Optimizing occlusal results for crown and bridge prostheses.

W hen preparing a single-unit crown, or multiple unit bridge, dentists inevitably follow a similar routine. The prepared tooth/ teeth are impressed in a good quality impression material such as a polyether, or the most widely used impression material, an addition silicone vinyl polysiloxane (VPS),1 which accounts for 95% of the impressions sent to the dental laboratory.2 The impressions are taken in a fullarch stock or custom tray, the bite registration is taken after the preparations are completed, and an opposing model is fabricated from alginate to allow mounting of the case in the laboratory. Once the prosthesis is returned to the dental practitioner and inserted; if it is found to be high in occlusion, the dental technician is often blamed for an error in technique.3 In reality, it is the built-in variability of the above technique sequence and material selection, which is still routinely taught in many dental faculties, that leads to clinical frustration and valuable time wasted in trying to make the unit/units “fit.” Why is it that a 12 times greater accuracy in the maximal intercuspal position is found with the dual-arch cast?4