Tooth structure removal associated with various preparation designs for posterior teeth

The amount of tooth structure removed for various innovative and conventional preparation designs for fixed prosthodontics was quantified. Four Typodont resin teeth representing maxillary and mandibular premolars and molars were prepared in various abutment designs: adhesive, box (A2); adhesive, wing and groove (A3); mesioocclusal or distoocclusal inlay; mesio-occlusodistal inlay (13); mesio-occlusodistal onlay; partial crown; half crown (only molars); complete crown, 0.8-mm circumferential tapered chamfer (F1); complete crown, 1.0-mm circumferential rounded shoulder; and complete crown, 1.4-mm axial reduction facial shoulder, 0.7-mm lingual chamfer (F3). After tooth preparation (10 per group), the root was separated from the anatomic crown at the cementoenamel junction. Removal of tooth structure was measured by gravimetric analysis in a high-precision balance. Preparations A3 and F3 were assigned as abutments for metal-supported restorations, whereas all other preparations were used for all-ceramic restorations. When the mean structure removal of all teeth tested was compared, the adhesive and inlay abutments were the least invasive preparation designs, ranging from approximately 5.5% (A2) to 27.2% (13) tooth structure removal. Complete crowns required the most invasive preparations, ranging from 67.5% (F1) to 75.6% (F3) tooth structure removal. The tooth structure removal required for F3 retainers was almost 14 times greater than for an A2 preparation. Tooth structure removal was also influenced by the morphology of the tooth. The first comprehensive tooth preparation design classification system was introduced. The measurement system used in this study provides an accurate method of quantifying tooth structure removal for fixed prosthodontic preparations. The innovative preparation designs studied conserved significant amounts of tooth structure, yielding a better prognosis for the restored tooth.