NEWER COMPOSITES Although, the first composite resin was designed for restoration of anterior teeth, it was less than two years that a modified material was
introduced
for
restoration
of
the
posterior
teeth.
Resin
manufacturers have filled the fire by preaching the use of composite
for post teeth for several years. But no proper long term clinically experienced studied have proved any good results about posteior composite mateial. In light of this we have a major subject for debate: i.e. should composite resin be used in posterior teeth ? Amalgam and gold have stood the test of time, can we talk about composite as amalgam alternative. Currently amalgam alternatives are defined as any restorative material used in place of amalgam. The term now a days is referred to describe direct placement system of composite. Because according to DCNA 1990, an ideal post composite should possess the following properties. 1. Esthetics.
2. High resistance to clinical wear. 3. Permanent marginal integrity. 4. Minimal cavity preparation. 5. Provision of a sealing bond and a retentive bond to tooth structure. 6. Non-brittle material with adequate tensile and compressive strength. 7. Radiopacity. 8. Self-bonding properties should additional restoration become necessary. 9. Ease of manipulation. 10.Non-toxic. 10. Resistance to formation of secondary caries. 11. Minimal or no galvanic and thermal shock properties.
Amalgam and gold have: -
Resistance.
-
Radiopacity. But lack most above mentioned properties whereas composites
can fulfil atleast half. Till date there has been no evident classification for the newer materials developed so far and also these materials are difficult to be placed in the conventional classifications. Therefore for ease and understanding, I would be describing the newer materials under 3 categories, viz. 1. Direct placement systems: a. Condensable / packable composite (PRIMM). b. Flowable composites. c. Compomers. d. Universal composites. 2. Indirect placement systems: -
Artglass.
-
Belle glass.
-
Fibre-reinforced materials.
3. Miscellaneous
-
Cements.
-
Splinting.
-
Prostho veneers.
-
Core build up.
-
Pit and fissure sealant.
Evolution of condensable / packable: Posterior Composites: 1. The first improved posterior composite resin (p-10, 3M) consisted of small filler particles – resulted in wear of materials (5-10µ). 2. Next major modification was substituting barium silicate glass (Nuva fil) for traditional quartz filler. This reduced the wear rate. - The soft filler absorbed masticatory energy. - Barium-helped in radiopacity. 3. Next filler particles were further reduced to 1-3µ, filler remaining the same, loading increased. 4. Further it was reduced to 1µ.
5. Spherical type of fillers was used for stress concentration areas as in regularly shaped fillers the stresses were concentrated where the particle was angulated. 6. Then came materials with filler particles consisting of ceramic or glass inserts, megafillers where they used β-quartz. 7. Later cancel the evaluation of fused glass fibre powder, PRIMM. Confusion in Terminologies: Now-a-days posterior composites are marketed with different terminologies. Some market it as condensable material. Condensable is defined as able to be compacted or made denser by reducing volume. This is to market them as being similar to amalgam placement which is not true as composites do not require condensation to guarantee a coherent, void-free mass therefore a better description is packable composite. Packable is defined as the ability to organize the composition of
in
order
to
achieve
favourable
or
hoped-for
result.
This
terminology, fits better as the material has to be packed in the cavity and not condensed.
They can also be termed as heavy body as described by Jackson as they are stiffer and are highly viscous. Packable composites generally: 1. Altered filler characteristics: -
They have larger than average filler particles.
-
There increase in filler amount where the resin matrix is chemically modified to allow the increase.
-
Because of filler volume – high viscosity i.e. resistance to flow is seen.
2. Non tacky. 3. Have little internal resistance to matrix band. 4. Non-sticky –forming either agglomerates. 5. This is achieved by – or fibrous fillers are added. Or by changing the packing arrangement. PRIMM- can be discussed as condensable: Polymeric rigid inorganic matrix material. A new concept was developed which consisted of a resin and a ceramic component (filler) by Dr. Lars Ehrnford of Sweden (M.E.D. U.S.A.).
-
Rather than incorporating the filler particle into the composite resin matrix, he devised a unique system by which ceramic fibers
incorporated
into
the
filler
network
thus
forming
scaffolding of ceramic fibers. -
Fibers are composed of – silicone dioxide, aluminium oxide. These individuals fibers are superficially fused together at selected sites which then generated a continuous network of smaller chamber or cavities which later gets filled with BISGMA or UDMA after silanation.
Properties: 1. Increased resistance to wear a marginal deterioration. 2. Consistency is similar to freshly triturated mass of amalgam. 3. Colloidal silica ultrafine particles are also incorporated to control the: -
Handling properties.
-
Viscosity.
-
Condensability.
-
Reduced stickiness.
4. Greater
the
condensation
pressure
used,
greater
is
the
expression of residual resin and greater is the density of the inorganic phase. Hence all these properties result in: Advantages: 1. Better marginal adaptation. 2. Lower potential for incorporation of microscopic porosities. 3. Less polymerization shrinkage. 4. Optimum mechanical characteristics. 5. Wear resistance is only several micrometers more than enamel. E.g. P-50, Adaptic. The arrows show the direction in which the resin tends to shrink during polymerization process. Since the surface of the ceramic fibres is silanated, the polymerizing resin does not pull away from the surface. Let us now discuss some of the commonly used packable composites: -
Solitaire.
-
Alert.
-
Surefil.
-
Filtek P-60.
-
Prodigy.
-
Pyramid.
-
Glacier.
-
Synergy compact.
-
Definite
-
Ariston pHc (White amalgam)
-
Heliomolar.
-
TPH spectrum.
BISGMA – Bisphenol A ethylene glycol diether dimethacrylate. Most commonly used are: -
Filtek P-60.
-
ALERT.
-
Surefil
Solitaire – porous filler gets loaded by resin matrix to improve packability. 1.
Com pan y
AL E RT J eneri c P ent ron
S URE FIL Dent spl y
FIL T E K P- 60 3M
2.
Year
1998
1998
1999
3.
Fi l l er l evel (vol %)
62- 70
58-66
61
C hopped m i crogl ass fi ber (Ba ri um gl asses
Mi di fi l l er Mi ni fi l l er Macrofi l l er
0.6µ m average part i cl e bari um gl asses
4.
Fi l l ers
5.
R esi n t ype
6.
Com posi t e st rengt h
7.
Tensi l e st ren gt h
8.
Fl ex ural st ren gt h
9.
Fl uori de rel ease
10.
– col l oi dal si li ca h yb ri d)
Bari um gl asses Al gi nat e si li cat e Si l i con di ox i de
z i rconi um i ncreases fl ex ural st rengt h
Et hox yl at ed B IS GMA
UDMA
B IS GMA, UDMA, GMA
305
433
390
66
81
79
170
125
154
No
Yes
No
Moderat e
Hi gh
Moderat e
2
2.1
2.1
Indi vi dual fi bers are 6µ m In di a and 20µ m in l engt h
Best handl i ng propert i es i nt erl ocki ng effect
BIS -
R adi opaci ty
11.
Shri nkage
Advantages of bonded direct posterior resins (in comparison to amalgam in general): 1. Good esthetics. 2. Conservation of tooth structure. 3. Improved resistance to microleakage. 4. Strengthening of tooth structure by direct bond. 5. Low thermal conductivitiy. 6. Completion in one appointment. 7. No corrosion.
Disadvantages: 1. Very technique sensitive: -
Moisture can break the silane bond between resin and filler.
-
In Class II restoration, care should be observed in placing and positioning the matrix bands because posterior composites are almost entirely dependent upon the contour and position of the matrix for proximal contacts. Reflecting wedges are one more additional requirements for
better adaptation. -
Placing and packing composite is more time consuming than traditional amalgam.
-
Also curing methods are very important aspects to consider to reduce shrinkage.
2. Higher coefficient of thermal expansion than tooth structure. 3. Low modulus of elasticity. 4. Biocompatibility of some components are unknown. 5. Limited wear resistance in high stress areas. 6. Polymerization shrinkage. Indications:
1. Esthetics. 2. Class I and II cavities which can be properly isolated and where some centric contacts on the tooth structure is present. 3. Class V defects – because cavitated carious lesion, abrasion and erosion lesions. 4. Veneers for metal restoration. 5. Repair of fractured areas. 6. Interim restorations. 7. Restoration of a weakened tooth that can be strengthened by bonding resins. Contraindications: 1. Operating site cannot be well isolated. 2. When all occlusal contacts will be on the composite. 3. Heavy occlusal stresses – bruxism. 4. Deep subgingival areas. 5. High caries index. Flowable Composites: -
Since 1995, a new type of composite described as flowable has become popular. Flowable composites were developed mainly
in response to requests for special handling properties for composite resins rather than any clinical performance criteria i.e. fluid injectibility. These were created by: -
Retaining the same small particle size of hybrid composite but by
-
Reducing the filler content.
-
Increasing the resin matrix to reduce viscosity.
-
But according to DCNA 2001 – predominantly – minifillers, macrofillers – (0.02-0.04).
-
To make composite of low viscosity of flowable:
1. Particle size is increased. 2. Filler amount is decreased. Range of applications suggested by: Manufacturers for flowable composites are: 1. Amalgam margin repair. 2. Class I, II, III, IV and V restoration. 3. Composite repairs. 4. Core build up.
5. Crown margin repair. 6. Enamel defect repair. 7. Incisal edge repair. 8. Liners. 9. Pit and fissure. 10.
Porcelain repairs.
11.
Porcelain veneer cement.
Some of the manufactured flowable composites are: Type of CR
Manufact ures
Fi l l er Inf orm at i on
1. Eli t efl o
Bi sco
Type : Bari um gl ass col l oi dal sil i ca Avg. S iz e: 0.7µm Wt : 60%
2. Fl orest ore
Dent Mat . C orp.
Type : S il i ca bari um gl ass Bari um fl uorosi li cat e Avg. S iz e: 0.7µm Wt % : 50
3. Fl ow- it
Jeneri c/ P ent ron
Type : Bari um borosi l i cat e Avg. S iz e : 1.5µm Wt % 70.5
4. R evol ut i on
Kerr
Type : Bari um gl ass S ynt het i c si l i ca Avg. siz e: 1µ m Wt % 62
5. Ul t raseal XT pl us
Ul t radent
Type : Gl ass i onom er gl ass
Avg. siz e 1-1.5Âľ m Wt % 60
Other are: Tetric flow Helio molar flow Perma flow Versa flow Physical properties: 1. Surface roughness is more. 2. Wear rate is more because decreased filler. 3. Coefficient of thermal expansion is higher. 4. Low elastic modulus. 5. Toughness is said to be more because of increased resin matrix. 6. Viscous.
The physical properties show a ray of confusion whether this material is favorable or not. Not many studies and laboratory tests have been performed on the efficacy of these materials. Because it is advised not to use these materials in higher stress concentration areas and wear associated areas. [Although it can be used under a packable composite in a Class II cavity preparation especially in the gingival seat area to avoid
voids and also because of low elastic modulus, it can compensate for stresses under a restoration]. UNIVERSAL COMPOSITES -
This composite was designed for use in all classes of cavity preparation.
-
The filler size ranges between 0.6-0.9Âľm.
-
They contain varying amounts of colloidal silica to control handling characteristics.
-
Main fillers are barium and zirconia.
Advantages: 1. High surface luster. 2. Sufficient wear resistance for Class I and Class II cavity preparation (15Âľm / year). 3. Increases flexural strength. Disadvantages: 1. Undergoes fracture in high stress cones areas.
2. Restoration exhibits fractional marginal ditching or crevicing in high stress areas i.e. lower tensile fatigue strength because of decrease in filler size. E.g. Charisma (Kulzer), Prisma A and H (Dentsply), Herulite (Cdteme), Tetric Ceram (Ivoclar), Z-100 (3M). COMPOMERS Polyacid modified resins: McLean and Nicholson defined this material as “materials that may contain either or both of the essential components of a glass ionomer cement but at levels insufficient to promote the acid-base curing reaction in the dark�. This material is essentially a resin composite in which the filler is a glass similar in many ways to the ionomer glass, it also has dehydrated polyalkenoic acid incorporated with the filler but this does not become available to react with glass until there has been some water intake in the restoration. There is limited degree glass ionomer type of acid-base reaction which will release small quantities of fluoride. The adhesion system has to based on the resin to dentin method because of ion-
exchange method cannot arise at any stage. Hence photoactivation is absolutely necessary for this type of material. Indications: 1. Sealing and filling of occlusal pits and fissures. 2. Restoation of deciduous teeth. 3. Minimal cavity preparation or tunnel preparation. 4. Lining of all types of cavities where a biologic seal and cariostatic action is required. 5. Core build-up. 6. Repair of defective margins in restorations. 7. Class V repairs. 8. Erosion. 9. Retrograde filling materials in endo-emergencies.
Advantages: 1. Easily adapts to tooth. 2. Good esthetics. 3. Fluoride release which is sustained. e.g. Dyract, Compoglass, Hytact, F-2000, Elan
Lately, flowable compomers are appearing in the market which have similar inferior properties as other flowable composites. Not much literature has been published – Dyract flow; compoglass flow. RESIN MODIFIED / REINFORCED GIC According to Nicholson, “Resin modified GC materials are those that are modified by the inclusion of resin, generally to make them partly photocurable.” As soon as the powder and liquid are combined the acid base reactions begins as usual and continues for many weeks. However, there is a light command available over the top of this reaction which will immediately protect the acid-base reaction from problems of water balance and stabilize the setting cement. According to Christensen (JADA 1997) These materials are termed as “tricure” as it sets by 3 phenomena. i.
Acid
base
reaction
between
the
components
of
conventional GIC. ii.
Light cure reaction stimulated by light application activates the initiator catalyst resin cure system.
iii.
Autocure reaction when powder and liquid are mixed together.
Composition: -
Resin-HEMA.
-
Fluoroaluminosilicate glass particles.
-
Conventional GIC.
Properties: 1. Decreased translucency. 2. Composite strength and hardness values are less than GIC and compomers. 3. Higher bond strength to composte resin when used as base. 4. Increased poly shrinkage. 5. Sufficient working time. 6. Fluoride release is greater than compomer. 7. Repairs can be carried out as bond between old and new material is strong. 8. Low wear resistance and increased fracture rates. E.g. Fuji II CC, Photofil, Vitrebond, Vitremer, XR-Ionomer.
Uses: -
Liner, bases, pit and fissures.
-
Core build up.
-
Repair materials.
-
Retrograde filling materials.
INDIRECT METHODS Because
of
the
major
clinical
problems
clinicians
have
experienced with direct posterior composite system such as: -
Polymerization shrinkage.
-
No proper adaptability.
-
Securing proper morphology.
-
Wide defects. The indirect inlay or onlay systems were introduced. Since
these restorations are made on die rather than directly on the tooth, the restoration has: -
Superior adaptation.
-
Superior contact.
-
Superior proximal contact.
-
Better characterization. Also the increase the wear resistance of the material Wendt
demonstrated that heat curing and thermocycling after light curing
procedure improved the mechanical properties appreciably (JADA 1997 May). He demonstrated that heat curing for 5 minutes at 123째C increases the wear resistance properties and hardness by 60-70%. But other studies
demonstrate
there
is
hardly
any
difference.
No
significant clinical studies have been done to support such articles. A number of highly improved indirect systems are available for the clinicians. Two systems have been marketed having: -
Excellent wear resistance property apart from o Better esthetics. o Marginal adaptation
-
Decreased cuspal fracture o Less complex laboratory procedures. o Control over polymerization shrinkage. o Enhanced physical properties.
1)
ARTGLASS (Hareus / Kulzer) Since 1995 it is marketed as non-conventional dental polymer.
Uses: -
Inlays.
-
Onlays.
-
Crowns.
In some situations of full crown restoration Artglass is used in conjunction with metal substrate (Ni-Cr or gold based alloys). The polymer is bonded to the metal substrate by applying acryl nitrite copolymer to the metal surface before placing and curing. Composition: 1. The resin matrix is comprised: a. Resin with bifunctional molecular. b. A 4-6 functional groups i.e. BISGMA, UDMA. -
This configuration provides opportunity for more double bond corrosions.
-
It provides a higher level of cross linking and better control over the positions along the carbon chain where cross linking occurs.
-
Thus, it aids in improving mechanical properties, increases wear resistance.
2. Filler: Radiopaque barium glass (0.7Âľm), colloidal silica (handling properties). This system is photocured using a special Xenon Stroboscopic light.
Emission
range
320-500nm
(470nm).
At
excitation of initiator camphorquinone is optimized.
470nm
the
Advantages: 1.
Artglass is considerably more wear resistant than conventional light cured composite (3-4Âľm/year).
2.
Good marginal adaptation.
3.
Esthetics.
4.
Proximal contact and contour are good.
2)
Belleglass HP This material was introduced by Belle Le St. Claire in 1996. In this system, the resin matrix is similar to BISGMA
restorative
systems.
The
mechanism
of
curing
associated
is
considerably different. -
Belleglass HP is polymerized under pressure at an elevated temperature and in pr of nitrogen gas.
-
The elevated temperature (130°C) increases the polymerization rate.
-
Increased pressure reduces the vaporization potential of the monomer at high temperature.
-
Nitrogen gas produces an oxygen-free environment – which in turn results in a higher level of polymerization and more translucency of mass.
Oxygen: 1. Inhibits the curing process. 2. When entrapped in resin mass inhibits polymerization in areas of direct contact because decreases using – because decreases wear and resistance. 3. It makes the mass appear opaque. Uses: -
Inlays.
-
Onlays.
-
Veneers.
Advantages: -
Esthetically appealing.
-
Highly wear resistant.
Some other indirect composites: 1. Concept (Ivoclar). 2. Alaxxim (Ceramco). 3. Targis / Vectris (Ivoclar).
4. Sculpture Fibrekor (J/P). 5. CR inlay (clearfil). 3)
FIBRE-REINFORCED
INDIRECT
COMPOSITES When high flexural strength is desired and indirect composite is the restoration of choice, the use of polyethylene or glass fibres incorporated in the composite core before curing results in materials termed as fibre-reinforced indirect composite (DCNA 2001). Fibers can be introduced into fluid matrices in various forms. These composite materials are then shaped or molded and the matrix material hardness or sets. Different fibers effect the properties of the resultant composite. Also their orientation also matters. Format
Morphology
Effects Properties
1. Short staples
----------------
-
Reduce matrix vol.
-
Improve wear resistance.
-
Can improve strength and stiffness.
-
Act to hold # matrix
-
Can improve stiffness and
2. Long lengths
3. Woven material
______________
#############
on
strength -
Assist forming structure
in
Types of fibres used: 1. Ceramic 2. Metal
Range between 3-300µm.
3. Polymeric 4. Silicon nitride whiskers – Latest approach to improve the strength. These are much smaller than fibres (0.4µm) which enable them to bridge micronsized cracks in the set matrix effectively and thus constrain growth of cracks. 5. Ceramic whiskers now-a-days are being coated with fused silica particles which are only 0.04µ in diameter (fusing them at high temperature and then silanation procedure is carried out) [Den Mat, Dental Update Nov. 2000]. The silanes form chemical bond between ceramics and polymers which helps – increased strength and fracture resistance. Kranze et al (1989) discovered that mechanical properties of BISGMA improved after incorporation of silane coated glass fibre, which were 5µ diameter and 25µ long. Willem et al (1992) reported that Restolux SP by Lee pharma, contained fibers 300µ long which improved strength and stiffness but were rough and produced wear on opposing tooth.
Xu et al using silicon nitride whiskers together with procured glass ionomer particles improved the properties of composite and produced the material that releases modest amounts of fluoride. 1. Targis / Vectris (Ivoclar). 2. Sculpture – Fibrekor (J/P). 3. Belleglass – Connect (Kerr). 4. Belleglass – Vectris (Some labs).
Miscellaneous: 1. Composite resin cements (DCNA 2001) When luting a tooth colored restoration whether it is an indirect composite, fiber reinforced indirect composite or porcelain, the cement must contribute to the overall retention through adhesion. -
These cements are composite resins.
-
They are filled to a lesser degree than hybrids to facilitate handling properties.
-
They come as two catalysts in different viscosities to initiate autocure mode.
-
Shades are available as try-in pastes that match closely the shades of real material.
-
These systems are also light cured when using under thin indirect composite or porcelain.
-
When seating inlays, onlays and crowns, the catalyst is mixed in, to ensure use in areas not reached by light.
Some of the system available are: 1.Nexus (Kerr). 2. Calibra (Caulk).
3. Choice (Bisco). 4. Insure (Cosmodent). 5. Variolink II (Ivoclar). 6. Lute-it (J/P). 7. Panavia F (J. Morita). 8. Flexi flow (EDS). 2. Core-build up composites: -
Because of their – tooth colour, ability to bond to tooth, ability to allow preparation in same appointment, composite core materials are used extensively.
-
They are available in one or 2 shades.
-
One simulates dentin colour.
-
Other is a contrast.
-
They are available as: o Light cure. o Dual cure. o Self cure
-
Care should be taken in choosing the adhesive as some adhesive systems do not bond to self cure systems.
Example: 1. Ti-Core (EDS).
2. Core paste (Den-Mat). 3. Build-it (J/P). 4. Bis-core (BISCO). 5. Corestore (Kerr). 6. Fluorocore (Caulk). 7. Clearfil photocure (J-Morita). 3. Composite splints Resins along with the reinforcement of fibers can also be used as splints for esthetic purposes. -
These fibers are strong and durable.
-
These are applied with flowable or hybrid composites.
-
They are available in different: o Thickness. o Breadth. o Pattern.
E.g. 1. Ribbond (Ribbond). 2. Connect (Kerr). 3. Splint-it (J/P). 4. Glass span (Glassspan). 4. Pit and fissure sealants: -
They can be compared with flowable composites.
-
Available as filled or unfilled.
-
Resin system include: o Cyanoacrylates. o Polyurethaes. o BIS-GMA.
-
Self cure or light cure.
-
Unfilled are available as – colourless, tinted transparent.
-
Filled – Opaque, tooth coloured.
-
Surface hardness was good as less air comes in contact because of viscosity.
-
Manufacturers have attempted to add tiny glass filler particles for reinforcement and radiopacity but disadvantage is that it may abrade the opposing dentition.
5. Prosthodontic veneering resins -
The initial resin, veneering materials employed were basically heat cured polymethyl methacrylate.
-
These were subsequently improved by the addition of fillers and cross linking agents.
-
Then came microfilled with either BISGMA, UDMA.
-
These resins were polymerized using light of wavelength between 320-520nm or by combination of heat and pressure.
-
As far as the bonding of these resins to the underlying metal substrates is concerned, these resins were initially bonded MECHANICALLY using wireloops or retention beads.
-
The recent developments in bonding mechanism have included micro-mechanical retention created by acid-etching the base metal alloy and use of chemical bonding system i.e. 4-META, phosphorylated methacrylate or epoxy resins.
-
Other method is use of silicondioxide that is flame sprayed to metal surface followed by application of silane coupling agent. These
materials
have
advantages
and
ceramics.
Advantages: 1. Ease of fabrication. 2. Predictable intraoral reparability. 3. Less wear of opposing teeth or restoration. 4. Esthetics. Disadvantages:
disadvantages
over
1. Low proportional limit. 2. Pronounced plastic deformation that contributes to distortion on occlusal loading. 3. Leakage of oral fluids if mechanically bonded. 4. Discoloration and stains. 6.
Root Posts Resin reinforced with carbon or quartz fibers have been used to
produce black or white root posts with stiffness similar to that of dentin. Fiberglass resin posts – refracts and transmits light to the luting resin cements even after light curing cycle. 7.
Fluoride releasing composites (Dent Mat 2001) Fluoride release is a desirable attribute for a material used in
dental applications. GIC have long been accepted as materials that satisfy these demands but lacks in potential physical and mechanical properties.
Many
new
materials
have
been
combination of resins and GIC as discussed earlier.
available
with
a
But resin based composite which would eliminate the need for mixing and would have acceptable physical strength properties along with fluoride release is the next hunt for manufacturers. Manufacturers have tried incorporating inorganic fluoride such as NaF, but failed as it requires water diffusion methods which created a voids in the mass. Then organic flouorides were examined as additives to polymer matrices. Tanaka et al used methacryloyl fluoride – methyl methacrylate copolymer in pit and fissure sealant where fluoride delivery lasted for 2 years (MF-MMA). Kwan et al used Lewis acid i.e. BF3 and Lewis base i.e. diethylaminoethyl methacrylate into dental resin system fluoride is released by hydrolysis at a rate of 2-5µg/cm 2 /day for 1 year. Other
experiments
are
still
under
progress
using
–
morpholinoethyl methacrylate hydrofluoride – tetrabutyl (ammonium tetrafluoroborate). 8.
Ormocers: -
An acronum for “organically modified ceramics.”
-
Chemically
are
methacrylate
substituted
alkosilanes
i.e.
organic-inorganic copolymers. -
Alkylsilyl group of silane forms Si-O-Si network by hydrolysis and polyne to give cross linked strength.
-
Manufacturers claim: o Low shrinkage. o High abrasion resistance. o Condensability. o Timeless esthetic. o Biocompatible o Anticariogenic. e.g. Definite (Degussa).
9.
Smart Composites Ivoclar introduced a material in 1998 named Ariston pHC (pH
control) which was claimed to release: -
Fluoride
-
Hydroxide when the pH in restoration in the material
-
Calcium This
was
of cell to less than 5.5 said
to
neutralize
acid
and
counter
act
the
decalcification of enamel and dentine. There are no long term independent data which supports the claims of this mterial being
cariostatic. Most recently this material has been formulated to incorporate a bonding system. 10.
Superficial sealing microfills (JADA 1999) Approximately 50% silicon dioxide – filled clear resin based
composites intended to be used as a superficial “skin� over completed resin restorations have become popular. It is believed that if a newly placed restoration is acid etched and sealers are applied on their surfaces, filling of microscopic in margins occurs. Although companies are optimistics about these materials, it is doubtful that these materials could withstand long term matsticatory forces. Conclusion: As in all areas of dental research and practice, it is difficult and risky to try and predict what future holds, particularly in the field of dental polymers. The future promises to be exciting with substantial progress in the development of adhesive, wear resistant dental polymers. This ends a short glance at, but a few of the exciting events occurring in esthetic restorative materials through new products and
concepts. However it is intimated that although research solves problems it also creates others. I hope that this discussion may have whetted the appetite of all present here for the ever-changing menu that is being offered through research.