Written by Ross W. Nash, DDS Friday, 30 April 2010 19:00
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.
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.
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.
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.
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.
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.
This case illustrates the use of a modern composite resin and bonding agent to restore a mandibular second premolar tooth that had interproximal caries form after the placement of a porcelain veneer. The patient is a dentist who found that he was packing food in the contact area between his second bicuspid and the molar (Figure 1).
The patient was anesthetized and a rubber dam (Hygenic [Coltène Whaledent]) was placed for proper isolation. I have found that rubber dam isolation is desirable when utilizing resin bonding agents and composite resin restorative materials. After the proximal area was prepared and the caries removed, no pulpal exposure was detected (Figure 2). (The dentist and patient did not wish for the stained pits to be included in the preparation.)
|Figure 1. Mandibular second premolar with open distal contact and caries.||Figure 2. The completed preparation.|
Figure 3. A sectional matrix band (Tab Matrix [Triodent]), wedge (V-Wedge [Triodent]), and separating ring (Triodent) were placed to ensure a proper interproximal contact. Then a self-etching dentin and enamel bonding agent (All-Bond SE [Bisco]) was applied.
Figure 4. Flowable composite resin (N’Durance Dimer Flow [Septodont]).
Figure 5. The flowable composite base was light-cured (LED) for 20 seconds.
Figure 6. Composite resin restorative material placed (N’Durance Dimer Flow).
Figure 7. Composite resin was sculpted.
Figure 8. The composite resin was light-cured.
Figure 9. The final restoration demonstrating an ideal interproximal contact and natural aesthetics.
Figure 10. Radiograph of final restoration illustrating the radiopacity of both the restorative material and the flowable composite resin.
A sectional matrix band (Tab Matrix [Triodent]) was applied, and a wedge (V-Wedge [Triodent]) was placed interproximally to seal the matrix against the gingival margin. A separating ring (Triodent) was used to slightly separate the teeth and hold the matrix tight against the unprepared proximal surfaces. The preparation was thoroughly rinsed and left slightly moist for the wet bonding procedure. A self-etching dentin and enamel bonding agent (All-Bond SE [BISCO]) was liberally applied to the moist prepared surfaces (Figure 3) and dried with oil- and water-free air in order to remove the moisture and the solvent carrier in the bonding agent. The bonding agent was then light-cured for 10 seconds with an LED curing light (Bluephase [Ivoclar Vivadent]).
A radiopaque flowable composite resin (N’Durance Dimer Flow [Septodont]) was applied to the dentin surface (Figure 4) and thinned with an explorer before light-curing for 10 seconds (Figure 5). A posterior composite resin material (N’Durance Dimer Flow) was added in approximately 2-mm increments (Figure 6) and condensed with a metal instrument (Plastic Filling DE No. 1 [Hu-Friedy]) (Figure 7). Each layer placed was light-cured for 20 seconds (Figure 8) before adding the next layer.
A carbide finishing bur (ET OS1 [Brasseler USA]) was used to refine the anatomy and to remove any excess composite resin from the margins of the restoration. After the rubber dam was removed and the occlusion adjusted, the final restoration was thoroughly polished using composite polishing cups (ComposiPro [Brasseler USA]).
The final result is shown in Figure 9. Figure 10 shows a radiograph of the restoration in place illustrating the radiopacity of the restorative material and the flowable composite resin. The patient in this case reported no postoperative sensitivity problems and was extremely satisfied with the aesthetic and functional result.
DISCUSSION: COMPOSITE RESIN MATERIALS USED
This particular composite resin restorative material (N’Durance Dimer Flow) is reported to have high conversion (75%) of monomer to polymer, resulting is less free monomer and increased durability. Its nanodimer conversion technology also provides low polymerization shrinkage (1.2%), decreasing the chances of microleakage and bonding failures. It is reported to have optimized nanofillers at 81% by weight designed for high strength, high wear resistance, improved polishability, and high gloss. It is highly radiopaque and can easily be seen on a radiograph for verification of margins and detection of recurrent caries. This composite resin is made with a dimethacrylate based mix of monomers (BIS-GMA free) making it compatible with regular bonding agents. Its special dimer acid formulation is reported to result in more hydrophobicity and better color stability. And it is reported to have zero solubility and thus enhanced functional integrity of the restoration.
In my clinical experience, I have found that a well-placed posterior composite resin can last for many years. I have found that many patients desire tooth-colored, natural looking alternatives to amalgam or gold. A direct composite resin, properly executed, can be a viable option for such patients.
Disclosure: Dr. Nash reports no conflicts of interest.
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