Ross W. Nash, DDS, presents his technique for the proper placement of posterior composite resin restorations, talking about the heightened interest that patients have for natural-looking restorations.
INTRODUCTION
The demand for aesthetics in restorative dentistry has risen dramatically in the last few decades. Now, some patients even desire that their posterior restorations resemble natural tooth structure rather than be fabricated from nonaesthetic alternatives such as gold or amalgam. Early attempts by manufacturers to produce composite resins that could be placed directly were disappointing. However, with the advances achieved in bonding agents and composite resins, today’s materials are proving to be more than acceptable for use in this area of dentistry.
CHEMISTRY
Composite resins are made up of filler particles (most often glass) in a resin matrix. The matrix begins as short chain molecules called monomers. These molecules can be manipulated and moved easily. When a catalyst initiates a cure, these molecules begin to join together to form more complex molecules which are longer and more rigid. This monomer-to-polymer conversion is called polymerization. The percentage of polymerization in direct composite resin materials has been shown to be in excess of 60%. The remainder is uncured resin, and this is where pigments from fluids can be absorbed over time, causing discoloration. Filler content varies, but most are in the neighborhood of 80% by weight.
Physical Properties
Modern composite resins for posterior use differ in handling properties. Some have a more viscous or “packable” consistency, and others are less viscous in nature. Some have multiple shades for layering with dentin and enamel effects, and others have limited shades. More recently, flowable consistencies have been developed. These normally have lower filler content and most are not recommended for use in areas of occlusal function.
Radiopacity is an important property in a composite resin so that we can determine if a marginal seal has been achieved. In addition, the restorative material can easily be identified on a radiograph.
Bonding Agents
Another variable in composite resin restorations today is the bonding agent. Early bonding agents were disappointing, but modern agents are proving to be very effective. Total-etch and self-etch bonding agents are available. The use of self-etching agents is said to reduce the potential for postoperative sensitivity because it does not remove the smear layer from the dentin surface.
Technique Considerations
Placement technique can be the difference between success and failure when it comes to direct composite resin restorations. It makes sense that the polymerization shrinkage can result in open margins, internal stresses, and fracture of tooth structure during polymerization. Discomfort upon biting has been reported by some patients after they have received direct composite resin restorations. This may be due to the shrinkage of the composite away from the pulpal floor, resulting in a micro-gap at the base of the restoration. It is conceivable that pulpal fluids can enter these gaps and then the pressure from biting forces can cause pain due to the movement of this fluid.
Proximal contacts are sometimes more difficult to achieve with direct composites compared to amalgam restorations. Condensing pressure on amalgam can be used to push the matrix band against the proximal tooth. This is more difficult to do with composite resins, but techniques for excellent contacts have been developed. Some dentists prefer to overbuild the occlusal surface and cut back the anatomy with a high-speed bur.
An accurate build-up technique can eliminate the need for much of this post cure adjustment and result in beautiful anatomy.
Clinical Technique
A technique that I have found helpful in reducing or even eliminating biting sensitivity is the application of a flowable composite resin liner to the dentin surface, after placing and curing the bonding agent. This layer is not meant to be part of the restorative material, but only acts as a base between the restorative material and the tooth surface. It should be radiopaque so that it can be easily identified on a radiograph. After light-curing for 10 seconds, multiple layers of restorative composite can then be added without the pull-back that I believe causes the biting sensitivity which my patients experienced in earlier years. In my experience, I also find that the flowable material results in making it less likely to develop a marginal gap, since it easily flows into nooks and crannies of the preparation. The restorative composite resin is then added in 2-mm increments and light-cured for 20 seconds each before finishing and polishing procedures are initiated. I make an effort to create anatomy during the buildup process rather than cutting in the anatomy after curing the composite resin. In this way, I am able to create more lifelike aesthetics.
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