The most difficult indirect restoration to fabricate from an esthetic perspective is the maxillary central incisor. (See Fig. 1.) The technician’s objective is to produce only a single restoration that matches the surrounding dentition, but that is not always possible – even for master level ceramists using the most sophisticated techniques and materials.
All aspects of the esthetics can be more critically evaluated (e.g. color, intensity of color, value, translucency, form, surface texture, and surface luster) between central incisors because of their proximity to each other. In contrast, when observing a lateral or a cuspid, the human eyes cannot see the contralateral tooth at the same time. When matching a lateral or cuspid next to another tooth, the esthetic aspects being compared are different.
Dentists should expect that it could take multiple attempts to produce a crown or veneer that meets the esthetic needs of the patient, and not become frustrated by the process. I personally consider the first attempt at producing a single central similar to producing custom shade guide, because inserting and photographing it gives the technician a better idea of how the ceramic will appear intraorally.
There are several reasons why a single central incisor is difficult to match:
- Dehydration of the teeth occurs during shade analysis, tooth preparation and try-in procedures. Dehydration influences the apparent value (brightness) and chroma (color intensity) of the tooth being observed.
- When fabricating all ceramic restorations such as veneers or crowns, the esthetic outcome is not only determined by the ceramic, but by the combined effects of the tooth, cement, ceramic properties and the thickness of the ceramic. A try-in paste must be used that is representative of the final cured resin or cement. It must be of the same color, value and relative opacity. A significant problem occurs because try-in pastes do not replicate the outcome with 100 percent accuracy. Clinically significant differences have been found between the same shade of try-in paste and cured resin.1 Some clinicians try their restorations in "dry" to check the final esthetics. This is not recommended because the air space between the ceramic and the prepared tooth creates an optically inaccurate shade. The gap between the ceramic and tooth must be closed with a try-in paste or fluid. Other clinicians use water or glycerin when trying in a restoration; these do not produce the same visual effect as resin or cement that is used for final cementation, when compared to try-in paste.
- The technician cannot duplicate the esthetic appearance of the underlying tooth in the laboratory. This is why the laboratory requests the dentist send photographs to communicate the nuances of the prepared tooth. (See Fig. 2.)
Photographs of a shade tab next to the prepared tooth and the other central incisor are extremely valuable. Ivoclar Vivadent (IPS Natural Die Material Shade Guide) and Vita (Simulate Preparation Material Guide) have specific shade guides designed for this process. One method used by technicians to approximate the color of the prepared tooth, is to use a corresponding resin to these shade tabs.They will inject it into the restoration and compare the final look to the photos they have received. Unfortunately, it is generally not a very good representation of the actual tooth. (See Fig. 3.)
Understanding the challenges associated with matching natural dentition with indirect restorations, helps the clinician set and communicate realistic expectations with the patient. In addition, it is important that your staff be trained to understand these clinical and technical challenges, so they can appropriately communicate with the patient to help them achieve their desired esthetics. (See Fig. 4.)
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- AlGhazali N, Laukner G, Jarad, FD, Smith PW, & Preston AJ. An investigation into the effect of try-in pastes, uncured and cured resin cements on the overall color of ceramic veneer restoration: An in vitro study. J Dent. 2010; 38:e78-e86.