Strength and fracture pattern of monolithic CAD/CAM-generated posterior crowns.
OBJECTIVE
This study evaluated the strength and fracture pattern of monolithic posterior CAD/CAM crowns hypothesizing that zinc-phosphate cemented lithium disilicate crowns might show the same fracture strength as adhesively cemented crowns.


METHODS
Two sets of monolithic posterior crowns each with uniform occlusal and lateral wall thickness of 1.5mm were fabricated from three types of block ceramic (1) lithium disilicate glass, (2) leucite glass and (3) feldspathic ceramic using CEREC 3 CAD/CAM. Crowns (n = 15) of ceramics (1), (2) and (3) each were (A) zinc-phosphate cemented, (B) adhesively cemented on resin-based composite dies and loaded until fracture. Load data was analyzed using ANOVA and Scheffé tests. Crack pattern was evaluated on an additional three sample cross-sections for each group at start of fracture.


RESULTS
Radial cracks originated early at the cementation interfaces and cone cracks were observed finally at the loading sites. Mean load values (SD) of A-crowns at fracture start/end (1) 807 (91) N/2082 (192) N; (2) 915 (193) N/1130 (166) N; (3) 985 (199) N/1270 (301) N were all significantly (P < 0.001) lower when compared to their B-crown analogs (1) 1456 (205) N/2389 (84) N; (2) 1684 (395) N/2469 (171) N; (3) 1548 (304) N/2392 (75) N, rejecting the authors hypothesis. A-1 crowns had significantly (P < 0.001) higher fracture load than A-2 and A-3 crowns. The A-1 crown fracture load data, even if significantly (P < 0.001) lower, came close to the B-1 values.


CONCLUSIONS
Adhesive cementation balanced the strength of weak ceramics with that of strong ceramic and recommended itself for leucite glass ceramic and feldspathic ceramic crowns. Zinc-phosphate cementation appeared feasible for lithium disilicate crowns.
Bindl
Andreas
A
Division of Aesthetic and Computer Restorations, Department of Preventive Dentistry, Periodontology and Cariology, Center for Dental and Oral Medicine, University of Zurich, Zurich, Switzerland. andreas.bindl@zzmk.unizh.ch
Lüthy
Heinz
H
Mörmann
Werner H
WH
D000538:Aluminum Silicates / Q000737:chemistry; D002484:Cementation / Q000379:methods; D002516:Ceramics / Q000737:chemistry; D017076:Computer-Aided Design; D003442:Crowns; D001840:Dental Bonding; D003776:Dental Porcelain / Q000737:chemistry*; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D005898:Glass / Q000737:chemistry; D006801:Humans; D018020:Lithium Compounds / Q000737:chemistry; D008422:Materials Testing; D017680:Potassium Compounds / Q000737:chemistry; D017640:Silicates / Q000737:chemistry; D013314:Stress, Mechanical; D015036:Zinc Phosphate Cement / Q000737:chemistry
D000538:Aluminum Silicates; D018020:Lithium Compounds; D017680:Potassium Compounds; D017640:Silicates; D003776:Dental Porcelain; C016447:feldspar; C078519:leucite; C074543:Cerec; D015036:Zinc Phosphate Cement