Effects of Preparation and Luting System on All-Ceramic Computer-Generated Crowns

Purpose: Computer-aided design/computer-integrated machining (CAD/CAM) allows defect-oriented custom-shaping of the inside surfaces of all-ceramic crowns. The urpose of this study was to examine the effect of inside crown form on fracture strength of cemented and bonded crowns. Materials and Methods: Four preparation types were used: (1) classic with a butt should of 1.2 mm, abutment height of 4 mm, and 6-degree convergence, (2) like type 1 with mesio-occlusodistal cavity, (3) like type 1 with height reduced by 50%, and (4) like type 1 with abutment reduced by 100% plus a pulp chamber cavity. Crowns were CAD desgined on preparations 1 to 4 using identical outside morphology. Machined crowns were placed on abutments (a) without any media as controls (n = 15), (b) ceme nted (n = 15), and (c) bonded (n = 15), and wre loaded until fracture. Results: Zinc phosphate-cemented crowns (1b, 2b, 3b, and 4b) showed significant (P 0.001) increase of fracture load values compared to uncemented control crowns (1a, 2a, 3a, 4a). Fracture load values of bonded crowns (1c, 2c, 3c) were significantly (P 0.001) higher than those for cemented crowns. Bonded crowns with thick occlusal dimensions (3c and 4c) showed the highest fracture load values. Conclusion: Bonded all-ceramic CAD/CIM crowns with defect-oriented inside morphology and increased occlusal dimensions showed high fracture load values.