My previous article reviewed the clinical aspects of tooth preparation design. That article discussed the fact that to close the gingival embrasure space the finish line of the preparation must be subgingival. If a veneer restoration is planned, the interproximal finish line is palatal to the interproximal contact. In this article I will provide a description/rationale of how these clinical aspects impact the technical considerations when fabricating restorations.
1. By placing the preparation finish line subgingivally at an adequate depth, it allows the technician to create a convex morphology to the restoration.
- This emerges from the sulcus, applying mild pressure on the papilla to change its form. Commonly it will move it coronally 0.5 to 1.0 mm depending on the size of the interdental space (Figure 1).
- If the finish line is not placed within the sulcus, the technician must extend lateral wings of ceramic above the papilla to close the interdental space. This has no impact on the shape or height of the papilla, but can lead to periodontal breakdown (Figure 2).
2. If a veneer restoration is planned with the finish line adequately placed on the palatal aspect of the tooth, the technician can design the restoration with a convex morphology which extends to the interdental contact, forming a smooth transition from the tooth to the ceramic restoration (Figure 3).
- If the interproximal finish line is too close or labial to the interdental contact, the technician will need to extend lateral wings of ceramic to establish the contact. This creates concave areas just palatal to the contact point and may "close" the interdental space, but it creates a noncleansable area which may lead to carious lesions (Figure 4).
The probability of minimizing or eliminating the “black triangle” is improved if the clinician incorporates proper preparation design into the planning phase of patient treatment. It should not be left up to the laboratory to try and compensate for deficiencies in this step of the process.
(Click this link to read more dentistry articles by Dr. Bob Winter.)
Bob Winter, D.D.S., Spear Faculty and Contributing Author