Re: CROWN SELECTION

Porcelain fused to metal crowns (PFM), also called metal-ceramic crowns, are undoubtedly most versatile combining strength with aesthetics. Tooth preparation to accommodate both metal and porcelain can be very destructive (Fig. 3) so the design, particularly the distribution of porcelain, needs to be carefully thought through. Metal surfaces require less tooth destruction, are easier to construct and adjust, and do not chip like porcelain. Porcelain coverage should only be used where it is required for aesthetics, or possibly when opposing other porcelain surfaces (as metal does not wear well against porcelain, especially the metal backs of anterior crowns).
If full porcelain coverage is required for a PFM the amount of tooth preparation may be reduced slightly by using a special metal composite coping (Captek, Schottlander, Letchworth, UK). This type of coping is 0.1–0.2 mm thinner than a cast coping made from a noble metal alloy.

Composite crowns which use newly developed laboratory materials have not been fully evaluated. Specific indications and limitations have yet to be defined. Manufacturers are currently recommending that the tooth be prepared in the same way as for a HSPC.

The major factor to be considered before selecting the most suitable type of crown is the amount of tooth destruction you are willing to allow in order to give the aesthetics you want. You may also want to consider the need for the crown to incorporate special features, for example:

* A metal anterior guidance surface
* Rest seats and other features to retain a partial denture
* Metal occlusal surfaces for a bruxist