BIAXIAL FLEXURAL STRENGTH AND HARDNESS OF RESIN-MATRIX CERAMIC CAD/CAM MATERIALS

This study evaluated the biaxial flexural strength (BFS) and hardness of four resin-matrix ceramic CAD/CAM materials namely, Vita Enamic (EN), Lava Ultimate (LU), Cerasmart (CS), Crystal Ultra (CU) and one glass-matrix ceramic material, Vitablocs Mark II (VM2). Disc-shaped specimens (12 mm in diameter and 1.2 mm in thickness) were prepared from the CAD/ CAM materials and were accordingly allocated into two groups. One group was used for baseline measurements and the other group was subjected to ageing by thermal-cycling (TC) for 10,000 cycles. The BFS and hardness was evaluated by a universal testing machine and a Vickers hardness tester, respectively. A two-way ANOVA, one-way ANOVA with Tukey's post hoc test, and Student's t-test (= 0.05) were used to analyse the data (alpha = 0.05). The highest and lowest BFS was seen in CS and VM2 and the difference in the BFS among the materials was statistically significant (p < 0.05). The comparison between the baseline and TC groups showed significant difference in the BFS for EN (p < 0.001), LU (p < 0.001), and CS (p < 0.012) but no difference was seen for VM2 (p = 0.238) and CU (p 0.159). The Vickers hardness number (VHN) ranking of the materials for the baseline and TC specimens, was VM2 EN > LU > CS > CU and VM2 > EN > LU > CU > CS, respectively. Following the TC, all the materials showed a significantly lower VHN (p < 0.05) except for VM2 (p = 0.727). The CS material had the highest BFS among the baseline and TC groups; however, it had the lowest hardness among the materials in the baseline group and had comparable values to CU after the TC. Ageing by thermal-cycling significantly lowered the BFS of the CAD/CAM materials except for VM2 and CU, and lowered the hardness of the resin-matrix ceramic materials.