Effects of preparation and luting system on all-ceramic computer-generated crowns.
OBJECTIVE
Computer-aided design/computer-integrated machining (CAD/CIM) allows defect-oriented custom-shaping of the inside surfaces of all-ceramic crowns. The purpose of this study was to examine the effect of inside crown form on fracture strength of cemented and bonded crowns.


METHODS
Four preparation types were used: (1) "classic" with a butt shoulder 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 designed on preparations 1 to 4 using identical outside morphology. Machined crowns were placed on abutments (a) without any media as controls (n = 15), (b) cemented (n = 15), and (c) bonded (n = 15), and were 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.


CONCLUSIONS
Bonded all-ceramic CAD/CIM crowns with defect-oriented inside morphology and increased occlusal dimensions showed high fracture load values.
Department of Preventive Dentistry, University of Zurich, Switzerland. moermann@zzmk.unizh.ch
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Mörmann
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Bindl
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Lüthy
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Rathke
D000704:Analysis of Variance; D002484:Cementation; D002516:Ceramics; D017076:Computer-Aided Design; D003442:Crowns; D001840:Dental Bonding; D003776:Dental Porcelain; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D008422:Materials Testing; D019231:Tooth Preparation, Prosthodontic; D015036:Zinc Phosphate Cement
D003776:Dental Porcelain; D015036:Zinc Phosphate Cement