International Dentistry Australasian Edition - Vol. 13, No. 3 - 2018

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VOL. 1 3 NO. 3 IN THIS ISSUE

Gianfranco Roselli Paradigm shift in composite restorations: The extraoral chairside technique Tomas LinkeviÄ?ius Is zero bone loss a possibility when placing implants?

Casper H Jonker Negotiation of an S-curved root canal using an EDM machined CM instrument: A case report Juergen Manhart and Hubert Schenk Anterior full ceramic crown after a complicated crown fracture of the natural tooth Barry Oulton The comfortable dental injection technique Johan Hartshorne Essential guidelines for using cone beam computed tomography (CBCT) in implant dentistry. Part 1: Technical considerations

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Professor Marco Ferrari

Professor Simone Grandini

Editor-in-Chief Emeritus

Editor

The passage of time is eternal, bringing with it inevitable change. Twelve years ago, I took on the post as Editor-in-Chief of a relatively unknown, national publication, Dentistry South Africa. The aim was to take the journal to a new level, to achieve international status and recognition.

With a new title, a shift in editorial policy and the formation of a new Editorial Board, International Dentistry South Africa (now African Edition) was transformed into a journal publishing peer-reviewed clinical and scientific content, serving an international readership. A second title was launched in 2006, International Dentistry – Australasian Edition.

The advent of the digital age has resulted in multiple platforms to disseminate information, including dentistry. International Dentistry African and Australasian Editions will be embracing this new era, while maintaining its standards in editorial excellence as well as its timeless hard copy format. It thus gives me great pleasure to hand over the role as Editor to my colleague, Prof Simon Grandini, who will advance the journal into the modern generation My deepest thanks to all my colleagues on the Editorial and Review Board for their commitment and support, as well as to all our readers and advertisers for accepting our new direction and supporting our goals.

I would also like to thank the Publisher, Ursula Jenkins, who was always available to help me in my job, and who spends so much effort and energy on the Journals MARCO FERRARI, MD, DDS, PhD Editor-in-Chief Emeritus

In 2006, it was my pleasure to join the Editorial Board of International Dentistry South Africa, under the Editorship of Prof Dr Marco Ferrari. Over the past 12 years, under his guidance, the journal has continued to grow and be recognized as a leading dental publication, not only on the continent of Africa, but also in Australasia.

With the change of title to International Dentistry – African Edition, came the appointment of Prof Dr Ferrari as Editor-inChief, while I joined Professors Cecilia Goracci and Andre van Zyl as Associate Editors.

I am now honoured to take over as Editor as we bid farewell to Prof Dr Marco Ferrari, who is stepping down from his position as Editor-inChief. Together with Professors Goracci and Van Zyl and the members of our Editorial Board, we thank him for his contribution and leadership and will continue his legacy of striving to provide clinical and scientific articles with a high standard to our readers.

Dentistry is undergoing major changes, from the advent of Digital Dentistry to our always-increasing use of social media platforms, both for personal and professional purposes.

For many years a recurring question in the scientific world has been “Is digital dentistry the future?” Despite it being a tricky answer to give, evidence is telling us that traditional workflows have firstly been sided with and, in some cases, substituted by digital workflows.

The workflow resulting from this close interconnection allows us to enjoy the best of both worlds: the traditional workflow can compensate for the grey areas in the digital world, which are still in need of further scientific research.

Why, then, not consider how social media platforms are shaping our vision of the world and sketching out a new way to approach our job? With social media being a great showcase of someone’s scientific knowledge and clinical know-how, the horizons of a private clinic have definitely been broadened. Connecting daily with patients through social platforms is something we now do unconsciously and sharing parts of our daily practice has become second nature.

Cutting-edge technology is slowly revolutionizing our clinical workflows as well as our interaction with both patients and our peers.

Another dimension has been added to our job, and it’s called Digital.

SIMONE GRANDINI, DDS, MSc, PhD Chair of Endodontics and Restorative Dentistry Head of Department of Endodontics and Restorative Dentistry Dean of the School of Dental Hygienists University of Siena, Italy

Professor Simone Grandini graduated from the Dental School of Florence University. He obtained postgraduate certificates in Periodontology (University of Genoa), Restorative Dentistry (University of Florence), and a PhD (University of Siena). Prof. Grandini has published more than 300 papers in national and international journals, and over the last 20 years has given more than 700 lectures on Endodontics and Restorative Dentistry in Europe, the Americas, Asia, Africa and Australasia.

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Contents Volume 13 No. 3

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Clinical

18

Paradigm shift in composite restorations: The extraoral chairside technique Gianfranco Roselli

Clinical Is zero bone loss a possibility when placing implants?

Tomas LinkeviÄ?ius

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Clinical Negotiation of an S-curved root canal using an EDM machined CM instrument: A case report Casper H Jonker

26

Clinical

42

Clinical

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Anterior full ceramic crown after a complicated crown fracture of the natural tooth Juergen Manhart and Hubert Schenk

The comfortable dental injection technique Barry Oulton

Clinical Essential guidelines for using cone beam computed tomography (CBCT) in implant dentistry. Part 1: Technical considerations Johan Hartshorne

63 Products

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Would you like to volunteer in Tanzania?

Around 75% of the world’s population has no access to even the most basic emergency dental care. In Tanzania, there are only 495 dental professionals for a population of 55 million people! This equates to 1 dental professional for every 110,000 people and only 1 dentist for every 495,000 people. The majority of the professionals live in the cities and 80% of the population live in rural areas so the problem is even more complicated. Bridge2Aid believes the solution is to train locally-based medically-trained health workers to care for their own rural communities.

Be part of the solution Bridge2Aid originated in the United Kingdom and, since 2004, has trained over 500 health workers, providing access to urgent care for more than 5 million people. They deliver intensive practical emergency dental and oral health care training to rural health workers who are then able to serve their local communities and keep people out of pain in a sustainable, safe way. The goal is to alleviate dental pain which will in turn lead to a reduction in poverty.

Henry Schein Halas, through the Henry Schein Cares Foundation, has teamed up with Bridge2Aid, and are launching in Australia. We are pleased to announce two scholarships for volunteering Australian Dentists and Dental Auxiliary Staff with Bridge2Aid in August 2019. This trip to Tanzania will, for the first time, be made up of all Australian volunteers and you could be one of them.

There are two ways you can be involved 1. Join the 2 week training program and use your unique skills to make an ongoing difference. Meet like-minded people and change lives – open to dentists, dental nurses, assistants, hygienists or therapists (don’t forget to apply for your Henry Schein Cares scholarship) 2. Sign your practice up to become a Practice Partner and help fund the training of a rural health care worker. Each person trained gives access to safe emergency dental care for 10,000 people. Your fundraising/donation will go a long way.

To find out more about Bridge2Aid visit www.bridge2aid.com.au or to apply for one of the scholarships please request an application form by emailing scheincares@henryschein.com.au

Vol. 13 No. 3 ISSN 2071-7962 PUBLISHING EDITOR Ursula Jenkins

EDITOR Prof Simone Grandini

ASSOCIATE EDITORS Prof Cecilia Goracci Dr Andre W van Zyl

EDITOR-IN-CHIEF EMERITUS Prof Dr Marco Ferrari

EDITORIAL REVIEW BOARD Prof Paul V Abbott Dr Marius Bredell Prof Kurt-W Bütow Prof Ji-hua Chen Prof Ricardo Marins de Carvalho Prof Carel L Davidson Prof Massimo De Sanctis Dr Carlo Ercoli Prof Roberto Giorgetti Dr Patrick J Henry Prof Dr Reinhard Hickel Dr Sascha A Jovanovic Dr Gerard Kugel Prof Ian Meyers Prof Maria Fidela de Lima Navarro Prof Hien Ngo Dr Hani Ounsi Prof Antonella Polimeni Prof Eric Reynolds Prof Andre P Saadoun Prof Errol Stein Prof Lawrence Stephen Prof Zrinka Tarle Prof Franklin R Tay Prof Manuel Toledano Dr Bernard Touati Prof Laurence Walsh Prof Fernando Zarone PRINTED BY KHL PRINTING, Singapore International Dentistry - Australasian Edition is published by Modern Dentistry Media CC, PO BOX 76021 WENDYWOOD 2144 SOUTH AFRICA Tel: +27 11 702-3195 Fax: +27 (0)86-568-1116 E-mail: dentsa@iafrica.com www.moderndentistrymedia.com

© COPYRIGHT All rights reserved.

No editorial matter published in International Dentistry Australasian Edition may be reproduced in any form or language without the written permission of the publishers. While every effort is made to ensure accurate reproduction, the authors, publishers and their employees or agents shall not be held responsible or in any way liable for errors, omissions or inaccuracies in the publication whether arising from negligence or otherwise or for any consequence arising therefrom.

Published in association with

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Paradigm shift in composite restorations: The extraoral chairside technique Gianfranco Roselli1

Abstract In restorative dentistry, onlays are a good choice for the posterior region, as they can replace or postpone the need for a prosthetic restoration in some cases. An onlay is a partial restoration. Whether the dentist decides on this form of treatment or a direct restoration depends on the indications – the boundaries here are not clearly defined, though, and leave room for interpretation. However, the two techniques differ particularly in terms of the cost involved for the patient. Depending on the technique chosen by the dentist, the treatment may entail costly and time-consuming procedures such as dental laboratories and/or CAD/CAM techniques. The technique described here heralds a paradigm shift. It unites the advantages of the direct and indirect techniques like no other.

Key words: Composite, semi-direct technique, chairside technique, inlay, partial crown restoration, onlay.

Introduction

1

Dr Gianfranco Roselli Bari, Italy E-mail:gianfrancoroselli88@gmail.com

The physical and chemical properties of composite resins have improved considerably in recent years and now offer, among other things, higher abrasion resistance (Spreafico and Roulet, 2009), improved biomimetic characteristics and, in particular, better control over polymerisation shrinkage. All these factors have resulted in a broader spectrum of indications for the use of composite resins (microhybrid, nanofiller and nanohybrid) in the posterior region. However, achieving an optimal approximal and occlusal anatomy as well as perfect restoration margins always remains a challenge, especially in the case of large cavities and hard-to-reach areas. In view of this, indirect partial restorations (e.g., onlays) are indicated in such clinical situations in which direct restorations are pushed to their technical limits. This is especially true in the case of complex cavities with margins in the direct vicinity of the gingiva or below the dentinoenamel junction.1.8 The decision of whether a direct or indirect restoration is indicated is often a difficult one for dentists – especially since both options offer similar results with regard to their longevity (Van Dijken, 2000; Wassel et al., 2000; Pallesen and Qvist, 2003) 1,2,3,4.

Whichever type of restorative treatment is ultimately selected, the objectives are always the same: - Diagnosis and removal of carious lesions; - Anatomical, functional and aesthetic restoration of the removed or absent dental tissue; - Protection of pulp and dentine; - Long-term preservation; - Prevention of caries and periodontal recurrence.1,2 However, there are clinical situations, such as the loss of one or multiple cusps, approximal subgingival preparation margins and the preparation of approximal boxes with very open lateral walls that are far apart, in which the dentist is forced to turn to indirect techniques.

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Figure 1: Before treatment: Loss of restoration in tooth 26.

Figure 2: Isolation of operating site with rubber dam.

Why an onlay?

be seen as an additional option and ultimately as a rediscovered accomplishment of restorative dentistry.

Today, indirect restorations – in this case the onlay – are seen as the preferred form of treatment in the posterior region and a viable alternative to a full crown or a direct restoration.

There are a number of associated factors: • The result is an aesthetic and functionally well integrated, conservative restoration which allows both restorative (corrections prior to cementation and later repairs) and endodontic revision ⇨ although this also applies for other restorations; • Optimal occlusal anatomy and contact points without the complications sometimes associated with direct restorations.

The problems associated with the direct technique resulted in the development of semi-direct techniques (Mӧrmann et al. 1983; Blankenau et al. 1984; Mӧrmann et al. 1989) with the aim of improving the quality of large Class I and II restorations.2,5,21 The disadvantages associated with onlays compared with direct restorations are: • Dental laboratory costs and the associated time required – impact on cost for patient and patient compliance; • Higher loss of healthy dental tissue associated with the build-up of divergent walls; • At least two sessions required.

In light of the above, a semi-direct technique offers clear added value. It has the same indications but offers a great advantage in that preparation, modelling and cementation of the restoration can be performed in a single session and at the same cost as a direct restoration.

An analogue technique is cost-effective, easy to perform and not associated with the high expense or problems involved with a digital chairside technique. As such, it can

The Semi-Direct Technique This term exclusively applies to restorative techniques which involve both intraoral and extraoral steps and can be completed chairside in one treatment session. The restorations fabricated from composite are cemented using an adhesive technique.

Compared with intraoral restorations, extraorally fabricated restorations generally offer better anatomical and aesthetic potential, which is attributable to the more precise layering. This type of restoration is recommended in the following cases: • Medium-sized cavities extending towards the dentinoenamel junction which rule out a direct technique or render it not recommendable; • A limited number of teeth are affected.5 According to the literature, non-rigid models for inlays and onlays allow extraoral fabrication of restorations in a singlevisit procedure because these models cure quickly. The studies by Hirata R. et al. revealed that the predictability of the result can be ensured by using the optimal combination of an alginate impression and a working model made of silicone, or a silicone or polyether impression and a working model made of plaster.1,6,7 The advantages of these techniques are illustrated in detail in the following case study.

Methods and Materials Case study A 24-year-old patient presented in the practice complaining of sensitivity to cold in tooth 26 (upper left first molar). The

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Figure 3: Tooth preparation comprises the mesiovestibular cusp and rounding off the preparation angle.

sensitivity was due to the loss of a composite restoration.

According to the patient, the restoration had only been placed 11 months earlier using a single-visit procedure (Fig. 1).

With the exception of the morphofunctional deficiency of the tooth specified above, there was nothing remarkable in the patient’s medical or dental history.

Treatment An intraoral x-ray (Fig.1, inset) was taken to exclude the possibility of endodontal involvement. We decided on restoration with an extraorally fabricated composite partial crown (semi-direct/indirect onlay) so as to ensure better predictability compared with a direct restoration, and also due to the absence of the mesiovestibular cusp, the thinness of the bevelled enamel and of the mesial margin of the cavity, which was close to the gingiva.5 Anaesthetic was applied in the area of teeth 26/27 and the operating site then isolated using a rubber dam (Fig. 2).

The damaged dental tissue was removed and the cavity prepared in accordance with the adhesive guidelines.

We performed “coronal repositioning of the margins” as described by Dietschi and Spreafico (1998)16 in order to simplify the clinical steps of the cementation procedure. This technique has proven its worth as an atraumatic alternative to clinical crown extension. It involves the placement of a matrix to ensure cervical sealing (in this case, a Tofflemire metal matrix), a 3-step etch-and-rinse procedure and cervical build-up with a flowable composite (x-tra base, VOCO Cuxhaven) with a maximal thickness of 1 mm to reduce gingival microleakage and improve marginal integrity.17,18,19,20

Following successful build-up with a nanohybrid composite (GrandioSO, VOCO), we performed preparation of the tooth, comprising the mesiovestibular cusp and rounding off the preparation angle so as to remove undercuts, preserve as much dental tissue as possible and adapt the cavity walls (Fig. 3).1,9,10 The prosthetic restoration can be fabricated using two different techniques: • indirect technique in the dental laboratory; • semi-direct chairside technique.

We decided to fabricate one onlay with the first technique and another with the second technique so as to illustrate the advantages and disadvantages of each.

The indirect technique comprises: - Taking an impression with polyether (Impregum, 3M) using an impression tray and a single-stage technique in both jaws (Werrin and Wilson, 1983); - Fabrication of a super-hard plaster model (type IV) with a model tray system and the opposing jaw; - Preparation of the plaster model for layering of the composite (sectioning, application of the plaster hardening agent, blocking of the undercuts with wax and insertion of the anchorage); - Layering of the composite.10 The semi-direct, extraoral technique (GrandioSO Inlay System, VOCO) comprises: - Taking an impression with alginate in one jaw; - Drying the impression and fabrication of a model with addition-curing silicone (Die Silicone, VOCO); - Layering of the composite following complete curing of the silicone (4 mins).

The clear advantage of the chairside technique compared with the indirect technique is that no dental laboratory is required, which helps keep costs low. The significance of this aspect should not be underestimated, especially in patients with large carious lesions and where a prosthetic solution can be avoided for a long period of time without excessive expense.5 When the working times for impression taking, model casting and fabrication (with the exception of the layering of the composite, as this is more or less comparable for both techniques) are compared, it becomes evident that the extraoral, semi-direct technique takes less time than the indirect (semi-direct = 5 minutes 45 seconds vs indirect = 1 hour 27 minutes).

The shortening of the working time makes it possible to fabricate the onlay in a single session. There is no need to insert a temporary restoration.

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10 Figures 4-10: Making of model and subsequent layering of composite to fabricate two onlays.

Figure 11: Prior to placement, the composite restorations were photothermally treated in a special furnace.

After making the model, we performed the layering of the composite (GrandioSO, VOCO) and fabricated two onlays for the same preparation (the individual steps for the layering of the composite on silicone are shown in figures 4 to 10).

Then an Iwanson calliper gauge was used to compare the accuracy of fit of the silicone model cast in alginate with that of the super-hard plaster model cast in polyether. The width between two defined points (distal point of the preparation and the intersection point between the palatal gingival

margin and the palatal intercuspal sulcus) was the same on both models (6 mm). The two onlays were switched on the models as an additional check of the accuracy of fit. No movement of the restoration and no marginal gap were observed.

The only disadvantage of the extraoral, semi-direct technique described in the literature is that the occlusal surfaces are built up without an opposing jaw model, and the requisite adaptations can therefore sometimes prove

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Figure 12: Placement of the onlay and subsequent light curing.

self-etch bonding agent (Futurabond DC, VOCO) to the prepared area and the interior surface of the onlay; • Injection of resin-based dual-curing cement (Bifix QM, VOCO) into the cavity; • Placement of the onlay and removal of the occlusal excess using a probe and dental floss, application of glycerine gel along all margins and subsequent light curing for approx. 1.5 minutes on each side (Fig. 12).11,12,13,14,15,22,23 This was followed by shaping and recontouring of the restoration using flexible polishing wheels with medium, fine and ultrafine grit sizes for the smooth approximal surfaces and with abrasive strips along the gingival margin. Any premature occlusal contacts were removed with a fine and ultrafine diamond bur.25 Figure 13 shows the finished clinical case after polishing with a single-stage diamond/silicone polisher (Dimanto, VOCO) and the perfect marginal integrity of the restoration following the intraoral follow-up radiograph.

The outstanding biomimetic integration of the restoration is still evident after 6 months (Fig. 14).

challenging.5 Following the layering, the restorations were finished, polished with diamond compound and sandblasted with aluminium oxide/silicone dioxide. The surfaces were sealed with adhesive (Seal Coat, DEI, Italy).

We decided to cement the onlay layered on the silicone model. The cementation technique comprises: • Trying-in of the restoration; • Isolation of the operating site; • Cleaning of the tooth surfaces with chlorhexidine gel, pumice stone and a Robinson brush as well as sandblasting so as to produce efficient microretention for the luting cement; • Selective enamel etching and application of a dual-curing

The extraoral, semi-direct technique has the same indications and advantages as the indirect technique, but additionally offers the convenience and the “single-visit advantage” of the direct chairside technique.

Considerable cost savings are also possible, as no laboratory or other technology is required. This technique heralded a paradigm shift in restorative dentistry.

Figure 13: The onlay was ground occlusally and then polished.

Figure 14: Situation after six months.

Conclusion

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Acknowledgements The author would like to thank VOCO for its technical support in the compilation of this article.

References 1. Hirata R. TIPS: dicas em odontologia estética. Brasil: Panamericana Publishing Co. Inc., 2011.

2. Brenna, Breschi, Cavalli, Devoto, Dondi, Dall’Orologio, Ferrari, Fiorini. Odontoiatria Restaurativa – Procedure di trattamento e prospettive future. Italy: Elsevier – Masson, 2009.

3. Spreafico RC, Krejci I, Dietschi D. Clinical performance and marginal adaptation of class II direct and semidirect composite restorations over 3.5 years in vivo. J Dent July 2005; 33 (6): 499-507.

4. van Dijken, JW. Direct resin composite inlays/onlays: an 11 year follow-up. J Dent July 2000; 28(5): 299-306.

5. Dietschi D, Spreafico R. Adhesive metal-free restorations: current concepts for the aesthetic treatment of posterior teeth. Berlin: Quintessence Publishing Co. Inc., 1997.

6. Gerrow JD, Price RB. Comparison of the surface detail reproduction of flexible die material system. J Prosthet Dent.

Oct. 1998; 80 (4): 485-9.

7. Price RB, Gerrow JD. Margin adaptation of indirect composite inlays fabricated on flexible dies. J Prosthet Dent.

March 2000; 83(3): 306-13.

8. Veneziani M. Restauri adesivi dei settori posteriori con margini cervicali subgengivali: nuova classificazione e approcio terapeutico differenziato. Il dentista moderno. Oct. 2008; 44-86.

9. Magne P. Composite resins and bonded porcelain: the postamalgam era? J. Calif Dent Assoc. Feb. 2006; 34(2): 135-47.

10. Kuroe T, Tachibana K, Tanino Y, Satoh N,Ohata N, Sano H, et al. Contraction stress of composite resin build-up procedures for pulpless molars. J Adhes Dent. Spring 2003; 5(1): 71-7.

11. Mak YF, Lai SC, Cheung GS, Chan AW, Tay FR, Pashley DH. Micro-tensile bond testing of resin cements to dentin and an indirect resin composite. Dent Mater. Dec. 2002, 18(8); 609-21.

12. Swift EJ Jr, Perdigao J, Combe EC, Simpson CH, 3rd, Nunes MF. Effect of restorative adhesive curing methods on dentin bond strengths. Am J Dent. June 2001; 14(3): 137-40.

13. Van Meerbeek B, Perdigao J, Lambrechts P, Vanherle G. The clinical performance of adhesives. J Dent. Jan. 1998; 26(1): 1-20.

14. Bayne SC, Heymann HO, Sturdevant JR, Wilder AD, Sluder TB. Contributing co-variables in clinical trials. Am J Dent. Oct. 1991; 4(5): 247-50.

15. Kramer N, Lohbauer U, Frankenberger R, Adhesive luting of indirect restorations. Am J Dent Nov. 2000 13 (Special Edition): 600-760.

16. Dietschi D, Spreafico R. Current clinical concepts for adhesive cementation of tooth-coloured posterior restorations.

Pract Perio Aesthet Dent 1998; 10: 47-54.

17. Estafan D, Estafan A. Flowable composite: a microleakage study. J Dent Res 1998; 77 (Special Edition B): 938-942.

18. Labella R, Lambrechts, Van Merbeek B, Vanherle G. Polymerization shrinkage and elasticity of flowable composites and filled adhesives. Dent Mater 1999; 15: 128-137.

19. Dietschi D, Olsburg S, Krejci I, Davidson C. In vitro evaluation of marginal and internal adaptation after occlusal stressing of indirect class II composite restorations with different resinous bases. Eur J Oral Sci 2003; 111: 73-80.

20. Chersoni S, Suppa P, Grandini S et al.In vivo and in vitro permeability of one-step self-etch adhesives. J Dent Res 2004; 83(6): 459-464.

21. Jiang W, Bo H, Yongchun G, LongXing N. Stress distribution in molars restored with inlays or onlays with or without endodontic treatment: a three-dimensional finite element analysis. J Prosthet Dent Jan. 2010; 103(1): 6-12.

22. Shawkat E, Shortall A, Addison O, Palin W. Oxygen inhibition and incremental layer bond strengths of resin composites. Dent Mater 2009; 25: 1338-46.

23. Park H, Lee I. Effect of glycerin on the surface hardness of composites after curing. JKACD 2011; 36 (6): 483-9.

24. Dickinson GL, Leinfelder KF, Mazer RB, Russel CM. Effect of surface penetrating sealant on wear rate of posterior composite resins. J Am Dent Assoc 1990; 121: 251-255.

25. Pettini F, Corsalini M, Savino M, Roselli G, Sibio G, Madeo D M, Pellegrino M, Di Venere D. Profilometric analysis of composite materials (microfilled, nanofilled and silorane) after different finishing and polishing procedures.

Minerva Stomatologica Apr. 2014 - Volume 63, No. 4 Insert 1.

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Is zero bone loss a possibility when placing implants?

Tomas Linkevičius

Dr Tomas Linkevičius is a presenter at the 10th International Quintessence Symposium

Dr Tomas Linkevičius, DDS, Dip Pros, PhD Private Practice, Vilnius, Lithuania Contact: linktomo@gmail.com

Crestal bone stability around dental implants remains one of the most important and foremost factors of successful implant treatment. Besides major clinical advantages to the patient, a positive long-term outcome due to stable marginal bone provides the clinician with psychological comfort and satisfaction (Fig 1). Therefore it is necessary to be aware of possible causes which can lead to loss of crestal bone stability and to use every method to prevent bone resorption.

For almost a decade, platform switching was considered to be the most effective way to achieve this. It was so effective that almost all implant companies implemented platform switching as an essential feature of implant manufacturing. Everyone came to the conclusion that implant design was more important that the biology itself. However, recent clinical research conducted by our group has shown that soft tissue thickness is an important factor in preserving crestal bone stability around implants. It was determined that if vertical soft tissue thickness is 2mm or less, there will be crestal bone resorption of 1.5mm extent during formation of biological seal between soft tissues and implant/abutment/restoration surfaces (Fig 2).

Furthermore, it was clearly shown that even implants with platform switching modification could not maintain bone if vertical soft tissues were thin at the time of implant placement (Fig 3). This leads to the discussion of what is more important: biology or implant design? Vertical soft tissue thickness, the prerequisite of the biological width around implants starts to form at the time of healing abutment connection and is completely finished after 8 weeks. This biological seal is the only and most important protection barrier of the osseonintegrated implant from a contaminated intraoral environment. Thus there is a direct connection between pre-implant mucosa of edentulous alveolar ridge and periimplant soft tissues.

Soft tissue thickness required to protect underlying bone around implants is approximately 4mm, which is wider than the biological width around teeth. There are 2 ways how biological width around implants can be formed: with crestal bone loss or without bone resorption. All clinicians should carefully consider the best option.

There are no current guidelines to follow should thin vertical tissues at the time of implant placement be diagnosed.

However steps need to be taken to prevent because crestal bone resorption.

This is especially important for short Figure 1: Crestal bone stability around implant/ implants, the use of which are becoming abutment matching implant. common practice. Today, implants of (Biohorizons Tapered, Biohorizons, USA)

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Figure 2: Thin, vertical soft tissues measured at the crest (≤ 2mm)

8mm length are no longer considered short. There is sufficient data that shows that 6mm length implants are as effective as longer ones in the posterior areas of both jaws. However, in a situation where a 6mm implant is placed in the mandibular posterior jaw region, where thin vertical soft tissues are frequently present, there would be approximately 2mm of bone resorption, due to biological width formation. It would leave only 4mm of implant surface osseonintegrated. That is a risk of implant failure, keeping in mind the prosthetic suprastructure and implant/crown ratio. With the launch of 4mm length implants by some implant manufacturers, soft tissue thickness is even more important for the users of these products.

What strategy should therefore be implemented? There are several options - some already researched clinically; some based on clinical expertise without any serious evidence. The initial thought is to simply place the implant deeper subcrestally (Fig 4). The surgeon should however bear in mind that a safety margin be maintained between the implant site and vital anatomical structures such as the inferior alveolar nerve and maxillary sinus. Placing the implant sub-crestal may damage such structures if care is not taken.

Extensive sub-crestal positioning of the implant does not prevent crestal bone loss, Extensive sub-crestal positioning of the implant, without platform switching or without stable conical connection will not prevent the formation of an inflammatory infiltrate, which will resorb the bone anyway.

However it is likely that the implant will not have soft tissue recession nor rough surface exposure, which usually follow bone resorption. It is well known that the exposure of the rough implant surface enhances plaque accumulation and development of peri-implantitis.

Consequently, the third option may be used – vertical reconstruction of soft tissue thickness, which in the author’s

Figure 3: Crestal bone loss around implant with platform switching.

opinion is the most logical approach. Increasing soft tissue thickness vertically compensates the lack of vertical tissue thickness. A JOMI 2009 paper, “The influence of soft tissue thickness on crestal bone changes around implants: a 1-year prospective controlled clinical trial”1 has suggested that clinicians, “consider the thickening of thin mucosa before implant placement”. This concept is therefore not entirely new. The idea is to place some sort of autogenic, allogenic or xenogeneic material over the implant in that way increasing soft tissue thickness after healing.

A connective tissue graft is considered the golden standard for soft tissue augmentation around implants. However this technique has some considerable disadvantages, such as

Figure 4: Subcrestal placement of the implant (Biohorizons Tapered Plus, USA)

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Figure 5a and 5b: a. Original vertical soft tissue thickness. b. Soft tissue thickness after augmentation with acellular dermal matrix (AlloDerm, Biohorizons, USA)

donor site morbidity and, in the case of a general practitioner as opposed to a specialist, the challenges of the harvesting procedure. Allogenic substitutes may therefore be considered as a viable option to replace autogenous grafts in vertical soft tissue reconstruction. The use of accelular dermal matrix so far is the only approach backed by solid clinical research, including a controlled clinical prospective study.2 In this study, implants were placed in 3 groups of patients with (1) thin vertical tissues, (2) thick vertical tissues and (3) thin vertical tissues augmented with acellular dermal matrix material. Radiographic assessment showed the reduction of crestal bone loss from 1.74mm in the thin tissue group to 0.32mm in the augmented group. In addition, the soft tissue thickness increased by 2.33mm – from 1.50mm to 3.83mm after augmentation with allograft (Figs 5a,b). This research shows that the lack of vertical soft tissue thickness required for biological width formation without crestal bone loss can

be compensated by the use of accelular dermal matrix material at the time of implant placement.

In conclusion it must be emphasized that diagnosis of thin vertical soft tissues is a very important aspect in implant treatment. Only by acknowledging that tissue thickness is a significant factor, can the protocols which allow the reconstruction of vertical peri-implant tissues and reduction of crestal bone loss be used.

References 1. Linkevicius T, Apse P, Grybauskas S, Puisys A. The influence of soft tissue thickness on crestal bone changes around implants: a 1-year prospective controlled clinical trial.

Int J Oral Maxillofac Implants. 2009 Jul-Aug;24(4):712-9.

2. Puisys A, Vindasiute E, Linkeviciene L, Linkevicius T. The use of acellular dermal matrix membrane for vertical soft tissue augmentation during submerged implant placement: a case series. Clin Oral Implants Res. 2015 26(4) 465-470

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Negotiation of an S-curved root canal using an EDM machined CM instrument: A case report

Casper H Jonker1

Introduction

1

Casper H Jonker: BChD, Dip.Odont, Msc. (Pret.). Module of Endodontics. Department of Operative Dentistry, School of Oral Health Sciences, Sefako Makgatho Health Sciences University, Gauteng, South Africa.

Corresponding Author Casper H Jonker: Module of Endodontics, Department of Operative Dentistry, School of Oral Health Sciences, Sefako Makgatho Health Sciences University, Gauteng, South Africa. E-mail: casper.jonker@smu.ac.za

During root canal treatment, the shaping sequence plays a vital role in the endodontic procedure and can ultimately determine the outcome. Historically, shaping of root canals was done with stainless steel files, but in the early 1980’s nickel- titanium provided the revolutionary turn-around in the shaping procedure.1 The introduction of nickel titanium provided substantial benefits which include protecting the original canal shape and reducing iatrogenic errors during cleaning and shaping (zipping, ledges and perforations).2 In modern times, numerous rotary file innovations have been introduced to the endodontic market and rotary file systems differ in their designs from one system to the other. The different approaches in designs are an effort to eliminate procedural errors. However, the management of curved canals remains a huge challenge for any instrument even in the hands of the experienced clinician.3 Recently, an innovative endodontic instrument design has been introduced. It is manufactured using controlled-memory (CM) nickel-titanium wire and the Electric Discharge Machining (EDM) manufacturing process. Controlled memory can be defined as the process where the shape memory of the nickel-titanium alloy is removed by a special thermomechanical process.4 The EDM procedure is a process where there is no contact between the work piece and manufacturing apparatus and only a pulsating electric current removes parts of the alloy. The metal alloy is immersed in a dielectric medium which allows electric discharge flow between an electrode and the metal alloy.

Melting and evaporation of the alloy occur in a controlled and repeatable way.5,6 The end result is an extremely flexible endodontic file where areas of the surface are superficially removed leaving a surface with evenly distributed craters (Figure 1).7 The following case report presents a detailed approach on the use of the HyFlex EDM rotary endodontic system in the negotiation of a tooth with challenging anatomy.

Figure 1: The EDM manufacturing process creating the “sand paper” appearance of the file

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Case Report Visit 1 A 26 year old female patient was referred to the Department of Operative Dentistry at Sefako Makgatho Health Sciences University for endodontic treatment on her upper right second molar. Emergency root canal treatment was performed on a previous visit. The patient presented with an uncomplicated medical history and the patient reported no further symptoms on the treated tooth after the initial visit.

A pre-operative radiograph revealed the upper right second molar with challenging anatomy, narrowing of the root canal spaces and an apical radiolucency on the apex of the mesial root (Figure 2).

The tooth was anaesthetized, the temporary restoration was removed and straight line access was achieved. A rubber dam was placed, the orifices of the mesio-buccal, distal and palatal canals were located, but sclerotic tooth structure covered the pulp floor and location of a potential second mesio-buccal canal (MB2). Sclerotic tooth structure was carefully removed with a long shank slow round carbide bur (Komet Dental, Brasseler, Germany) (Figure 3) and ultrasonics (Start-X number 3, Dentsply Sirona Endodontics) (Figure 4) under magnification using the Dental Operating Microscope (Carl Zeiss, Oberkochen, Germany ), but no orifice(s) was detected after careful investigation of the pulp floor map (Figure 5).

The remaining canals were scouted and negotiated and length determination was done using the electronic apex locator (Propex II, Dentsply Sirona Endodontics), a size 10 K-file (Dentsply Sirona Endodontics) and RC Prep (Premier Dental, Plymouth Meeting, USA) as lubrication. Length determination was confirmed with conventional radiographs and a double curve/S-Curve was noted in the mesio-buccal canal (Figure 6).

The orifices were enlarged with the HyFlex EDM Orifice Opener (Coltene-Whaledent, Langenau, Germany) (Figure 7). The instrument was used with RC-Prep as lubricant and gentle apical pressure to avoid binding to the root canal walls and a brushing motion away from the furcation region. The initial glide path was created to a loose size 10 K-file with RC-Prep as lubricating agent in all canals. All canals were irrigated using 3.5% sodium hypochlorite, patency confirmed, recaptulated and re-irrigated to remove debris and prevent dentinal mud. With sodium hypochlorite left in-situ and following the manufacturer’s instructions to use the instrument in a brushing motion and gentle apical pressure on the outstroke, the HyFlex EDM Glidepath File (ColteneWhaledent, Langenau, Germany) (Figure 8) was used to

Figure 2: Pre-operative radiograph revealing challenging root canal morphology and an apical radiolucency on the apex of the mesial root

Figure 3: Long shank slow round carbide bur used under magnification for the removal of sclerotic tooth structure

Figure 4: Start-X number 3 ultrasonic tip used under magnification for the removal of sclerotic tooth structure

complete glide path preparation on each canal to full working length. Before introduction to each canal, the file was inspected for unwinding under high magnification, but no visible signs of alteration were identified. All canals were irrigated in a similar method as described above and patency confirmed. After completion of glide path preparation, the HyFlex EDM OneFile (Coltene-Whaledent, Langenau, Germany) (Figure 9) was used to prepare each canal to full working length and sodium hypochlorite was left in-situ as lubricating and disinfection agent. The controlled memory effect of the instrument allowed pre-curving and access into all canals especially the mesio-buccal canal (Figure 10).

The file was used in a similar technique as described with the HyFlex EDM Glidepath File. Canals were dried with

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Figure 5: Removal of sclerotic tooth structure in an effort to locate MB2. No orifice(s) was detected after investigation of the pulp floor map

large paper points and dressed with calcium hydroxide paste (Calasept Plus, Nordiska Dental, Sweden) and the tooth temporarized (Ketac Molar, 3M ESPE, Seefeld, Germany).

Post-operative instructions were provided after the preparation phase of the treatment and the patient was rescheduled for the final phase for filling.

Visit 2 The patient was seen 2 weeks after the previous visit and reported no discomfort since the last visit. The temporary restoration was removed and rubber dam isolation achieved. All canals were irrigated with 3.5 sodium hypochlorite and dried with large paper points. As a final rinse, 17% EDTA solution (Smear Clear, Kerr Dental, Orange, USA) was left in-situ for 1 minute to remove the smear layer and dried with large paper points. The HyFlex EDM OneFile gutta-percha cones were fitted and measured in all canals to confirm correct length. Canals were obturated using cold lateral condensation with Guttaflow Bioseal root canal sealer (Coltene-Whaledent, Langenau, Germany). The appropriate Electric Heated Pluggers (40/03 plugger for mesial and distal canals, 60/06 plugger for the palatal canal) (Calamus Dual, Dentsply Sirona Endodontics) were selected for gutta-percha burn-off and removal of a small coronal portion of obturation material from each canal (Figure 11). Obturations were vertically compacted after burn-off using Machtou pluggers (Dentsply Sirona Endodontics). Heated gutta-percha and vertical condensation with Machtou pluggers were used to fill the coronal void of root canal space (Calamus Dual,

Figure 6: Confirmation of the S-curved root canal configuration in the mesiobuccal root during the length confirmation radiograph with a size 10 K-file

Dentsply Sirona Endodontics) (Figure 12 and 13). A temporary restoration was placed and the patient was rescheduled for the restorative phase.

Discussion According to literature, it is well documented that the extend of curvatures in the areas where root canal instruments operate play a vital role in instrument fatigue and fracture.2 There is always the possibility that 2 or more curves can exist in the same root when a tooth is endodontically treated. The presence of a “double curve” or the “S”-curve as referred to in endodontic circles, can be one of the most challenging scenarios a treating clinician can face. The “S”-curve causes increased strain on nickel-titanium instruments during cleaning and shaping.8 The presence of extreme curvature can also be hidden from a clinician in the fact that it may not be visible on conventional radiographs. A study conducted by AlSudani et al. (2012)9 found that instrument fatigue occurs very quickly once the file encounters a double curvature.

Therefore, the treating clinician has a short amount of time for canal preparation especially in the apical region of these root canals.

An investigation of available literature revealed limited information on cyclic fatigue resistance of nickel-titanium endodontic instruments in “S”-curved canals. Bending stress or cyclic fatigue can be described as the force generated within the nickel-titanium alloy by rotating an instrument in a curved root canal. This will result in repeated compression and flexing at the point of maximum curvature - a very destructive form of loading of the instrument, despite the fact

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that nickel-titanium has superior elasticity and that there is no binding to the canal wall.8 In the presented case, the operator utilized a pumping motion with brushing on the outstroke during shaping in an effort to distribute forces over a greater area of the file and reduce the risk of cyclic fatigue and instrument fracture.

A factor that could greatly influence the failure rate of nickel-titanium endodontic files is the creation of a glide path.

A smooth glide path will allow a relatively safe passage for subsequent rotary instruments to follow. West (2006)10 described a glide path as a smooth, continuous channel extending from the orifice of the root canal in the pulp chamber to its most apical exit at the apex of the root. VarelaPatiňo et al. (2005)11 found that fewer fractures occurred when a wide and smooth-walled glide path was created and the canal was pre-flared before the introduction of rotary files into the root canal. West (2010) 12 suggested that a loose 10 K-file moving freely to working length should be considered the minimum size for a glide path before rotary file introduction. It must also be emphasized that the glide path must be reproducible and free of any obstructions to avoid ledge formation, fracture of instruments, inadequate irrigation and obturation.13 The operator in this case report followed the above guidelines before the HyFlex EDM Glidepath File was introduced and the loose 10 K-file allowed adequate progression of rotary instrumentation.

As stated before, the HyFlex EDM nickel-titanium file range has recently been introduced to the endodontic market by Coltene Whaledent. The system is unique in its EDM manufacturing process of controlled-memory (CM) nickeltitanium wire. Shen et al. (2013) stated that Controlled Memory (CM) nickel-titanium wire increases file flexibility and resistance to cyclic fatigue and also has the ability to limit iatrogenic errors during cleaning and shaping (ledge formation and instrument fractures) of curved canals.4 According to the manufacturers, the instrument also has a “regenerative effect”. The instrument has the ability to return to its original shape after a cycle in the autoclave once unwinding of the flutes is observed. In most cases, only 2 instruments are needed to complete root canal preparation once a loose number 10 K-file on working length is confirmed. The HyFlex EDM Glidepath File has a tip size of 0.10 and 5% taper and is operated at a rotation speed of 250-300 rpm’s with 1.8 N.cm torque setting whilst the HyFlex EDM OneFile has a tip size of 0.25 with an 8% taper in the first 5mm’s of the cutting tip and then 4% taper from 515 mm’s from the cutting tip. The OneFile is operated at a high rotation speed of 500 rpm’s with 2.5 N.cm torque

Figure 7: The HyFlex EDM Orifice Opener used in a brushing motion and gentle apical pressure to enlarge the root canal orifices

Figure 8: The HyFlex EDM Glidepath File used in a brushing motion to complete the glide path preparation to full working length

Figure 9: The HyFlex EDM OneFile used in a brushing motion to complete shaping of all root canals to full working length

Figure 10: The controlled memory effect allowing pre-curving and access of the HyFlex EDM OneFile in canals difficult to access

setting. The system also include the optional HyFlex EDM 0.25 12% Orifice Opener to create coronal flaring. In the reported case the operator used a well-lubricated HyFlex EDM Orifice Opener with gentle apical pressure and a brushing motion for coronal enlargement of the orifices.

Coronal enlargement reduces torsional resistance allowing the instrument to progress without the operator using excessive apical force. Torsional resistance can be described as the amount of stress generated within the instrument when it engages the root canal wall or when the operator subjects the instrument to increased apical force.14 The controlled memory effect of the HyFlex EDM instruments allows pre-curving and bent to adapt to root

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Figure 11: Coronal portion of obturated material removed from mesio-buccal canal with 40/03 electric heated plugger

Figure 12: Obturation complete in all canals using a combination of cold lateral condensation and warm vertical condensation with Electric Heated Pluggers (EHP’S) and Calamus Dual

canal curvature (Figure 10). This feature enables the instrument to maintain the original root canal shape without the “straightening” effect caused by nickel-titanium file memory. Instruments with a dominant austenite crystalline structure are generally stiffer with increased file memory compared to instruments with martensitic crystalline structure.15 The unique EDM manufacturing process causes an increase of the austenite finish temperature of the CMWire alloy. In any instrument where the austenite finish temperature of the file is superior to body temperature, the alloy will be in a mixed martensitic, R-phase and austenitic structure at root canal temperature at the time of canal preparation. According to literature, the austenite finish temperature of the HyFlex EDM files is 52°.16 It can be speculated that HyFlex EDM instruments can maintain most of its martensitic properties at body temperature during shaping, but further investigation will be required to confirm this speculation. Pre-curving of CM-Wire instruments also facilitates working on teeth with limited access (second and third molars) and allows management of root canals with ledges.17 This statement can be confirmed in the presented case where limited access was encountered especially the mesio-buccal canal. The pre-curving advantage enabled the operator to gain adequate access into the root canals.

Finally, Topcuoğlu and co-workers (2016)2 compared CMWire instruments to traditional nickel-titanium instruments using simulated S-shaped canals. The CM-Wire instruments evaluated in this study showed increased cyclic fatigue resistance compared to traditional nickel-titanium

Figure 13: Mesially-angulated radiographic view separating the roots and illustrating individual obturated canals

instruments.2 It can only be speculated whether traditional nickel-titanium instruments would have been able to negotiate the challenging morphology found in the treated case.

Conclusion The presented case illustrates the ability of the HyFlex EDM rotary file system to safely and efficiently negotiate challenging anatomy in spaces with limited access. The file system also provided sufficient resistance to cyclic and torsional fatigue to treat the “S” curve with reduced risk of instrument separation.

The author has no conflict of interest which may arise from any form of commercial association with the content of the manuscript.

References 1. Peters OA. Current challenges and concepts in the preparation of root canal systems: a review. J Endod 2004; 30: 559–567.

2. Topcuoğlu HS, Topcuoğlu G, Akti A, Düzgün. In vitro comparison of cyclic fatigue resistance of Protaper Next, Hyflex CM, Oneshape, and Protaper Universal instruments in a canal with a double curvature. J Endod 2016; 42: 969–971.

3. Yared G. Canal preparation using only one Ni-Ti rotary instrument: preliminary observations. Int Endod J 2008; 41: 339–344.

4. Shen Y, Zhou HM, Zheng YF, Peng B, Haapasalo M. Current challenges and concepts of the thermomechanical

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treatment of nickel-titanium instruments. J Endod 2013; 39: 163–172.

5. ColteneEndo. The New File Generation Hyflex.

Available at: https://www.coltene.com/fileadmin/Data/ EN/Products/Endodontics/ Root_Canal_Shaping/HyFlex_EDM/6846_0915_HyFlex_EN.pdf. Accessed March 2, 2016.

6. Jameson EC. Electrical discharge machining. Society of manufacturing engineers: USA 2001.

7. Guo Y, Klink A, Fu C, Snyder J. Machinability and surface integrity of Nitinol shape memory alloy. Manuf Technol 2013; 62: 83–86.

8. Pruett JP, Clement DJ, Carnes DL. Cyclic fatigue testing of nickel-titanium endodontic systems. J Endod 1997; 23: 77–85.

9. Al-Sudani D, Grande NM, Plotino G, et al. Cyclic fatigue of nickel-titanium rotary instruments in a double (Sshaped) simulated curvature. J Endod 2012; 38: 987–989.

10. West J. Endodontic update. J Esthet Restor Dent 2006; 18: 280-300.

11. Varela-Patiňo P, Martin-Biedma B, Rodriguez LC,

Cantatore G, Bahillo JG. The influence of a manual glide path on the separation rate of Ni-Ti rotary instruments. J Endod 2005; 31: 114-116.

12. West J. The endodontic glide path: Secret to rotary safety. Dent Today 2010; 29: 86-93.

13. Van der Vyver PJ. Proglider: clinical protocol. Endod Prac 2014; May: 12-9.

14. Sattapan B, Palamara JEA, Messer HH. Torque during canal instrumentation using rotary nickel-titanium files. J Endod 2000; 26: 156-160.

15. Aoun CM, Nehme WB, Naaman AS, Khalil. Review and classification of heat treatment procedures and their impact on mechanical behaviour of endodontic files. Int J Curr Res 2017; 9: 51300-51306.

16. Iacono F, Pirani C, Generali L, Bolelli G, Sassatelli P, Lusvarghi L, Gandolfi MG, Giorgini L, Prati C. Structural analysis of HyFlex EDM instruments. Int Endod J 2017; 50: 303–313.

17. Sides E. Keep your eye on the prize: predictable root canal shaping with the restored tooth in mind. Oral Health 2012; May: 87-93.

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Anterior full ceramic crown after a complicated crown fracture of the natural tooth Juergen Manhart1 and Hubert Schenk2

Abstract In the maxillary anterior region, the integrity of the teeth is of great importance to many people. For heavily damaged anterior teeth, all-ceramic crowns are a reliable and proven therapy option for restoring function and aesthetics.

1

Prof. Dr. Juergen Manhart, DDS Department of Restorative Dentistry Dental School of the LudwigMaximilians-University Goethe Street 70 80336 Munich, Germany E-mail: manhart@manhart.com www.manhart.com www.dental.education

2

Hubert Schenk, CDT Dentalplattform Goethe Street 47 80336 Munich, Germany E-mail: Hubert.Schenk@t-online.de www.hubertschenk.de

Introduction The integrity of their anterior teeth is of paramount importance for most patients due to their prominent position. The impairment of teeth in the anterior aesthetic zone by carious defects, chipping or fractures, clearly visible fillings, discolorations, anomalies in shape, alignment and position within the dental arch often results in considerable restrictions for the patients. Therefore, dentists should take into account all aspects of treatment, including a team of different specialists, in order to preserve or restore the natural dentition.

Today, the range of therapies of modern dentistry offers a variety of methods to restore or optimize the function and aesthetics of teeth in the anterior region. These include depending on the initial situation and depending on the degree of destruction of the individual teeth - polychromatic multilayer direct composite restorations, laboratory-made or industrially manufactured composite veneers, ceramic veneers, partial veneers (additional veneers), veneer crowns, full crowns (metal ceramics, all-ceramics) and orthodontic measures.1-3 A majority of today's patients asks for aesthetic restorations and metal-free alternatives to traditional prosthodontic approaches. All-ceramic restorations have gained in popularity during the last 30 years for a number of reasons, especially their favorable optical properties, excellent and durable aesthetic appearance, wear resistance, color stability, chemical inertness and durability, biocompatibility, and strengthening of the remaining tooth structure when they are adhesively bonded.4-17 This trend has been supported in large part by the increasing number of patients requesting esthetic restorations and metal-free alternatives to traditional prosthodontic approaches.18 In the last three decades, many different all-ceramic systems have been introduced to the dental profession.19 Dental ceramics can be classified according to their material composition, fabrication workflow (e.g. powder-liquid-slurry, slip-casting, pressable ceramics, CAD/CAM millable), or clinical indications. 20-22 Nowadays, the most common clinical indications for all-ceramic restorations consist of inlays, onlays, partial crowns, full crowns, bridges, veneers, posterior occlusal veneers (table tops / posterior cuspal protection restorations), implant abutments and implants23-36. These restorations present a scientifically proved, high-quality permanent treatment option for the esthetically challenging anterior and load-bearing posterior regions when the indications and limitations of the respective ceramic systems are respected and an appropriate luting procedure is employed; their reliability has been documented in literature.18, 32, 37-56 Allceramic restorations are used meanwhile on a routine basis in everyday dentistry.

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1a

1b

Figure 1a & 1b: Initial situation: 24-year old female patient after trauma. In addition to the fractured tooth 11, there is extensive injury to the lower lip. The first treatment of the soft tissue injury occurred at the venue of the accident abroad.

2a

2b

Figure 2a: One week later, the patient appeared in our dental office. Tooth 11 had a complicated crown fracture with exposure of the pulp.

For single-unit restorations, lithium-disilicate (LS2) glass ceramic is the material of choice for many dental practitioners because of its good mechanical strength (IPS e.max Press: 470 MPa mean biaxial flexural strength), excellent aesthetic properties and its versatility. It can be used in monolithic form, when maximum strength is required (e.g. table-top restorations for increasing the vertical dimension of occlusion or posterior crowns), or in a layered form (pressed LS2 coping with additional veneering porcelain) when aesthetics is of utmost importance. Single-unit LS2-crowns demonstrate an excellent longevity for anterior57-59 and posterior teeth,5659 comparable to the survival rate of metal-ceramic crowns.60, 61

This clinical report illustrates the restoration of a maxillary central incisor affected by a complicated crown fracture with a veneered lithium-disilicate glass ceramic crown after endodontic therapy.

Figure 2b: The incisal half of the clinical crown of tooth 11 had fractured horizontally.

Clinical case report

Initial situation A 24-year old female patient presented in our dental clinic with a trauma-related fractured right maxillary central incisor. The accident had already occurred one week earlier abroad, where the patient (medical student) was in the context of a clinical traineeship. Since the collapse occurred in a developing country with medical and dental treatment localities not corresponding to modern standards, the patient decided - after the initial treatment of soft tissue injuries on the spot by a fellow student (Fig. 1 a and b) - to cancel the stay abroad for the dental therapy, because she preferred a treatment in the familiar environment according to modern standards.

During the examination in our clinic one week after the incident, the patient presented a still untreated trauma-injured tooth 11 (Fig. 2 a and b). The clinical inspection showed a

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3

4a

Figure 3: Exposure of the pulp was diagnosed at the mesial aspect of the fracture site.

4b Figure 4b: Periapical radiograph to determine the working length.

4c Figure 4c: Control radiograph of the root canal filling in lateral condensation technique.

5b

Figure 4a: Root canal treatment was initiated, since the pulp had already been exposed to the oral cavity environment for one week.

5a Figure 5a: Long-term provisional build-up of the tooth with a direct composite restoration.

6

Figure 5b: The composite restoration remained until completed soft tissue healing.

Figure 6: After 3 months, the soft tissue situation presented in perfect condition.

complicated crown fracture with exposure of the pulp (Fig. 3), the incisal half of the clinical crown had been completely lost62, 63. Patient assessment revealed a sharp painful response to cold thermal stimulus using refrigerant spray and a pathologic response to percussion of the respective tooth.64 The pulp had already been exposed to the oral cavity environment for one week, the tooth showed unprovoked pain symptoms and root growth was complete; thus, we

decided together with the informed patient, to completely remove the infected pulp with subsequent root canal treatment (Fig. 4 a to c).

The patient was informed about various therapeutic approaches (direct composite restoration, ceramic veneer, full ceramic crown, PFM crown) including their respective advantages and disadvantages and associated costs. The patient decided in favor of an adhesively luted glass ceramic

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7a

7b

7c

7d

Figure 7a-d: Aesthetic analysis by the dental technician. The distribution of the different shades and translucent or opaque tooth areas in the area to be restored are determined.

8 Figure 8: Ceramic layering concept as result of dental aesthetic analysis.

crown made of veneered lithium disilicate ceramics. This restoration type can be recommended as evidence-based treatment in the anterior region.65 In the literature, survival rates of between 93.8% and 96.8% are reported at 5, 8 or 10 year observation periods.57-59 After completion of the root canal treatment, a long-term provisional build-up of the tooth was carried out with an adhesive direct composite restoration (Fig. 5 a and b) in

order to spare the patient a preparation and impressions until the soft tissue situation had completely healed. After a waiting period of 3 months, a new clinical examination was carried out, in which the tooth 11 and its adjacent teeth, including the antagonists in the lower jaw, were inconspicuous (Fig. 6). The patient was asked to present herself the next day for shade determination and in general for dental aesthetic analysis in the dental laboratory.66 A

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9a

9b

9c

Figure 9a and 9b: Tooth 11 was prepared for a full ceramic crown with a circumferential shoulder with rounded inner edges.

10 Figure 10: Tooth substance removal was controlled in dynamic occlusion to ensure sufficient thickness of the glass ceramic framework.

11a

Figure 9c: Incisal view of the final preparation with a circumferential shoulder of 1 mm depth.

11b

Figure 11a and 11b: Placing a retraction cord to displace the marginal gingiva and expose the finish line before taking an impression.

basic requirement for accurate color determination is that the teeth are not dehydrated, otherwise they appear lighter and more opaque.67-69 As part of the aesthetic analysis by the dental technician, the distribution of the different shades of color and translucent or opaque tooth areas in the area to be restored is determined (Fig. 7a to d). The age-appropriate design of the restoration with corresponding individual characteristics (e.g. enamel cracks, white spots, mamelons, halo effect), the appropriate surface texture and the correct gloss level are also analyzed. In principle, in the dental aesthetic analysis by the ceramist technician already a “virtual layering” of the restoration is done, with determination of the necessary ceramic masses. The result of this “virtual layering” is recorded in the ceramic buildup scheme (Fig. 8). This procedure is done on site in the dental laboratory under ideal lighting conditions - which are often not found in dental practices - by the ceramist technician, who will ultimately also fabricate the restorations. If the color analysis is performed directly by the dental technician and not by the dentist or other practice staff, there is usually no misunderstanding and the responsibilities for this important aspect in the treatment process are clearly assigned. Such a procedure eliminates the risk of communication breakdowns

and prevents valuable time from being spent at the dentist's chair on this sometimes longer-lasting and, from the dentist's point of view, unproductive step. Only the direct contact with the patient enables the dental technician to produce an aesthetically perfect matching ceramic crown. The independent aesthetic analysis of the intraoral situation by the ceramist is thus a basic requirement for success.

Tooth preparation In the next appointment, the tooth 11 was prepared for receiving a full ceramic crown with a circumferential shoulder with rounded inner edges (Fig. 9 a to c).

The strength of all-ceramic restorations is determined by the type of ceramic used with the resulting inherent mechanical stability of the respective ceramic material.

Furthermore, the fracture strength is determined by the geometry of the restoration and thus by the shape of the cavity or crown preparation. The basic principle of preparation design for all-ceramic restorations avoids tensile stresses in the material as much as possible and loads the restoration primarily in compression mode by an adequate preparation geometry.70, 71 Fracture strength of the restorations is determined by size, volume, shape and

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12a Figure 12a: Chairside fabrication of a direct provisional restoration.

13b Figure 13b: First bake of the veneering porcelain.

12b

13a

Figure 12b: The provisional was seated using an eugenol-free temporary cement.

13c

13d

Figure 13c: Second bake of the veneering porcelain.

surface characteristics of the ceramic material and additionally by structural inhomogeneities introduced during the manufacturing process.72 The dentist must be aware of the fact that the shape and finish of the tooth preparation have a major impact on the clinical success and longevity of all-ceramic restorations.73-75 The preparation should exhibit a retention form and resistance form optimal for a ceramic crown:73, 76, 77 • height of prepared tooth (abutment height) minimum 4 mm • occlusal convergence angle between 6 and 10 degrees • finish line: circumferential shoulder with rounded inner edges or obvious deep chamfer with 1 mm width • incisal / occlusal reduction of 1.5-2.0 mm (adhesively luted full contour lithium-disilicate crown: minimum 1.0 mm) • axial reduction depth (sufficient circular crown thickness) of 1.2-1.5 mm • in the anterior region: a rounded incisal edge • rounded internal line angles and point angles • smooth surface texture Tooth substance removal was controlled in all dimensions.

Attention was paid to the possibility of a sufficient palatinal layer thickness of the crown framework to be produced, even in positions which the tooth occupies - in addition to the static

Figure 13a: Pressed crown framework made of lithium disilicate-reinforced highstrength glass ceramic.

Figure 13d: Finalized full ceramic crown made of a pressed lithium-disilicate coping and individually layered veneering porcelain.

occlusion - in dynamic occlusion (Fig. 10).

After tooth preparation During the fabrication of highly esthetic restorations, the influence of the shade of the prepared tooth on the final result is a decisive aspect. The shade of the prepared tooth substance was documented by the dentist with a digital photo referencing to a special shade guide (IPS Natural Die Material shade guide, Vivadent, Schaan, Liechtenstein). The image file was then made available electronically to the dental laboratory. This enables the technician – who otherwise has no information about the color of the tooth stump - to fabricate a model die similar in color to the preparation of the patient, on the basis of which the correct shade, translucency and brightness values of the all-ceramic restoration may be selected.

In order to achieve a good impression, the marginal gingiva was displaced with a retraction cord (Fig. 11 a and b). After taking impressions of the prepared tooth and the antagonistic dentition, an occlusion protocol with Shimstock foil was made, intermaxillary registration was carried out fabricating an interocclusal record in maximal intercuspal position and a facebow record was performed.78

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13e Figure 13e: The ceramic crown exhibits a natural-looking, life-like surface texture.

14 Figure 14: Situation after removal of the provisional restoration. The marginal gingiva presents in perfect condition.

13f

13g

Figure 13f: The circular 1-mm shoulder is clearly detectable.

15

16

Figure 15: Placing a retraction cord to expose the finish line prior to the adhesive luting procedure.

A diagnostic template made from a gypsum duplicate of the analytical wax-up using a transparent polyethylene matrix allows the chairside fabrication of a direct provisional restoration with correct dimensions and alignment (Fig. 12 a). The provisional was seated using an eugenol-free temporary cement (Fig. 12 b).

Laboratory work In the dental laboratory, the ceramic crown for tooth 11 was produced. For this purpose, a crown framework made of lithium disilicate-reinforced high-strength glass ceramic was pressed corresponding to the anatomically correct shape of the respective tooth (Fig. 13 a). This coping was subsequently finalized by individual veneering with layered porcelain (press-layer-technique) (Fig. 13 b to g).

Try-in and adhesive luting procedure One week after impressioning, the final appointment was scheduled. After removal of the provisional restoration and cleaning of the tooth with a rotating brush and fluoride-free prophylaxis paste, the gingiva presented in healthy condition (Fig. 14). Using colored, glycerin-based, try-in pastes, the aesthetics of the ceramic crown was checked intraorally with reference to hydrated adjacent teeth and the correct shade

Figure 13g: Palatal surface of the ceramic crown.

Figure 16: Etching the inner surface of the lithium-disilicate glass ceramic crown with hydrofluoric acid for 20 s.

of the luting resin was determined.79-81 Subsequently, the precise fit of the crown on the prepared tooth and quality of proximal contacts were checked before minor functional interferences during protrusive and laterotrusive movement paths were eliminated.

The method of cementation of the crown to the prepared tooth was by adhesive luting, as opposed to conventional cementation. This gives a positive effect on the overall strength of the restoration, in particular for glass ceramic materials, which are more prone to bulk fracture and chipping effects than zirconia. Ceramic materials with fracture strength less than 350 MPa are not indicated for conventional cementation.36 Among those are feldspathic porcelains and leucite-reinforced glass ceramics that mandatory have to be placed adhesively using bonding agents and luting resins. Due to the adhesive bond between the ceramic restoration and enamel or dentin, a considerable increase in strength can be obtained because the inner surface of the ceramic restoration no longer acts as a mechanical boundary line at which fracture causing cracks can initiate due to tensile stresses.82 Prior to the luting procedure, the marginal gingiva was displaced to expose the complete shoulder using a retraction cord (Fig. 15). Afterwards, the inner surfaces of the lithium-

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17 Figure 17: The intaglio surfaces of the glass ceramic crown are treated with a silane.

19b Figure 19b: Air-thinning the adhesive.

18

19a

Figure 18: Etching the tooth surfaces with 37% phosphoric acid.

20a

Figure 19a: Application of an Etch-andRinse-adhesive.

20b

Figure 20a: The ceramic crown is positioned on the tooth with a dual-curing luting composite.

20c

Figure 20b: The excess resin cement is carefully removed using a foam pellet.

20d

Figure 20c: Placing a glycerin gel on the luting gap to avoid the formation of an oxygen-inhibited superficial composite layer.

Figure 20d: Light polymerization of the dual-cure resin cement.

disilicate glass ceramic crown were etched with hydrofluoric acid for 20 s (Fig. 16). After thoroughly rinsing and drying the crown, the fitting surfaces were silanized (Fig. 17).83-86 After adhesive pretreatment of the prepared tooth by conditioning enamel and dentin with 37% phosphoric acid (Fig. 18) and applying an Etch-and-Rinse-adhesive (Fig. 19 a and b), the ceramic crown was adhesively luted using a dual-curing resin cement (Fig. 20 a to d).

Two weeks after placement, the restoration exhibited an optimal functional and aesthetic integration into the neighboring teeth (Fig. 21 a and b). Background illumination

demonstrates the excellent light transmittance capacity of the glass ceramic crown, which impresses by having virtually the same optical properties as the surrounding natural dentition (Fig. 22). Ultraviolet light activates the inherent fluorescence properties of the restoration, which are equal to natural tooth structure (Fig. 23). Silicate ceramics exhibit translucency effects and light-optical properties that are comparable to natural hard tooth substance, making them ideal for fabricating restorations that have to meet highest aesthetic demands. The light scattering of silicate ceramics also supports a natural vital appearance of the adjacent gingiva.

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21a

21b

Figure 21a: The ceramic restoration exhibits a perfect functional and aesthetic integration into the neighboring teeth.

22

Figure 21b: The incisal view shows a copy of the natural central incisor.

24

23

Figure 22: Excellent light transmittance capacity of the ceramic crown, indistinguishable from the neighboring dentition.

25a

Figure 23: Ultraviolet light activates the inherent fluorescence properties of the glass ceramic restoration, which equals natural tooth structures.

Figure 24: The ceramic crown shows a perfect harmony with the architecture of the lips.

25c

25b

Figure 25a-c: Five years after incorporation, there is still an excellent integration of the crown into neighboring dentition.

25d

25e

Figure 25d & 25e: In the right and left lateral views, the crown also presents inconspicuously.

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26 Figure 26: The patient was fully satisfied with the result and presented a warm and big smile as a reward for the completed treatment.

The difference to this "pink aesthetics" becomes clear in comparison with metal-supported restorations, which block this light conduction towards the marginal soft tissue and often cause a grayish shading on the marginal gingiva.87, 88 At the end of the successful treatment, the patient's smile was no longer compromised (Fig. 24).

Five years after adhesive cementation of the ceramic crown, there is still an excellent integration in the surrounding teeth, both in habitual intercuspation and in dynamics (Fig. 25 a to e). The crown still harmonizes in dialogue with the lips (Fig. 26).

Conclusion All-ceramic restorations have achieved an excellent quality and are an indispensable therapeutic means for modern conservative and prosthetic dental treatment procedures[89].

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87. Magne, P., M. Magne, and U. Belser, The esthetic width in fixed prosthodontics. J Prosthodont, 1999. 8(2): p. 106-18.

88. Magne, P., M. Magne, and I. Magne, Porcelain Jacket Crowns: Back to the Future Through Bonding. QDT Quintessence Dental Technology, 2010: p. 89-96.

89. Santos, M.C., et al., Current All-Ceramic Systems in Dentistry: A Review. Compend Contin Educ Dent, 2015. 36(1): p. 31-37.

90. Friedman, M.J., A 15-year review of porcelain veneer failure - a clinician's observations. Compendium of Continuing Education in Dentistry, 1998. 19: p. 625-636.

91. Swift, E.J., Jr. and M.J. Friedman, Critical appraisal. Porcelain veneer outcomes, part I. J Esthet.Restor.Dent, 2006. 18(1): p. 54-57.

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The comfortable dental injection technique Barry Oulton1

Introduction A survey carried out by Dr Joe Bulger in Toronto, Canada, in 2010 listed the top ten reasons why patients do not attend the dentist; these included poor service, off-putting sounds and smells, the lectures, bad memories and the drill. The top two reasons for nonattendance, however, were No 2: ‘the pain’ and No 1: ‘the needle’.1 An article printed in Dentistry Today 2004 by Jennifer de St Georges outlined the top reasons why patients do return to see their dentist. Unsurprisingly, the top two reasons why patients continue to attend a particular dentist are the same as before: No 2: ‘he/she does not hurt’; and No 1: ‘a painless injection’.2 It makes sense, therefore, that when we develop a technique of giving a local anaesthetic that is not only completely comfortable but almost virtually undetectable, by learning and practising this technique with your own patients, you will develop an unrivalled reputation for being caring, gentle and skilful. Learning this technique will not only impact your reputation; it will also increase patient retention, recommendation and ultimately your profits.

The aim of this article is to familiarise the reader with certain aspects of the most up to date technique in providing modern dental anaesthesia - ‘The Comfortable Dental Injection Technique’ (CDIT). This has been developed over the last twenty-five years of being a dental surgeon and practice owner, with extensive training in hypnotherapy, neuro-linguistic programming (NLP) and human needs psychology; then combining this knowledge and experience with that of key opinion leaders from dental hospitals and universities.

To be fully understood, an appreciation of the physiology and psychology of pain is beneficial, the reasons to choose the best equipment, materials, the simple CDIT protocol and the use of hypnotic (suggestive) language. In this article, I will discuss the influence of language on the effectiveness of your injection technique and the perceptions of your patient. Further information about the other aspects can be found via the Septodont training courses and website.

Pain and its modulation

1

Barry Oulton DPDS, BChD Private Practice, Haslemere, UK

The way we experience pain is complex. Whilst I cannot go into an in-depth explanation about the physiology and psychology of pain in this short article, it is important to be aware of several aspects of both in order to understand why the CDIT works.

Our current theory of pain – The Gate Theory – stems from the neuroscientists Melzack and Wall in 1965, in which they attempted to explain how pain signals may be

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modulated.3 From your undergraduate training, you will remember that there are several different types of nerve fibres. They can be thin, thick, myelinated and nonmyelinated.

A-alpha fibres are thick and myelinated and transmit signals of motor origin very quickly (touch, pressure, vibration). C-fibres, on the other hand, are thin and nonmyelinated and transmit signals of nociception (pain, temperature, chemical) very slowly in comparison to A-alpha.

The Gate Theory proposes that only one signal can pass through the dorsal horn of the spinal cord, where there is a synapse, enabling us to ‘close the gate’ to pain if we stimulate the faster signal of touch, vibration or pressure sensation. You already know this because we have all been in situations where we have hurt ourselves or others have, accidentally and our immediate response is to rub the painful area. This ‘rubbing’ sensation stimulates the faster fibres of touch, thus closing the ‘gate’ to pain. In practical terms, if we rub the area we are about to inject, stimulating A-alpha fibres we can close the gate to pain.

Equally, whilst we can modify the pain signal from the source ‘upwards’ to the cerebral cortex, we can also modify the pain signal from higher centres downwards. ‘Top down’ modification is best explained by an example of a footballer who breaks his leg during a game but is so focused on playing that it’s only after the game that he feels the pain or discovers the break.

Top down modification can dial the pain up or down!

Memories can dial it up but our behaviour and our language can dramatically impact the perceived signal either way. For example, if we as Dentists are relaxed, in rapport and are careful with our words, we can easily dial down our patient’s perception of pain. Conversely, if we are careless, rushed or even stressed, we can influence our patient to perceive pain, even if we aren’t causing it.

Whilst words are just a small percentage of our communication (approximately 7%), our language and its effect on the subconscious mind is huge. In fact, one of the first things I learned about the language of was that our subconscious mind cannot process a negative. If I were to say to you, ‘Don’t think of a dental chair’, you have to imagine a dental chair in order NOT to think of a dental chair. Even for a brief, fleeting moment, you will have an internal representation (thought) of a dental chair.

When my daughter was young, and I hadn’t learnt this, I would say things like, ‘Careful, don’t spill the juice’ or, ‘Careful, don’t trip’. Whilst I had a positive intent for her to keep the juice in the glass and for her to stay upright and

not hurt her knees, I was increasing the likelihood of her spilling her juice or even falling over.

Why? Because for her to understand and process what ‘not spilling her drink’ meant, she had to create a picture, sound or movie in her head (an internal representation) of spilling the drink. It was almost like a mini rehearsal for the main event that invariably resulted in me on my hands and knees mopping up juice and chastising her. Wow, what a situation; the poor child gets told off for doing exactly what I had, unintentionally, told her to do.

So, once I learnt this nugget of information, I would make every effort to catch myself from using a negative phrase and change it to a positive one before I spoke. For example, ‘Please, carry your glass really carefully’. I had the same positive intent and dramatically increased the likelihood of her keeping the liquid in the glass, because she had to create an ‘internal representation’ of carrying the glass carefully rather than spilling it. Make sense?

So, how can this be useful in our lives as dentists to benefit our patients? Let’s look at some of the things that you and your team say to patients every day that might be creating an Internal Representation of something that is negative.

Firstly, a disclaimer; I know that you have a positive intent for your patients and with some practise and effort you will be able to influence them even better than you already do.

In my dental practice to reassure our patients, we used to say things like: • ‘It’s ok, it won’t hurt’ • ‘There won’t be any pain’ • ‘Don’t be scared’ • ‘Don’t worry’ • ‘This won’t be uncomfortable’ • ‘I don’t want you to be nervous’ What internal representations do you think these statements created in the minds of our patients? Now, clearly, we had a positive intent of reassuring our patients and wanting them to be and feel comfortable, yet we were increasing the anxiety of our patients, creating pictures, sounds and images in their minds of pain, worry, nervousness and hurt.

The CDIT process in brief 1. Use positive language ALL THE TIME with your patients: ‘I am going to make sure everything we do today is completely comfortable’.

2. The most important thing today is that we make sure that you are completely comfortable. In order to make sure you are comfortable, I am going to gently rub in a magic numbing cream that will numb your gum which means that

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whilst I look after you, everything is gentle and completely comfortable.’

3. Applying topical: ‘So I’m gently rubbing in the numbing cream which will make your gum feel completely comfortable and numb, so that when I gently press on your gum in a minute, (with the needle) it’s a gentle sensation and touch.’

4. Be aware of the direction of the bevel of your needle.

Have it parallel to the mucosal surface so that you can engage the needle very superficially whilst rubbing the area with a cotton bud, thus invoking the gate theory.

5. Inject just a few drops very, very slowly: ‘You will feel me gently touch your gum’. (Whilst continuing to rub/ agitate the area).

6. ‘That’s right, very good (positive language). Now you will begin to feel that the area is becoming more and more comfortably numb,’ (stroking the lip/cheek with your finger as a marker – a hypnotic suggestion).

7. Wait 20/30 secs and then proceed to administer the required amount of articaine for you to treat the tooth at a pace of 1ml a minute whilst progressing the needle (this time bevel to bone) to the desired location. Drip drip drip!!!!

8. Ask your patient for a score out of 10 for how comfortable that was. Often, they will ask you what you just did!! A score of less than 10 is feedback for you to adapt your technique.

References 1. Bulger J. Top 10 reasons people hate dentists. https://www.youtube.com/watch?v=Ld6T1tpxAUU. Accessed 29 May 2018 2. de St Georges J. How dentists are judged by patients.

Dentistry Today 2004; 23(8):96, 98-99 3. Melzack R, Wall PD. Pain mechanisms: a new theory.

Science 1965; 150: 971-979

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Essential guidelines for using cone beam computed tomography (CBCT) in implant dentistry. Part 1: Technical considerations Johan Hartshorne1

Summary The development of inexpensive x-ray tubes, high-quality detector systems and powerful personal computers has paved the way for commercially available and affordable 3D CBCT imaging systems for the dental practice. The purpose of Part 1 of this series is to provide clinicians with an overview of the technical considerations relating to: (i) the basic elements of CBCT hardware, (ii) types and characteristics of different CBCT units, (iii) the fundamental principles of the CBCT imaging workflow chain, (iv) the benefits and limitations of incorporating a CBCT unit into your practice, and (v) to provide some guidelines and recommendations on what factors must be considered when purchasing a CBCT unit. These technical considerations will enhance the practitioners understanding of the fundamental principles required for safe and effective use of this technology. CBCT technology is increasingly being introduced into the dental practice setting due to its invaluable diagnostic and communication capabilities, high quality and accurate images, easy to use, and very suitable for the dental office setting.

Introduction

1

Johan Hartshorne B.Sc., B.Ch.D., M.Ch.D., M.P.A., Ph.D., (Stell), FFPH.RCP (UK) General Dental Practitioner, Intercare Medical and Dental Centre, Tyger Valley, Bellville, 7530 South Africa jhartshorne@kanonberg.co.za

Intra-oral and extra-oral two-dimensional (2D) radiographic imaging procedure (periapical, lateral cephalometric, and panoramic), traditionally used for pre-operative dental implant diagnostics and treatment planning, suffer from the same inherent limitations common to all planar 2D projections namely, magnification, distortion, superimposition, and misrepresentation of structures.1 Although numerous efforts have been made towards developing three-dimensional (3D) radiographic imaging (e.g., stereoscopy, tuned aperture computed tomography (TACT), and multi-detector computed tomography (MDCT), the use of these advanced CT imaging techniques have been unavailable or limited for most dental practitioners because of cost, physical complexity and size, and high radiation dose considerations.1 The development of inexpensive xray tubes, high-quality detector systems and powerful personal computers have paved the way for commercially available and affordable 3D CBCT imaging systems, small enough to be used in dental practice.2 Since CBCT’s introduction for the maxillofacial region by Italian co-inventors Attilio Tacconi and Piero Mozzo in 1998, CBCT imaging has become an important and established diagnostic tool for the clinical assessment and treatment planning of patients needing dental implants.3-5 The value of CBCT imaging as a diagnostic tool has also been reported for various other fields of dentistry such as oral-maxillofacial surgery, dental traumatology, endodontics, temporo-mandibular joint, periodontology, orthodontics and forensic odontology.1,6

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Figure 1: Basic elements of CBCT imaging hardware – X-ray source on the left, Image detector or sensor on the right, and the gantry or rotating platform that connects the x-ray source and the detector.

The widespread use of CBCT scanners however, has resulted in several concerns for clinicians regarding: (i) indications, justification and optimization of CBCT exposures; (ii) training to optimize safe and effective use of CBCT in the clinical setting; and (iii) quality assurance of CBCT scanners.

It is therefore important for clinicians to have a full understanding of the technical principles of dental CBCT imaging in order to purchase the correct machine, and using it correctly and effectively to reap the full benefit of this technology, whilst minimizing radiation-related patient risk.7

Purpose The purpose of Part 1 of this series is to provide clinicians with an overview of the technical considerations relating to: (i) The basic elements of CBCT hardware; (ii) Types and characteristics of different CBCT units; (iii) The fundamental principles of the CBCT imaging workflow chain; (iv) The benefits and limitations of incorporating a CBCT unit into your practice; and (v) To provide some guidelines and recommendations on what factors must be considered when purchasing a CBCT unit.

What are the nuts and bolts of CBCT imaging hardware?

CBCT Imaging hardware consists of three basic elements: (i) an x-ray source (x-ray generator), (ii) an image detector (sensor), and (iii) a gantry (C-arm or rotating platform) that connects the x-ray source and the detector. (Fig. 1)

(i) X-ray source An X-ray beam is generated in a tube containing an electrical circuit with two oppositely charged electrodes (i.e. a cathode

Figure 2: Basic elements of a CBCT X-ray source.

and anode) separated by a vacuum (Fig. 2). The cathode is composed of a filament that gets heated when an electric current is applied, inducing the release of electrons through an effect known as thermionic emission. Because of the high voltage between the cathode and anode, these released electrons will be accelerated towards the anode, colliding with it at high speeds at a location called the focal spot.

Ideally, this focal spot is point sized, but typical focal spots in CBCT are 0.5-mm wide; the size of the focal spot is one of the determinants of image sharpness.8 The energy generated through this collision are mainly lost as heat, but a small part is converted into X-rays through an effect known as Bremsstrahlung. X-rays are emitted in all directions, but absorption within the anode and the tube housing results in a beam emerging from the tube perpendicular to the electron beam. The anode surface is slightly tilted in order to maximize the outgoing X-ray beam through the exit window of the tube.8 A lead-alloy collimator is used to block X-rays that are not passing through the scanned volume or region of interest (ROI), thus reducing patient exposure. Most CBCT systems have multiple pre-defined field-of-view (FOV) sizes, so a collimator will have several pre-defined openings according to the FOV sizes.8 Thus collimation of the x-ray beam by adjustment of the FOV limits the radiation to the ROI only. Furthermore, collimation defines the width and height of the primary x-ray beam and therefore the size of the reconstructed FOV. The cone-shaped X-ray beam has two primary characteristics: quality and quantity. X-ray beam quality refers to the overall energy of the photons in the x-ray beam.

Factors that affect (increase or decrease) X-ray beam quality are peak kilo voltage (kVp), filtration and the type of waveform used. X-ray beam quantity on the other hand refers to the number of photons in the x-ray beam. When the number of photons increases, beam intensity increases, thus

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2D detector array

CMOS Flat Panel Sensor Step 4: Digital data is sent to a computer for 3-D reconstruction.

X-ray Source Step 1: X-ray source produces cone-shaped beam that irradiates a patient’s mouth and jaw as the arm rotates.

Step 2: Cesium iodide scintillator converts x-rays into visible light.

Step 3: Photosensitive pixels convert scintillator’s light into electrical signals. On-chip circuitry turns electrical signals into digital output.

X-ray tube

Scanned volume 180° to 180° rotation

Figure 3: Conversion of in-coming X-ray photons to an electrical signal by the image detector.

Figure 4: The x-ray source and reciprocating image detector synchronously moves 180° to 360° around the patients head.

affecting X-ray beam quantity. X-ray beam quantity is affected by change in tube anode current (mAs), kVp, filtration and changes in distance from the tube. Beam hardening refers to the process in which the quality (energy) of an x-ray beam is increased by removing lower energy photons with appropriate filtration. Exposure can be controlled either automatic or manual adjustment of kVp or mAs.

a partial (180°) or full rotation (360°) around the patients’ head in which the x-ray source and the reciprocating area detector synchronously move around the patient’s head. (Fig. 4) Some CBCT devices offer the opportunity to select a partial rotation (180°) with a reduction of radiation dose to the patient8 The patients’ head is stabilized during the rotation process with a head restraint device, while capturing multiple 2-D images at different intervals, also known as “basis” images of the FOV. These series of basis images are referred to as the projection data or data volume.8 The head restraint mechanism (Fig. 5) is used to minimize movement and to limit motion artifacts during the 3-D scanning process.1

(ii) Image Detector X-ray detectors convert the incoming X-ray photons to an electrical signal and are therefore a crucial component of the imaging chain (Fig. 3). There are basically two types image detectors (also referred to as ‘sensors’) used in contemporary CBCT units. A scanner will have either a charge-coupled device with a fiber-optic image intensifier detector (IID), or an amorphous silicon flat-panel detector (FPD). During the initial introduction of CBCT, most units were constructed with the large, bulky image-intensifier detectors.

Currently, most CBCT scanners have nearly all transitioned to the smaller, flat panel linear array detectors.9 Besides being less bulky and having a smaller footprint, the flat panels have minimal distortion of the image dimensions at the periphery of an image display; have a higher dose efficiency, a wider dynamic range and can be produced with either a smaller or larger FOV8 hence, these units are considered to generate better data volume sets.

(iii) Gantry Most dental CBCT systems have a fixed C-shaped rotating platform or gantry with the X-ray source and the image detecto r mounted on opposite sides of the C-arm or gantry.

(Fig. 4) During a CBCT scan, the C-arm or gantry performs

Types of CBCT machines There are several different dental CBCT machines that vary in their design, footprint, detector configurations and protocol selection features.

CBCT machines can be categorized according to: (i) orientation of the patient during image acquisition (i.e. sitting, standing or supine) (Fig. 6); or (ii) the scan volume, also referred to as the FOV irradiated.1 (Fig.7)

a. CBCT machines based on patient orientation during image acquisition There are three different types of CBCT gantries that can scan patients in three different positions (Fig. 6): (i) seated patient position (ii) standing patient position and (iii) supine patient position. Each have their own advantages and disadvantages. Scanners allowing for standing patient positioning, are usually more accommodating for wheelchairs (Fig. 8), and occupy no more space than a

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X-ray tube

X-ray beam

Detector

Figure 5: Head restraint mechanism to minimize movement and limit motion artefacts during the 3-D scanning process.

Figure 6: Different types of CBCT units categoprized according to orientation of the patient during image aquisition: Left: Seated patient position; Middle: Standing patient position; Right: Supine patient position.

panoramic radiography device. However, some standing units may not be able to be adjusted to a height to accommodate wheelchair-bound patients. Seated units on the other hand are the more comfortable. However, fixed seats may not allow scanning of physically disabled or wheelchair-bound patients. Additionally, scanners with a built-in chair or table occupy a larger space. CBCT-scanners that require the patient to lie supine physically occupy a larger surface area or physical footprint and may not be accessible for patients with physical disabilities.

b. CBCT systems based on scan volume or FOV CBCT machines can also be categorized according to the available FOV or selected scan volume height as follows (Fig. 7): • Localized region: approximately 5 cm or less (e.g., dentoalveolar, temporo-mandibular joint) • Single arch: 5 cm to 10 cm (e.g., maxilla or mandible) • Interarch: 7 cm to 10 cm (e.g., mandible and superiorly to include the inferior concha)

• Maxillofacial: 10 cm to 15 cm (e.g., mandible and extending to Nasion) • Craniofacial: greater than 15 cm (e.g., from the lower border of the mandible to the vertex of the head) The FOV is an important parameter that defines a CBCT imaging protocol. It represents collimation of the beam size to a predetermined area. Adjusting the FOV determines the size of anatomic coverage, image resolution and patient radiation dose. In general, clinicians should select the smallest FOV that provides adequate anatomic coverage and adequate image resolution.10 For most units, a smaller FOV is acquired using a smaller voxel size, and thus, has higher spatial resolution. Additionally, the reduced scatter radiation with a smaller FOV also contributes to improved image quality. Typically, the radiation dose decreases with a smaller FOV size.11 FOV limits depend on the detector size and shape, beam projection geometry and the ability to collimate or not. It is desirable to limit the FOV to the smallest volume that can accommodate the region of interest.

How does the image workflow of a 3-D CBCT scanner work?

CBCT image production workflow consists of four stages: (1) acquisition, (2) detection, (3) reconstruction, and (4) display of the image.1 (Fig. 9) Full View 17x13cm

TMJ View 17x6cm

Sinus View 17x11cm

Single Arch View 10x5cm

Dual Arch View 10x10cm

Focused View 5x5cm

Figure 7: CBCT units can also be categorized according to scan volume or field of view (FOV) irradiated.

1. Acquiring the scan Depending on the type of cone beam imaging system used, the subject may be positioned in a standing, sitting or supine position, with the head or area of interest placed at the center of the CBCT system. Upon situating the patient in place, the patient’s head is stabilized with a restraint mechanism and chin rest, to minimize movement during the scanning process. The frame rate, speed of rotation, FOV and completeness of the trajectory arc are set manually or

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Figure 8: Scanners allowing for standing patients are usually more accommodating for wheelchairs.

automatically to get the image desired by the dental practitioner.

The x-ray source produces a cone-shaped beam of ionizing radiation that passes through the center of the ROI in the patients’ head to the x-ray detector on the other side.

A single partial (180°) or full rotational (360°) scan from the X-ray source takes place while the reciprocating detector moves synchronously with the scan around a fixed fulcrum within the region of interest (ROI).1 This fulcrum acts as the centre of the final acquired volume imaged. During the scan rotation each projection image is made by sequential image capture of the attenuated x-ray beam by the detector.1 Whilst rotating, the x-ray source emits radiation in a continuous or pulsed mode allowing 2-D projection radiographs or “basis images”.1 In a single rotation, the detector can generate between 150 to 600 high-resolution 2-D basis images.8 The series of basis images are referred to as the projection data. Typical rotation times range between 10 and 40 s, although faster and slower scan protocols exist.

Technically, the easiest method of exposing the patient is to use a continuous beam of radiation during the scan rotation and allow the x-ray detector to sequentially sample or capture single images of the attenuated x-ray beam in its trajectory. However, continuous radiation emission does not contribute to the formation of the image and results in greater radiation exposure to the patient.9 In most contemporary units the x-ray beam exposure is pulsed to coincide with the detector sampling. Pulsed x-ray beam exposure at intervals allows that there is time between basis-image acquisition for the signal to be transmitted from the detector area to the datastorage area and the detector to rotate to the next site or angle of exposure. Hence, the x-ray tube does not generate x-rays for the entire rotational cycle, and which means that actual radiation exposure time is markedly less than scanning time. 9 The total scan time is equivalent to exposure time where the x-ray tube allows only continuous exposure. In comparison, CBCT scanners using pulsed exposure the exposure time is markedly less than the scan time. Thus, pulsed X-ray beam generation is preferable as it results in less radiation dosage to the patient. Pulsed x-ray beam exposure is a major reason for considerable variation in reported cone-beam unit dosimetry.1 Depending on the mAs, a 180° rotation protocol can lead to a slight or more pronounced increase in noise than in a 360° protocol. A partial rotation (180°) and reduced sampling associated with shorter scan time tends to decrease overall image quality due to the amount of noise associated with reduced mAs.8 More projection data from a 360° rotation protocol provides more information to reconstruct the image; allow for greater spatial and contrast resolution; increase the signal-to-noise ratio, producing ‘‘smoother’’ images; and reduce metallic artifacts. However, more projection data usually necessitate a longer scan time, a higher patient dose, and longer primary reconstruction time.

2D detector array

X-ray tube

Scanned volume

Image acquisition

180° to 180° rotation

Raw data (2D projections)

Image reconstruction (3D dataset)

Visualization (2D slices, etc)

Figure 9: Image workflow stages of a 3D CBCT scanner.

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In accordance with the ‘‘as low as reasonably achievable’’ (ALARA) principle, the number of basis images should be minimized to produce an image of diagnostic quality.1

2. Detecting the image During scan rotation, a divergent pyramidal or cone-shaped source of ionizing radiation is directed through the middle of the ROI (fulcrum) and the transmitted attenuated radiation is projected onto the detector on the opposite side (Fig. 4).

The X-ray source emits x-ray photons. The scintillator in the detector absorbs the x-ray photons and converts them into light. The photodiode array in the amorphous silicon panel absorbs the light and converts it into an electronic charge.8 Each photodiode represents a pixel or 2-D picture element.

(Fig.10) The electronic charge at each pixel is read out by low-noise electronics to provide digital data. This data is then transmitted to and collected at a dedicated computer.

The pixel size of the detector is the principle determinant of the voxel size (3-D picture element) (Fig.10). Detectors with small pixel size capture fewer x-ray photons per voxel; and result in more noise. In CBCT, pixel size can vary from .12 mm to .4 mm. The lower pixel-size image takes more exposure time (20 to 40 seconds) and more radiation. It is very susceptible to movement distortion. Thus, even though small pixel-size images lend more definition to smaller object areas, the risk of movement distortion makes it impractical for most applications. Therefore, imaging subtle pathology such as caries, root fractures, or periodontal bone loss is not practical due to movement-related distortion.

3. Reconstructing the image In a single rotation, the detector can generate anywhere between 150 to 600 high-resolution 2-D basis images.2 The basis images, each with more than one million pixels with 12 to 16 bits of data assigned to each pixel, is transferred to a processing computer (work station) for reconstruction using software programs incorporating sophisticated algorithms (FDK algorithm) including back filtered projection to construct a 3D image, also known as a volumetric data set.2 The most widespread form of 3-D filtered back projection used in CBCT uses the Feldkamp–Davis–Kress (FDK) algorithm.8 Reconstruction time is usually less than 3 minutes for standard resolution scans.1 Reconstruction time is usually dependent on the quality of the software and computer hardware. Once the basis images are reconstructed they can be recombined into a single digital 3-D image or volumetric data set for visualization by the clinician.

The voxel is the smallest individual volume element in the 3-D environment and determines the spatial resolution of the image (Fig. 10). They are cubic in nature and equal in all dimensions (isotropic). When viewed as a digital image, the pixel size controls the resolution. The smaller pixel size yields a higher resolution image, and conversely, the larger the pixel size, the lower the resolution or quality of the image.

More projection data provide more information to reconstruct the image; allow for greater spatial and contrast resolution; increase the signal-to-noise ratio, producing ‘‘smoother’’ images; and reduce metallic artifacts. However, more projection data usually necessitate a longer scan time, a higher patient dose, and longer primary reconstruction time.

In accordance with the ‘‘as low as reasonably achievable’’ (ALARA) principle, the number of basis images should be minimized to produce an image of diagnostic quality.1

4. Displaying and manipulating the image CBCT technology provides a complete digital model at the end of the process. The software also provides the dental clinician with a relatively large choice of display formats, allowing for 2-D, 3-D and panoramic views of the mouth and head, along with other viewing options to help focus in on areas of interest.

The default presentation of the 3-D volumetric data set is a compilation of all available voxels and presented to the clinician in real time on screen as secondary reconstructed 2-D cross-sectional images in three orthogonal planes (axial, sagittal and coronal) for visualization and manipulation. (Fig. 11) Axial planes are a series of slices from top to bottom in the volume. Sagittal planes are a series of 2D slices from left to right, and coronal planes are a series of 2-D slices from anterior to posterior (front to back). Each panel of the display software presents one of a series of contiguous images in that plane. Each image is inter-relational such that the location of each image in the sequence can be identified in

Figure 10: Pixel is the basic 2D basis image picture element, whilst a voxel is 3D picture element and thus represents the smallest individual volume element of a 3D scan.

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Stage 1

Stage 2

Sagittal

Axial

Stage 3

Coronal

Figure 11: The 3D volumetric data set is a compilation of all available voxels presented to the clinician (Stage 2) and presented to the clinician in real time on screen as secondary reconstructed 2-D cross sectional images in three orthogonal planes (axial, sagittal and coronal) (Stage 3).

the other two planes.

CBCT data should be considered as a volume to be explored from which selected images are extracted.

Technically, four stages are recommended to provide an efficient and consistent systematic approach to optimize CBCT image display before interpretation namely: (a) reorientation; (b) optimization; (c) viewing; and (d) formatting the data.

a. Reorientation of the data One of the advantages of CBCT is that the resultant volumetric data set can be reoriented in all three planes using PC-based software. Initial adjustment of the volumetric data set should include reorientation, such that the patient’s anatomic features are realigned symmetrically according to three orthogonal reference planes, namely: axial or

horizontal plane (top to botom cross sections), coronal or frontal plane (front to back crosss section), and sagittal plane (right to left or buccal to lingual cross sections). (Fig. 12) This stage is particularly important for aligning subsequent crosssectional, transaxial images perpendicular to the structure of interest, such as to visualize single tooth pathology, or to measure the maximal height and width of the residual alveolar ridge in an edentulous segment for implant site assessment.

Data can be reoriented so that the patients’ anatomic features are realigned. Cursor-driven measurement algorithms provide the clinician with an interactive capability for realtime dimensional assessment and pre-implant treatment planning in all three planes. On screen measurements provide dimensions free from distortion and magnification.

Basic image enhancement includes magnification.

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b. Optimize the data Great variability can exist in the overall density and contrast of orthogonal images between CBCT units and within the same unit depending on patient images and scan parameters selected. Therefore, to optimize image presentation and to facilitate diagnosis, it is often necessary to adjust contrast (window) and brightness (level) parameters to favor bony structures. Although CBCT proprietary software may provide for window and level presets, it is advisable that these parameters be optimized for each scan. After these parameters are set, further enhancements can be performed by the application of sharpening, filtering, and edge algorithms. The use of these functions must be weighed against the visual effects of increased noise in the image. After these adjustments, secondary algorithms (e.g., annotation, measurement, magnification) can be applied with confidence.

c. Viewing the data Because there are numerous component orthogonal images in each plane, it is impractical to display all slices on one display format. Therefore, it is necessary to review each series dynamically by scrolling through the consecutive orthogonal image “stack.” This is referred to as a “cine” or “paging” mode. This review process will be described in greater detail in Part 2 of this series.

CBCT software programs allow scrolling through the stack of images. A cursor represented by 2 crossing lines indicates the precise localization in virtual space. The data set can also be rotated, panned, or zoomed to allow visualization of the region of interest; at any angle, scale, or position, a rendered image can be created. It is recommended that

Figure 12: The volumetric data can be re-orientated so that the region of interest are realigned symmetrically in three orthogonal planes: Axial or horizontal plane (top to bottom views) (upper left); Sagittal (right to left or mesial to distal) (upper right); Coronal or frontal plane (front to back) (buccal to lingual) (lower right); and 3D rendering is lower left) for real time visual and dimensional assessment.

scrolling be performed cranio-caudally (i.e., from head to toe) and then in reverse, slowing down in areas of greater complexity (e.g. inferior alveolar nerve, maxillary sinus). This scrolling process should be performed at least in the coronal and axial planes. Viewing orthogonal projections at this stage is recommended as an overall survey for disease and to establish the presence of any asymmetry.

d. Formatting the data CBCT software provides three basic non-orthogonal display formatting options for 3D volumetric data: (i) multiplanar reformatted images (linear oblique, curved oblique (ii) ray sum images (Fig. 13); or (iii) volume rendering (indirect or direct) (Fig.13), or serial trans-axial (Fig. 14);. Each image display option should be selected on visualizing specific

Figure 13: Ray sum image (upper right) and Volume rendering image (Lower left).

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Figure 14: Example of Serial trans-axial images.

anatomic features or functional characteristics of the volumetric data set. These images can be used to highlight specific anatomic regions and diagnostic tasks. Overall, selection should be based on applying thin sections to show detail and thicker sections to demonstrate relationships.

Protocols incorporating field of view (FOV) scan exposure parameters and display modes should be applied selectively to highlight anatomic features or functional characteristics within a specific diagnostic task.

Most volumetric data sets can be sectioned nonorthogonally to provide multiple or a series non-axial 2D images, referred to as multi-planar reformation.

Personal computer based (original equipment manufacturer), or third party, software facilitates dynamic interaction with the clinician to provide task specific display modes useful in dentistry (Figure 2). Strategies that are useful in OMF imaging include: The non-orthogonal display mode options available for CBCT volumetric data are: (i) multiplanar reformatted images (linear oblique, curved oblique, or serial trans axial); (ii) ray sum images; or (iii) volume rendering (indirect or direct).

These images can be used to highlight specific anatomic regions and diagnostic tasks

(i) Multiplanar Reformatting (MPR) Because of the isotropic nature of image acquisition, the volumetric data set can be sectioned non-orthogonally to provide nonaxial two-dimensional planar images referred to as multiplanar reformatting (MPR). In a multiplanar reformation (MPR) window, axial, coronal and saggital orthogonal planar views are related through intersection lines or crosshairs, allowing for straightforward orientation and navigation.8 Multiplanar reformation. A, C and S indicate

intersection lines corresponding with axial, coronal and sagittal planes, respectively. MPR modes can be viewed in three basic formats namely, linear oblique, curved planar, and serial trans axial reformations.2 • The linear oblique technique creates non-axial 2D images by transecting a set or “stack” of axial images. Several anatomic structures are not particularly well visualized and represented as displayed in orthogonal planes, and oblique reformatting can be useful in these instances.

Oblique images are most often used to transect and evaluate specific structures such as the mandibular condyle, TMJ and impacted third molars.2 • The curved oblique technique for planar reformation creates non-axial 2D images by aligning the long axis of the imaging plane with a specific anatomic structure. This mode is useful in displaying the dental arch, providing familiar panorama-like thin-slice images (Fig. 12 & 13).

Images are undistorted so that measurements and angulations made from them have minimal error.2 Panoramic MPR reconstructions are useful for jaw evaluation. Such reconstructions must be thick enough to include the entire mandible to avoid missing disease.

• Serial trans-axial technique produces a series of stacked sequential cross-sectional images orthogonal to the oblique or curved planar reformation. Images are usually thin slices (e.g., 1 mm thick) of known separation or interval (e.g., 1 mm apart). Resultant images are useful in the assessment of specific morphologic features such as alveolar bone height and width for implant site assessment, the inferior alveolar canal in relation to impacted mandibular molars, condylar surface and shape in the symptomatic TMJ or evaluation of pathological conditions affecting the jaws.2 Cross-sectional images are optimal for examining teeth and alveolar bone. (Fig. 14) (ii) The Ray Sum technique is used to produces images of increased sliced thickness. The slice thickness of orthogonal or MPR images can be “thickened” by increasing the number of adjacent voxels included in the display. This creates an image slab that represents a specific volume of the patient, referred to as a ray sum. (Fig. 13) The thickness of the slab is usually variable and determined by the thickness of the structure to be imaged. Full-thickness perpendicular ray sum images can be used to generate simulated projections, such as a panoramic X-ray or lateral cephalometric images. This mode can be used to generate simulated panoramic images by increasing the slice thickness of curved planar reformatted images along the dental arch to 25–30 mm, comparable to the in-focus image layer of panoramic radiographs. (Fig. 13)

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In contrast to conventional radiographs, these ray sum images are without magnification and parallax distortion.

However, this technique uses the entire volumetric data set, and interpretation is negatively affected by “anatomic noise”—the superimposition of multiple structures—also inherent in conventional projection radiography. Unlike conventional radiographs, these ray sum images are without magnification and are undistorted.3 (iii) Volumetric rendering techniques also referred to as 3D renderings (Fig. 12, 13), allow the visualization of 3D data by selective display of voxels This can be achieved by direct volume rendering (DVR) providing a volumetric surface reconstruction with depth, or indirect volume rendering (IVR), most commonly as a maximum intensity projection (MIP). MIP is used to demonstrate high intensity structures by providing a “pseudo” 3D reconstruction.

For simplicity, some viewer software has set pre-defined threshold values for different anatomical structures. From different threshold values result in different forms of 3D surface rendering, thus one needs to keep in mind that 3D rendering is for visualization purposes only, not for diagnosis and analysis.8 A variety of 3D image qualities with varying render times can be provided by the visualization software.8

e. Exporting data CBCT produces two data products: (i) the volumetric image data from the scan, and (ii) the image report generated by the operator. All these images are saved in the DICOM (Digital Imaging and Communication in Medicine) format.

CBCT data can be exported in the non proprietary DICOM file format standard and imported into task specific third party diagnostic and planning software to facilitate virtual implant placement and/or create diagnostic and surgical implant guidance stents; and assist in the computer-aided design and manufacture of implant prosthetics.

Figure 15: CBCT used to communicate valuable information to the patient.

Images are superior to conventional 2D imaging The potential benefits of using CBCT in dentistry for assessment and diagnosis of pathologies and pre-surgical planning is undisputed. Experience has shown that CBCT imaging is superior to conventional 2D images in demonstrating the location and extent of pathology, the quantity and quality of bone, and the spatial relationships of an object relative to critical anatomical structures.12 It provides clear images of highly contrasted structures and is extremely useful for analysing bone.

No image distortion and high accuracy CBCT volumetric data is isotropic, which means all three dimensions of the image voxels are the same. This makes it possible to reorient the images to fit the patient’s anatomic features and perform real-time measure-ments without any distortion.12

High Image resolution and quality Benefits of implementing CBCT into your practice Invaluable diagnostic and communication tool CBCT provides superior diagnostic and patient communication capabilities.

The patients are amazed by the technology, and it gives them a far greater understanding of any dental problems they may be having. Seeing things in three dimensions greatly increases patients’ understanding of the problem and its location. Large monitors in front of the patient chair allow patient’s to sit with the clinician and co-diagnose their problems and do their virtual treatment planning. This is very exciting, for both the patient and the clinician. (Fig. 15)

Image voxels sizes (a 3D cuboid unit of images) can be generated ranging from 0.4mm to as small as 0.125 mm in dimension, which contributes to its superior image resolution and quality. The resolution obtained with CBCT often exceeds the highest grade multi-slice CT.12

X-ray beam limitation and reduced radiation dose Reducing the size of the irradiated area by collimation of the primary x-ray beam to the area of interest (FOV) minimizes the radiation dose. Most Cone Beam CT units can be adjusted to scan small regions of interest for specific diagnostic tasks. Others are capable of scanning the entire

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craniofacial complex when necessary. The smaller the FOV, the greater the resolution and lesser radiation dose exposure for the patient.12

Compact size and design, less expensive and easier to use than conventional CT Compared to conventional CT equipment, the compact size and cost of CBCT makes it ideal and suitable for the dental office setting. Another advantage is that CBCT software for use in planning implants is usually much easier to use and far more useful than is software available with CT.12,13

Easy reorientation Because the CBCT volu-metric data set is isotropic the entire volumetric data set can be reoriented in all three reference planes (axial, coronal, sagittal) using the PC-based soft-ware so that the patient’s anatomic features are realigned. Aligning reference planes perpendicular to the structure of interest, facilitates visualization of single tooth pathology, vital anatomical structures and allows accurate measure-ment of the residual alveolar ridge in an edentulous segment for preimplant site assessment.12

Reformatting and display ability Reconstruction of CBCT data is performed natively by a personal computer. This provides the clinician with the opportunity to use chair-side image display, real-time analysis and MPR modes that are task specific. Moreover, a CBCT image can be reconstructed in many formats with which the oral care provider is already familiar. For instance, a CBCT image can be reformatted to panoramic, cephalometric, or bilateral multiplanar projections of the temporomandibular joint. These images, in turn, can be annotated, assessed, and measured for diagnostic and treatment planning purposes. In addition, cursor-driven measurement algorithms allow the clinician to do real-time dimensional assessment.12

Rapid scan time Because CBCT acquires all basis images in a single rotation, scan time is rapid (10–70 seconds). Although faster scanning time usually means fewer basis images from which to reconstruct the volumetric data set, motion artifacts due to subject movement are reduced.

Lower radiation dose than CT Risks have also been noted in the radiation dose needed with CBCT although it is generally believed that the radiation dose of CBCT is significantly lower than a conventional CT.

The effective dose of radiation required for conventional fan beam CT (average range 36.9–50.3 microsievert [µSv]), is significantly reduced by up to 98% compared with the effective radiation dose for CBCT (average range for mandible 1,320–3,324 µSv; average range for maxilla 1,031–1,420 µSv).

14

Improved clinical outcomes and reduced risk of complication The diagnostic and treatment planning capabilities of CBCT contributes towards improved clinical outcomes, lesser risks and complications for the patient and thus increased patient satisfaction.

Medico-legal reassurance CBCT is increasing being seen as the standard of care in many fields of dentistry. Using a CBCT correctly where indicated will prevent and eliminate risks and complications and will therefore play an essential role in preventing medicolegal litigation.

Positive return on investment Reimbursement drives adoption in new technologies. Investing in this technology provides increased opportunities for superior diagnostics, whilst increasing the standard of care in all fields of dentistry.

Limitations of CBCT Requires expertise en specialized monitoring equipment Referral to an Oral Maxillofacial Radiologist may be indicated for need of expertise and because a proper monitor, ambiente lighting, and equipment settings may be available only in a specialist radiologist envirenment.12

CBCT is more expensive CBCT is more expensive than classic 2D radiologic assessments. However, the counterarguments is that 2D radiologic assessments does not have the diagnostic and treatment planning capabilities and benefits that CBCT has.

Increased radiation dose risk Currently available CBCT units from different manufacturers vary in dose by as much as 10-fold for an equivalent FOV examination.15 As most devices exhibited effective doses in the 50-200 μSv range, it can be stated that CBCT imaging results in higher patient doses than standard radiographic methods used in dental practice for dental therapy but significantly lower than a conventional MDCT.14,15 The

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effective radiation dose for a CBCT is 2-4 times greater than for a cephalometric X-ray; 3-6 times greater than a panoramic X-ray and 8-14 times greater than a peri-apical x-ray.

The effective radiation dose of CBCT can be affected to an order of magnitude by the factors: patient size, FOV, region of interest, and resolution. A careful selection of all these parameters is needed to optimize diagnostic information and to reduce the patient’s radiation exposure.16 In general, imaging parameters (i.e. kV, mAs, and FOV size) has an effect on the effective radiation dose as well as image quality parameters (spatial resolution, contrast, noise and artefacts).8 In terms of optimization of exposure, the most straightforward imaging parameter are FOV size, as larger FOVs increase radiation dose to the patient. Significant dose reduction can be achieved by reducing the FOV to the actual region of interest.15 In addition; larger FOVs increase the relative amount of scattered radiation reaching the detector, leading to an increase in noise and artefacts. Therefore, FOVs should always be kept as small as possible, covering only the ROI.8,10

Requires training and has a learning curve It requires new competencies from the clinician and the value of information obtained is interpretation sensitive. This requires training and new knowledge from the clinician.

Poor soft tissue contrast One major disadvantage of CBCT is that it can only demonstrate limited contrast resolution. If the objective of the examination were hard tissue only, then CBCT would not be a problem. However, CBCT is not sufficient for soft tissue evaluation as it provides limited resolution to deeper (inner) soft tissues and MRI and CT are better for soft tissue imaging.12

Imaging artifacts Artefacts are any dis-tortions or errors in the image that is unrelated to the subject being studied, Such image artefacts can be inherently related to the image acquisition and reconstruction process of the CBCT machine, or patient related (i.e. metal artefacts, or motion artefacts).12 Metal artefacts, are the result of high X-ray absorption by highdensity objects. These artifacts contribute to image quality degradation and can lead to inaccurate or false diagnosis.

It is important to note that a CBCT user has little influence on metal artefacts, as increasing exposure settings (e.g. mA and number of projections) do not improve the appearance

of metal artefacts substantially enough to justify the increased radiation dose.8 Depending on the amount of motion during image acquisition, slight blurring or severe artefacts may occur. Due to the relatively long scan times in CBCT, motion is an important issue. Any movement artefacts affect the whole dataset and thus the whole image.

Motion artefacts however, can be controlled by the CBCT user by using a head restraint device with long scan times and selecting a protocol with a short scan time for patients at risk for excessive motion.

Bone density and grayscale CBCT is commonly used for the assessment of bone quality primarily for pre-implant treatment planning. Traditionally bone quality has been based on bone density, estimated throiugh the use of Hounsfield units derived from multidetector CT (MDCT) data sets. However, due to crucial differences between MDCT and CBCT, which complicate the use of quantitative gray scale values (GV) for assessment of bone density with CBCT17 Experimental and clinical research suggest that the qualitative use of GV in CBCT to assess bone density should be avoided at this stage.17 Current scientific literature suggests a paradigm shift of bone quality assessment from a density-based analysis to structural evaluation.17

Considerations and guidelines for purchasing CBCT imaging equipment The number of CBCT devices available on the market has increased substantially and new models are being developed and released on a continuous basis. Currently there are more than 50 types of cone beam computed tomography models available, including multimodal types for additional panoramic and/or cephalometric imaging, and cheaper primary panoramic machines with a small fieldof-view three-dimension button.18 These devices exhibit a wide variability in terms of capabilities, and crucial exposure parameters.19 Additionally, 3D radiographic technology is continuously evolving and improving. Each dentist has to identify what he wants out of the device and then pitch his purchase towards the strong points of the popular and/or available brands that will meet his specific needs. A good place to start is to consult with other users, and suppliers of CBCT devices.

Decision-making when purchasing a CBCT machine is primarily based on four parameters: needs and benefits, hardware capabilities, software capabilities and cost considerations.

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Needs and benefits Critical questions that a potential buyer must ask is: Why do I need a CBCT device, and what benefits do I expect my patients will get from having a CBCT machine?

CBCT machines are generally used for diagnostics and treatment planning in dental implantology, endodontics, oral and maxillofacial surgery (wisdom teeth, TMJ, trauma, orthognatic surgery), and orthodontics (cephalometric skeletal tracing, naso-pharyngeal airway analysis). CBCT machines can also be integrated with CAD/CAM and/or digital printer devices for fabrication of surgical guides, prosthodontics and orthodontic appliances.

Potential purchasers also need to understand that acquisition of this technology has a learning curve on how to use the device and that learning how to interpret and read images requires time, effort and experience. Therefore, make certain the manufacturer has a technical support service and get more than one opinion before buying.20 Needless to say, and important guideline is to get a machine that is very easy to use.

Patients appreciate the convenience of having a CBCT machine in your office, and that it will improve the diagnosis the outcome of their treatment and reduce treatment complications.

Hardware capabilities What type of machine should I get and what features should it have?

CBCT machines can be categorized according to: (i) design of the device or orientation of the patient during image acquisition (i.e. sitting, standing or supine); or (ii) the scan volume, also referred to as the FOV irradiated.1 The advantages and disadvantages of the different orientations are already described elsewhere in this article. First decision is to make sure that there is sufficient space available to accommodate the footprint of a sitting, standing or supine CBCT machine in the practice.

A basic CBCT machine should have the capability to allow for a small FOV for a single tooth clinical situation (i.e.

5 x 5 FOV), a full upper or lower jaw (i.e. 5 x 10 FOV), or to view the upper and lower jaw simultaneously (i.e. 10 x 10 FOV) Additionally, most dentists require that a CBCT machine should at least have the capability to take Panorex X-rays as well (also referred to as multimodal capability). If you are doing orthodontic treatment your CBCT device should preferably also have a 2D cephalometric X-ray capability.

Oral and Maxillofacial surgeons require an extended field of view (full skeletal 3D view) to manage trauma, orthognathic and TMJ cases.

Software capabilities Three important guidelines that CBCT has to comply with are: (i) the software must have all the required tools and easy to use; (ii) there should be a bridge to, and be compatible with the office management software; and (iii) it must be compatibility with optical scanners.

Features or software capabilities (characteristics) that should be looked for or considered when purchasing a CBCT machine are the following: (i) automatically converts DICOM files; (ii) Imports STL files; (iii) nerve mapping; (iv) implant site measurement tools; (v) virtual implant library; (vi) implant abutment library; (vii) prosthetic planning; (viii) cephalometric tracing; (ix) airway space analysis; (x) surgical guide fabrication; (xi) radiology reporting capability.21 Various software packages are available for the interpretation of Digital Imaging and Communications in Medicine (DICOM) files generated from CBCT scans.

Cost and return on investment Is the return on investment worth the purchase price? The current cost of a cone beam device is high, typically around R750,000 to R1,500000. Purchasing a CBCT machine that has a multimodal functionality (i.e. can also take periapical, bitewings, panorex or cephalometric x-rays) helps to pay for the machine.

Thus when observing the high financial outlay for a cone beam device, prudent practitioners should determine how often they would use the device in their practices. Typical current fees for cone beam imaging in the South Africa range from R1200 to R4600. It is easy to multiply the number of images anticipated in a typical month of practice by the individual image fees to see if the return on investment is worth the expense. The various fee levels and frequency of use will make this analysis different for each practice. A word of caution related to any high-cost technology - when practitioners have such devices, there is a tendency to overuse them for financial reasons, which is unethical practice.

Besides costs of a CBCT unit, having inadequate space for a machine and having to learn and maintain additional software and hardware – probably the major reason that is emerging as a barrier for acquiring a CBCT unit, relates to skills and competencies required for interpretation of images.22

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Conclusion The development of inexpensive x-ray tubes, high-quality detector systems and powerful personal computers have paved the way for commercially available and affordable 3-D CBCT imaging systems for the dental practice.

Over the past decade, CBCT has revolutionized dentomaxillofacial radiology by providing 3D imaging for the dental setting, overcoming the major limitations of traditional 2D intra-oral, panoramic and cephalometric radiographs.

Despite the lack of universal standards of care for dentistry, 3D CBCT imaging capabilities for diagnostics, pre-surgical planning, and improving treatment outcome in dental implantology, is now rapidly moving towards being the standard of care. As with any emerging technology, dental professionals need adequate theoretical and practical training to use CBCT effectively and safely.

Finally, dentists have an ethical duty to preserve the health of their patients and to prevent or limit risks, and always seek the best treatment in such a way that the benefits will always exceed the risks. The quest begins with the radiographic assessment that requires the least amount of radiation dose to treat the patient appropriately.

References 1. Scarfe WC, Farman AG. What is Cone Beam CT and how does it work: Dent Clin N Amer 2008; 52: 707-730.

2. Scarfe WC, Farman AG, Sukovic P. Clinical applications of Cone-Beam Computed Tomography in dental Practice. J Can Dent Assoc 2006; 72(1): 75-80.

3. Sato S, Arai Y, Shinoda K, Ito K. Clinical application of a new cone-beam computerized tomography system to assess multiple twodimensional images for the preoperative treatment planning of maxillary implants: case reports. Quintessence Int 2004; 35(7): 525–8.

4. Kobayashi K, Shimoda S, Nakagawa Y, Yamamoto A. Accuracy in measurement of distance using limited cone-beam computerized tomography. Int J Oral Maxillofac Implants 2004; 19(2): 228–31.

5, Hatcher DC, Dial C, Mayorga C. Cone beam CT for presurgical assessment of implant sites. J Calif Dent Assoc 2003; 31(11): 825–33.

6. Alamri HM, , Sadrameli M, , Alshalhoob MA, , Sadrameli M, , Alshehri MA. Applications of CBCT in dental practice: a review of the literature. Gen Dent 2012; 60: 390–400.

7. Schulze R, Heil U, Bruellemann DD, Dranischnikow E, Schwancke U, Schoemer E. Artifacts in CBCT. Dentomaxillofac Radiol 2011; 40(5); 265-273.

8. Pauwels R, Araki K, Siewerdsen JH, Thongvigitmanee SS. Technical aspects of dental CBCT: State of the art. Dentomaxillofac

Radiol 2015; 44(1): 20140224, 9. Abromovitch K, Rice DD. Basic principles of Cone Beam Computed Tomography. Dent Clin N Am. 2014; 58: 463-484.

10. SEDENTEXCT Radiation Protection No. 172. Cone Beam CT for Dental and Maxillofacial Radiology (Evidence-based Guidelines).

2011. www.sedentexct.eu/files/ radiation_protection_172.pdf.

Accessed October 24, 2017.

11. Mallya SM. Evidence and professional guidelines for appropriate use of cone beam computed tomography. J Calif Dent Assoc 2015; 43(9): 512-520.

12. Adibi S, Zhang W, Servos T, O’Neil P. Cone beam computed tomography in dentistry: What dental educators and learners should know. J Dent Educ 2012; 76(11): 1437-1442.

13. Tyndall DA, Price JB, Tetradis S, Ganz SD, Hildebolt C, Scarfe WC. Position statement of the American Academy of Oral and Maxillofacial Radiology on selection criteria for the use of radiology in dental implantology with emphasis on cone beam computed tomography. Oral Surg Oral Med Oral Pathol Oral Radiol 2012;113:817-826.

14. Schulze D, Heiland M, Thurmann H, Adam G. Radiation exposure during midfacial imaging using 4 and 16-slice computed tomography: cone beam computed tomography systems and conventional tomography. Dentomaxillofac Radiol 2004; 33: 83–6.

15. Bornstein MM, Scarfe WC, Vaughn VM, Jacobs R. Cone beam computed tomography in Implant dentistry; A Systematic review focussing on guidelines, indications and radiation dose risk.

Int J Oral Maxillofac Implants 2014; 29 (Suppl): 55-77.

16. European Academy of Dental and Maxillofacial Radiology.

Basic principles for use of dental cone beam CT. At: www.camosci.cz/public/files/pages/00000202_ basicprinciplesforuseofdentalconebeamct.pdf. Accessed: February 18, 2018 17. Pauwels R, Jacobs R, Singer SR, Mupparapu, M. CBCTbased bone quality assessment: Are Hounsfield Units applicable?

Dentomaxillofac Radiol 2015; 44(1): 20150238.

18. Jacobs R, Quirynen M. Dental cone beam computed tomography: justification for use in planning oral implant placement.

Periodontology 2000. 2014; 66: 203–213.

19. Pauwels R, , Jilke Beinsberger J, Collaert B, Theodorakou C, Rogers J, Walker A, Cockmartin L, Bosmans H, Jacobs R, Bogaerts R, Horner K, The SEDENTEXCT Project Consortium. Effective dose range for dental cone beam computed tomography scanners. Eur J Radiol (2011), doi:10.1016/j.ejrad.2010.11.028 20. Giacobbi T. 3D Images for 21st Century Dentaltown Magazine, August 2007, http://www.dentaltown.com/ magazine/articles/1438/3d-images-for-21st-century-dentistry.

21. Scherer MD. Presurgical Implant-Site Assessment and Restoratively Driven Digital Planning. Dent Clin N Am 2014; 58: 561–595.

22. Friedland B. Medicolegal issues related to cone beam CT. Semin Orthod 2009; 15: 77-84.

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The Colgate® ProClinical® 150 battery toothbrush uses sonic cleaning motion to remove plaque while ultra-thin bristles gently clean the gumline.

Ideal for patients wishing to transition from a manual to a power toothbrush • Replaceable brush head • Soft thin-tipped bristles • 2 minute timer • Slim, lightweight handle • Sonic vibrations up to 20,000 Strokes/min *vs. a manual flat-trimmed toothbrush

All products available from: HENRY SCHEIN HALAS • Tel: 1300 65 88 22 • www.henryschein.com.au

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PRODUCTS

KURARAY NORITAKE

EMS

CLEARFIL UNIVERSAL BOND QUICK

AIRFLOW PROPHYLAXIS MASTER

APPLY AND PROCEED CLEARFIL™ Universal Bond Quick is a single component, fluoride-releasing, bonding agent indicated for all direct and indirect restorations, enabling all etching modes (total-etch, self-etch or selective-etch). Incorporating Kuraray Noritake Dental’s original MDP monomer and new Amide monomers, CLEARFIL™ Universal Bond Quick delivers Rapid Bond Technology. New Amide monomers rapidly permeates dentine & enamel, eliminating waiting time during application, while dramatically reducing water absorption. CLEARFIL™ Universal Bond Quick reduces technique sensitivity & application time without compromising bond strengths, sealing or desensitizing. CLEARFIL™ Universal Bond Quick is also indicated for the surface treatment of zirconia and silica-based glass ceramics by incorporating a silane coupling agent to ensure universal application.

THE GAME CHANGER Introducing the New AirFlow Prophylaxis Master from EMS - the latest innovation from the world’s No.1 prophylaxis provider.

• Heated water system = increased patient comfort • Improved powder consumptions rate • Easier to operate & clean • No more clogging - simpler to maintain • Wireless foot pedal - eliminates trip hazard

SCHEU

PHILIPS

MINISTAR S - NEW GENERATION

PROTECTIVE CLEAN BY PHILIPS SONICARE

PROTECTIVE CLEAN • A toothbrush with advanced notification technology that delivers superior sonic technology results while caring for your teeth and gums.

New generation, handy pressure moulding machine with barcode scanner. Quick, compact and precise. The scanner reads the coded material to allow the programming of all important parameters such as heating time, temperature and cooling time.

The new generation is equipped with a user-friendly membrane keypad and a large display. All operating parameters are monitored and indicated in the display.

• Pressure Sensor Smart Brush head recognition • Removes up to 7 x more plaque • Improves gum health up to 100% • Up to 3 brushing modes: Clean, White and Gum Care • BrushSync replacement reminder

All products available from: HENRY SCHEIN HALAS • Tel: 1300 65 88 22 • www.henryschein.com.au

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