Relationship Between Internal Accuracy and Load-Bearing Capacity of Minimally Invasive Lithium Disilicate Occlusal Veneers

Abstract

Purpose: To test whether internal accuracy affects the load-bearing capacity of 0.5-mm-thick occlusal veneers made out of milled or heat-pressed lithium disilicate (LS2). Materials and Methods: Extracted human molars (N = 80) were divided into four groups (n = 20 each) depending on the bonding substrate (enamel [E] or dentin [D]) and the fabrication method (milling [CAD] or heat pressing [PRE]) for the occlusal LS2 veneers: (1) E-CAD; (2) D-CAD; (3) E-PRE; or (4) D-PRE. After restoration fabrication, the abutment teeth and the corresponding restorations were scanned and superimposed in order to measure the marginal and internal accuracy. After adhesive cementation, the specimens were thermomechanically aged and thereafter loaded until fracture. The load-bearing capacities (F-max) were measured. F-max and the marginal and internal accuracy between the groups were compared using Kruskal-Wallis test (P < .05) and pairwise group comparisons. In addition, the relationship between F-max and the internal accuracy was analyzed using Spearman rank correlation. Results: Median F-max values (and first and third quartiles) per group were as follows: 1,495 N (Q1: 932, Q3: 2,318) for E-CAD; 1,575 N (Q1: 1,314, Q3: 1,668) for E-PRE; 1,856 N (Q1: 1,555, Q3: 2,013) for D-CAD; and 1,877 N (Q1: 1,566, Q3: 2,131) for D-PRE. No statistical difference was found between the groups (P = .0981). Overall, the internal accuracy in the areas of the cusp (P < .0007) and fossae (P < .0001) showed significant differences. While no significant differences were detected in the marginal area (P= .3518), a significant correlation with a negative linear relationship was found between the 3D internal accuracy and the F-max values (P= .0007). Conclusion: An increase in the internal accuracy raised the load-bearing capacity of minimally invasive LS2 occlusal veneers. In general, the restorations bonded to dentin in the occlusal regions showed a better accuracy compared to those bonded to enamel.