In the previous article in this series I showed an example of masking isolated discoloration with composite and using a translucent porcelain veneer and translucent cement on a single central incisor. In this article I'll discuss a single central where the entire prep is extremely discolored.
Case 4: Â Discolored endodontically treated central incisor with existing dark porcelain veneer.
This patient presented unhappy with the discoloration of the right central incisor. The tooth has been successfully treated endodontically for years but it has become very dark. Additionally, the existing veneer is unacceptable from a color perspective and the margin is visible (Fig. 1).
Removing the veneer revealed an extremely dark prep. The decision that had to be made was whether to consider bleaching the tooth and staying with a veneer, which brings the risk of relapse and darkening over time, or converting to a full crown and masking the darkness. Since the patient had already experienced the tooth and veneer darkening, the decision was made with the patient to switch to a full crown (Fig. 2).
There are two different approaches to masking the discolored prep of this tooth. The first is to use opaque composite and bond it to the tooth, effectively making a more normal color prep. This allows the use of a more translucent final restoration The other option is to leave the prep the color as it is, create space for 1.2 to 1.4mm of restorative material thickness on the facial and use a restoration with an opaque core and more translucent ceramic over the core.
In these types of cases there are several different material options that could be used for creating the opaque coping to provide the masking, Lithium Disilicate, Zirconia, Alumina, or metal. If Lithium Disilicate was used itâs possible that the full crown prep wouldnât have been necessary since the Lithium Disilicate can be easily etched and bonded to provide the resistance and retention form. It still would require the same facial reduction.
In this case the technician wanted to use Alumina as the core. Although it can be bonded, the decision was made to use a full crown prep to provide mechanical resistance and retention form. In order for the Alumina to adequately mask the discoloration itâs necessary for it to be .5 to .6mm thick (Fig. 3).
At this thickness it essentially removes the prep from the equation as can be seen in this image where it completely masks a dark black dot placed on the die (Fig. 4).
The other key to these types of cases is subgingival placement of the margin, typically .5 to .7mm below tissue unless the sulcus is deeper then 1.5mm. If the sulcus is deeper the risk of recession is higher, and I would generally place the margin half the depth of the sulcus below tissue to minimize the risk of margin exposure later on down the road.
The one thing the crown canât accomplish is to brighten the root below tissue. In the final result the tissue over the root is slightly lower in value over the right central then the left, but the patient is very satisfied (Fig. 5).