Abstract
OBJECTIVES: This study aimed to analyze the effect of core and veneer porcelain thickness and resin cement on the opalescence property (OP) of glass-ceramic veneers, which were used to restore discolored teeth. METHODS: IPS e.max CAD LT A3 ceramic specimens were fabricated by computer aided design and computer aided manufacturing (CAD/CAM). The thickness values of core porcelain groups were 0.25 and 0.50 mm, and those of the core/veneer porcelain groups were 0.25 mm core/0.25 mm dentin, 0.50 mm core/0.25 mm dentin, 0.50 mm core/0.50 mm dentin, and 0.50 mm core/0.25 mm dentin/0.25 mm incisal. To simulate the clinical bonding procedure of porcelain veneer, resin cement Variolink N Bleach XL was coated at the bottom of CAD/CAM porcelain veneer specimens to make composite specimens of CAD/CAM porcelain veneer and resin cement. The L*a*b* values of specimens in the reflection and transmission pattern were measured by a spectrophotometer. Then, the OP was calculated. RESULTS: The OP values of 0.25 and 0.50 mm core porcelain groups, and 0.25 mm core/0.25 mm dentin, 0.50 mm core/0.25 mm dentin, 0.50 mm core/0.50 mm dentin, and 0.50 mm core/0.25 mm dentin/0.25 mm incisal core/veneer porcelain groups were 6.10±0.50, 7.00±0.24, 6.40±0.24, 7.08±0.28, 7.16±0.21, and 7.86±0.11 respectively. With increasing thickness of core porcelain, the OP values increased significantly (P<0.05). When 0.25 mm-thick dentin porcelain was added, no significant difference was found in the OP values of specimens with the same core porcelain thickness (P>0.05). For the 0.50 mm core porcelain group, no significant difference was found between 0.25 and 0.50 mm-thick dentin porcelain groups (P>0.05), but the OP values increased significantly after increasing the 0.25 mm incisal porcelain (P<0.05). The OP values of 0.25 mm core/0.25 mm dentin, 0.50 mm core/0.25 mm dentin, 0.50 mm core/0.50 mm dentin, and 0.50 mm core/0.25 mm dentin/0.25 mm incisal CAD/CAM porcelain veneer-resin cement composite specimens were 6.29±0.31, 7.56±0.36, 7.67±0.30, and 8.65±0.53. The OP values increased with increasing thickness of the porcelain layer (P<0.05), but no statistically signi-ficant difference was found between the groups of 0.50 mm core/0.25 mm dentin and 0.50 mm core/0.50 mm dentin (P=0.733). The influence of porcelain layer thickness and resin cement on the OP value was statistically different (P<0.05), and no interaction was found between the total thickness and the presence of resin cement (P>0.05). CONCLUSIONS: When using glass-ceramic veneers for discolored teeth, the following are recommended to improve the OP and obtain a natural and realistic effect: adopt the design of direct sintering incisal porcelain with core porcelain; appropriately increase the thickness of core porcelain; and select resin cement with opaque effect.