Managing Open Interdental Spaces with Indirect Veneer Restorations: The Interdental Finish Line Location (Part 2)

This is the second in a series of articles on managing open interdental spaces, diastemas or black triangles, using a convex restorative form. In Part 1, I addressed the interproximal gingival margin location relative to the initial sulcus depth. Part 2 will focus on the interdental margin location relative to the interdental contact.

It is easier to visualize and understand the problem when a diastema is present. However, the methods used to close the open interdental space are 100% applicable to the black triangle. It is imperative to position the interdental axial finish line for a veneer lingual to the interdental contact that already exists when there is a black triangle, or the proposed contact in the case of a diastema. The greater the distance between the teeth, the greater the veneer must wrap around the tooth, becoming similar to a three-quarter crown.

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The goal is to establish a smooth transition from the interproximal aspect of the tooth to the restorative material, establishing an ideal contour. Imagine dental floss contacting the tooth and the restoration uniformly. If the finish line is positioned too close to the desired interdental contact, a lateral wing of restorative material extends away from the tooth. This leaves a concavity lingual to the restoration and the tooth. When a concavity is formed between the restoration and the tooth interdentally, the concavity becomes a food or plaque trap because there is not a smooth contiguous surface between the ceramic and the tooth. You are unable to properly clean the restoration or the tooth because dental floss skips over the concavity at the margin.

You need to not only evaluate the distance between the anatomic crowns of the teeth, but more importantly, the roots of the teeth subgingivally at approximately one-half the measured sulcus depth. The anatomic form of the tooth gets smaller subgingivally and the amount of space between the roots increases depending on the root angulation. The distance between the teeth is less incisal to the papilla than subgingivally. The greater the distance between the teeth, the further lingual the finish line needs to be moved.

A guideline is as follows:

• If there is 1.00 mm distance between the teeth, move the finish line 1.00 mm lingual to the desired interdental contact
• If there is 2.00 mm distance between the teeth, move the finish line 2.00 mm lingual to the desired interdental contact
• If there is 3.00 mm distance between the teeth, move the finish line 3.00 mm lingual to the desired interdental contact

The finish line must be lingual to the papilla tip to correctly influence its position. If you are ever in doubt about its location, make it more lingual. The most common error is not positioning the finish line far enough lingual, resulting in a wing of ceramic that extends at a 90-degree angle from the tooth.

With the combination of placing the gingival margin subgingivally and the interdental finish line to the lingual of the contact, the papilla can be influenced predictably. Part 3 of this series will address the necessary communication to the dental technician to accomplish the correct restorative contours.

Robert Winter, D.D.S., is a member of Spear Resident Faculty.