Flexural resistance of heat-pressed and CAD-CAM lithium disilicate with different translucencies

Objective: To compare flexural strength of CAD-CAM and heat-pressed lithium disilicate. 

Methods: For Pressed specimens (Group A), acrylate polymer blocks were cut with a saw in bars shape. Sprueing, investing and preheating procedures were carried out following manufacturer's instructions. IPS e.max Press ingots (Ivoclar-Vivadent) were divided into subgroups (n = 15) according to translucency: A.1 = HT-A3; A.2 = MT-A3; A.3 = LT-A3; A.4 = MO2. Ingots were then pressed following manufacturer's instructions. For CAD-CAM specimens (Group B) blocks of IPS e.max CAD (Ivoclar-Vivadent) were divided into subgroups: B.1 = HT-A3; B.2 = MT-A3; B.3 = LT-A3; B.4 = MO2. Specimens (n = 15) were obtained by cutting the blocks with a saw. Final crystallization was performed following manufacturer's instructions. Both Press and CAD specimens were polished and finished with silica carbide papers of increasing grit. Final dimensions of the specimens were 4.0 ± 0.2 mm, 1.2 ± 0.2 mm, and 16.0 ± 0.2 mm. Specimens were tested using a three-point bending test. Flexural strength, Weibull modulus, and Weibull characteristic strength were calculated. Flexural strength data were statistically analyzed. 

Results: The overall means of Press and CAD specimens did not differ significantly. Within the Press group different translucencies were found to have similar flexural strength. Within the CAD group, statistically significant differences emerged among the tested translucencies (p < 0.001). Specifically, MT had significantly higher flexural strength than HT and MO. Also, LT exhibited significantly higher flexural strength than MO. 

Significance: The choice between IPS e.max Press and IPS e.max CAD formulations can be based on different criteria than flexural resistance. Within each formulation, for IPS e.max Press translucency does not affect the flexural strength while for IPS e.max CAD it is an influential factor.