STATEMENT OF PROBLEM: Although investigators have evaluated the effect of ceramic veneer preparation design, limited information is available regarding preparation design in association with the condition of existing tooth structure. PURPOSE: The purpose of this in vitro study was to evaluate the effect of preparation design and the amount of existing tooth structure on the fracture resistance of pressable ceramic laminate veneers. MATERIAL AND METHODS: Thirty-two extracted human maxillary central incisors were allocated into 4 groups (n=8) to test for 2 variables: (1) the preparation design (a 2 mm incisal reduction shoulder finish line with or without palatal chamfer) and (2) the existing amount of tooth structure (non-worn tooth or worn tooth). Measurement of the remaining enamel thickness on the inciso-occlusal surface was made after the tooth was prepared. All prepared teeth were restored with pressable ceramic (IPS Empress) veneers, and the veneers were luted with resin cement (Rely-X Veneer). These luted specimens were loaded to failure in a universal testing machine, in the compression mode, with a crosshead speed of 0.05 mm/min. The data were analyzed using a 2-way ANOVA and Tukey's HSD multiple comparison test (α=.05) RESULTS: Preparation design and the amount of existing tooth structure had a significant effect on the load to failure value (P<.001); however, the interaction between preparation design and existing amount of tooth structure was not significant (P=.702). Mean (SD) load to failure values were as follows: a preparation design with a palatal chamfer margin with a non-worn tooth (166.67 N (28.89)) revealed a significantly higher failure load than the group with a shoulder finish line alone (131.84 N (18.88)) (P<.01). The preparation design with a palatal chamfer margin for worn teeth (119.56 N (23.88)) revealed a significantly higher failure load than a shoulder finish line design alone (90.56 N (9.32)) (P<.05). The preparation design with a shoulder finish line for worn teeth had a significantly lower failure load than those on non-worn teeth (P<.003). CONCLUSIONS: Preparation design and the amount of existing tooth structure had a significant effect on load to failure for ceramic veneers. This study revealed that using a palatal chamfer margin design significantly increased the load to failure compared to a shoulder finish line.
STATEMENT OF PROBLEM: Although investigators have evaluated the effect of ceramic veneer preparation design, limited information is available regarding preparation design in association with the condition of existing tooth structure. PURPOSE: The purpose of this in vitro study was to evaluate the effect of preparation design and the amount of existing tooth structure on the fracture resistance of pressable ceramic laminate veneers. MATERIAL AND METHODS: Thirty-two extracted human maxillary central incisors were allocated into 4 groups (n=8) to test for 2 variables: (1) the preparation design (a 2 mm incisal reduction shoulder finish line with or without palatal chamfer) and (2) the existing amount of tooth structure (non-worn tooth or worn tooth). Measurement of the remaining enamel thickness on the inciso-occlusal surface was made after the tooth was prepared. All prepared teeth were restored with pressable ceramic (IPS Empress) veneers, and the veneers were luted with resin cement (Rely-X Veneer). These luted specimens were loaded to failure in a universal testing machine, in the compression mode, with a crosshead speed of 0.05 mm/min. The data were analyzed using a 2-way ANOVA and Tukey's HSD multiple comparison test (α=.05) RESULTS: Preparation design and the amount of existing tooth structure had a significant effect on the load to failure value (P<.001); however, the interaction between preparation design and existing amount of tooth structure was not significant (P=.702). Mean (SD) load to failure values were as follows: a preparation design with a palatal chamfer margin with a non-worn tooth (166.67 N (28.89)) revealed a significantly higher failure load than the group with a shoulder finish line alone (131.84 N (18.88)) (P<.01). The preparation design with a palatal chamfer margin for worn teeth (119.56 N (23.88)) revealed a significantly higher failure load than a shoulder finish line design alone (90.56 N (9.32)) (P<.05). The preparation design with a shoulder finish line for worn teeth had a significantly lower failure load than those on non-worn teeth (P<.003). CONCLUSIONS: Preparation design and the amount of existing tooth structure had a significant effect on load to failure for ceramic veneers. This study revealed that using a palatal chamfer margin design significantly increased the load to failure compared to a shoulder finish line.