Posterior Composite Restorations
Direct or Indirect Technique?
In its most recent formulations (microhybrid, nanoparticles, nanohybrid), composite resin has become the most widely used material for restoring posterior teeth because of its biomechanical and esthetic properties.
Improved enamel-dentin adhesives, combined with less polymerization shrinkage, deliver good marginal quality that is stable over time, significantly reducing microleakage (Perdigão and colleagues, 2000; Lopes and colleagues, 2002) (Figure 10-1).
Figure 10-1 A, Preoperative image. Proximal lesions and infiltrations at the cervical margins mean that the restorations must be replaced. The treatment plan requires four direct composite restorations: OD on tooth 5, MOD on tooth 4, MODV on tooth 3, and OM on tooth 2. B, The quadrant a few months after treatment. C, Clinical checkup 6 years later.
Better physical and chemical properties and enhanced polymerization of materials have greatly increased wear resistance (Spreafico and Roulet, 2009), and the problem finally seems to have been solved, at least for medium-sized restorations (Ferracane, 2006).
However, optimal proximal and occlusal anatomy and defect-free margins are difficult to achieve, especially when dealing with large cavities and areas that are difficult to access. Adhesives inlays have shown better behavior than direct restorations in complex cavities with cervical margins close to or extending beyond the cemento-enamel junction (Krejci, 1992; Roulet, Gotz, and Losche, 1993; Dietschi and Herzfeld, 1998). The main goals of restorative dentistry are as follows:
Simpler and less invasive techniques are always preferred—that is, those that permit placement of the material with minimal sacrifice of healthy tissue, are as rapid as possible, and are the least expensive for patients.
The direct technique is undoubtedly the most widely used restoration method for posterior teeth. It is the technique of choice for restoring small and medium-sized Black Class I and II cavities, and at times it is also used for medium-large restorations without cuspal coverage.
Cavity margins are finished with fine-grain diamond burs (30 to 40 microns). The aim here is to smooth the cavity margins and remove unsupported enamel prisms. The importance of preparing chamfered margins is still subject to debate. Chamfering is designed to expose the upper surface of enamel prisms and increase the bonding surface, thereby improving adhesion values (Porte and colleagues, 1984). Consequently, chamfering promotes better marginal quality (Han, Okamoto, and Iwaku, 1992; Schmidlin and colleagues, 2007).
Based on this information, I prefer to chamfer the occlusal, buccal, and lingual margins, and I prepare a sharp cervical margin. In fact, the cervical chamfer is often hidden or covered by the matrix band, which has been pushed on the margin by the dental wedge.
The introduction of sectional matrices and retainer rings has made it possible to attain optimal proximal anatomy. Because they are precurved, these matrices facilitate the creation of rounded anatomic marginal ridges and effective points of contact.
Lutz and Kull (1980) were the first to demonstrate the good marginal adaptation of layered composite restorations in vitro. It should be noted that effective dentinal adhesives were not available at the time, and that composites were subject to greater polymerization shrinkage than current materials.
Through in vitro experiments several authors later demonstrated the effectiveness of layering in controlling polymerization stress (Lutz, Krejci, and Luescher, 1986; Lutz, Krejci, and Oldenburg, 1986; Tjan, Bergh, and Lidner, 1992; Park and colleagues, 2008).
Nevertheless, based on a comparison of the bulk technique and multilayered techniques, not all authors believe that layering can produce satisfactory margin quality (Versluis and colleagues, 1996; Jedrychowski, Bleier, and Caputo, 1998; Kuijs and colleagues, 2003).
In any case, in order to obtain adequate polymerization, the thickness of the material should not exceed 2 mm, even when high-intensity irradiation lamps are employed (Rueggeberg, Ergle, and Mettenburg, 2000). Therefore the composite must be layered (the number of increments will depend on the size of the cavity) using a thickness of 2 mm as a benchmark.
Based on this information and my own clinical experience, I prefer to restore medium-sized Class I cavities with three increments of composite resin and use a four-increment technique for medium-sized Class II cavities (a medium-sized cavity is a cavity whose occlusal width is less than two thirds of the intercuspal distance).
In medium-sized Class I cavities the first increment consists of a thin layer of material (about half a millimeter of flowable composite), and the second is a layer of dentin mass, leaving enough room for the last layer of enamel mass. All layers are applied horizontally.
It must be noted that the use of flowable composite is controversial. In an in vitro study on Class V cavities, Kemp-Scholte and Davidson (1990) showed that an intermediate elastic layer placed between the bonding agent and the restoration decreased stress by 20% to 50% while preserving marginal integrity.
Many professionals have investigated this over the years, but no unequivocal conclusions have been reached. Some have shown that a layer of flowable composite improves marginal adaptation (Attar, Turgut, and Gungor, 2004; Li and colleagues, 2004, 2006), whereas others have found no improvement (Braga, Hilton, and Ferracane, 2003; Lindberg, van Dijken, and Horstedt, 2005). At the same time, however, no one has ever shown that the quality of restoration deteriorates. In my clinical experience, the use of flowable composite reduces postoperative sensitivity to practically zero.
Class II cavities are usually restored with four increments of material. The first is a layer of enamel mass that transforms the cavity into a Class I cavity by placing the composite against the matrix (the thickness of the proximal wall should be about half a millimeter). The Class I cavity can then be restored as usual.