Crown selection
The usual indications for full veneer crowns are:
* To protect weakened tooth structure
* To restore the tooth to function
* To improve or restore aesthetics
* For use as a retainer for fixed bridgework
However, recent developments in dental materials mean that the use of less destructive alternatives such as veneers, onlays, and suitably designed plastic restorations are often an option. Where crowning is in the patient’s best interests the type of crown provided will usually depend on the functional requirements, the strength and vitality of the remaining tooth and the patient’s aesthetic demands. Occasionally, the choice may be limited by a patient’s concerns, real or imagined, over biocompatibility of proposed materials.
Full veneer metal crowns (VMC) have the advantage of requiring relatively little tooth preparation. They are generally limited by aesthetics to the back of the mouth, but bear in mind that some people may favour an anterior display of gold.
Porcelain jacket crowns (PJC) are indicated in areas of critical aesthetics, but problems of fracture under occlusal load limit their use to anterior teeth.
High strength porcelain crowns (HSPC), using modern ceramics without the need for a metal substructure, may be used on posterior teeth and in certain selected cases for anterior bridgework especially where the use of metal is an issue. However, not all systems are suitable for these purposes. The preparation design for a posterior HSPC is important2, 3 and relatively destructive. Enough tooth tissue needs to be removed to permit an adequate thickness of porcelain while the degree of taper should be greater than for a conventionally cemented crown, and all corners and line angles need to be rounded to allow unhindered, passive seating of the crown. At least one system (Procera AllCeram, Nobel Biocare, Göteburg, Sweden) provides burs designed to cut a deep chamfer at the finish line to allow the profile of the die to be scanned with a digital profilometer for the production of a high strength ceramic core.
Resin bonded porcelain crowns (RBPC) are similar to porcelain veneers but provide coverage on all surfaces and are very conservative of tooth tissue. The strength of these restorations is largely reliant on the resin bond as there is no reinforcing ceramic core. Excellent aesthetics are possible and a much less destructive preparation can be used than for either PJCs or porcelain fused to metal crowns (look at Fig. 2). RBPCs may be particularly useful in younger patients who have large, vulnerable pulps. Long term follow-up is lacking but a similar success rate to veneers might be expected. In our experience this type of restoration is not suited to areas of heavy occlusal load (eg where tooth wear has been caused principally by parafunction) as the porcelain may fracture.
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