The effects of machining on the flexural strength of CAD-CAM materials
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OBJECTIVES: To evaluate the effects of different machining modes on the flexural strength CAD-CAM restorative materials. MATERIALS AND METHODS: Four different CAD-CAM materials were used: VITA MARKII, VITA Enamic (VITA Zahnfabrik), Empress CAD, and e.max CAD (Ivoclar Vivadent). Rectangular bars for each material (except e.max CAD) were made by three procedures: saw cut, normal mill and fast mill. Each subgroup had a sample size of 5. Saw cut bars were cut by a BUHLER diamond blade saw. Milled bars were made using SIRONA CEREC MCXL milling unit. The 3-point flexural strength test was performed using a universal testing machine. Surface roughness was measured using a profilomer. Student t-test and Tukey-Kramer statistical analysis were performed to check significant differences. RESULTS: e.max CAD saw cut group was significantly stronger than the milled group. There was no difference in the strength of the Empress CAD groups. Enamic saw cut group was significantly stronger than the normal milled but not the fast milled one. There was no significant difference between the Enamic milled groups. Vita MKII saw cut was significantly stronger than both milled groups. There was no difference in the strength between the milled MKII groups. The surface roughness of the saw cut groups in all materials were significantly less than their milled counterparts in both longitudinal and transverse measurements. CONCLUSION: Machining had a significant effect on the surface roughness of materials. Damage from machining can cause the material to have lower flexural strength.