Clinical Success with Composite Restorations
Parameters that affect clinical success with modern composite resins
Robert A. Lowe, DDS
Placement of composite resins is a technique-sensitive, multi-step procedure that requires strict attention to detail to ensure the best results. Although many dentists would like the material to be a tooth-colored amalgam, where placement is relatively “technique-insensitive” with few clinical steps, composites do not behave in this manner. Also, since composite is a more “universal” material, being used for both anterior and posterior applications, there are different functional and esthetic demands depending upon which region of the mouth that they are placed.
For years, it has been a clinical goal to have a single universal composite material that can be placed in both esthetic anterior locations and on stress-bearing posterior occlusal surfaces. This is a difficult task, because the most esthetic and polishable composites often do not have the physical properties to be used for posterior applications. The reverse is also true. Composites with physical properties that can withstand the forces of occlusion often cannot be finished and polished, or have the optical properties necessary to create lifelike anterior esthetics. Therein lies the dilemma. For most clinicians, it is still necessary to have different composites for anterior and posterior applications.
Composite selection for anterior teeth comes down to the basics of tooth histology. Dentin and enamel have different opacities and optical qualities that make using a single material difficult. The color and opacity of the intermediate dentin dictates the overall shade of the tooth. Therefore, choosing the restoration shade should be predicated on that fact, one layer to replace the dentin, and another to replace the enamel. Vita shades have been a standard in the profession since the 1950s. However, a Vita shade represents a “composite” of dentin and enamel on top of one another to give an A1 or A2 “effect.” There is no correlation to actual color and opacity of the dentin when choosing a shade in this manner. It is taught in dental school to choose the shade of the tooth prior to preparation. This makes no sense based on the fact that the dentin color and opacity is the primary determinant of tooth color. The tooth should be prepared first so that the intermediate dentin can be visualized and matched to a shade tab. Most translucent enamel or incisal shades will blend well with the surrounding tooth if the correct dentin shade is chosen first. While there are many nanomicrohybrid composites on the market based on Vita shades, there are also a few composites that are based on choosing the shade of the dentin first. Another area of the tooth that is difficult to match in esthetic areas is the cervical third where the enamel is thin and the warmth of the underlying dentin is close to the surface. Dedicated cervical shades can make this easier to accomplish. Vita A3.5 shades alone are often not warm or opaque enough to create a good match in the gingival third of facial and labial surfaces.
For a long time, composite selection in posterior teeth has not differed much from anterior teeth because of the constraints of 2-mm incremental placement. This has been advocated due to potential problems associated with polymerization shrinkage and shrinkage stress associated with bulk placement. The profession has long wished for a posterior composite that could be placed in bulk, similar to amalgam, to simplify placement of direct posterior composite restorations. Today, there are several bulk-fill materials that can help reduce placement time. Because the esthetic requirements for posterior occlusal surfaces are not as critical as they are with anterior teeth, different opacities for dentin and enamel are not as important. What is important is depth of cure. Most bulk-fill materials on the market cure to a depth of 4 mm. Bulk-fill flowables are popular as dentin replacements because they are low in viscosity and can be easily adapted to the geometry of a cavity preparation. Bulk-fill flowables are typically more translucent to allow for greater depth of cure and not designed for occlusal stress-bearing areas. A conventional nanomicrohybrid is needed for the enamel layer because they exhibit better physical properties and chameleon effect when using bulk-fill flowables to replace the dentin.
Remember, composite materials are not condensable like amalgam. Alloy can be “pushed” into corners and deform matrix bands to create proximal contact. Condensing composite is similar to pushing mashed potatoes around in a cavity preparation. Placing it in the same fashion as alloy can lead to voids and ultimate restorative failure.
The purpose of a matrix is to confine the restorative material to the limits of the tooth preparation during placement of the restorative material. Conventional amalgam dentistry (and for many, composite as well) used a “tofflemire” type of matrix for posterior Class II cavity preparations that was cylindrical and did not help replicate natural tooth anatomic surfaces. For posterior teeth, a matrix must not only help restore proximal contact to the adjacent tooth, but must also reproduce proximal tooth anatomy, which is convex, not flat. The purpose of a properly placed and fitted matrix should be to greatly limit the amount of contouring (overhangs and excess) that will need to be done with rotary instruments after the material is cured. For proximal cavities in the anterior region, traditional mylar strip matrices make it impossible to create proper proximal contour, let alone contact. Preformed mylar tooth forms are not “customized” enough to be easily used and still make creation of contacts extremely difficult to achieve.
In the posterior region, sectional matrices that use a contoured matrix material to re-create proximal tooth form and a separator ring that gently push teeth apart by compression of the periodontal ligament to ensure tight contact when using a non-condensable material such as composite is essential for optimal clinical success. The gingival seal is also critical, so the proximal wedge and wedge design is also important when the matrix does not seal proximal root concavities, which are common occurrences when dealing with subgingival Class II margins. The sectional matrix is concave on the inside and convex on the outside. Some have gingival extensions for deep Class II cavities or proximal extension to help contain restorative material in larger Class II or cusp replacement situations.
The words “light cure according to manufacturer’s instructions” are in all directions for use that accompany composite materials. This critical step in composite placement and success is often understated and ignored by many clinicians. How efficient is the curing light being used? What is its depth of cure? When was the output last checked? Do we really know if the deepest part of the composite restoration is ever cured? Since most of our composite materials do not have a dual-cure capability, the answers to these questions become very important. For Class 2 composite restorations, even when using bulk-fill materials, using transtooth illumination (curing) techniques is recommended to ensure maximal depth of cure in proximal box areas. One of the most important aspects of light-curing any composite material is to get the light as close to the material as possible. Remember, one cannot over-cure. An extra 10 or 20 seconds of curing time is fine. Also, all curing lights are not created equal. Make sure the output, wavelength, and spot size is adequate for the clinical requirements of the composite that is used.
Placement of composite restorations is a complex, multistep process where attention to detail is crucial for clinical success. Choose a material that best fits the clinical requirements of the case. Don’t just rely on any one material because it’s a favorite. Accurate placement of the matrix and wedge will ultimately determine how long it takes to complete a restoration and how well it will replicate natural anatomic tooth form. Don’t start the restorative process until the matrix is properly placed to limit any excess material that may extend from the intended final contour of the restoration. Finally, just because the surface of the material is set, don’t assume the entire restoration has cured. Use a quality curing light and cure from multiple sides to ensure complete and thorough cure of the composite prior to completing the finishing and polishing process.