Considerations for Preparation Design and Facial Margin Placement: Part VBy Frank Spear on June 6, 2016 | comments
(Click the links for earlier articles in this series: Part I, Part II, Part III and Part IV.)
Here is a male patient with a discolored right central incisor and mild incisal wear. He desires the best and most predictable match possible between the two centrals. Figure 1
Restoring a single central incisor to match perfectly with the adjacent central is one of the most difficult things in restorative dentistry. Doing it when the tooth is significantly discolored makes it more difficult. One question that always arises is whether to do both centrals to make the result more predictable.
Generally, I prefer not to do both, especially if the adjacent central is in excellent condition, but if you choose to do only one central, the patient has to accept that it may take multiple appointments and modifications from the lab to get it close to perfect. In addition, it may end up costing as much as if both centrals were done, depending upon the number of try-ins and remakes necessary. Bottom line: Matching a single central is more art then it is science.
(Click this link to find out more on why it's so difficult to match a single central incisor.)
In this patient the left central has good color and mild wear of the incisal edge, which could be corrected with composite. In this case, however, the patient's decision was to do both centrals for a more predictable result, meaning less risk of multiple try-ins, remakes and appointments.
Here are some considerations in regards to preparation design and margin placement when dealing with the discoloration of the left central.
- A tooth like this can be handled several ways, including non-vital bleaching prior to tooth preparation. The risk here is that the tooth may discolor later, and the restoration with it.
- Use a product like feldspathic porcelain, (stacked ceramics), laying down a more opaque layer first for masking, then more translucent ceramics over the top.
- Use a product like Empress or e.max lithium disilicate, make it thick enough, and opaque enough to mask the darkness, then cut back the incisal 2/3 and fire a more translucent ceramic for improved esthetics.
- Fabricate an opaque core out of lithium disilicate, zirconia, alumina or metal ceramics, then fire stacked ceramics over the top, or press translucent lithium disilicate over the top. For this patient, an opaque core .5 mm thick was fabricated out of zirconia, then stacked ceramics was fired over the coping. The left central veneer was also done out of stacked ceramics. Figure 2
All of these techniques have been used successfully by different clinicians and technicians. It comes down to the skill and comfort level of what system the technician knows best, as well as having an adequately reduced tooth preparation.
The preparation requirements are similar no matter which approach is taken: subgingival margin placement to hide the junction of the discolored tooth and restoration, and adequate facial reduction of 1.2-1.4 mm to manage the discoloration. Figure 3
In this case, the left central has approximately .7 mm of facial reduction to allow the ceramist some thickness of veneer to better match the veneering porcelain used on the right central. In addition, the left central margin is also placed subgingival to better match the contour and appearance of the right central restoration.
The right central could be placed with a resin-modified glass ionomer cement, or bonded with a dual-cure adhesive and cement. The left central was placed with a light-cured dentin adhesive and light-cured resin cement. Figure 4
(Click this link for more dental articles by Dr. Frank Spear.)