Evaluation of occlusal rest seat depth in bicuspids: an experimental study

Objective: Since premolars may be used as abutment teeth of removable partial dentures, the aim of this study was to evaluate the depth of occlusal rest seats in premolars and its relation with dentin and enamel. Methods: Twenty-nine premolar teeth (extracted for orthodontic reasons) were randomly selected from patients at a University Clinic. The mesio-distal and buccal-lingual dimensions were measured. Rest seats were prepared with round burs (1.0-1.5 mm) in premolar mesial and distal fossae. Rest seats were cut with a microtome and observed in a scanning electron microscope. Tooth abrasion was also evaluated using the Gourdon indice. Results: Significant differences were observed in the enamel thickness before and after rest seat preparations. Maximum enamel thickness in the deepest part of the rest seat was 625 μm in distal and 500 μm in mesial. In more than 50% of the teeth, dentin was reached. Almost 80% were not abraded. Conclusion: In most situations it is not possible to prepare a rest seat with 1.5 mm depth only in enamel. In teeth not abraded it is possible to prepare rest seats with 1.0 mm without reaching dentin. There are significant differences between enamel thickness in distal and mesial, before and after rest seat preparation.