Direct Resin Posterior Restorations

Allowing adequate time for proper technique and using excellent materials are critical to long-term success.

Direct Class II posterior composite restorations are extremely popular. Unfortunately, studies examining the longevity of posterior composite restorations tend to be dated with variable results. In a 2007 study published in the Journal of the American Dental Association, researchers found that small amalgams and composites performed similarly, but that 50% of 4+ surface composites failed over a 7-year period, compared to 28.2% for amalgam.¹ It has been suggested that posterior composites should be limited to smaller fillings due to the relatively low fees that insurance allows, and the fact that larger posterior composites cannot be done properly in the time frame that these low fees justify.² The same author suggested that the survival of composite restorations varied greatly from one practitioner to another, implying that these restorations are technique-sensitive. In a recent retrospective study of one dental practice (presumably with good technique), after 12 years, composite restorations had a greater survival rate for low-caries-risk groups than amalgam (1.8% failure for composite vs. 12.2% for amalgam).³

It has been the author’s observation that moderate to large composite restorations can be highly successful when the dentist allows time for proper technique and uses excellent materials. As with any restorative procedure, oral hygiene, caries susceptibility, parafunctional habits, and other factors play a role in the longevity of the work. Dentists must always strive to understand the etiology of the patient’s problem before offering solutions. Composite is not the answer to every problem, but neither are any of the other materials at the clinician’s disposal. It is important that clinicians be aware that when adequate time is allocated—with an appropriate fee for that time— it is possible to place composite restorations that offer excellent longevity and value.

Technical Challenges with Posterior Composites

Achieving predictably excellent results with posterior composites is possible. The following tips (denoted in italics) address common problem areas with posterior composites and include ideas to help manage these problems.

Wear loupes (at least 3.25x). Nothing makes it easier to work on very small spaces than magnification. Use a rubber dam whenever possible. The rubber dam controls moisture, movement of the cheek and tongue, and humidity in the working field. When placed routinely, time is actually saved during the procedure. For patients who are nervous about the dam, the dentist can let them know that its use will prevent them from ingesting the old amalgam/mercury (when removing an old amalgam) and that it helps the dentist place a restoration that will last more predictably. For patients who are claustrophobic, the dentist can offer to place an airhole (an approximately 1-cm hole toward the anterior). In the author’s experience, this has made acceptance by reluctant patients close to 100%.

Prepare with a round-ended, non-cross-cut bur. The author uses an 1157 or 1158. Round internal line angles reduce the chance of stress-crack formation and they increase the ease of adapting the composite. Inspect for internal cracks.Internally cracked cusps or pulpal floors often lead to complications. When internal cracks are present, full-coverage restorations are often recommended. Patients should be informed that as a result of the cracks, symptoms that could lead to the need for endodontic treatment may develop. This short conversation at the time of treatment makes it much easier to manage patient relations related to addressing those teeth that do develop symptoms. Ensure complete removal of caries in the proximal box region—especially if using minimally invasive concepts. Clearly, if infected dentin or enamel is present, the new restoration will suffer early failure.

Properly adapt the matrix band. Use contoured sectional matrix bands, and consider one proximal at a time. On a mesio-occlusal-distal (MOD), the author recommends placement of two matrices, but only one wedge and ring. Etch and apply bonding agent to the entire preparation, then layer composite occlusal to the contact that has the wedge and ring. Move the wedge and ring to the other proximal and complete the restoration. Clinicians should ensure that the matrix is intimately adapted to the proximal box cervical margin. Improved proximal wall adaptation (and reduced finishing time) can be achieved with use of matrices such as the Composi-Tight^® Gold (Garrison Dental Solutions,http://www.garrisondental.com) Composi-Tight^® 3D (Garrison), or the Triodent V3 Ring^® matrix (Triodent, http://www.triodent.com). After placing the matrix, wedge, and ring, a ball burnisher is used to provide final adaptation of the matrix.

Always etch enamel and dentin when appropriate for the bonding agent. After etching and bonding, sparing use of a flowable restorative material will help create a seal at the proximal cavosurface margins (along the matrix band) and along the internal line angles in the preparation. This seal helps to nearly eliminate proximal flash or overhangs and greatly reduces finishing time. Provide additional curing time in the proximal box for the bonding agent, the flowable, and the first layer of composite. The added distance from the light reduces light intensity and increases necessary curing time. Also, dentists should ensure the light is not missing the mesial aspect of the proximal box on second molars.

The use of bulk-fill composites is not recommended. To date, results for these materials have been disappointing. However, if an effective material is developed and verified with independent testing in the future, these materials may become more useful. Carefully adapt each increment to avoid voids.

Choose a material that has low shrinkage and radiopacity, handles well, has low wear, high fracture toughness and other physical properties, and maintains surface polish. Advanced clinicians may try sculpting the final increment of composite to final contour to reduce finishing time. This technique also proves absolutely necessary for dentists who are using multi-shade techniques for anterior teeth. Placement of appropriate shades in the correct 3-dimensional space is necessary to arrive at the correct shade and effects. The ability to not overfill each layer makes it possible to attempt multi-shade restorations.

Clinicians who are interested in building artistic skill for multi-shade anterior composites should consider using a different enamel shade for the final layer in their posterior restorations. This involves taking a basic body shade from the cervical one third, with the final enamel layer generally one to two shades lighter and fairly thin. The benefit of using an enamel shade for the final layer goes beyond the need for posterior restorations. Clearly, these restorations are generally very esthetic as single-shade restorations. When a thin enamel shade is used for the final layer in posterior restorations, and it is sculpted to near-final contour prior to curing, the dentist is able to practice layering in a setting in which he or she cannot fail. By learning to judge the effect of a second shade on the appearance of the final restoration, the dentist can build skill that will make it much easier to be successful with anterior restorations.