated the risk associated with use of bovine thrombin.[16]

Preparation The armamentarium includes, blood collection kit, 10-mL dry glass test tube (without anticoagulant), and a table centrifuge. Blood sample must be collected aseptically from the patient by venipuncture and immediately transferred into the test tube and centrifuged at 3000 rpm or 10 minutes.

[17,18] One another protocol suggested to use 2700 rpm for 12 minutes and found similar results.[19]

Figure 1 b – The PRF clot (Schematic) [22] splits the components of blood and as a result three layers are formed: the RBC base layer, acellular plasma top layer and a PRF clot in the middle.(Fig 1a,b,c) The PRF clot basically is a strong fibrin mesh with a complex three dimensional structure in which concentrates the platelets and leucocytes.[20]

a diffuse way and a clot without any firm structure and a small amount of fibrin gel will result.

can act as an effective biologic glue to seal tissues due to greater rigidity.(Fig 3)[12]

Material Aspect

Biologic Properties

The fact that the polymerization occurs naturally is that main advantage of this material. Since no thrombin is added, the thrombin concentration action on the fibrinogen is almost physiologic. This determines the structure of the fibrin mesh. During the gelling process, the fibrin is assembled in two architecture - condensed tetramolecular or bilateral junctions and connected tri molecular or equilateral junctions.[18] In PRF process the centrifugation results in formation of equilateral junctions, result in weak thrombin concentration that ensures fine, flexible fibrin network. This fine mesh entraps cytokines and allows cell migration. Moreover, this structure will give great elasticity to the fibrin matrix.

[19] (Fig 2) But in PRP, the two step centrifugation

Unlike other fibrin adhesives the PRF results from progressive polymerization during centrifugation.

Thus it forms a three dimensional organization, coherent than natural clots. As polymerization progresses, the fibrin mesh becomes more intricate and traps the circulating platelets and intrinsic cytokines.(Fig 4)This ensures sustained release and action of cytokines throughout healing and remodeling. PRF promotes the production of phosphorylated extracellular signal-regulated protein kinase (p-ERK) and osteoprotegerin

Mechanism Absence of anticoagulant triggers platelet activation and fibrin polymerization immediately after it contacts the glass surface. Centrifugation Figure 2 – Model of condensed tetra molecular fibrin structure [22] results in formation of bilateral junctions result in thickened fibrin polymers, which are not favorable for cytokine enmeshment and cellular migration, but

Figure 4 – Platelets and cytokines trapped in fibrin mesh [22] (OPG). This inturn induces proliferation of the osteoblasts.[20] This upregulation of osteoprotegerin and alkaline phosphatise was also found to stimulate the differentiation of cells in human dental pulp.[21,22]

Effects on Tissue Healing Angiogenesis, immunity and epithelial cover are considered as the key elements of any tissue healing. The PRF and the PRF membrane is found to support all the three phenomena.

Figure 1 c – PRF clot

Figure 1 a – Schematic representation of the centrifugation strata. [22] Page 16

The success of this technique entirely depends on the speed of blood collection and transfer to the centrifuge. Quick handling is the only way to obtain a clinically usable PRF clot. Without the anticoagulant, the sample starts to coagulate immediately on contact with the glass. If delay in centrifugation occurs, the fibrin will polymerize in Ann. SBV, July - Dec 2014;3(2)

Angiogenesis

Figure 3 - Model of condensed bilateral fibrin structure [22]

Ann. SBV, July - Dec 2014;3(2)

The intricate fibrin mesh entraps the platelets which eventually release growth factors that promote angiogenesis like fibroblast growth factorbasic (FGFb), vascular endothelial growth factor (VEGF), angiopointein and platelet-derived growth factor (PDGF). Moreover, the fibrin in the clot regulates Page 17

Annals of SBV

PLATELET RICH FIBRIN (PRF) IN PERIODONTAL REGENERATION

Disadvantages

Figure 5 (a) PRF clot mixed with bone graft, (b) – PRF membrane expression of integrin by endothelium that helps the cells to bind to fibronectin and vitronectin.[22,23,24, 25] Immune Modulation: Migration of neutrophils and monocytes are regulated by fibronectin the chemical and physical properties of fibrin and by chemotactic agents trapped in its meshes.[26] The fibrin mesh and the entrapped fibrinogen degradation products increase the expression of CD18. This in turn stimulate the migration of neutrophils.[27] FDP in mesh also modulates phogocytosis and enzymatic degradation of neutrophils [28].

Epithelial Cover: Growth factors like PDGF, TGF b, and epithelial growth factor, modulate the expression of receptors and integrins that aid in epithelial migration. Fibrin matrix acts as a guide for epithelial migration to cover the injured tissue.[29]

PRF And Tissue Engineering Tissue engineering triad includes Scaffold, Stem cells and Growth factors. In the past few years, many researches have been conducted to use PRF for tissue engineering.

Gassling et al.[30] in his study concluded that PRF was superior to collagen when used as scaffold in tissue engineering. Moreover, PRF traps the circulating stem cells and also aids in their differentiation due to concentration of growth factors. PDGF acts as chemo attractant for fibroblasts that’s aid regeneration.[31,32] In addition its immune functions, like regulation and activation of cytokines like IL-1, IL-4, IL-6 and TNF-β mediates tissue healing and regeneration.[18] Page 18

PRF in Periodontal Regenration The obtained PRF clot can be mixed with the bone graft material and used for regeneration or the clot can be squeezed to form a membrane, which can be adapted over the root or bony surface. (Figure 5a, b) For root coverage: In a randomized controlled trial conducted

by Janovich S et al, 2012 the results showed that PRF and CTG procedures were equally effective in treatment of gingival recessions.[33] PRF group showed enhanced wound healing and decreased postoperative discomfort. Martinez Zapata et al in his systematic review concluded that use of autologous PRF improved gingival recession.[34] For regeneration in intrabony defects: A randomized clinical trial was done bySharma et al.[35] for the treatment of three walled intrabony defects and they found that addition of PRF to the bone graft material resulted in greater bone fill than the controls. In another study by Thoratet al.[36]it was concluded that PRF with bone grafts resulted in more positive results than open flap debridement alone for intrabony defects. Chang et al,[37] found better radiographic bone fill following six months of treatment in the sites with bone graft and PRF as compared to bone grafts alone.

PRF in furcation defects: Sharma et al studied the effects of PRF in grade II furcation defects and concluded that PRF with bone grafts are a better treatment option as compared to bone grafts alone.[38] Ann. SBV, July - Dec 2014;3(2)

The main disadvantage is the very little amount of material obtained which might be insufficient for periodontal regeneration. Another disadvantage is that it cannot be stored and used at a later point of time since it has to be used immediately after preparation. Storage also results in risk of bacterial contamination of the membrane. Delay in use will result in alteration of the structural and biological properties. Dehydration of the membrane will result in membrane shrinkage, decrease the concentration of growth factor and adversely affect the leukocyte viability.[9]

Conclusion With these fundamental considerations, PRF is considered as a favorable biomaterial that can protect and glue the wound surface and accelerate tissue healing. Moreover the entrapment of leucocytes and the growth factors promotes true regeneration.

References 1. Alpiste FM, Buitrago P, de GradoCP, FuenmayorFV, Gil FJ. Periodontal regeneration in clinical practice. Med Oral Patol Oral Cir Bucal 2006;11:e382-92.

2. Zander HA, Polson AH, Heijl LC. Goals of Periodontal Therapy. Journal of Periodontology 1976; 47: 261-66.

3. Listgarten MA, Rosenberg MM. Histological study of repair following new attachment procedures in human periodontal lesions.J Periodontol. 1979; 50:333-44.

4. Chen TH, Tu YK, Yen CC, Lu HK. A systematic review and meta-analysis of guided tissue regeneration/osseous grafting for the treatment of Class II furcation defects. Journal of dental sciences 2013; 8: 209-24.

5. Tu YK, Needleman I, Chambrone L, Lu HK, Faggion CM Jr. A Bayesian network meta-analysis on comparisons of enamel matrix derivatives, guided tissue regeneration and their combination therapies. J ClinPeriodontol. 2012; 39:303-14.

6. Singh J, Prasad K, Lalitha RM, Ranganath K. Buccal pad of fat and its applications in oral and maxillofacial surgery: A review of published literature (February) 2004 to ( July) 2009. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2010;110:698–705.

7. Soltan M, Smiler D, Soltan C. The inverted periosteal flap: a source of stem cells enhancing bone regeneration. Implant Dent. 2009;18:373-9.

8. Eppley BL, Pietrzak WS, Blanton M. Platelet-rich plasma: a review of biology and applications in plastic surgery.

PlastReconstr Surg. 2006;118:147e-159e.

9. Anitua, E, Andia, I, Ardanza, B, et al. Autologous platelets as a source of proteins for healing and tissue regeneration.

Thromb. Haemost. 2004;91(4):12-18.

10. Desai CB, Mahindra UR, Kini YK, Bakshi MK. Use of Platelet-Rich Fibrin over Skin Wounds: Modified Secondary Ann. SBV, July - Dec 2014;3(2)

Intention Healing. Journal of Cutaneous and Aesthetic Surgery 2013;6:35-37.

11. Civinini R, Macera A, Nistri L, Redl B, Innocenti M. The use of autologous blood-derived growth factors in bone regeneration. Clinical Cases in Mineral and Bone Metabolism 2011;8:25-31.

12. Khiste SV, Tari RN. Platelet-Rich Fibrin as a Biofuel for Tissue Regeneration. ISRN Biomaterials 2013; 2: 1-6.

13. Dohan E, EhrenfestM, Rasmusson L, Albrektsson T. Classification of platelet concentrates: from pure platelet rich plasma (P-PRP) to leukocyte and platelet - rich fibrin (LPRF).Trends Biotechnical 2009; 27: 158- 67.

14. Marx, R.E. Platelet rich plasma (PRP): What is PRP and what is not PRP? Implant Dentistry 2001;10:225-28.

15. Sanchez AR, Sheridan JP, Kupp LI. Is the platelet rich plasma the perfect enhancement factor? A current review.

Int J Oral Maxillofac Implants 2003; 18: 93-103.

16. Sunitha VR, Naidu ME. Platelet rich fibrin: Evolution of a second generation platelet concentrate. Ind J Dent Res 2008; 19: 42-6.

17. Dohan DM, Del Corso M, Charrier JB. Cytotoxicity analyses of Choukroun’s platelet-rich fibrin (PRF)on a wide range of human cells: The answer to a commercial controversy. Oral Surg Oral Med Oral Pathol Oral RadiolEndod 2007;103: 587- 93.

18. Appel TR, P¨otzsch B, M¨uller J, von Lindern J, Berg´e SJ, Reich RH. Comparison of three different preparations of platelet concentrates for growth factor enrichment. Clinical Oral Implants Research 2002; 135, 522– 8.

19. Kiran NK, Mukunda KS, Tilakraj TN. Platelet concentrates: a promising innovation in dentistry. Journal of Dental Sciences and Research 2011; 2: 50-61.

20. Dohan, O.M. et al. Ptobelet-ricri fibrin (PRF): a second generation platelet concentrate. Part II: platelet-related biologic features. Oral Surg. Oral Med. Oral Pathol. Oral Radiol. Endod. 2006;101: e45-e50.

21. Dohan DM. Platelet-rich fibrin (PRF): a second generation platelet concentrate. Part 111: leucocyte activation: a new feature for platelet concentrates?. Oral Surg. Oral Med. Oral Pathol. Oral Radiol. Endod. 2006; 101: e5i-e55 22. Dohan, DM, Choukroun J, Diss A, Steve L. Anthony JJ, Mouhyi J, Gogly B. Platelet-rich fibrin (PRF): A secondgeneration platelet concentrate. Part I: Technological concepts and evolution. Oral Surg Oral Med Oral Pathol Oral RadiolEndod 2006; 101: e37-44.

23. Chang IC, Tsai CH, Chang YC. Platelet-rich fibrin modulates the expression of extracellular signal-regulated protein kinase and osteoprotegerin in human osteoblasts. J Biomed Mater Res 2010;13:327–32 24. Huang FM, Yang SF, Zhao JH, Chang YC. Platelet-rich fibrin increases proliferation and differentiation of human dental pulp cells. J Endod 2010;36:1628 – 32.

25. Feng X, Clark RA, Galanakis D, Tonnesen MG. Fibrin and collagen differentially regulate human dermal microvascular endothelial cell integrins: stabilization of alphav/beta3 mRNA by fibrin1. J Invest Dermatol 1999;113:913-19.

26. Sahni A, Odrljin T, Francis CW. Binding of basic fibroblast growth factor to fibrinogen and fibrin. J BiolChem 1998;273: 7554-59.

27. Nehls V, Herrmann R. The configuration of fibrin clots determines capillary morphogenesis and endothelial cell migration. Microvasc Res 1996;51:347-64.

Page 19

Annals of SBV

28. Kazura JW, Wenger JD, Salata RA, Budzynski AZ, Goldsmith GH. Modulation of polymorphonuclear leukocyte microbicidal activity and oxidative metabolism by fibrinogen degradation products D and E. J Clin Invest 1989;83:1916-24.

29. Lanir N, Ciano PS, Van de Water L, McDonagh J, Dvorak AM, Dvorak HF. Macrophage migration in fibrin gel matrices. II. Effects of clotting factor XIII, fibronectin, and glycosaminoglycan content on cell migration. J Immunol 1988;140: 2340-49.

30. Gassling V, Douglas T, Warnke PH, Acxil Y, Wiltfang J, Becker ST.Platelet-rich fibrin membranes as scaffolds for periosteal tissue engineering Clin Oral Implants Res 2010; 21: 543–49.

31. Gray AJ, Bishop JE, Reeves JT, Laurent GJ. A alpha and B beta chains of fibrinogen stimulate proliferation of human fibroblasts. J Cell Sci 1993;104:409-13.

32. Brown LF, Lanir N, McDonagh J, Tognazzi K, Dvorak AM, Dvorak HF. Fibroblast migration in fibrin gel matrices. Am J Pathol 1993;142:273-83.

33. Jankovic S, Aleksic Z, Klokkevold P, Lekovic V, Dimitrijevic B, Kenney EB, et al. Use of platelet-rich fibrin membrane following treatment of gingival recession: A randomized clinical trial. Int J Periodontics Restorative Dent. 2012;32:e41–50.

Annals of SBV

34. Martínez-Zapata MJ, Martí-Carvajal A, Solà I, Bolibar I, Angel Expósito J, Rodriguez L, et al. Efficacy and safety of the use of autologous plasma rich in platelets for tissue regeneration: A systematic review.Transfusion. 2009;49:44– 56.

35. A. Sharma, A.R. Pradeep. Treatment of 3-wall intrabony defects in patients with chronic periodontitis with autologous plateletrich fibrin: a randomized controlled clinical trial. J Periodontol 2011; 82: 1705–12.

36. Thorat M, Pradeep AR, Pallavi B. Clinical effect of autologous platelet-rich fibrin in the treatment of intra-bony defects: a controlled clinical trial. J ClinPeriodontol 2011; 38: 925–32.

37. Chang YC, Wu KC, Zhao JH. Clinical application of platelet-rich fibrin as the sole grafting material in periodontal intrabony defects. Journal of Dental Sciences. 2011; 6: 181 188.

38. Sharma A, Pradeep AR. Autologous platelet-rich fibrin in the treatment of mandibular degree II furcation defects: a randomized clinical trial. J Periodontol. 2011; 82:1396-403.

DENTAL BIOMATERIALS IN NON-OPEraTIVE MANAGEMENT OF DENTAL CARIES Carounanidy Usha

Abstract Dental caries is a disease that results in destruction of tooth structure called as carious lesions. The formation of carious lesion over a period of time is a sequel of alternating sequence of demineralization and remineralization of the hydroxyapatite crystals in the tooth structure. The yesteryears’ management was focused on the lesions alone, in the surgical model of ‘drill and fill’. Currently the disease prevention is receiving its due attention, a paradigm shift which is a result of a better and deeper understanding of the etiopathogenesis of carious disease. The formation of new lesions as well as remineralization of initial lesions are prevented by targeting various causative factors using biomaterials. These preventive materials and their current modifications are used in the non-operative treatment of caries, focusing on the preservation of the healthy tooth structure. This article highlights the latest advances in biomaterials used for the nonoperative treatment of dental caries.

Key words: Dental caries, remineralization, demineralization, carious lesions, non-operative treatment, operative treatment, dental biomaterials

Introduction Dental Caries is a disease that results in tooth destruction called as carious lesion. It is defined as a disease that is characterised by the localized destruction of susceptible dental hard tissue by acidic by-products from bacterial fermentation of dietary carbohydrates.

[1] As evident by the definition, it is a multifactorial disease where multiple causes interact in a complex and dynamic manner. The biological factors that act in concert are the susceptible tooth structures, salivary factors, dietary sucrose and the cariogenic biofilm with predominance of Mutans streptococci.

Mutans streptococci in the dental biofilm, metabolize the dietary sucrose, which is an easily fermentable sugar, to release acidic by-products.

This reduces the pH of the dental biofilm. In the acidic ambience minerals are dissolved from the tooth hydroxy apatite crystallites. Such a loss of calcified material from the tooth structure is called as demineralization. Continuous demineralization that occurs over time, on and within the tooth structure

can result in changes ranging from initial microscopic demineralization to macroscopic cavitation. These detectable changes that occur on the tooth are called as carious lesions.

But the demineralization process may not be continuous always. The unfavourable ambience and factors causing demineralization can be altered by beneficial salivary factors or by specific intervention by the operator, resulting in re-deposition of minerals to the tooth structure. This net gain of calcified material within the tooth structure, replacing that which was previously lost by demineralization is called as remineralization. [1] The management of dental caries in the yester years focused only on the removal of carious lesions and restoration of the defect with a dental biomaterial.

This was called as the surgical model, where drill and fill was the norm. Though the structure and function of the tooth was effectively restored, this method

* Professor, Department of Conservative Dentistry and Endodontics, Indira Gandhi Intitute Dental Science, Sri Balaji Vidyapeeth, Puducherry 607402, India.

Page 20

Ann. SBV, July - Dec 2014;3(2)

Ann. SBV, July - Dec 2014;3(2)

Page 21

Annals of SBV

sacrificed precious healthy tooth structure also in the process of cavity preparation.

A restored tooth might also undergo repair or replacement throughout its life cycle, resulting in more and more loss of tooth structure, which can eventually lead to complete removal of the tooth. This is called as the restoration cycle. [2] Albeit the significant improvements in the mechanical, chemical and biological properties of the restorative materials, the artificial materials, do not perform as effective as the natural enamel and dentin.

Thus with this understanding that tooth structure is a precious material to be preserved and also that the remineralization process is an inherent repair mechanism in the process of caries, the surgical model has weaned off to a large extent, reserved only for large cavitated lesions. The medical model of management has replaced the surgical model, where various causative factors are targeted using noninvasive strategies and materials, to prevent their interaction to cause dental caries.

Yet another factor contributing to this paradigm shift towards the medical model is the advancement in diagnosis and detection of dental caries at the very early incipient stages. Therefore the medical model is not only used in primary prevention of caries, but also in arresting the ongoing demineralization and remineralizing a new incipient lesion, called as secondary prevention. [3] The medical model uses therapeutics that prevents or slows down demineralization and that which aids the remineralization process. This is done at all the causative levels such as at the microbial biofilm level, at the host/ tooth level, at the dietary level and at the salivary level.

Non-operative therapeutic biomaterials that act at the tooth level The tooth-level treatments act by two ways in caries prevention; a. by increasing the tooth’s resistance to demineralization b. By blocking the ecological niche on the tooth surface where the cariogenic organisms preferentially grow. Minerals such as fluorides and calcium-phosphate fortify the tooth against cariogenic acid attack. Laser ablation is another method that is being used to increase resistance of surface enamel to dissolution. The Page 22

DENTAL BIOMATERIALS IN NON-OPEraTIVE MANAGEMENT OF DENTAL CARIES

ecological niches are blocked by using pit and fissure sealants to prevent the proliferation of cariogenic organisms in this site.

Fluorides

Glass beads that dissolve over a period of time, releasing fluoride, have also been evaluated. These beads can store fluoride in concentrations from 13.3% to 21.9% and release it even up to two years.

[7]

The anticariogenic effect of fluoride is well established with robust scientific evidence. Formation of fluorapatite crystals that are more acid resistant than hydroxyapatite crystals has been attributed as the primary mechanism of action. [4] The critical dissolution pH for fluorapatite is much lower than that for the hydroxy apatite crystals.

Systemic fluorides have been used largely to incorporate resistance to the tooth both in the preeruptive and post eruptive stage. But the presence of free fluoride ions in the biofilm and the oral fluid is recently considered to be more important than the concentration of bound fluoride in the enamel.

It has been found that, under an acid attack, it is the free fluoride ions, along with the calcium ions, that influence the remineralization process. Thus emerged the wide spread use of topical fluorides, where free fluoride ions were made available at the tooth’s vicinity in high concentration.

Fluoridated dentifrice and mouthwashes are the most common topical applications. But they do not ensure continuous availability of fluoride ions in the tooth vicinity. Therefore retention rate and sustained release of fluoride from the topical applications are considered imperative for prolonged action of fluoride. Gel and varnish as the modes of delivery provide better retention of fluoride over the enamel.

Highest level of evidence is available on the superior anti-caries effect of both delivery methods. [5] Sustained and controlled release of fluoride is being tried by the use of slow-release fluoride devices.

[6] These devices are attached to the tooth surface by means of an adhesive. The fluoride from these reservoirs is then slowly released to the surrounding.

A copolymer membrane device is available that is a small pellet made of a fluoride containing copolymer matrix surrounded by a rate controlling copolymer membrane. When the matrix gets hydrated, the fluoride dissolves and saturates the matrix. Thus, the ions move from saturated matrix to less saturated membrane and then to the saliva. This device can release 0.02-1 mg F/day, for up to 180 days.

Ann. SBV, July - Dec 2014;3(2)

Mixture of hydroxyapatite and sodium fluoride is under evaluation as a slow-release device. Brackets that are bonded to the tooth structure can hold a slow fluoride releasing pellet and it is claimed that they can be retained over 20 years also in the tooth.

[8] The fluoride releasing devices should also be able to recharge themselves. Polymerizable monomers containing chelating groups and fluoride-exchanging metal chelates that can “recharge” by taking up fluoride from fluoridated toothpaste or mouthwash is currently developed. [9] Casein phosphopeptide stabilized amorphous calcium phosphate (CPP-ACP): The fluoride uptake is influenced by concentration of calcium and phosphate ions in the saliva or biofilm. For every two fluoride ions, ten calcium ions and six phosphate ions are required to form one unit cell of fluorapatite (Ca10(PO4)6F2). Thus, topical applications of calcium and phosphate complexes are being used to enhance fluoride remineralization.

Unstabilized amorphous calcium phosphate (ACP), casein phosphopeptide stabilized amorphous calcium phosphate (CPP-ACP) and bioactive glass containing calcium sodium phosphosilicate are some of these systems available. [10] CPP-ACP is available in dentifrice formulation, as a mouth rinse and as a non-sugar containing chewing gum. They are also available in combination with fluoride. The minerals are released under an acid challenge to supersaturate the saliva and help in remineralization. CPP-ACP binds strongly to hydroxyapatite. It increases the calcium phosphate level at the tooth biofilm interface.

Thus it reduces the plaque pH, as well as promote remineralization and prevent demineralization. They may be an important and effective adjunct to fluoride topical therapy in treatment of incipient lesions [11]

Non-operative therapeutic biomaterials that act at the biofilm level Chemo prophylactic agents are used to modify the microbial colony in the dental biofilm. They act either by 1. Inhibiting initial adhesion/colonization Ann. SBV, July - Dec 2014;3(2)

2. Inhibiting growth/metabolism 3. Disrupting mature biofilm.

Chemical agents such as chlorhexidine and triclosan are some of the commonly used caries prophylactic agents. The antimicrobial effect of an agent is determined by its potency, substantivity and bio availability. Bioavailability means the delivery of the agent to the intended site of action in a biologically active form and at effective doses. Topical application is the best method of delivery for oral antimicrobial agents to provide such bio availability. Substantivity means the agents’ ability to bind to the oral surfaces and its subsequent rate of release form its binding sites. Thus an effective oral antimicrobial agent should be able to adhere to the mucosal, tooth pellicle surface or to the biofilm surface and provide its effect over a long period. The dose/ frequency of application of various agents depend on this property. For instance, a medication with low substantivity needs to be applied frequently to be bio available. Antimicrobials are available as mouth rinses, sprays, dentifrices, gels, varnishes and chewing gums/ lozenges.

Chlorhexidine (CHX) Chlorhexidine is a bis-biguanide which is bactericidal and fungicidal. It is a broad spectrum agent targeting both the gram positive and gram negative organisms. Gram positive microbes such as Mutans streptococci are very sensitive to CHX. The antibacterial effect of this medicament is attributed to the following: 1. It is a cationic agent that readily binds to negatively charged microbial surfaces. This results in cell wall disruption and cell death.

2. At high concentrations chlorhexidine it is bactericidal and in low concentrations bacteriostatic.

3. It inhibits the glucosyl transferase enzyme essential for microbial adhesion and the phosphoenolpyruvate phospho transferase essential for glucose transport across the cell membrane.

CHX is commonly available as 0.2% and 0.12 % solution / mouth rinse. Chlorhexidine has high substantivity which is a main reason for its superior antimicrobial effect. It is released in the mouth up to 8 hours after rinsing. Thus it is very effective as a topical chemo prophylactic agent.

However it does not specifically target the cariogenic organism. Long term use results in Page 23

Annals of SBV

DENTAL BIOMATERIALS IN NON-OPEraTIVE MANAGEMENT OF DENTAL CARIES

undesirable alteration in the entire oral microbial ecology. In addition there is no clinical correlation between its use and decline in caries incidence.

Weighing its established side effects and the inconclusive evidence for benefits, the clinical usage of chlorhexidine is even being dissuaded.[12] However, ‘inconclusive’ evidence does not necessarily mean ‘not effective’; therefore, the use of antimicrobials, in the current times, has been restricted to cariesactive individuals and to high caries risk individuals.

Instead of prescribing it as a routine medication, it is prescribed as a regime for a short duration for a high risk individual, only if the risk assessment points toward a dominant microbial cause. [13]

medicine. Recently, their use in targeting the Mutans streptococci has been investigated. They bind to the lipopolysaccharide of the microbial cell membrane, leading to cell death [22]. Recently an AMP is derived from milk protein that is suggested to be incorporated in the oral care products.[8]

Yet another common problem in the use of topical chemo prophylactic agent is the inability to maintain the minimum inhibitory concentration (MIC) of the drug in oral cavity. Chlorhexidine gels and chewing gums have been introduced to overcome this problem of retention. However these agents provide only a short term retention and sustenance of the MIC. Certain chewing gums have incorporated two types of antimicrobial agents which are released over a period of time and maintain the dosage above the MIC topically. Polymeric delivery systems have been patented where the agent is bonded to the copolymer, which hydrolyses to release the agent slowly into the oral cavity. [8] Recently, a mineralbinding micellar drug delivery system was developed, which could quickly bind to the tooth surface and release encapsulated drug over a prolonged period of time. [14]

Probiotics and Replacement Therapy

Herbal interventions Owing to various challenges in the use of such potent synthetic agents, studies on the anticariogenicity of various plant products has increased in the last decade. The herbal interventions have shown efficacy in the inhibition of glucosyl transferases (GTFs) activity and insoluble glucan synthesis, inhibition of acid production from sucrose and inhibition of S. mutans adhesion on hard surface.

However bactericidal effect has been found to be less in the herbal medicine. [15-21] Scientifically established herbal extracts have been introduced in the tooth pastes and certain mouthwashes.

Anti-microbial Peptides (AMP) Antimicrobial peptides are known for their broad spectrum antibacterial effect in the other fields of Page 24

But short half-life due to proteolytic degradation of the peptides is the current challenge in making it widely available for caries prevention. Target specific anti-microbial peptides are being developed which target only the mutans streptococci species. This is a promising concept in contrast to the other broad spectrum chemo prophylactic agents.[23]

Instead of using chemicals, the micro-organism can be countered with another micro-organism. This is the concept behind the replacement therapy or the probiotic therapy. The disease causing ‘wild strains’ of bacteria can be displaced from their ecological niche, by introducing genetically modified form of the same organism, called as the ‘effector strain’. These effector strains saturate these niches and prevent the colonization and multiplication of the wild strains again. A common example for a probiotic approach is the use of lactobacilli in intestinal infections. The mutans streptococci are genetically re-engineered to form strains that lack the inherent pathogenicity.

One such strain developed lacks the enzyme lactate dehydrogenase, and so is incapable of producing lactic acid responsible for demineralization. Yet another genetically engineered streptococci that produces alkali instead of acid in the biofilm metabolism is under evaluation. [24] Vaccines Passive immunization is currently being adopted in caries immunization.[25] Instead of actively producing antibodies in the host system, ready-made antibodies to a specific antigen, produced elsewhere, is administered locally to obtain the desired result.

The antigen, when administered to a cow or a hen, stimulates the production of antibodies that are secreted in the milk and in the egg yolk, respectively.

Recombinant monoclonal antibodies are also being used in passive immunization. All have shown a short-term reduction in the colonization of s. mutans in the rats and monkeys.

Ann. SBV, July - Dec 2014;3(2)

Lately, the transgenic antibody from plants (tobacco and potato), also called as the ‘plantibody’, has been manufactured and is under a clinical trial.

These antibodies are applied locally to the tooth, mostly in the form of mouth rinse.

However, only a transient drop in the microbial count lasting only for few hours does not satisfy the requirement of a vaccine, which is to provide a sustained availability of antibodies. This form of passive immunization is akin to any other mouth rinse, where lack of substantivity and retention might reduce the efficacy of the antibodies, necessitating frequent applications.

Non-operative therapeutic biomaterials that act at the dietary/ salivary level Dietary sucrose is readily fermented by the Mutans streptococci, to release lactic acid that initiates the demineralization of the hydroxy apatite crystals. Drastically curtailing the sugar intake to prevent caries is not a prudent advice as it will yield poor patient compliance. Instead, sugar substitutes have been suggested. Sugar substitutes are of two types: 1. Intense (non-caloric) sweeteners – e.g. saccharine and aspartame 2. Bulk (caloric) sweeteners – e.g. sorbitol and xylitol.

3. It has inhibitory effect on glycolysis of streptococci.

4. It also reduces the adhesiveness of the bacteria by interfering in the polysaccharide formation.

Xylitol is mainly added in chewing gums. Along with salivary stimulation, it has been found to be effective in reducing caries. It is also available as candies.[27] The recommended dosage is 6 – 10 gms/ day; 2 tabs of gum or two candies four times daily.

However as has been discussed previously in this article, retention rate and constant availability of the medicament in the oral cavity is a concern with xylitol as well. Thus studies are focusing on novel delivery systems to improve the drug availability in the tooth vicinity, that too, on demand.

Conclusion 1. Dental caries is still evading the sincere attempts of science towards eradication. This is mainly due to the multifactorial and complex nature of the disease.

2. Though a plethora of preventive NOT strategies are available and are being well researched, a well-designed and custom made treatment plan is mandatory to take complete advantage of them.

The anti cariogenicity of these sugars is due to the fact that these are not readily metabolised to acids by the cariogenic organisms. Some like sorbitol are metabolised very slowly. Xylitol possess antibacterial property as well, apart from being non-acidogenic.[26]

3. Biomaterials used as topical agents constitute the majority of the NOT procedures. Innovative delivery modes and methods are the need of the hour to face the challenges regarding constant bio availability, retention rate and substantivity.

Sugar substitutes are added to the diet and beverages. But addition to the chewing gums is the common mode of delivery. The chewing gums also improve the salivary flow. With improved salivary flow, the other factors in saliva, such as the pH and buffer also improve, thus enhancing remineralization.

4. Role of genetics in the modification of the cariogenic biofilm dominates current research.

Xylitol Xylitol is a sugar alcohol with five carbon atoms, a pentitol. The anti-cariogenic property of this sugar has been attributed to the following: 1. Most oral streptococci do not ferment xylitol. Thus it is a non-acidogenic sugar 2. Entry of xylitol into the bacterial cell and accumulation as xylitol-5-phophate results in lysis of the cell. Thus it has a bacteriostatic action over the streptococcus mutans.\ Ann. SBV, July - Dec 2014;3(2)

5. Fluoride is still considered as the gold standard in caries prevention through remineralization.

Research is focusing on the identification of alternate to fluorides in the abundant plant products.

References 1. Longbottom C, Huysman MC, Pitts NB, Fontana M. Glossary of terms. In: Pitts NB, editor. Detection, assessment, diagnosis and monitoring of caries. Basel, Krager: Monogr Oral Sci; 2009. pp. 209-16.

2. Simonsen R J, Stallard R E. Sealant-restorations utilizing a dilute filled composite resin: one year results. Quintessence Int 1977;23: 307–315.

3. Steinberg SI. Understanding and managing dental caries: a medical approach. Alpha Omega 2007;100(3):127-34.

Page 25

Annals of SBV 4. SBU. Swedish Council on Technology assessment in health care. 2002. Prevention of dental caries: A systematic review.

Rep No 161; pp. 1–26 5. American Dental Association Council on Scientific Affairs.

Professionally applied topical fluoride: Evidence-based clinical recommendations. J Am Dent Assoc. 2006;137:1151– 9.

6. Pessan JP, Al-Ibrahim NS, Buzalaf MA, Toumba KJ. Slowrelease fluoride devices: a literature review. J Appl Oral Sci. 2008;16:238–46.

7. Andreadis GA, Toumba KJ, Curzon ME. Slow-release fluoride glass devices: in vivo fluoride release and retention of the devices in children. Eur Arch Paediatr 2006;7(4):258–61.

8. Chen F, Wang D. Novel technologies for the prevention and treatment of dental caries: a patent survey. Expert Opin Ther Pat. 2010;20(5):681-94.

9. Bayrak S, Tunc ES, Aksoy A, Ertas E, Guvenc D, Ozer S. Fluoride Release and Recharge from Different Materials Used as Fissure Sealants. European Journal of Dentistry 2010;4(3):245-250.

10. Reynolds EC. Calcium phosphate-based remineralization systems: scientific evidence? Aust Dent J 2008; 53(3):268-73.

11. Azarpazhooh A, Limeback H. Clinical efficacy of casein derivatives. a systematic review of the literature. J Am Dent Assoc 2008;139:915–24.

12. Autio-Gold J. The role of chlorhexidine in caries prevention.

Oper Dent 2008;33:710–6.

13. Anusavice KJ. Present and future approaches for the control of caries. J Dent Educ 2005;69:538–54.

14. Chen F, Liu XM, Rice KC, et al. Tooth-binding micelles for dental caries prevention. Antimicrob Agents Chemother 2009;53(11):4898–902.

15. Al-Hebshi NN, Nielsen O, Skaug N. In vitro effects of crude khat extracts on the growth, colonization, and glucosyltransferases of Streptococcus mutans. Acta Odontol Scand 2005;63(3):136–42.

16. Rahim ZH, Khan HB. Comparative studies on the effect of crude aqueous (CA) and solvent (CM) extracts of clove on the cariogenic properties of Streptococcus mutans. J Oral Sci 2006;48(3):117–23.

17. Koo H, Nino de Guzman P, Schobel BD, et al. Influence of cranberry juice on glucan-mediated processes involved in Streptococcus mutans biofilm development. Caries Res 2006;40(1):20–7.

18. Yu HH, Lee DH, Seo SJ, You YO. Anticariogenic properties of the extract of Cyperus rotundus. Am J Chin Med 2007;35:497–505

Annals of SBV 19. Brighenti FL, Luppens SB, Delbem AC, et al. Effect of Psidium cattleianum leaf extract on Streptococcus mutans viability, protein expression and acid production. Caries Res 2008;42(2):148–54.

20. Yu HH, Lee JS, Lee KH, et al. Saussurea lappa inhibits the growth, acid production, adhesion, and water-insoluble glucan synthesis of Streptococcus mutans. J Ethnopharmacol 2007;111:413–7.

21. Papetti A, Pruzzo C, Daglia M, et al. Effect of barley coffee on the adhesive properties of oral streptococci. J Agric Food Chem 2007;55(2):278–84.

22. Guggenheim B, Giertsen E, Schupbach P, Shapiro S. Validation of an in vitro biofilm model of supragingival plaque. J Dent Res 2001;80(1):363–70.

23. Eckert R, He J, Yarbrough DK, et al. Targeted killing of Streptococcus mutans by a pheromone-guided “smart” antimicrobial peptide. Antimicrob Agents Chemother 2006;50(11):3651–7.

24. Meurman JH, Stamatova I. Probiotics: contributions to oral health. Oral Dis 2007;13:443–51.

25. Abiko Y. Passive immunization against dental caries and periodontal disease: development of recombinant and human monoclonal antibody. Crit Rev Oral Biol Med 2000;11:140– 58.

26. Borges Yáñez SA. Sugar substitutes in the prevention of dental caries: review of the literature. Pract Odontol 1991;12(8):59-60.

27. Antonio AG, Pierro VS, Maia LC. Caries preventive effects of xylitol-based candies and lozenges: a systematic review. J Public Health Dent 2011;71(2):117-24.

THE “PHYSICS AND CHEMISTRY” BEHIND THE “BIOLOGY” OF PULPAL REGENERATION Dr. R.Sathyanaryanan

Abstract Root canal therapy for the management of pulpo-periapical diseases involves three phases access to the pulp space, removal of the necrotic content from the canals and obturating the space with synthetic biomaterials.

Majority of the failures in root therapy is attributed to the last phase of obturation. Persistence of infection or reinfection is mainly due to the re-establishment of the microbes in the canal space establishing through the interface between the natural root dentin and the artificial sealers and obturating materials. Thus the focus started on filling the space with the natural pulp and dentin structures in the root canal without resorting to synthetic materials. Thus emerged the concept of Pulpal Regeneration. Revascularization of the pulp, use of stem cell engineering are few concepts in this. This article focuses on the current tend and practice of pulpal regeneration and the biomaterials that are used for regeneration and tissue engineerings.

Key words: Revascularization of pulp, pulpal regeneration, Dental pulp stem cells (DPSC), Stem Cells from Human Exfoliated Deciduous teeth (SHED)

Introduction “Restitutio as integrum” is the ultimate goal for all medicinal therapy including pulpal regeneration.

Regeneration of pulp can be accepted only when newly formed pulpal tissue has vascularized connective tissue, neural tissue and functional odontoblast lining the dentin wall of the pulp chamber.[1,2] This goal is yet to be achieved in the science and the following review will highlight the path till travelled by the researchers of the past and present.

Techniques for Pulp regeneration The concept of tissue engineering was coined and explored by Langer and Vacanti in 1993.

Regeneration and Repair of pulp are two different biologic processes for replacement of lost pulpal tissue with different outcomes. Repair of pulp with biomaterials will lead to formation of new tissue that is devoid of function and structure similar to

the original pulp tissue (Scar tissue). Regeneration means to restore the lost tissue by new tissue which will not bedifferent from the original tissue in structure and function. Revascularization is another terminology that is used in pulpal regeneration, which is ill defined and many times synonymously used with regeneration. Scientific documentation of revascularization dates back to 1960, when NygaardOstby et al reported pulpal healing of infected root canals by mechanical creation of blood clot.[3] The following are the pulpal regenerative techniques that are being explored for the clinical applications:[4] 1. Root canal revascularization via blood clotting 2. Stem cell based therapies 3. Cell free therapies: scaffold implantation 4. Cell free therapies: injectable scaffold delivery 5. Pulp implantation 6. Three dimensional cell printing 7. Gene therapy

Professor and Head, Department of Conservative Dentistry and Endodontics, Indira Gandhi Intitute Dental Science, Sri Balaji Vidyapeeth, Puducherry 607402, India.

Page 26

Ann. SBV, July - Dec 2014;3(2)

Ann. SBV, July - Dec 2014;3(2)

Page 27

Annals of SBV

THE “PHYSICS AND CHEMISTRY” BEHIND THE “BIOLOGY ” OF PULPAL REGENERATION

Revascularization

Stem Cell Based Therapies

The present clinical strategy for formation of apical root that has been damaged by trauma or necrotic pulp is the apexification procedure with calcium hydroxide.[5] The disadvantage of this procedure is long treatment plan, unpredictable outcome, weakening of roots structure because of placement of calcium hydroxide.

Stem cells are non specialized cells of either embryonic origin or post natal. The embryonic origin stem cells are totipotent in nature with capability of forming new organ. Post natal stem cells are multipotent in nature with ability to differentiate to other cell types. All stem cells have self renewal property. Stem cell division can either be symmetrical or asymmetrical. The asymmetrical division is responsible for cell with different properties. Two population of dental stem cells are present that give rise to two different tissues. Epithelial stem cells (EpSC) for ameloblasts and Mesenchymal stem cells (MSC) for odontoblasts, cementoblasts, osteoblast and fibroblast.[12]

Difference between the conventional approach for apexification or apexogenesis and the pulp revascularization is that in the former only the root apex is closed, thus leaving the wide canals that can be prone for fracture in long run. Whereas in pulp revascularization, along with the apical closure, there will be continuous root development and increased dentinal walls.[6] This finding has been supported with many case reports and case series.[7,8] However, in current status, the predictability of the outcome is not there.[9] The classical technique and the material that is used for revascularization for irreversible pulpitis with apical periodontitis cases is as follows;[10] 1. Access cavity and disinfection of root canal with sodium hypochlorite and chlorhexidine irrigation.

2. Placement of intracanal medicament with tri-antibiotic paste namely Ciprofloxacin, Metronidazole and Minocycline paste.

3. Creation of blood clot mechanically at cemento-dentinal level 4. Permanent coronal seal with MTA and restoration with resin composite Disadvantage of tri-antibiotic paste was that, it leads to discoloration of clinical crown as it contains minocycline. To overcome this, the coronal dentinal tubules of access cavity were sealed with bonding agents and flowable composite before placement of tri-antibiotic paste.[11] The four different types of tissue replacement that can be present following revascularization:

1. Complete dentin formation with obliteration of the pulp canal space 2.Cementum and periodontal ligament formation

3. Cementum, periodontal ligament and bone formation from the apical region.

4. Bone and bone marrow formation Currently, it is not possible to predict or know the type of tissue replacement that occurs in the revascularization cases.

Page 28

Stem cell niche for epithelial stem cells have been identified in the cervical loop of rodent incisor and is yet to be isolated in the human. As there is no technology to identify the stem cells directly, indirect assessment are done with markers. Hence its absence cannot be said with certainty in any tissue. The assessments of all physical property of the stem cell are non specific. Only way to prove the function of stem cells is by evaluation of self renewal to show its “Stemness”. Some of the markers for identification of Mesenchymal stem cells are STRO-1, CD146 or CD 44.[13] Treatment option with stem cells can be either cellular approach or acellular approach. Cellular approach requires harvesting and cultivating the stem cells of interest in ex vivo and placing it back in the pulp canal space. For the cellular approach, the stem cells can be cultured either by enzymedigestion method or by explant outgrowth method.

Enzyme digestion method had higher proliferation rate than the outgrowth method. Stem cell lines are established with one of the culture method. Then it can be differentiated into odontoblast, which under the controlled mineralization-regulatory influence of three non-collagenous proteins namely dentin phosphophoryn(DPP), dentin sialoprotein(DSP) and dentin matrix protein-1(DMP-1) can produce mineralized tissue.[14] However this has major limitations because of the non availability of specific markers. Currently this treatment option is not possible in the clinical practice.[15, 16] Acellular approach is an in-situ condition, wherein the scaffold and signaling molecules are Ann. SBV, July - Dec 2014;3(2)

placed to attract the stem cells from nearest niche.

Currently the research is more focused on the acellular approach. Cell free approaches may be easier to translate from laboratory to clinical setting with satisfactory predication for pulpal regeneration.

[17]

Biomaterials For Pulp Regeneration[18] The Biomaterials required for the pulp regeneration are the Stem cells, Signaling molecules and Scaffolds.[19]The following are sources of the dental stem cells: • Dental pulp stem cells (DPSC) • Stem Cells from Human Exfoliated Deciduous teeth(SHED) • Stem cells from Apical Papilla • Dental Follicle Progenitor cells • Periodontal Ligament stem cells Stem cell will come into play and differentiate to form tissues based on the trigger from the signalling molecules. Signalling molecules are proteins in the form of growth factors and morphogenic factors which bind to the specific membrane receptors and trigger a series of events which eventually leads to formation of new tissue.

The following growth factors signal the reparative process in dentin and pulp • Transforming growth factors β • Bone morphogenic protein (BMP) • Platelet Growth factor • Fibroblast Growth factor • Vascular Endothelial Growth factor(VEGF) Environment plays an important role for formation of tissues. Extra cellularmatrix in the natural tissues have the best physical and chemical properties for formation of new tissues. For iatrogenic pulpal regeneration protocols, scaffolds of natural and synthetic polymers have been tried and tested based on the physical and chemical properties such as degradation rate, pore size and mechanical resistance. The followingare some of biodegradable and biocompatiblematerials used as scaffolds for pulp regeneration:[20,21] • Collagen • Hyaluronic acid • Chitosan • Poly -(I-lactic acid)(PLLA) • Poly-(glycolic acid) (PGA) • Co polymer poly-(lactic-co-glycolic acid) (PLGA)[22] Ann. SBV, July - Dec 2014;3(2)

To translate the pulp regeneration from laboratory to clinical scenario, one of the obstacles is adaptation of the rigid scaffolds to the dentinal walls of the root canal system. Rosa et al., tested and proved the hypothesis that injecting the scaffold of recombinant human collagen containing SHED will lead to differentiation of functional odontoblast on full length of the root canal.[23] Pulpal regeneration requires sufficiently disinfected dentinal walls and pulp canal space.

Current use of non specific disinfection protocol in the root canal treatment is not sufficient for achieving regeneration. Also the disinfection material should not interfere with the regeneration process. Sodium hypochlorite and chlorhexidine may interfere with the regeneration, whereas EDTA, a weak anti microbial may be more important for regeneration. With its chelating property, it will release the bioactive growth factors from the dentin matrix, which may aid in the regeneration of pulp tissue.[24] The regeneration potential of Dentin Pulp Stem cells (DPSC) from normal and inflamed pulp, formed similar type of mineral deposition in immune-compromised mice. However the osteo/ dentinogenic potential of DPSC of inflamed pulp was less than normal pulp.[25] Vasculogenesis and Angiogenesis are two processes essential for pulp regeneration. Vasculogenesis is defined as formation of new blood vessels. The biomaterial of choice identified as of now is VEGF signalled SHED and DPSC.Angiogenesis, on the contrary is the formation of new blood vessels from pre-existing vasculature. Thus it may come into play during revascularization procedures. In gene therapy and pulp implant, genes and pulp is transferred to the pulp canal space. In cell printing the position of the cells is precisely calculated, suspended in a hydrogel and implanted into the root canal space

Missing Links In Pulpal Regeneration[26] Some of the important concepts have not been addressed in the pulp regeneration. They are as follows: 1. In all wound healing and regeneration, the size of the defect is important. Beyond a certain size the tissue cannot regenerate without introduction of supportive approaches. The current regeneration protocol as well as the research does not address this issue and still there is no guideline Page 29

Annals of SBV

what is the critical size defect for pulp and dentin.

2. In the cell free approach for pulpal and dentin regeneration, migration of cells from nearby should occur to differentiate into odontoblastic lineages. Thus non-odonblastic lineage differentiating into the odontoblastic lineages and its predictability is not ascertained till now.

3. While it has been proven that the pulpdentin regeneration does occur in the experimental condition using cell based approach, non-cell based approaches have failed to do the same.

Moreover, the quality of the pulp and dentin formed in terms of function and prevention of further bacterial insult, is not being addressed.

4. Good manufacturing practice facilities are not cost effective to initiate stem cell based pulp regeneration; the importance given is not much may be pulpal disease is not a life threatening issues.

Conclusion The current status of literature has also raised valid questions such as” Is odontoblast mandatory for regenerated tissue?”; “Is complete mineralization or just healthy connective tissue considered as the acceptable outcome of root canal therapy?” [2] To translate the bench work to clinics, the directions should be clear whether the goal is repair or regeneration. Most importantly, what is the replacement tissue needed as the end result of the regenerative therapies? The research and growth in the pulpal regeneration is rapidlyevolving and in one/ two decades, there will be a paradigm shift in the clinical treatment protocol. Along with this, there may be demand for newer diagnostic tools and new disease classification. This will enable preservation of healthy tooth structure, as more natural and biologic material will be used for replacement for lost pulpdentin tissue.

References 1. Goldberg M. Pulp healing and regeneration: more questions than answers. Adv Dent Res.2011;23(3):270–4.

2. Schmalz G, Galler KM. Tissue injury and pulp regeneration. J Dent Res. 2011;90(7):828–9.

3. Andreasen JO, Bakland LK. Pulp regeneration after noninfected and infected necrosis, what type of tissue do we want?

A review. Dent Traumatol. 2012;28(1):13–8.

4. Murray PE, Garcia-Godoy F, Hargreaves KM. Regenerative endodontics: a review of current status and a call for action. J Endod. 2007;33(4):377–90.

5. Friedlander LT, Cullinan MP, Love RM. Dental stem cells

Page 30

Annals of SBV and their potential role in apexogenesis and apexification. Int Endod J. 2009;42(11):955–62.

6. Trope M. Regenerative potential of dental pulp. J Endod.

2008;34(7 Suppl):S13–7.

7. Huang GT-J. A paradigm shift in endodontic management of immature teeth: conservation of stem cells for regeneration. J Dent. 2008;36(6):379–86.

8. Jung I-Y, Lee S-J, Hargreaves KM. Biologically based treatment of immature permanent teeth with pulpal necrosis: a case series. J Endod. 2008;34(7):876–87.

9. Hargreaves KM, Giesler T, Henry M, Wang Y. Regeneration potential of the young permanent tooth: what does the future hold? J Endod. 2008 ;34(7 Suppl):S51–6.

10. Banchs F, Trope M. Revascularization of immature permanent teeth with apical periodontitis: new treatment protocol? J Endod. 2004;30(4):196–200.

11. Reynolds K, Johnson JD, Cohenca N. Pulp revascularization of necrotic bilateral bicuspids using a modified novel technique to eliminate potential coronal discolouration: a case report. Int Endod J. 2009;42(1):84–92.

12. Petrovic V, Stefanovic V. Dental tissue--new source for stem cells. ScientificWorld Journal . 2009;9:1167–77.

13. Cells B. Stem cells for tooth engineering. European cells and matierals.2008;16:1–9.

14. Peters O a. Translational opportunities in stem cell-based endodontic therapy: where are we and what are we missing? J Endod . 2014;40(4 Suppl):S82–5.

15. Li Y, Shu L-H, Yan M, Dai W-Y, Li J-J, Zhang G-D, et al. Adult stem cell-based apexogenesis. World J Methodol.

2014;4(2):99–108.

16. Saber SEM. Tissue engineering in endodontics Key Elements for Tissue Engineering. J Oral Sci. 2009;51(4):495–507.

17. Galler KM, Eidt A, Schmalz G. Cell-free approaches for dental pulp tissue engineering. J Endod . 2014;40(4 Suppl):S41–5.

18. Casagrande L, Cordeiro MM, Nör S a, Nör JE. Dental pulp stem cells in regenerative dentistry. Odontology. 2011;99(1):1– 7.

19. Nakashima M, Akamine A. The Application of Tissue Engineering to Regeneration of Pulp and Dentin in Endodontics. J Endod. 2005;31(10):711–8.

20. Demarco Flávio Fernando, Conde Marcus Cristian Muniz, Cavalcanti Bruno Neves, Casagrande Luciano, Sakai Vivien Thiemy NJE.Dental Pulp Tissue Engineering . Braz Dent j.

2013;22(1):3–13.

21. Kitamura C, Nishihara T, Terashita M, Tabata Y, Washio A. Local regeneration of dentin-pulp complex using controlled release of fgf-2 and naturally derived sponge-like scaffolds. Int J Dent. 2012;2012:190561.

22. El-Backly RM, Massoud AG, El-Badry AM, Sherif R a, Marei MK. Regeneration of dentine/pulp-like tissue using a dental pulp stem cell/poly(lactic-co-glycolic) acid scaffold construct in New Zealand white rabbits. Aust Endod J. 2008;34(2):52– 67.

23. Rosa V, Zhang Z, Grande RHM, Nör JE. Dental pulp tissue engineering in full-length human root canals. J Dent Res. 2013;92(11):970–5.

24. Fouad a F. The microbial challenge to pulp regeneration. Adv Dent Res. 2011;23(3):285–9.

25. Alongi DJ, Yamaza T, Song Y, Fouad AF, Elaine E. Tissue regeneration potential. 2011;5(4):617–31.

26. Huang GT-J, Garcia-Godoy F. Missing Concepts in De Novo Pulp Regeneration. J Dent Res. 2014;93(8):717–24.

Ann. SBV, July - Dec 2014;3(2)

ADVANCES IN PROSTHODONTIC BIOMATERIALS Dr. P. S. Manoharan, Dr. Balaji J

Abstract

Prosthodontics is a specialty that involves the replacement and restoration of lost dental structures with artificial substitutes. Many biomaterials have been developed to satisfy the demands laid by the functional, esthetic requirements of the stomato-gnathic system. The considerable advancements in this particular field, have often left the practicing dentist perplexed with regards to the correct choice. This paper provides an overview of the key recent advancements and milestones in biomaterial science in prosthodontics Key words: Prosthodontic biomaterials, impression materials, Ceramics, Implants, silicones.

Introduction Biomaterials used in the field of prosthodontia are those used for the replacement of the lost dentition. Of the plethora of Prosthodontic biomaterials available, the clinician is often puzzled with the choice of an appropriate biomaterial because of lack of sound scientific rationale and thorough knowledge and understanding of these materials. Most commonly, the clinician is guided by hearsay knowledge of the use of materials from other clinicians and medical representatives.

Evidence based practices should be encouraged to gain confidence in the use of dental biomaterials by any dental practitioner.

Advances are aimed at improving the existing materials and to welcome new materials, so that the final restoration is made biocompatible and survive in the oral environment for considerable period of time. It is important to be aware of the current trend of dental practices and recent advancements of materials so that the dentist and the patient would be benefitted.

Biomaterial can be understood as any biologic or synthetic substance that can be introduced into body tissue as part of an implanted medical device or used to replace an organ, bodily function, etc. The

following discussion will be based on the various commonly encountered biomaterials with their state of art and recent updates.

Laboratory Materials Denture Base Resins Flexible denture base material These materials evolved as a result of dentist satisfying the patient’s need for a softer clasp and ease of insertion. This material (polyamide) is considered to be ideal for partial dentures. The resin is a biocompatible nylon thermoplastic. Its unique physical and aesthetic properties provide unlimited design versatility and eliminates the concern about acrylic allergies. [1] The denture is thin and lightweight and flexible enough to enter below the undercuts. But it is unbreakable and does not stain easily. It is comfortable to the patient as no tooth or tissue preparation is needed. The denture is esthetically very pleasing.

Microwave Cured Denture Base Resin This resin is manipulated similar to conventional resins up to the point of curing. The microwave makes curing easier than conventional methods.

* Dr. P. S. Manoharan, Prof and Head, *Dr. Balaji. J, Sr. Lecturer, Department of Prosthodontics and Crown & Bridge, Indira Gandhi Intitute Dental Sciences, Sri Balaji Vidyapeeth, Puducherry 607402, India.

Ann. SBV, July - Dec 2014;3(2)

Page 31

Annals of SBV

Three minutes and a standard 500 watt microwave are needed to cure higher quality and more precise dentures. This process saves time, while increasing the accuracy and strength of denture bases. Source of the activator is the heat generated by the colliding molecules which moves or vibrates around their axis.

[2, 3]

Ultra high impact heat-cured denture base resins These resins evolved with the demand for high impact strength for the denture base material. These materials incorporate reinforcing materials and a curing temperature range that render them to be superior in their physical properties. These resins are claimed to be easily finished and polished, offer accurate fit and require at least 2 hours for heat polymerization. [4, 5] Glass fiber reinforced denture base resins Several types of fibers, including carbon, aramid, woven polyethylene and glass fibers, have been used to strengthen denture base resins. Carbon and aramid fibers strengthened the resin but caused clinical problems, such as difficulty in polishing and poor aesthetics. Woven polyethylene fibers are more aesthetic, but the process of etching, preparing, and positioning layers of woven fibers may be impractical for the dental office. Silanated glass fibers are the fibers of choice for reinforcing denture base polymers. Improvement in flexural properties and fatigue resistance are seen with the use of glass fibers. [6-9]

ADVANCES IN PROSTHODONTIC BIOMATERIALS

of the cross-linked and micro-filled composite teeth.

[10]

graphite die to erode the metal to final shape via spark erosion. [12-14]

need for the patient to have a bone graft, making the surgery simpler, faster and cheaper.

Titanium and its Alloys

Waxes

Clipping implant systems

Titanium is the most popular and commonly used among the metallic biomaterials in the field of medicine and dentistry. Titanium and its alloys are getting much attention for biomedical applications because of excellent biocompatibility, light weight, excellent balance of mechanical properties and corrosion resistance. Pure titanium and alpha + beta type titanium alloys including the Ti-6Al-4V, were originally designed for use as general structural materials, especially for aerospace structures, and only later adopted for biomedical applications.

However, the toxicity of the beta-stabilizing element Vanadium was later pointed out. Therefore V in the Ti-6Al- 4V has been replaced by other betastabilizing elements Fe or Nb, both of which are considered to be safer for the living body

Light curing waxes

This screw-less dental implant system connects implant and supra structure with a novel clipping mechanism. Fatigue of material, resulting in loose or broken screws and unintended malformations, is a possibility. [19]

Low-modulus beta-type titanium alloys composed of nontoxic and non-allergic elements, such as Ti-29Nb-13 Ta- 4.6 have been developed for medical and dental applications. The low modulus of this alloy effectively accelerates the healing of bone fracture and re-growth of bone. This type of alloy is also expected to be used in dental implants as well as in fixed dental prostheses such as crowns, inlays, bridges, and dentures. Very recently, nickel free shape-memory and/or super elastic betatype titanium have been developed for biomedical applications.

Denture Teeth

Casting titanium

Composite Denture Teeth

Titanium has a high melting point (16600c) and is melted using electric plasma arc or inductive heating in a melting chamber filled with inert gas or held in a vacuum. The molten metal then is transferred to the refractory mold via centrifugal or pressurevacuum filling. [11]

Micro filled denture teeth and Nano-filled denture teeth are available. Knoop hardness values (KHN) ranged from 28.2 to 29.8 for micro-filled composite, 18.9 to 21.6 for cross-linked acrylic, 22.7 for nano-composite, and 18.6 for conventional acrylic teeth. All micro-filled composite teeth were significantly harder than other teeth. The wear depth values were 90.5 μm for the nano-composite, 69.8 to 93.0 μm for the micro-filled composite, 80.8 to 104.0 μm for the cross-linked acrylic, and 162.5 μm for conventional acrylic teeth. The nano-composite tooth was harder and more wear resistant than the acrylic teeth but not significantly different from most Page 32

Machining titanium Dental implants generally are machined from billet stock of pure metal or alloy. Dental crowns and bridge frameworks also can be machined from solid metal stock via computer-aided machining.

Another method for fabricating dental appliances is electric discharge machining, which uses a fabricated Ann. SBV, July - Dec 2014;3(2)

The wax patterns of the metallic frameworks of the removable partial dentures could be made directly on the cast, using profiled waxes like: TiLight or LiWa (light curing waxes). These waxes eliminate duplicating techniques for the working models and saves time. They are used for all types of metal works, crowns, bridges, implants. After modeling, these waxes can be cured by any standard lab UV or halogen light. These waxes are easy to use, economic, cures quickly, has appreciable strength an elasticity and they are odorless and stable. [15, 16]

Magnets in Prosthetic Dentistry Magnets have generated great interest within dentistry and their application are numerous. The two main areas of their interest are in the field of orthodontics as well as removable prosthodontics.

The reason for their popularity is related to their small size and strong attractive forces that allows them to be placed in prosthesis without being obtrusive within the mouth.

The main magnetic materials used is the rare earth elements Neodymium-Iron ­Boron (Nd, Fe, and B). Other materials used include RE Alloy, Samarium-Cobalt (Sm-Co). Samarium iron nitride is a promising new candidate for permanent magnet application.

Another advancement includes the encapsulation of the pre-existing magnets within a relatively inert alloys such as stainless steel or titanium. [17, 18]

Implant Systems Porous Titanium Foam Implants The new porous titanium foam dental implants has been developed at the NRC Industrial Materials Institute (NRC-IMI) in Longueil. Unlike current solid titanium implants, the NRC-IMI material is porous. This provides a site for bone cells to grow into the implant and more solidly anchor it. This new porous yet durable material facilitates the creation of implants in smaller sizes. Its use will avoid the Ann. SBV, July - Dec 2014;3(2)

Surface modifications Dental implant surfaces are modified by titanium plasma spraying, acid etching, laser sintering or sandblasting. Surface coating with crystalline and amorphous phases of titanium fluorapatite and hydroxyapatite is done to enhance the osseointegration ability of titanium to bone. The titanium implant surface oxide layer modification can be done by anodically oxidising Ti in a proprietary electrolytic solution resulting in an increased thickness of oxide layer (coronally 1-2µm and apically 10µm) and a porous surface topography.

Bio-chemical modifications of implant surfaces by incorporation of bone morphogenetic proteins and growth factors have done in the intention to enhance the bone formation around the surface of the implant.

One approach for controlling cell-biomaterial interactions utilize cell adhesion molecules.

Since identification of the Arg-Gly-Asp (RGD) sequence as a mediator of attachment of cells to several plasma and extra cellular matrix proteins, including fibronectin, vitronectin, Type I collagen, osteopontin and bone sialoprotein, researchers have been depositing RGD – containing peptides on biomaterials to promote cell attachment. Cell surface receptors in the integrin super family recognize the RGD sequence and mediate attachment. [20] A second approach to biochemical surface modification uses biomolecules with demonstrated osteotropic effects. Many growth factors have been cloned and are recombinantly expressed.

They have effects ranging from mitogenicity (e.g., interlukin growth factor-1, FGF-2 and platelet rich plasma to increase activity of bone cells (e.g.

Transforming growth factor –1. (TGF—1) enhances collagen synthesis) to osteoinduction (e.g., bone morphogenetic proteins (BMPs). By delivering one or more of these molecules which normally play Page 33

Annals of SBV

ADVANCES IN PROSTHODONTIC BIOMATERIALS

essential roles in osteogenesis , directly to the tissueimplant interface, it is possible that bone formation may be promoted in implant applications. Platelet rich plasma (PRP) , a modification of fibrin glue made from autogenous blood, is being used to deliver growth factors in high concentration to sites where bone formation is needed. Growth factors released from plasma includes platelet derived growth factor (PDGF), transforming growth factor(TGF), platelet derived epidermal growth factor, platelet derived angiogenesis factor, insulin growth factor 1(IGF-1) and platelet factor. [21]

Stay put

Gingival Retraction Systems

Dental Ceramics are non-metallic, inorganic, structures primarily containing compounds of oxygen with one or more metallic or semi-metallic elements. They are characterized by their refractory nature, high hardness, susceptibility to brittle fracture at relatively low stresses and chemical inertness.

Recent advances in ceramic materials are In Ceram, Empress, Tech Ceram, Cad/Cam, Procera system, Captek system,

Expasyl It is temporary gingival retraction system. It is an alternate to traditional gingival retraction procedures (gingival retraction cords). It is a painless, fast, reliable and high quality system for temporary opening of sulcus.

Stay put is so pliable that it stays where you put it. Stay-put is a unique combination of softly braided retraction cord and an ultra fine copper filament which can be easily adapted and can be preformed.

It does not lift out of the sulcus, does not unravel, no overlapping is required and it is non-impregnated; but can be impregnated with an astringent or hemostatic solution as required. (22 23)

Ceramics

Expasyl is aluminum chloride in paste form.

Expasyl system separates marginal gingiva from tooth without harming the epithelial attachment.

Opening of sulcus does not cause bleeding. The risk of gingival recession or bone resorption that are sequel to damage caused to epithelial attachment is eliminated.

In-Ceram

Magic foam cord

A slurry of one of these materials is slip cast on a porous refractory die and heated in a furnace to produce a partially sintered coping. The partially sintered core is infiltrated with glass to eliminate porosity and strength slip core. Its fracture toughness is higher than conventional porcelain. In-ceram Spinel is indicated for anterior single unit inlays, on lays, crowns and veneers. In-ceram Alumina is indicated for anterior and posterior crowns and Inceram Zirconia is indicated for posterior crowns and FPD. The collective advantages of all three glassinfiltrated core materials are

1. Lack of metal.

2. Relative high flexural strength and toughness.

3. Ability to be use any luting cement.

Magic Foam Cord is the expanding PVS material. Magic Foam Cord is a Non-haemostatic gingival retraction system. Designed for easy and fast retraction of the gingival sulcus without the potentially traumatic and time consuming packing of retraction cord. Magic Foam Cord material is syringed around the crown preparation margins and a cap (Comprecap) is placed to reportedly maintain pressure. After five minutes, the cap and foam are removed and the tooth is ready for the final impression.

Advantages are non-traumatic method of temporary gingival retraction, easy and fast application directly to the sulcus without pressure or packing, effortless removal. It contains no hemostatic chemicals that may contaminate the impression

Page 34

In-Ceram is supplied as one of the three core materials

1. In Ceram Spinel

2. In Ceram Alumina

3. In Ceram Zirconia.

Empress This ceramic is hot pressed injection molded ceramics. It utilizes the lost wax technique. A Lucite re-enforced glass ceramic is pressed into the mold at 1050 temperature. The increased strength is Ann. SBV, July - Dec 2014;3(2)

attributed to finely dispersed Lucite crystals, which increase the resistance to crack propagation. [24] Advantages are lack of metal, translucent ceramic core, high flexural strength, Excellent fit and esthetics. Disadvantages are potential for fracture if used in posterior region. Its use is limited to use as a core material for crowns and very short span bridges.

Techcerem A thin (0.1 – 1.0) alumina core base layer is produced using thermal spray technique resulting in a density of 80 to 90%. Optimum strength and translucency are achieved by a sintering process at 1170°C. The range of base layer thickness makes this technique versatile and appropriate to a range of restoration types. Subsequent reproduction of aesthetics is achieved by the incremental application of a range of specially developed porcelains in the traditional manner CAD/CAM Computer aided designing and computer aided manufacturing (CAD/CAM) technology in dentistry is increasing, both in the dental laboratory and general practice settings, to fabricate all-ceramic inlays, onlays, crowns, and veneers. Only one CAD/ CAM system that is available for in-office chair side use, namely CEREC® 3D. A digital image is captured of the tooth preparation. This image contains three dimensional information regarding size of the tooth and defect being restored. The restoration is designed in the computer. A tooth colored block of ceramic or composite is then used to machine the restoration.

Improvements to the original system include new software, the introduction of finer grained porcelain blocks to reduce oppositional wear, a wider range of preformed ceramic block shades and conversion to an electric turbine with better cutting control for greater fitting accuracy. The newer milling systems include the use of the blocks in gradient form to mimic the translucency of the tooth structure. All the blocks which are being used in the recent past are bar coded, that holds the information of the block used with the CAD data, which would enable the technician to fabricate a similar restoration, in case of clinical failure of a restoration. [25, 26]

Ann. SBV, July - Dec 2014;3(2)

Procera System These all-ceramic individual restorations comprise a densely sintered alumina core. It contains 99.9% alumina and it the hardest among ceramics used. It can be used for anterior, posterior crowns, veneers, onlays and inlays. [27, 28, 29] Captek System Captek is acronym for capillary casting technology.

An alternative methodology for elimination of the casting process from metal-bonded crowns and bridges. This technique involves the adaptation of a wax strip, impregnated with a gold platinumpalladium powdered alloy, to a refractory die. Firing produces a rigid porous layer which is then in filled with gold from a second wax strip by capillary action.

The finalized metal coping is then veneered with porcelain. The advantages of this system are said to include improved marginal fit (attributed to use of the capillary cast, rather than the lost wax technique) and enhanced aesthetics and biocompatibility.[30]

Recent Core Materials and Technologies The most recent core materials for all-ceramic FPDs are the yttrium tetragonal Y-TZP-based materials. Y-TZP-based materials were initially introduced for biomedical use in orthopedics for total hip replacement and were highly successful because of the material’s excellent mechanical properties and biocompatibility. In the early 1990s, the use of Y-TZP expanded into dentistry (endodontic posts and implant abutments) and Y-TZP is currently being evaluated as an alternative core material for full-coverage restorations such as all-ceramic crowns and all-ceramic FPDs. Yttrium oxide is a stabilizing oxide added to pure zirconia to stabilize it at room temperature and to generate a multi phase material known as partially stabilized zirconia. The exceptional mechanical properties of Y­TZP (high initial strength and fracture toughness) are due to the unique physical property of partially stabilized zirconia. Tensile stresses acting at the crack tip induce a transformation of the metastable tetragonal zirconium oxide form into the monoclinic form.

This transformation is associated with a local increase of 3% to 5% in volume. This increase in volume results in localized compressive stresses Page 35

Annals of SBV

being generated around and at the tip of the crack that counteract the external tensile stresses acting on the fracture tip. This physical property is known as transformation toughening.

Because of their material-inherent advantages, Y-TZP-based all-ceramic restorative systems may allow prosthodontists to use traditional clinical procedures similar to those used in the fabrication of metal-ceramic restora­tions in terms of preparation design and cementation procedures. With Y-TZPbased systems that use a CAD/CAM technology, ceramists use new techniques and technologies in addition to traditional ones. Such new technologies may allow the production of consistent highquality Y - TZP frameworks in terms of design and fabrication, strength, fracture toughness, and stresscorrosion resistance.

They are esthetic, have clinically acceptable marginal fit, and allow the ceramist to use traditional veneering procedures with the compatible esthetic porcelain. In addition, such systems may prove to be simple to handle and less technique sensitive from a clinical standpoint while providing patients with esthetic and functional restorations.

The long-term results of these studies are paramount to the assessment of their long-term success and for the establishment of more specific guidelines for proper patient selection that will ensure long-term predictable esthetic and functional success. ­[31, 32]

Impression Materials Alginate is the most commonly used impression material and has the advantages such as quick setting time, low cost, and mild flavor. But it has considerable disadvantages like poor dimensional stability, messy, hazardous dust, and needs repetitive hand mixing.

Dustless Alginate To overcome these disadvantages various modifications have been done like dustless Alginate which Contain high algin content. Glycerin is incorporated on alginate particles. The high align content provides for a quality impression without the excessive flow.

Page 36

ADVANCES IN PROSTHODONTIC BIOMATERIALS

Fluoride containing alginate

Hydrophilic Polyvinyl Siloxane

Addition of NaF or SnF2 in an alginate impression material may result in effective release of fluoride without deteriorating the properties of material itself. Fluoride-containing dental alginate impression materials can exert a considerable reduction in enamel solubility

To improve hydrophilic properties, surfactant and hydrophilic monomer are added which result in a truly low contact angle. A lower contact angle measure means greater “wettability”, displacing oral fluids for a more detailed impression. These additives also increase surface energy within the material, and therefore increase detailed reproductions, even in the presence of blood and saliva. However, addition of surfactants makes the preparation of electroformed dies more difficult as the metallizing powder does not adhere well to the surface of hydrophilic addition silicone.[33]

Chromatic Alginate This alginate provides rapid processing and setting times. It has improved compatibility with plaster of paris. It is thixotropic, does not drip and only flows when pressure is exerted during the impression procedure. It is also uniform, smoother and the compact surface enables a higher definition of detail. Three-phases of chromatic alginate are as follows: Purple phase denotes mixing time, orange phase denotes processing time and the yellow phase indicates insertion into the mouth.

Auto-Mix Alginate AlgiNot is a time-saving, cost-effective alternative to traditional alginate. It is not hand mixed, improving the handling characteristics. Thus it saves time. This material is not affected by the disinfectant, thus infection control is assured.

Silgimix This is an alginate replacement impression material. Silgimix is developed from vinyl polysiloxane chemistry. It addresses the shortcomings of alginate materials by giving users the ability to disinfect, the option of pouring multiple times and the ability to scan the impression electronically.

Rubber based impression materials are nonaqueous impression materials. The most widely used rubber based impression material is polyvinyl siloxane (PVS). This widespread use is attributed to its dimensional stability, ease of handling, excellent elastic recovery, good detail reproduction, ability to pour multiple casts from single impression. A significant limitation of PVS is its hydrophobicity.

This causes difficulty in impression making procedure in presence of blood and saliva and also during pouring a cast. To overcome this limitation hydrophilic polyvinyl siloxane has been introduced.

Ann. SBV, July - Dec 2014;3(2)

Vinyl Poly ether Silicone Yet another effort to improve the mechanical and physical properties of the elastomer is the introduction of Vinyl Poly Ether Silicone which is a hybrid of poly-vinyl siloxane and polyether.

This material is made hydrophilic and relatively rigid by virtue of the polyether component and the properties of flow and detail reproduction is offered by polyvinyl siloxane.

This material is available in light body, monophase and heavy body consistencies which can be used in a single step technique, double step technique and putty wash technique. It is claimed that there may be a possible loss of detail reproduction if the material in incompletely mixed. Although the manufacturers claim mechanical and physical properties superior to other elastomers, further studies are required to substantiate the evidence.[34] Nano-filled Poly vinyl Siloxane Nano-fillers are integrated in poly vinyl siloxane impression material It has improved hydrophilic properties, better flow, enhanced detail and precision. The newest class of elastomeric impression materials is a vinyl-polyether hybrid material called SENN. SENN combines properties from addition silicone and polyether impression materials. It is a polymer with polyether and siloxane (addition silicone) groups. With the polyether groups, a hydrophilic material is produced without the use of a surfactant.

Ann. SBV, July - Dec 2014;3(2)

With the siloxane groups on the polymer chain, a material that is dimensionally stable and has good recovery from deformation is combined with hydrophilic properties that the polyether groups produce. SENN has a platinum catalyst. The tear strength is a little low, but the wetting properties of SENN are good. It is supplied as a putty - heavy, medium, and wash materials - in either a fast or regular set material. These hybrid materials have the intrinsic hydrophilicity necessary to improve impression making by wetting a tooth and allowing easy pouring for cast fabrication. [35]

Maxillofacial Prosthesis Materials [36,37] These biomaterials are developed to fabricate restorations of acquired or congenital maxillofacial defects. The polymethyl methacrylate resins are gold standard for rehabilitations intraorally. The extra oral defects need restorations which not only closes the defect but also resist the ravages of time, temperature and other mechanical and physical properties such as dimensional stability, colour stability etc. A few of the recently evolved maxillofacial materials have been discussed below, which has stood the test of time.

Isophorone Polyurethane A unique polyurethane elastomers based on a cycloaliphatic di isocyanate monomer is being developed and tested. The material is formulated as a three-component kit comprising an isocyanateterminated prepolymer, a triol as the cross-linking agent, and an organotin catalyst. The elastomers have unusually high strength compared to other aliphatic polyurethanes. This is due to cycloaliphatic isopherone moiety in the vulcanized network. The aliphatic nature of the polymer improves resistance to the sunlight degradation common to aromatic polyurethanes. The system is not hazardous to the prosthodontist or the patient.

SE-4524U This silicone is representative of family of polymers that require moderate to high temperatures for the initiation of the cross-linking reaction.

The Silastics 44514 and 44515 available from Dow Corning are of the same general type. General Electronic provides the SE-4524U material in the Page 37

Annals of SBV

form of unprocessed gum stock, with or without incorporated catalyst. The vulcanization reaction involves the combination of methyl groups on the polymer chains. An organic peroxide is used to initiate the cross-linking reaction.

With this material, the prostheses must be fabricated at a temperature high enough to cause decomposition of the peroxide catalyst.

PDM Siloxane It is a type of HTV silicone that has physical and mechanical properties that exceeded values considered clinically acceptable.

Q7-4635, Q7-4650, Q7-4735, SE-4524 U These are new generation of HTV silicones, which have improved mechanical and physical properties.

The processing characteristics of Q7-4635 and SE4524U were particularly favorable because of their single component system with unlimited shelf life.

MDX 4-4210 Because of remarkable improvements over the older Silastic polymers, this material has become increasingly popular in the maxillofacial clinics.

The elastomer is based primarily on a modified poly dimethyl siloxane (PDMS) structure, and the vulcanization mechanism involves the addition of Si-H groups to Si-vinyl units. A platinum catalyst initiates the cross-linking reaction; the curing reaction is sensitive to any contaminant which is capable of coordination with the platinum catalyst.

Amines, sulfur and tin compounds are especially troublesome and inhibit the cure of the material.

A-2186 It is a recently developed material whole physical and mechanical properties are inferior compared to MDX 4-4210.

Conclusion Although, marked breakthrough in technology and recent advancements in biomaterials present with a massive assortment of materials and techniques, it is ultimately the job of the practicing dentist to choose the materials to suit the biological, functional Page 38

ADVANCES IN PROSTHODONTIC BIOMATERIALS

and esthetic requirements of the restorations and replacements in the complex oral environment.

It is mandatary that clinicians should be updated about various biomaterials and their manipulative characteristics and technical considerations which would enable them to render quality care for patients.

References 1. Prashanti E, Jain N, Shenoy VK, Reddy JM, Shetty B T, Saldanha S. Flexible dentures: A flexible option to treat edentulous patients. Journal of Nepal dental association 2010; 11: 85-7.

2. Yannikakis S, Zissis A, Polyzois G, Andreopoulos A. Evaluation of porosity in microwave-processed acrylic resin using a photographic method. J Prosthet Dent 2002; 87: 613-9.

3. Levin B, Sanders JL, Reitz PV. The use of microwave energy for processing acrylic resins. J Prosthet Dent 1989; 61:38185.

4. Yadav NS, Elkawash H. Flexural strength of denture base resin reinforced with aluminum oxide and processed by different processing techniques. J Adv Dental Research 2011; 26: 214-19.

5. John J, Gangadhar SA, Shah I. Flexural strength of heatpolymerized polymethyl methacrylate denture resin reinforced with glass, aramid, or nylon fibers. J Prosthet Dent 2001; 86:424-27 6. Franklin P, Wood DJ, Bubb NL. Reinforcement of poly (methyl methacrylate) denture base with glass flake. Dent Mater 2005; 21:365-70.

7. Puri G, Berzins DW, Dhuru VB, Raj PA, Rambhia SK, Gunjan Dhir, Dentino AR, Effect of phosphate group addition on the properties of denture base resins. J Prosthet Dent 2008; 100: 302-08.

8. Vuorinen AM, Dyer SR, Lassila LVJ, Vallittu PK. Effect of rigid rod polymer filler on mechanical properties of polymethyl methacrylate denture base material. Dent Mater 2008; 24: 708–13.

9. Cheng Y, Sakai T, Moroi R, Nakagawa M, Sakai H Selfcleaning Ability of a Photo catalyst-containing Denture Base Material. Dent Mater 2008; 27: 179-86.

10. Suzuki S. In vitro wear of nano-composite denture teeth. Int J Prosthodont. 2004; 13(4):238-43.

11. Low D, Mori T. Titanium full crown casting: thermal expansion of investments and crowns accuracy. Dent Mater 1999; 15:185-90.

12. Hung CC, Hou GC, Tsai CC. Pure titanium casting into zirconia-modified magnesia-based investment molds. Dent Mater 2004; 20: 846–51.

13. Paulino SM, Leal BC, Pagnano VO, Bezzon OL. The castability of pure titanium compared with Ni-Cr and NiCr-Be alloys. J Prosthet Dent 2007; 98: 445-54.

14. Ellingsen JE, Johansson CB, Wennerberg A, Holmen A. Improved retention and bone to implant contact with fluoride modified titanium implants. Int J Oral Maxillofac Implants 2004; 19: 659-66.

15. William J.O’brein: Dental Materials and their selection: Quintessence Publishing Co., 3rd edition; 1985.

Ann. SBV, July - Dec 2014;3(2)

16. Kenneth J. Anusavice. Philips’ Science of dental Materials, W.B. Saunders Company; A division of Harcourt Brace & Company, 11th edition,1999.

17. Highton R, Caputo AA, Pezzoli M, Matyas J. Retentive characteristics of different magnetic systems for dental applications. J Prosthet Dent 1986;56:104-6.

18. Riley MA, Walmsley AD, Harris IR. Magnets in prosthetic dentistry. J Prosthet Dent 2001; 86:137–42.

19. Tomas A, Wennerberg A. Oral implant surface: part 2 – review focusing on clinical knowledge of different surfaces.

Int J Prosthodont 2004; 17: 544-64.

20. John B. Brunski. Biomaterials and Biomechanics of Oral and Maxillofacial Implants: Current Status and Future Developments. Int J Oral Maxillofac Implants 2000;15: 1546.

21. G. Ajay kumar. Recent Advances in Dental Implantology.

Journal of Dental and Medical Sciences 2012;3: 28-30.

22. Ferrari M, Cagidiaco MC, Ercoli C. Tissue management with a new gingival retraction material: a preliminary clinical report. J Prosthet Dent 1996: 75; 242-47.

23. Bowles WH, Tardy SJ, Vahadi A. Evaluation of new gingival retraction agents. J Dent Res 1991; 70: 1447-52.

24. Rouse JS. Use of heat-pressed leucite reinforced porcelain in “difficult” veneer cases: A clinical report. J Prosthet Dent 1996; 76(5): 461-63.

25. Dianne Rekow. Dental CAD CAM Systems. State of the art.

J Am Dent Assoc 1991;122: 43-48.

26. Werner H Mormann, Andreas Bindel. All ceramic, chairside computer aided dental restoration. Dent Clin N Am 2002: 46; 405-26.

27. Brunton PA, Smith P, Mc Cord JF, Willson NH. Procera allceramic crowns: a new approach to an old problem? Br Dent J 1999;186: 430 – 34.

Ann. SBV, July - Dec 2014;3(2)

28. Anusavice K J. Recent developments in restorative dental ceramics. J Am Dent Assoc 1993; 124: 72-84.

29. Jason AG. Recent advances in materials for all-ceramic restorations. Dent clin N Am 2007: 51; 713-27.

30. Rizkalla AS, Jones DW. Indentation fracture toughness and dynamic elastic moduli for commercial feldspathic dental porcelain materials. Dent Mater 2004; 20:198–206.

31. Luthardt RG, Holzhuter MS, Rudolph H, et al. CAD/ CAM-machining effects on Y-TZP zirconia. Dent Mater 2004;20:655-662.

32. Giordano R, Morgano S, Papanagiotou H, and Pober R. Invitro evaluation of low temperature aging effects and finishing procedures on the flexural strength and structural stability of Y-TZP dental ceramics. J Prosthet Dent 2006; 96:154-64.

33. Shetty R M, Bhander G R, Mehtha D. Vinyl polysiloxane ether – A breakthrough in Elastomeric impression material.

World journal of dentistry 2014; 5(2): 134-37.

34. Johnson GH, Chellis KD, Gordon GE, lepe X. Dimensional stability and detail reproduction of irreversible hydrocolloid and elastomeric impression disinfected by immersion. J Prosthet Dent 1998; 79: 446-53.

35. Wadhwani CP, Johnson GH, Lepe X, Wataha JC. Accuracy of reformulated fast set vinyl poly siloxane impression material using dual arch trays. J Prosthet Dent 2009; 101 : 332-41.

36. Woofaardt JF, Chandler HD, Smith BA. Mechanical properties of a new facial prosthetic material. J Prosthet Dent 1985; 53: 228-36.

37. John F Lontz. State of the art material used for maxillofacial prosthetic reconcstruction. Dent Clin N Am 1990: 34; 2-14.

Page 39

Annals of SBV

BIOMATERIAL ADVANCES IN ORTHODONTICS

Platinum Coated Brackets These bracket have five times the abrasion resistance of gold. A smoother, harder surface than stainlesssteel for reduced friction and improved sliding mechanics is achieved by using this system.

BIOMATERIAL ADVANCES IN ORTHODONTICS Arani Nandakumar, Anoop K. Mathew

Nickel-free Brackets (Fig 3)

Abstract The practice of orthodontics requires professional skill in the design, application and control of corrective appliances to bring teeth, lips and jaws into proper alignment and to achieve facial balance. To achieve this desirable end, knowledge and skill of an orthodontist, is strongly supported by the use of various biomaterials.

The materials used should possess not only adequate physical and mechanical strength to bring about biomechanical changes in the bone, but also should possess the biological properties to sustain in the harsh environment of the oral cavity. These material should also be able to maintain their metallurgical properties under stress and strain. This article highlights the recent advances in such materials used in orthodontics.

Key words: orthodontic brackets, ceramic brackets, arch wires, stainless steel wires, nickel titanium wires, micro implants

Introduction The biomaterials used in the oral cavity should possess certain qualities. It should be non-toxic, possess reasonable strength, hydrolytic stability, high purity and sterilizability. It should also possess reproducible quality and be resistant to tarnish and corrosion.Some of the biomaterials used by an orthodontist are brackets, arch wires, bands, elastics, adhesives and etchants, cements, impression materials, and micro implants.

Brackets One of the most important passive components of fixed appliances is brackets. They are merely handles for attachment of the force producing agents to move the tooth in all possible direction, similar to a door handle which allows us to open or close a door. They can affect the directions of the force vectors when torque, angulations, and in/out are built into the brackets.[1] In order to deliver the exact force from the wire to the teeth, brackets should have the correct hardness and strength. They should have a smooth

arch wire slot to reduce frictional resistance, and an otherwise smooth surface to reduce plaque deposition. Because most orthodontic brackets are produced with a three-dimensional prescription for each tooth, they should be accurately manufactured to reflect this. They should also have a high corrosion resistance and good biocompatibility. [2]

nickel sensitivity, and inadequate retention. Its onepiece construction requires no brazing layer, and thus it is solder and nickel-free.[3] Gold-Coated Brackets (Fig 2) Recently gold-coated steel brackets have been introduced and rapidly gained considerable popularity, particularly for maxillary posterior and mandibular anterior and posterior regions. Brackets are now available with 24 karat gold plating, plated with 300 micro inches of gold.Gold-coated brackets may be regarded as an esthetic improvement over stainless steel attachments, and they are more hygienic than ceramic alternatives. [4]

Stainless steel had been the material of choice for fabrication of many orthodontic components.

Stainless steel had shown tendency for corrosion, and also there was a constant need for esthetics, which led to the use of other materials for manufacture of the brackets. Titanium, polycarbonates, ceramic and gold are such material used for brackets.

Figure 3: Nickel-free Brackets

Titanium Brackets (Fig 1)

Ceramic Brackets

Titanium and titanium-based alloys have the greatest corrosion resistance of any known metals.

Titanium also has low thermal conductivity, and thus alleviates the sensitivity to extreme temperature changes often experienced by patients wearing metal appliances. They have also solved the problems of

* Dr. Arani Nandakumar, Professor and Head, Dr. Anoop K. Mathew, Sr. Lecturer, Department of Orthodontics and Dento-facial Orthopedics, Indira Gandhi Intitute Dental Sciences, Sri Balaji Vidyapeeth, Puducherry 607402, India.

Page 40

Figure 1: Titanium Brackets

Ann. SBV, July - Dec 2014;3(2)

Nickel free brackets are made of Cobalt chromium (CoCr) dental alloy. It is a one piece construction manufactured by metal injection molding,which gives more finish and less friction.

They also have a laser structure base finish for better retention.

Figure 2: Gold- Coated Brackets Ann. SBV, July - Dec 2014;3(2)

Ceramic brackets are esthetic, thus are popular among the patients. It also does not stain like the plastic brackets. However it is brittle and hard, thus tends to fracture. The bond strength to enamel is so high that the enamel fractures during debonding.

Ceramics used for the manufacturing of ceramic brackets were Alumina and Zirconia. Both can be found as tri-dimensional inorganic macromolecules.

Page 41

Annals of SBV

BIOMATERIAL ADVANCES IN ORTHODONTICS

The types of ceramic brackets are 1. Monocrystalline (Saffire)(Fig 4)

2. Polycrystalline alumina(Fig 5)

3. Polycrystalline zirconia-yttrium oxide partially stabilized zirconia (YPZC) [5,6]

in the range of 0.005 to 0.010. Five or seven wires are wrapped around a central wire. It is very flexible and requires less force. It is also less expensive than titanium alloys. [9]They are available as triple stranded, co-axial and braided.

Advances in Titanium wires Titanium Molybdenum alloy (TMA) This Beta titanium alloy is also called as Titanium niobium alloys. It is soft and easy to form with stiffness 70% lower than SS wires so that creative bends are easily made. This wire is used as finishing wire due to its low spring back and high formability. [10] However exposure to fluoride agents have been found to degrade the properties of the wire.

Super Cable

Arch Wires

Titanium Molium alloy

Advances in improving esthetics in wires

Orthodontic arch wires are one of the most important active elements of the orthodontic armamentarium. They generate the biomechanical forces transmitted through the brackets to effect tooth movement. It is a common saying that “An Orthodontist is as good as the arch wire he uses.”

The arch wires are broadly classified as metallic and non-metallic. The metallic ones include gold alloys, stainless steel, Cobalt-chromium, Nickel titanium, Beta and Alpha titanium. The non-metallic ones include polymers and composite/ coated materials.

This is an Alpha-beta titanium alloy and has been introduced recently. It has stiffness, elasticity and yield strength that are between stainless steel and beta-titanium wires [11]. It is more resistant to breakage, smoother for reduced friction, and highly polishable and aesthetically pleasing. It is excellent for all phases of treatment.

Teflon Coated NiTi

Figure 6: Ceramic with metal slot

Figure 4: Mono Crystalline brackets Comparison of frictional forces produced in ceramic and stainless steel brackets, when different wires were used, suggested that for most sizes, the wires in ceramic brackets produced significant greater

Advances in Stainless steel wires Nickel Free Stainless Steel

Figure 5: Poly Crystalline friction. To reduce frictional resistance, development of ceramic brackets with smoother slot surfaces and consisting of metallic (stainless steel and gold), silica lining or ceramic/plastic slot surfaces was considered and presently accomplished[7].(Fig 6) Page 42

The manufacturers have taken this process one step further introducing ‘variable transition temperature’within the same arch wire[12]. This takes the form of graded force delivery within the same aligning arch wire providing light force of approximately 80g anteriorly, and a heavier force of 300g posteriorly[13]. The level of force is therefore graded throughout the arch length according to tooth size[14].

The 18-8 stainless steel is the most commonly used arch wire. Though it exhibits good corrosion resistance, releases nickel and chromium in minor concentration resulting in hypersensitivity reactions.

Thus steel is alloyed with 10-14% manganese, and 0.9% nitrogen to compensate for nickel. It has high corrosion resistance and better mechanical properties.

Wires under the name Manzanium(Scheu) or Noninium(Dentaurum) are currently available. [8] Multi-stranded SS wires Multi-stranded wires are made of a varying number of stainless steel wire strands coaxially placed or coiled around each other in different configurations. Individual strands are of dimensions Ann. SBV, July - Dec 2014;3(2)

Advances in Nickel Titanium wires Popularly this alloy is called as the Nitinol and is characterised by high resiliency, limited formability, shape memory and pseudoelasticity or superelasticity. The last two features are attributed to the phase transformation from the austenitic to martensitic phase on stress. This elasticity allows a wide deflection and activation range by delivering low forces. Low formability, inability to weld and high cost are the disadvantages. The friction at the bracket-wire interface is also more when compared to other wires. They have excellent corrosion resistance.

Graded thermodynamic Nickel Titanium alloys The response of a tooth to force application and the rate of tooth movement is dependent on the amount of a constant and low force. It is possible to produce variation in arch wire force between arch wires of identical dimension by specifying transition temperature within given range.

Ann. SBV, July - Dec 2014;3(2)

Super cable is a seven-stranded round coaxial super elastic NiTi arch wire. The concept is similar to the multi stranded wires of stainless steel. The advantages are increased flexibility and a reduced load deflection rate. However if the wire is not cut with a sharp instrument it can fray. [15]

The development of coated arch wires is a testimony to the efforts in search of esthetics. There is a parent NiTi wire over which organic coating is placed.Teflon (polytetraflouro ethylene) is most commonly used for coating. The size of the parent wire for a given slot size is less to accommodate for the thickness of the coating which could significantly alter the force delivering characteristics.Teflon coated arch wires are available in natural tooth shades and in other colors such as blue, green, purple[14].

Other coated wires are Marsenol (coated with poly tetraethyl emulsion, ETE) and Lee White Wire (Epoxy coated).

Organic Polymer Wire(QCM) Organic polymer retainer wire is made from 1.6mm diameter round polytheline terephthalate.

This material can be bent with a plier, but will return to its original shape if it is not heat–treated for a few seconds at temperature less than 230°C(melting point). These wires are used for aesthetic maxillary retainers.

Optiflex This is a non-metallic orthodontic arch wire designed by Dr. Talass and manufactured by Ormco.

It has got unique mechanical properties with a highly Page 43

Annals of SBV

aesthetic appearance made of clear optical fiber. It comprises of 3 layers.1. A silicon dioxide core that provides the force for moving tooth 2. A silicon resin middle layer that protects the core form moisture and adds strength. 3. A strain resistant nylon outer layer that prevents damage to the wire and further increases strength.It is esthetic, stain resistant. It’s effective in moving teeth using light continuous force and is very flexible. [16] Fibre-reinforced composite arch wires Fibre-reinforced polymer composites are highly aesthetic, biocompatible, hydrolytically stable, and absorbs less water. It is as stiff as the metallic wires with desirable formability and frictional resistance. [17] The main advantage is that it can be directly bonded to the tooth obviating the need for the bracket. To reduce the abrasive wear of the composite and the subsequent leaching of the glass, it is coated with parylene. A new fibre which is reinforced with S2 fibre in Bis GMA matrix is available as ropes, woven or uni-directional strips. It is pre polymerized during manufacturing making them flexible and adaptable.

Micro Implants(Fig 7) One of the greatest single innovation in clinical orthodontics is advent of temporary anchorage

Figure 7: Micro Implants

Page 44

BIOMATERIAL ADVANCES IN ORTHODONTICS

devices widely known as mini-screws or miniimplants (TAD’S).The use of TADs allows the application of force vectors that were previously difficult to achieve.The use of bone screws has increased the envelope of orthodontic treatment, providing an alternative to orthognathic surgery and allowing asymmetric tooth movements in all three plane of space. [18]

Conclusion Technological and material advancement has progressed the quality of orthodontic treatment rendered for the patients. The advances in the biomaterials has enhanced the biomechanical principles used in the treatment of malocclusion.

Orthodontists rely so much on the materials that a sub discipline of orthodontic material science has evolved. It is imperative for an orthodontist to be abreast with the latest development so as to use them effectively in the light of scientific evidence.

13. Gil FJ, Planell JA. Effect of copper addition on the superelastic behavior of Ni-Ti shape memory alloys for orthodontic applications. J Biomed Mater Res Appl Biomat 1999;48:682-88.

14. Mertmann M. Processing and quality control of binary NiTi shape memory alloys. In: Yahia L’H, ed. Shape Memory Implants.Berlin, Germany: Springer-Verlag; 2000:24–25.

15. Sebastian B. Alignment efficiency of superelastic coaxial nickel-titanium vs superelasticsingle-stranded nickeltitanium in relieving mandibular anterior crowding. A randomized controlled prospective study. Angle Orthod.

2012;82:703–8.

16. Talass M E .Optiflex archwire treatment of a skeletal Class HI open bite. J Clin Orthod 1992;26:245-52.

17. Burstone CJ, Kuhlberg AJ. Fiber-reinforced composite in orthodontics. J Clin Orthod. 2000;34:271–9.

18. Suh HY, Lee SJ, Park HS. Use of mini-implants to avoid maxillary surgery for Class III mandibular prognathic patient: a long-term post-retention case. Korean J Orthod.

2014;44(6):342-9.

References 1. Thamizharasi, Senthilkumar. Evolution of Orthodontic Brackets. JIADS 2001;1(3):25-30 2. Oh KT, Choo SU, Kim KM, Kim KN. A stainless steel bracket for orthodontic application. Eur J Orthod. 2005;27(3):23744 3. Kusy RP. Materials and appliances in orthodontics: brackets, arch wires, and friction. Curr Opin Dent. 1991:1(5):634-44.

4. Leinfelder KF, Kusy RP. Age-hardening and tensile properties of low gold (10–14kt.) alloys. J Biomed Mater Res. 1981;15:117–35.

5. Mehrotra AK. Physical properties and clinical characteristics of ceramic brackets: A comprehensive review. Trends in Biomaterials and Artificial Organs 2007;20(2):101-15.

6. Kusy RP, Whitley JQ. Friction between different wire-bracket configurations and materials. Semin Orthod 1997;3:166–77.

7. Ghafari J. Problems associated with ceramic brackets suggest limiting their use to selected teeth. Angle Orthod.

1992;62:145-52.

8. Oh K, Kim Y, Park Y, Kim K. Properties of super stainless steels for orthodontic applications. J Biomed Mater Res Part B: Appl Bio mater 2004;69B:183-94.

9. Rucker BK, Kusy RP. Elastic flexural properties of multistranded stainless steel versus conventional nickel titanium archwires. Angle Orthod. 2002;72:302-9.

10. Dalstra M, Denes G, Melsen B. Titanium-niobium, a new finishing wire alloy. Clin Orthod Res 2000;3:6-14.

11. Krishnan V, Kumar J. Mechanical properties and surface characteristics of three archwire alloys. Angle Orthod 2004a;74:825–31 12. Goldberg AJ, Shastry CV. Age hardening of orthodontic beta titanium alloys. J Biomed Mater Res. 1984;18:155–63.

Ann. SBV, July - Dec 2014;3(2)

Ann. SBV, July - Dec 2014;3(2)

Page 45

Annals of SBV

NANOTECHNOLOGY IN ADHESIVE RESTORATIVE BIOMATERIALS

resin restorative materials use acid etching of the tooth structure to adhere micro mechanically. [3, 4] NANOTECHNOLOGY IN ADHESIVE RESTORATIVE BIOMATERIALS

Despite the numerous virtues of composite resins, strength, polymerization shrinkage and longevity have been their vices. Rigorous research is still going on to improve their mechanical properties, resulting in quick and effective succession of newer materials.

Dr. Carounanidy Usha, Dr. Bindu Meera John

Abstract Adhesive restorative materials are tooth coloured materials that adhere to the enamel and dentin, either using the micro-mechanical retention or chemical bonding. Adhesion to tooth structure has obviated many of the disadvantages experienced with metallic materials providing better tooth-restorative margins, excellent aesthetics and ultra-conservation of tooth structure. Therefore, adhesive dentistry is considered as a vital breakthrough in restorative dentistry. If aesthetics and adhesions are their positive points, strength and wear resistance are their week points. In order to meet up to the standards of ideal bio mimetic material , exhaustive attempts are being made in rendering them as effective bioactive materials, by adding antibacterial property and remineralizing capacity. Nano technology, a revolution in science at large has played a pivotal role in overcoming the negative aspects of the adhesive restorative materials. This paper highlights few of the avenues where nanotechnology has effectively influenced the way the adhesive restorative materials perform.

Key words: adhesive dentistry, nano technology, nano fillers, antibacterial activity, remineralizing capacity

Introduction: Restorations are artificial replacement of the lost tooth structure due to disease; it should restore the form, function of the tooth structure and also restore the aesthetics and phonetics of the patient.

Various metallic and non-metallic materials are used for this purpose of restoration.

Restorative–tooth junction is a biologically week interface. Marginal degradation of the material results in micro leakage, percolation and microbial growth in the interface leading to secondary caries.

Secondary caries is one of the major reason for restoration replacement. [1] This is more evident with the metallic restorative materials. These materials are retained in the tooth preparation with macro mechanical retention that also necessitates excessive removal of healthy tooth structure.

Though the metallic restorations are strong and last long, the patients’ acceptance is less due to their un aesthetic appearance.

Adhesive restorative materials are tooth coloured materials that adhere to the enamel and dentin, either using the micro-mechanical retention or chemical bonding. [2]Adhesion to tooth structure has obviated many of the disadvantages experienced with metallic materials providing better toothrestorative margins, excellent aesthetics and ultraconservation of tooth structure. Therefore, adhesive dentistry is considered as a vital breakthrough in restorative dentistry.

Resin based composites and glass ionomer cements are two major class of tooth coloured adhesive restorative materials that are currently in use. While glass ionomer cement adheres to the tooth structure by chemical bonding, the composite

Yet another vital area of advancement is towards rendering them anti-cariogenic. Addition of antibacterial and/or remineralizing elements into their composition makes these materials bioactive, thus preventing dental caries around and underneath them. The release of such components to the immediate vicinity of the tooth is easier due to the dynamic and repairable bond evident in certain materials with chemical bonding. [5] Nanotechnology, a major revolution in science, opens up new vistas in material science and other related technology, by providing ‘plenty of room at the bottom’, as stated by Richard P. Feynman.[6] It is defined as the direct manipulation of materials at the nanoscale. It studies the properties of materials at nanoscale dimensions. Nanoscale dimension is less than the atomic size. One nanometre (nm) equals 1 billionth of a meter. Nanomaterials behave very differently from the parent material. [7] The physical, mechanical and biological properties exhibited are highly desirable in nanoscale. Thus nanomaterials have the power of creating new products or modify the properties of a material at the atomic/ molecular level.

Use of nanotechnology is already wide spread in other sciences, and in restorative material science addition of nanoparticles to the chemical composition of the materials is done with the intent of accentuating their properties in all dimensions.

Especially, the adhesive restorative technology has effectively used nanotechnology in order to meet the ideal requirements of a restorative material.

Nanotechnology in Dental Composite resin Improvement in the mechanical properties

Dr. Carounanidy Usha, Professor; Dr. Bindu Meera John,Reader; Department of Conservative Dentistry and Endodontics, Indira Gandhi Intitute Dental Science, Sri Balaji Vidyapeeth, Puducherry 607402, India.

Page 46

Ann. SBV, July - Dec 2014;3(2)

Resin based composites are composed of a resin matrix reinforced with filler particles. The addition Ann. SBV, July - Dec 2014;3(2)

of filler particles to the composition is intended to improve the viscosity of the resin, to improve the strength and wear resistance, and also to improve the translucency. Silica is one of the major fillers used in composite resins. Various sizes and shapes of silica particles are added to generate different classes of composite resins such as macro filled (use of macro sized fillers of 50 μm), micro/ mini filled ( use of small/ micro sized fillers of 0.04 to 0.2 μm) and hybrid (use of a mixture of macro / mini/ micro fillers of 0.7 to 3.6 μm). Though the mechanical properties can be better with macro sized filler particles, the surface properties and polishability are better when the particle sizes are smaller. In addition it is impractical to load the matrix with larger size filler particles in higher volume percentage, which compromises on the matrix content. Hybrid composites that contained both macro and micro fillers had been the via media solutions for strength and aesthetics for a long time.

Recently fillers in nano sizes of 0.005 to 0.04 μm are added to composite resin and this new class is called as the Nanofilled composite resin. Barium boron fluoroalumino silicate glass, combination of aggregate zirconia/silicon cluster filler and silicon dioxide/fine particles of glass are some of the fillers used. The nanofillers used also varies in shape ranging from irregular to spherical. [8] Nanohybrid composites are improvisation in this concept. This is similar to the hybrid concept, where nano sized particles along with micro filled particles are used as fillers. [9] The addition of nano fillers result in the following enhancements in the restoration: [6, 10] 1. Nano size of the fillers enable addition of more number of fillers thus increasing the surface area of fillers. Thus mechanical properties such as strength and abrasion resistance re improved.

2. Translucency also is improved due to the same reason. In addition, as the size of the fillers are smaller than the wavelength of the light, the optical property is enhanced.

3. Surface roughness of the composite resins, largely depend on the tendency of the filler particles to dislodge from the matrix. Polishing procedures tend to dislodge the filler particles. In contrast to large sized fillers, nano sized fillers even if they are dislodged, do not result in rough surface. However the nano clusters are linked to the matrix monomer at an atomic level, thus dislodgement may occur at Page 47

Annals of SBV

all. This tendency to finish and polish the nano filled composites to a high gloss resulted in long lasting excellent aesthetics with reduced staining capacity.

4. A well-polished surface is also a poor substrate for bacterial adhesion and proliferation, thus tendency to cause biofilm related diseases such as dental caries and periodontal disease is less around the nano filled composite resins.

Improvement in the antibacterial property Composite resin inherently do not possess any antibacterial effect. In fact studies have proven that metallic restorative materials like silver amalgam possess more antibacterial effect against Mutans streptococci than composite resin. Compounding to this disadvantage is the polymerization shrinkage.

Conversion of the matrix monomer to polymer by polymerization process results in linear as well as volumetric shrinkage. The shrinkage stress generated can result in debonding at the toothrestoration interface leading to marginal leakage and secondary caries. Polymerization shrinkage is directly associated with the type and amount of the matrix present in the composite resin. Addition of higher volume percentage of the nano filler particles relatively reduces the matrix content, thus resulting in less polymerization shrinkage. Such resins form a class of low-shrinkage dental composites. [11] In addition attempts have been made in introducing antibacterial elements in nano size to the composition to combat the cariogenic organisms.

Broad spectrum antimicrobials such as metals and polymers have been used as nanoparticles.

Silver nanoparticles, zinc oxide nanoparticles and quaternary ammonium polyethylenimine nanoparticles are some used in the current generation of nanocomposites. [12] Silver nanoparticles The antibacterial action of silver is attributed to the release of silver ions which interact with peptidoglycan cell wall and the plasma membrane.

The effect is more in nano silver (NAg) that is directly proportionate to the high surface to volume ratio.

NAg exhibits strong antibacterial activity against Mutans streptococci and Lactobacilli. Nanosilver particles in the size of 2.7 nm have shown high antibacterial efficacy. The small size of the particles Page 48

NANOTECHNOLOGY IN ADHESIVE RESTORATIVE BIOMATERIALS

enable easy diffusion of Ag ions into the complex dental biofilm and into the dentinal tubules.

However, there can be a change in the aesthetics of the resin; therefore only 0.5 – 1% concentration has been recommended.[12,13]

fluorides into the resin composition was not successful. Despite their antibacterial effect and remineralizing capacity, their presence in the filling materials reduced the mechanical properties of the restoration. [17]

Zinc oxide nanoparticles

Recently fluoride is added as a nanomaterial in the form of Calcium fluoride. Addition of 2030% calcium fluoride has been found to have high fluoride release without compromising on the mechanical features of the restoration. Such a release was found to be highly associated with acidic pH of 5.5. [18] Calcium phosphate nanoparticles such as monocalcium phosphate monohydrate (MCPM) dicalcium phosphate anhydrous (DCPA) tetra calcium phosphate (TTCP) and amorphous calcium phosphate (ACP) are also incorporated into the resin to confer remineralizing capacity. Nanoparticle Amorphous calcium phosphate (NACP) has been found to be effective in this regard as it is readily converted to crystallites. Nano-hydroxyapatite (NHA) and nano-fluorhydroxyapaptite (N-FHA) are also evaluated for the same effect. [12]

These particles exhibit antibacterial effect on both gram positive and negative organisms. Its action is attributed to the production of H2O2 that inhibit the growth of planktonic organisms. It also releases zinc ions that inhibits biofilm formation and metabolism of sugar. But compared to nano silver, nano zinc is needed in higher concentration. Composite with 10% nanozinc has shown antibacterial action against mutans streptococci. [14, 15] Quaternary ammonium polyethylenimine nanoparticles (QAS-PEI) These cause bacterial lysis by binding to the cell membrane and cause cytoplasmic leakage. QAS salt containing polymers are immobilized in the polymer matrix to give long-lasting antibacterial property. But they can leach resulting in degradation of the mechanical properties over time. Thus they are incorporated into the composites as nanoparticles.

1% of QAS-PEI added as nano particles conferred anti-bacterial effect against S.mutans without altering the mechanical properties of the restorative materials. [16] Improcement in the remineralizing capacity Calcium, phosphate and fluorides play a major role in the remineralization-demineralization process of dental caries lesion formation. Tooth substance under acid attack releases these ions to the biofilm fluid and the saliva. This demineralization continues till the fluids are super saturated. The super saturated saliva then redeposit the mineral ions back to the tooth structure. A biomimetic material, should also behave in this way when used as restorative material. The chemical composition should ideally have calcium/ phosphate/ fluoride ions and leach them out on acidic attack to the nearby tooth structure assisting in tooth remineralization. They should also be capable of recharging themselves with remineralizing agents from the saliva. However such an ideal material is not present in the class of composite resins. Earlier attempts to incorporate Ann. SBV, July - Dec 2014;3(2)

Nanotechnology in Glass Ionomer Cement Glass ionomer cements (GIC) belong to the group of acid based cements. Aluminosilicate glasses when mixed with polyacrylic acid produces a tooth coloured cement that can chemically bond to the calcium, phosphate of the mineral content of the tooth and also to the collagen of the organic content of the tooth. Introduction of this material paved way for minimally invasive dentistry, where no elaborate tooth preparation is required to accommodate.

Interestingly GIC is considered cariogenic as it contains fluoride glasses that leach out fluoride ions to the tooth vicinity. It mimics the properties of dentin such as modulus of elasticity and insulating property, thus also called as artificial dentin. [19] The major drawbacks, such as poor wear resistance and low strength are the ones that are being improvised with nanotechnology. Nanoparticulated ionomer is one such attempt. These are resin-modified glass ionomer cements with nanotechnology, which combine the benefits of RMGIC and bonded Nano filler particles in the range of 0.1 to 100 nanometers on the nanoscale. This broad range of filler particle is attributed to better strength, optical properties, and abrasion resistance of the Nanoparticulated ionomer.

Also taking advantage of the fact that ions can readily travel in and out of the material, many antimicrobial additives such as nanoparticles of chlorhexidine hexametaphosphate (N-CHX HMP).

These GICs released soluble CHX over a period of at least 33 days, and the quantity of CHX released was dependent on the doping of nanoparticles in the cement. [21] Other synthetic remineralizing agents such as nano-hydroxyapatite (N-HA) and nano-fluorhydroxyapaptite (NFHA) are also used in glass ionomer cement. The addition of 10% nanoHA (60–100 nm) to glass ionomer cement resulted in an increased resistance to demineralization and acceptable bonding strength compared with microHA added to glass ionomer cement. [12]

Conclusion: Recent advances in adhesive technology point towards a constant and persistent attempts to further enhance the strengths of the adhesive restorative material and at the same time address and overcome the weaknesses. If aesthetics and adhesions are their positive points, strength and wear resistance are their week points. In order to meet up to the standards of ideal bio mimetic material , exhaustive attempts are being made in rendering them as effective bio active materials, by adding antibacterial property and remineralizing capacity. Such attempts that were not entirely successful earlier, currently are being realised in adhesive technology only with the introduction of nanotechnology in this field. The properties of any material is superior in its nano dimensions and with this has emerged unlimited possibilities in adhesive technology.

References 1. Mjör IA. Clinical diagnosis of recurrent caries. J Am Dent Assoc. 2005;136(10):1426-33.

2. Kugel G. Direct and indirect adhesive restorative materials: a review. Am J Dent. 2000;13(Spec No):35D-40D. 3. Francisconi LF, Scaffa PM, de Barros VR, Coutinho M, Francisconi PA. Glass ionomer cements and their role in the restoration of non-carious cervical lesions. J Appl Oral Sci. 2009;17(5):364-9.

4. Hervás-García A, Martínez-Lozano MA, Cabanes-Vila J, Barjau-Escribano A, Fos-Galve P. Composite resins. A review of the materials and clinical indications. Med Oral Patol Oral Cir Bucal. 2006;11(2):E215-20.

5. MJ Tyas, MF Burrow. Adhesive restorative materials: A review. Australian Dental Journal 2004;49:(3):112-121 6. Sule Tugba Ozak, Pelin Ozkan. Nanotechnology and dentistry. Eur J Dent. 2013; 7(1): 145–151.

[20]

Ann. SBV, July - Dec 2014;3(2)

Page 49

Annals of SBV

7. Freitas RA Jr. Nanodentistry. J Am Dent Assoc. 2000; 131(11):1559-65.

8. Mota EG, Hörlle L, Oshima HM, Hirakata LM. Evaluation of inorganic particles of composite resins with nanofiller content. Stomatologija, Baltic Dental and Maxillofacial Journal 2012 ;14: 103-7, 9. de Moraes RR, Gonçalves Lde S, Lancellotti AC, Consani S, Correr-Sobrinho L, Sinhoreti MA. Nanohybrid resin composites: nanofiller loaded materials or traditional microhybrid resins? Oper Dent. 2009;34(5):551-7.

10. Chen MH. Update on dental nanocomposites. J Dent Res. 2010;89(6):549-60.

11. Pitel ML. Low-shrink composite resins: a review of their history, strategies for managing shrinkage, and clinical significance. Compend Contin Educ Dent. 2013;34(8):57890.

12. Melo MA1, Guedes SF, Xu HH, Rodrigues LK. Nanotechnology-based restorative materials for dental caries management.Trends Biotechnol. 2013;31(8):459-67.

13. Yoshida K, Tanagawa M, Atsuta M Characterization and inhibitory effect of antibacterial dental resin composites incorporating silver-supported materials. J Biomed Mater Res. 1999; 47(4):516-22.

14. Hernández-Sierra JF, Ruiz F, Pena DC, Martínez-Gutiérrez F, Martínez AE, Guillén Ade J, Tapia-Pérez H, Castañón GM. The antimicrobial sensitivity of Streptococcus mutans to nanoparticles of silver, zinc oxide, and gold. Nanomedicine.

2008; 4(3):237-40.

Page 50

15. Aydin Sevinç B, Hanley L Antibacterial activity of dental composites containing zinc oxide nanoparticles. J Biomed Mater Res B Appl Biomater. 2010; 94(1):22-31.

16. Imazato S, et al. Antibacterial resin monomers based on quaternary ammonium and their benefits in restorative dentistry. Jpn Dent Sci Rev. 2012;48:115–125.

17. Kirsten GA, Takahashi MK, Rached RN, Giannini M, Souza EM. Microhardness of dentin underneath fluoridereleasing adhesive systems subjected to cariogenic challenge and fluoride therapy. J Dent. 2010; 38(6):460-8.

18. Xu HH, Moreau JL, Sun L, Chow LC. Novel CaF(2) nanocomposite with high strength and fluoride ion release.

J Dent Res. 2010; 89(7):739-45.

19. Khoroushi M, Keshani F. A review of glass-ionomers: From conventional glass-ionomer to bioactive glass-ionomer. Dent Res J. 2013; 10(4): 411–420 20. Konde S, Raj S, Jaiswal D. Clinical evaluation of a new art material: Nanoparticulated resin-modified glass ionomer cement. J Int Soc Prev Community Dent. 2012; 2(2): 42–47.

21. Hook ER, Owen OJ, Bellis CA, Holder JA, O’Sullivan DJ, Barbour ME.Development of a novel antimicrobial-releasing glass ionomer cement functionalized with chlorhexidine hexametaphosphate nanoparticles. J Nanobiotechnology.

2014;12:3.

Ann. SBV, July - Dec 2014;3(2)

Annals of SBV

Annals of SBV Sri Balaji Vidyapeeth

(D eemed

Page 52

to be

U niversity , u / s 3, UGC A ct , 1956)

Ann. SBV, July - Dec 2014;3(2)