Written by Richard D. Trushkowsky, DDS Tuesday, 30 September 2003 19:00
There has been an increased use of resin composite for posterior restorations. This is due to increased desire by the patient for aesthetic restorations and by the dentist for minimally invasive techniques. However, one of the main drawbacks of composite restorations in the posterior region has been their tendency to form marginal gaps due to polymerization shrinkage. The marginal seal of a class II posterior composite decreases when the apical termination of the preparation is located at or below the cementoenamel junction. Microorganisms may invade these marginal gaps and cause recurrent decay, pulpal inflammation, and sensitivity. Marginal adaptation may be further reduced by mechanical and thermal stress. Polymerization shrinkage stress may be reduced by (1) altering the configuration factor, (2) the use of lining materials, or (3) slowing the rate of polymerization.
THE DEVELOPMENT OF ORMOCERS
Ormocers (“ORganically MOdified CERamic”) were formulated in an attempt to overcome the problems created by polymerization shrinkage of conventional composites. Traditional composite filling materials have small molecules that lead to shrinkage during curing. Ormocer prepolymerized molecules, as represented by the material Admira (VOCO), which is used in this article’s case report, are up to 700 to 1,000 times larger. The end result is less shrinkage because the larger molecules present less space for shrinkage. The Ormocer is a 3-dimensionally cross-linked copolymer with a large “backbone” that is functionalized with polymerizable organic units, creating a 3-dimensional polymeric composite. Filler particles are incorporated into this cross-linked inorganic and organic network matrix.1
The inorganic backbone consists of silicium dioxide (ceramic) and carries other elements. The silicium dioxide and barium-aluminum-silicate glass provide high radiopacity (200% aluminum). Because of its size and preshape (prepolymerized 3-dimensional structure), it strongly reduces polymerization shrinkage.2,3 Each inorganic backbone carries approximately 100 polymerizable organic groups. This overabundance of polymerization opportunities allows the Admira material to cure without residual monomer, creating greater biocompatibility.3 A silane coating of the fillers increases the adhesion between the organic and inorganic components in the Admira system. The coefficient of thermal expansion is very similar to natural tooth structure.
|Figure 1. Tooth No. 3 with an old composite demonstrating wear and discoloration.||Figure 2. Close-up of tooth No. 3 with marginal degradation evident.|
|Figure 3. An inverted cone diamond stone is used to remove all of the old composite restoration.||Figure 4. Vococid (VOCO) is applied to the entire internal aspect of the preparation.|
The patient presented with several older composites that had undergone attrition, almost exposing the underlying dentin. Tooth No. 3 was the first tooth that was selected for replacement of the existing occlusal-lingual composite (Figures 1 and 2). The composite was removed entirely with an inverted cone diamond (Figure 3). The tooth was isolated, pumiced, and then the entire cavity was etched with Vococid (VOCO), starting from the enamel margin (Figure 4). The enamel was etched for approximately 20 seconds and the dentin was etched for no more than 15 seconds. The etching gel was removed by high-speed vacuum and rinsed for approximately 20 seconds, then excess moisture was removed with a high-speed vacuum. Do not overdry the dentin surface; the dentin should remain slightly moist. The enamel should exhibit a chalk-white/matte appearance. If not, repeat the etching procedure.
|Figure 5. Admira Bond (VOCO) is applied to all areas treated by the acid etchant.|
Admira Bond (VOCO) was dispensed by tilting the bottle and making sure the vent hole was upward. A Micro Tip (VOCO) was inserted into the dispenser and allowed to soak. Alternately, Admira Bond can be dispensed into a mixing well and the applicator is thoroughly wet. The Admira Bond was lightly scrubbed in a thin layer on all prepared enamel and dentin surfaces with a disposable brush applicator (Figure 5). After allowing it to stand for 30 seconds, it was gently dispersed with an air syringe and polymerized with a halogen light for 20 seconds. Admira Flow (radiopaque) was then placed in a thin layer over the axial floor of the preparation. Admira Flow is a thixotropic material, so it flows under pressure but holds its shape prior to light-curing. The thin layer may serve to minimize voids under the restoration. According to the manufacturer, Admira has a reduced rate of release of residual monomers in comparison to conventional composites. This and its reduced cytotoxicity will minimize any sensitivity.4
|Figure 6. The dentin shade selected is placed as the initial layer, with the formation of cusps and fossae.||Figure 7. The final layer (enamel) is placed, with the formation of cusps and fossae maintained.|
The dentin layer was then placed and contoured. Admira can be shaped without slumping. Cusps, grooves, and fossae can be initiated 0.5 mm shy of the margins of the preparation (Figure 6). An interproximal carver (Premier or Hu-Friedy) and a Heliomolar P-I (Ivoclar Vivadent) were used to establish this anatomy. The final translucent layer was then applied and brought to final contour.5 Egg- and flame-shaped finishing burs (Posterior ETO Carbide Kit, Brasseler) were used to remove any excess overlying the margins. Rubber impregnated points can be used to bring the surface to final luster (ComposiPro OneStep Polishers, Brasseler, or PDQ Single-Step Polishers, Axis). The average particle size of 0.7 µm allows a readily achieved smooth surface.1
The final restoration demonstrates the chameleon effect and sculptability of the material (Figure 7).
Ormocers were developed in an attempt to overcome the problems associated with polymerization shrinkage of resin composite. This article has presented a case report in which an Ormocer material was used to provide an aesthetic, functional posterior restoration.
1. Ormocer Marketing product profile. “Admira Ormocer—basic restorative system Voco R8D.” Cuxhaven, Germany.
2. Firla M. Admira: a new Ormocer-based restorative. Contemp Esthet Restor Pract. 2003;7:62-65.
3. Watts DC, Marouf AS. Optimal specimen geometry in bonded-disk shrinkage-strain measurements on light-cured biomaterials. Dent Mater. 2000:16:447-451.
4. Geursten W, Leyhausen G. Mater Determmination of Cytotoxity of admira and other light curing filling materials. J Biomed Mter Res. 1999;44:73-77.
5. Trushkowsky RD. Composite resin: fundamentals and direct technique restorations. In: Aschheim KW, Dale BG, eds. Esthetic Dentistry: A Clinical Approach to Techniques and Materials. 2nd ed. St. Louis, Mo: Mosby; 2001:69-93.
Dr. Trushkowsky maintains a private practice in Staten Island emphasizing aesthetic and restorative dentistry. He is a fellow in the Academy of General Dentistry, the Pierre Fauchard Academy, the Academy of Dental Materials, and the American and International College of Dentists. He is a member of the American Prosthodontic Society, the Academy of Osseointegration, and the American Academy of Cosmetic Dentistry. He has authored over 60 articles on aesthetics and dental materials, has spoken nationally and internationally at many major dental meetings, and is online with Dental Quest. He is on the editorial board of Contemporary Esthetics and Restorative Practice, is an evaluator for many leading manufacturers and CRA, and is a senior consultant to the Dental Advisor.
Disclosure: Dr. Trushkowsky has received an honorarium from VOCO.
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