Mechanical Properties of an Experimental Fluorophlogopite Glass Ceramic

Objectives: To compare the mechanical properties of three commercial millable ceramic materials, IPS e.max CAD^®; Vitablocs Mark II^®; Vita Enamic^®, with an experimental fluorophlogopite glass ceramic (FGC).
Methods: Each type of ceramic blocks were sectioned into beams (n=15) of standard dimensions 2 mm × 2 mm × 15 mm. Before mechanical testing, specimens of the e.max CAD group were further fired for final crystallization. Flexural strength was determined by the three-point bending test using a universal loading machine at a cross head speed of 1 mm/min. Hardness was determined by a hardness tester with five Vickers hardness indentations (n=5) using 200 g load and a dwell time of 15 seconds. Selected surfaces were examined by SEM and EDX. Data were analyzed by one-way ANOVA test and Weibull analysis (p<0.05). Weibull parameters, including the Weibull modulus (β), the characteristic strength at 63.2% (η) and 10.0% (B10), were obtained.
Results: Significant difference in flexural strength among groups was found (p <0.001) with IPS e.max CAD^® (341.88 ± 40.25 MPa) > Vita Enamic^® (145.95 ± 12.65 MPa) > Vitablocs Mark II^® (106.67 ± 18.50 MPa) and FGC (117.61 ± 7.62 MPa). Weibull modulus ranged from 6.925 to 18.338, with FGC showing the highest Weibull modulus among four materials. Weibull plot revealed that IPS e.max CAD^® > Vita Enamic^® > FGC > Vitablocs Mark II^® for the characteristic strength at both 63.2% (η) and 10.0% (B10). Significant difference in Vickers hardness among groups was found (p <0.001) with IPS e.max^® (731.63 ± 30.64 H_V) > Vitablocs Mark II^® (594.74 ± 25.22 H_V) > Vita Enamic^® (372.29± 51.23 H_V) > FGC (153.74 ± 23.62 H_V).
Conclusions: The flexural strength and Vickers hardness of IPS e.max CAD^® were significantly higher than that of the three materials tested. FGC’s flexural strength was comparable to Vitablocs Mark II^®. FGC’s Vickers hardness was the lowest among the materials tested but its Weibull modulus was shown to be the highest.