Anterior tooth preparation: well-planned steps to a successful clinical outcome

[drsushant]

 In order to avoid shadowing of the original tooth color, if we are utilizing partial coverage, the interproximal margin line must be placed to the lingual line angle of both contacts. This allows the technician to have control over the visual effect of the porcelain beyond the height of contour. The final color of an all-porcelain restoration is created by the combination of the underlying tooth, the resin cement, and the porcelain. The color and light properties of all three layers play a role in the final visual perception. When the underlying tooth is dark, we can begin to see the transition line at the incisal and the interproximal between where we have solid porcelain. To minimize this effect, we need to gradually increase the thickness of the porcelain as we approach the edge of the preparation. For severely discolored teeth, the most predictable results may still depend on full-coverage preparation and use of a restoration with a core that is then layered with porcelain.

The existing occlusal parameters and any proposed changes must be considered during tooth preparation. For patients with low functional risk, where we are accepting their existing occlusion, the concerns are minimal but still present. When planning for veneers, I mark the patient’s existing intercuspal position prior to beginning the prep. I want to plan for the final intercuspal stops to be on the porcelain or on the tooth, not at the interface between the two. The location of the stops may necessitate additional incisal reduction to move the margin. One consideration is the choice between full coverage and veneers. Many dentists simply feel more confident in these cases doing a full-coverage preparation. In either situation, care must be taken to create an exquisitely refined final occlusion. Paying very close attention to excursive movements, including protrusive guidance, edge to edge, and crossover, is critical after seating the final restorations. One of the parameters that I pay special attention to is fremitus. Anterior teeth that move during protrusive guidance are at higher risk of failure with veneers, especially if the porcelain is bonded to dentin. Another consideration for patients with extreme wear is bonding to secondary dentin and retention of the restoration if the lingual is not prepared.

Structural considerations include old restorations, endodontic therapy, and adequate tooth structure to retain the restoration. One of the advantages of bonding is decreased reliance on traditional retention and resistance form. Many practitioners are restoring anterior teeth with very minimal remaining tooth structure utilizing all porcelain that can be bonded. The quality of the remaining tooth structure, the amount of bonded surface to dentin, and the functional load the patient places on the teeth all have to be considered in these situations. When using full-coverage restorations and planning for cementation, we need to have adequate ferrule as well as adequate wall height to create retention form. Ferrule is the amount of natural tooth remaining. Our ability to bond posts as well as the final restoration has minimized these numbers. Failure occurs because of repetitive loading. Ferrule requires buccal and lingual walls of natural tooth as the interproximal does not play a role in structural longevity. At a minimum, plan to have 1.5 mm of ferrule and understand that the seal will fail at some point when the magic number of loads occurs. Previous restorations traditionally have been incorporated into the new restorative process. I still have a preference for placing my margins on sound tooth structure. I also remove all previous restorative materials so as not to bank the success of the new restoration on the bond of an old composite, or the lack of decay underneath.

The benefit of careful, well-planned tooth preparation includes predictably reaching the desired clinical outcome. This predictability means no compromises on the final esthetic results, long-term success, and not having to bring patients back to alter a preparation after they are already in provisionals. Work through all of the parameters of treatment planning and involve your ceramist in this process. Create a plan for preparing the teeth to effectively move from the present condition of the teeth to the planned outcome. The final preparations may be veneers or full coverage, minimal or extensive, but they will be appropriate for that patient to achieve the desired results.