Posterior resin-based composites have become an indispensable part of the restorative process. Many clinicians have used this class of materials quite successfully during the last five to 10 years.1 The performance of these materials at the time of their introduction three decades ago, however, was quite poor. There were a number of reasons for this: inadequate wear resistance, leakage, secondary caries and lack of appropriate proximal contact.2
Posterior composite is not at this time a total replacement for amalgam as a restorative material, but such a time is quickly coming.
The cause of most of these problems has been identified and, to a great extent, resolved. Other than wear, most of the problems associated with posterior resin-based composite can be linked to the clinician. Specifically, failure to understand and use the exacting and more clinically sensitive techniques associated with posterior resin-based composites accounted for nearly all the clinical problems listed above.
One of the most obvious advancements is related to wear resistance. While the original formulations exhibited an average annual wear rate of 100 micrometers or more, current formulations fall into the single-digit category for wear in micrometers.3,4
The other problems listed previously were related more to the clinician than to the material itself. A major reason for lack of clinical success undoubtedly was use of inappropriate techniques. Specifically, practitioners simply adopted the techniques they used for amalgam.5,6
On the basis of clinical research and clinical experience, it can be said that amalgam and resin-based composite have little in common. Amalgams, for example, require minimal dimension and bulk to resist fracture. Resin-based composites, on the other hand, do not. Furthermore, amalgam restorations require mechanical retention, whereas resin-based composites may be retained by a process of adhesion to the wall of the cavity preparation.
Early resin-based composite restorations failed, in part, because the preparations were substantially greater in dimension than necessary. Leakage and secondary caries were attributed to inadequate marginal adaptation. The proper use of dentin adhesives and flowable resin-based composites has contributed appreciably to the success of posterior resin-based composite restorations. In spite of all the advancements in this area, resin-based composites continue to be more technique-sensitive and take longer to place than the corresponding amalgam.
Resin-based composites eventually will replace amalgam as a direct restorative material because they possess many characteristics not inherent in amalgam. Some of the more important of these properties are esthetics, micromechanical bonding to tooth structure, smaller cavity preparations and better sealing potential. This change from amalgam to composite, however, may occur no little time into the future. Such a goal will not be achieved until each clinician using the procedure develops a thorough understanding of the material and of the exacting procedures for its placement. Owing to its inherent handling characteristics, the packable resin-based composite makes it easy for the clinician to create successful restorations.7
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EVOLUTION OF RESTORATIVE TECHNIQUE
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In the placement of early direct posterior composites, restorative technique centered on reducing polymerization shrinkage by using incremental addition and curing successive layers of composite one layer at a time. When placed in bulk and light-cured, these materials could shrink away from the cavosurface marginal areas, leading to a potential for bacterial infiltration and recurrent caries. In Class II restorations, proximal contacts often were difficult to obtain because of the materials’ thixotropic natures and their inability to "condense" and push the matrix tightly against the adjacent tooth, as could be accomplished with amalgam. When these materials are pushed with a condensing instrument, there is no resistance to the force placed on the material; the material does not move the composite in the direction of the force but merely pushes through it.
Owing to its inherent handling characteristics, the packable resin-based composite makes it easy for the clinician to create successful restorations.
As a result, techniques evolved to achieve proximal contact using different types of matrices that were developed to create anatomical precision. Examples include sectional matrix bands and BiTine Rings (Dentsply Caulk) and Contact Matrix (Danville Materials). Hand instrumentation also was developed that would allow the clinician to deform a matrix material by pushing it in the direction of the proximal contact while simultaneously light curing the composite material.8 Many such systems and devices were tried with varied success. The result was a compilation of techniques that made it difficult to get consistent results even for the most conscientious clinician.
There are other potential clinical problems that can arise when using traditional hybrid resin-based composites in Class II cavity preparations. Voids at gingival marginal areas can result from the inability to adequately adapt the materials to margins before curing. Postoperative sensitivity, open margins, light or open contacts and recurrent caries all are common problems that exist because of the material’s technique sensitivity. Because of this technique sensitivity and the associated inconsistent results, composite materials have not been embraced as a whole—and they will not be considered as an amalgam alternative until it is fully realized that the material cannot be handled in the same fashion as amalgam if a desirable result is to be obtained.
As manufacturers continue to search for a tooth-colored resin-based composite material that will have good physical properties and behave clinically like amalgam, the introduction of "pack-able" or "condensable" composites has taken dentistry a step closer. Some dentists focus on the semantics surrounding these materials, saying they are not truly condensable like amalgam, which is true. But do we "condense" amalgam? Although filled with glass at a higher percentage to increase viscosity and condensability, these newer composite materials do not feel like amalgam when condensed. But they can deform a matrix band, and they shrink less than do conventional hybrid materials.9–11 The true definition of condensation, however, is to compress and make particles smaller. Therefore, amalgam is not truly "condensed" either; rather, both materials are "packed," since, in both instances, the particles of material merely are moved closer together, not made smaller.
The following case report illustrates a technique to place a direct posterior resin-based composite restoration in much the same way as dentists have placed amalgams in the past. New materials that actually are "packable" and provide resistance to condensation allow the achievement of a tight proximal contact.12–15 Hydrophilic bonding agents that provide a strong bond to both enamel and dentin allow for predictable retention of restorations without excessive tooth reduction.16,17 A thin base of flowable composite is placed and cured before the bulk of composite is added. This keeps polymerization shrinkage from pulling the materials away from margins and thse internal aspect of the preparation, and it provides the opportunity for bulk placement of the restorative composite. Resin ionomer cements can be used without acid etching to serve as sealing agents in deep areas of excavation. Esthetic materials that simulate natural tooth structure make it possible to deliver restorations that are truly natural in appearance.
Esthetic materials that simulate natural tooth structure make it possible to deliver restorations that are truly natural in appearance.
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CASE REPORT
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One of the authors (R.W.N.) saw a patient who had a previously placed occlusal direct composite in the maxillary second premolar. However, clinical examination revealed proximal caries. There also were caries in the distal and occlusal surfaces of the first premolar. There were pinhole-sized lesions in the lingual cusp of the second pre-molar and the facial cusp of the first premolar. The dentist discussed amalgam, gold, direct composite, indirect composite and ceramic alternatives with the patient. The patient’s choice was a tooth-colored material; the clinician then chose direct composite for its one-appointment technique and its affordability for the patient.
After the area was anesthetized, the clinician placed a rubber dam and ligated it with dental tape for complete isolation. He used a 245-carbide bur to begin the preparation and a round bur to remove caries and round the internal line angles. An interproximal wedge protected the papilla and produced a slight separation of the two teeth.
The clinician removed the proximal caries in the second premolar and completed the preparation with a round bur, leaving the previously placed composite undisturbed. There was a deep area of caries in the midlingual area of the pulpal floor in the preparation of the first premolar. The clinician used resin ionomer (Geristore Bio-Cap, Den-Mat) as an indirect pulp cap. This material bonds to tooth structure with no acid etching, so it provides a seal and protection from subsequent chemical exposure to the pulp during placement.
Direct composite is an attractive choice because of its one-appointment technique and its affordability for the patient.
The proximal surface of the second premolar was repaired first. Figure 1
shows the first premolar prepared and ready for matrix placement. The clinician placed sectional matrix (Composi-Tight, Garrison Dental Solutions) at the distal aspect of the first premolar and wedged it tightly (Figure 2). He then placed phosphoric acid etching solution on the prepared surfaces for 15 seconds (Figure 3), rinsed it thoroughly and left it slightly moist for the wet-bonding process. He placed a liberal amount of one-step enamel/dentin bonding agent (Tenure Quik, Den-Mat) on the prepared tooth surfaces with a brush (Figure 4) and air-dried it. The bonding agent was light-cured for three seconds with a high-intensity xenon curing light (Virtuoso Xenon Power Arc, Den-Mat).
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ABSTRACT
EVOLUTION OF RESTORATIVE...
