Effect of Incisal Height on Fracture Resistance of Lithium Disilicate and Hybrid Ceramic Laminate Veneers.

Objectives: This in vitro study evaluated the effect of the incisal height and the type of restorative material on the fracture resistance of labial laminate veneers in teeth with severe loss of incisal edge. Methods: In total, thirty-two human maxillary central incisors were randomly allocated into two groups (n = 16). In one group the incisal edge was reduced 2 mm and in the other group 3.5 mm. In each group half of the laminates were made of lithium disilicate (IPS e.max CAD) and the other half of a polymer-infiltrated ceramic network (PICN; VITA Enamic). After cementation of laminates with a resin cement (Choice 2), all specimens were subjected to thermal cycling (5-55°C, dwell time 30 s, 5000 cycles) and cyclic loading (30 N, 1.3 Hz, 500,000 cycles). Next, specimens were loaded to failure in a universal testing machine, with a crosshead speed of 1 mm/min. The data were analyzed using two-way analysis of variance (ANOVA) and T-test (α = 0.05). Results: Mean load to failure of laminates with 2 mm and 3.5 mm incisal height was respectively, 620.11 N and 901.81 N, in e.max CAD; and 466.43 N and 460.14 N in the VITA Enamic group. Only in e.max CAD laminates was the difference between two subgroups was significant(p=0.025). Conclusions: According to the results of this study, increasing the incisal height of e.max CAD laminates increases their load to fracture. However, it has no significant effect on VITA Enamic laminates. Clinical Significance: For anterior teeth that have lost more than 2 mm of incisal height, laminates made of lithium disilicate can be considered as a reliable option.