Properly managing open interdental spaces is a challenge for many dentists and can also be a point of frustration for laboratory technicians. This five-part Spear Digest series addresses indirect veneer restorations and closing open interdental spaces.
This article will address the first aspect of preparation design that must be considered when using an indirect veneer restoration to close an open interdental space. Whether it is to correct or eliminate a diastema or the infamous “black triangle,” the same problems must be solved. The question is where to place the finish line gingivally and where to place it interdentally.
The gingival preparation finish line relative to the tip of the papilla must be positioned subgingivally and the interdental finish line must be positioned lingual to the interdental contact. The finish line must be positioned subgingivally to create a restorative form that is convex in nature. This contour emerges directly from the preparation finish line to decrease the volume of space between the teeth.
It is common belief that the greater the space between teeth, the more subgingival the finish line is placed. This concept is flawed, because the greater the distance between the teeth, the blunter the papilla becomes. The sulcus depth decreases as the papilla blunts. The only reason the soft tissue has its form and position is because of the hard structures that support it – whether it is bone, natural tooth structure or restorative material.
It is critical to measure the sulcus prior to preparing the tooth to determine the initial sulcus depth. The safest subgingival preparation depth is half the depth of the measured sulcus. When there is a larger space between the teeth, the goal of designing the restorations is to create a convex form to decrease the volume of space. By decreasing the volume of space, one would expect to see the papilla move more incisally to establish a normal papilla height and sulcus depth. The result is a preparation finish line that is conceivably deeper than half of the final sulcus depth due to the incisal movement of the papilla.
When the papilla decreases in height, the sulcus depth decreases. If there are adjacent teeth in normal approximation, the papilla is 4.5 mm in height with a sulcus depth of 2.5 mm. The most extreme situation occurs when there is a missing adjacent tooth. The papilla height will decrease in size to 3.0 mm, resulting in a sulcus depth of 1.0 mm. In both examples, there will still be a normal attachment of 2.0 mm.
When restoring adjacent teeth with a larger diastema or significant black triangle, the sulcus depth may be as little as 1 mm. In this example, since the original sulcus depth is only 1 mm, the finish line will be placed 0.5 mm into the sulcus. After the veneer is placed and papilla movement occurs, you will reestablish a normal sulcus depth of 2.5 mm. The resulting finish line will now be 2 mm apical to the tip of the papilla, which means it is 2 mm into the sulcus. The coronal movement of the papilla due to the convex shape of the restoration will cause a decrease in space and volume between the teeth moving the papilla 1.5 mm incisally. The papilla height is the sum of the gingival attachment plus the sulcus depth.
The restorations will establish an interdental contact. The apical extent of the contact should be positioned at the tip of the newly established papilla height, 4.5 mm from the bone.
One key factor to consider is if there is an open interdental space and normal initial sulcus depth of 2.5 mm, do not expect the papilla to move more incisally by decreasing the volume of space with a convex restorative form. Generally, it will not result in the formation of a super (greater than 4.5 mm) papilla. Instead, move the interdental contact to the current tip of the papilla. You should only expect incisal movement if the papilla is initially blunt.
The next article (Part 2) will address the location of the interdental margin location relative to the interdental contact, Part 3 will discuss provisional restoration fabrication, Part 4 will address communication with the technician, and Part 5 will highlight the fabrication of veneer restorations.
Robert Winter, D.D.S., is a member of Spear Resident Faculty.