Loss of tooth structure associated with preparation for two monolithic CAD-CAM complete coverage restorations

Statement of problem: Different techniques are used to fabricate complete coverage restorations. Each fabrication technique requires a specific preparation design that may violate a principle of tooth preparation, that is, conservation of tooth structure. Purpose: The purpose of this in vitro study was to compare the volume of loss of mandibular first molar structure associated with a preparation for computer-aided design and computer-aided manufacturing (CAD-CAM) versus conventionally fabricated complete coverage restorations. Materials and methods: Fifty artificial mandibular right first molars were weighed before and after preparation for complete coverage restorations of the following types: complete cast, monolithic zirconia, monolithic pressed lithium disilicate, monolithic milled lithium disilicate, and metal-ceramic crowns (n=10 per method). Tooth mass loss was measured by subtracting the mass after preparation from the mass before the preparation, and tooth volume loss was calculated by dividing the mass by the density of the material. A robust analysis of variance (ANOVA), followed by a post hoc test, was used to compare the volume of tooth loss (α=.01). Results: Mean tooth volume losses were 255.6 mm³, 270.0 mm³, 312.7 mm³, 331.7 mm³, and 309.9 mm³ for complete cast, monolithic zirconia, monolithic pressed lithium disilicate, monolithic milled lithium disilicate, and metal-ceramic crowns, respectively. Teeth prepared for monolithic CAD-CAM zirconia and lithium disilicate crowns did not exhibit a significantly lower (P>.01) decrease in volume loss than with complete cast and monolithic pressed lithium crowns. Conclusions: Preparation of teeth for monolithic CAD-CAM complete coverage restorations is not associated with a significantly higher volume of tooth loss than their conventionally fabricated counterpart preparations.