Longevity and failure load of ceramic veneers with different preparation designs after exposure to masticatory simulation

Statement of problem. Laminate veneers are widely used in the management of unesthetic anterior teeth. However, limited information is available regarding the influence of preparation design on longevity of ceramic veneers. Purpose. This study evaluated the influence of preparation design on longevity and failure load of ceramic veneers bonded to human maxillary central incisors after cyclic loading and thermal cycling in a dual-axis masticatory simulator. Material and methods. Sixty-four caries-free maxillary central incisors were divided into 4 groups (n = 16). The control group remained unprepared (NP). For Group WP, a window preparation was made. Specimens in Group IOP were prepared with an incisal overlap of 2 mm without palatal chamfer. For Group CVP, specimens were prepared with a complete-veneer design of 3-mm incisal reduction and 2-mm palatal extension. Forty-eight IPS Empress 1 ceramic veneers were bonded adhesively with dual-polyrnerizing composite (Variolink II). All specimens were subjected to cyclic mechanical loading (1.2 million cycles, cycle frequency 1.3 Hz, invariable palatal load 49 N) and thermal cycling (5 degrees C-55 degrees C, dwell time 60 seconds, 5500 cycles) in a masticatory, simulator. Failure was defined by bulk fracture of a specimen. Subcritical crack patterns were observed. Surviving specimens were loaded in a universal testing machine until fracture. The failure-load values (N) (1.5 mm/min crosshead speed) were automatically recorded by controlling software. Statistical analysis of data was performed by Kruskal-Wallis analysis of variance (alpha=.05) and pairwise Wilcoxon rank sum tests (alpha=.05). Results. Three specimens from group NP, I specimen each from the WP and CVP groups, and 2 specimens from group IOP fractured during fatigue. After 1.2 million cycles, the highest crack rates were observed for complete veneers and originated in the palatal concavity extending to the facial surface. The median (interquartile range = x(.25)-x(.75)) failure loads (N) were as follows: NP 713.3 (404.4-777.1), WP 549.5 (477.5-597.7), IOP 695.3 (400.0-804.6), and CVP 519.2 (406.1-732.9). No significant differences in longevity and failure load were demonstrated between natural teeth and teeth restored with ceramic veneers (P=.555). Conclusion. Maxillary teeth restored with the 3 types of IPS Empress I veneers showed fracture resistance similar to that of unprepared incisors (P=.555).