The effect of glazing and thermocycling on the surface roughness and microhardness of different CAD/CAM milled ceramic laminate veneers with SEM observations

The Purpose: The aim of this in-vitro study was to evaluate the effect of glaze and thermocycling to the surface roughness and microhardness values of four different ceramic CAD/CAM materials. Material & Methods: CAD / CAM laminate veneer shaped 80 samples were milled with CAD/CAM system (inLab MC XL Cerec, Sirona) after scan of plastic maxillary first incisor tooth of educational model with Omnicam scanner (Cerec, Sirona). Four different CAD/CAM ceramic materials were tested in this study: Lithium disilicate (IPS E.max CAD, Ivoclar), Leucite reinforced ceramic (IPS Empress CAD), Feldspathic ceramic (Cerec, Sirona) and a Nanoparticle-filled resin ceramic (Cerasmart, GC) (CS). Four groups from 80 samples (20 samples for each group, n=20) were allocated to two subgroups (10 samples, n=10): Glazed and non-glazed. All specimens were subjected to 10.000 thermo cycles. Surface roughness and Vickers hardness values were obtained in three stages: After milling (Initial), after glazing, after thermocycling. Sem images (100x, 250x, 500x, 1000x magnifications) of each material were obtained from every group (After milling (Initial), after thermocycling). Results: There is a statistically significant difference between materials in terms of initial surface roughness averages. The initial surface roughness of the Emax group was significantly higher than that of the Empress. CS, and Cerec groups (p<0.05). When evaluating the glazed surface, there was a statistically significant difference between the materials in terms of post-glazing microhardness averages (p<0.05). The microhardness of the Emax group after glaze was significantly higher than that of the CS, Empress and Cerec groups (p<0.05). When evaluating the glazed surface, there is a statistically significant difference between the materials in terms of microhardness averages after the thermo cycle (p<0.05) The post-thermo-cycle microhardness of the Emax group was significantly higher than that of the CS, Empress and Cerec groups (p<0.05). When evaluating the surface of CS material; there is a statistically significant difference between the mean microhardness at baseline, after glazing and after thermo cycle (p:0.000; p<0.05). Initial surface roughness was found to be statistically significantly higher after glaze and after thermo cycle (p1:0.000; p2:0.000; p<0.05). When evaluating the surface of Emax material; initial surface roughness was found to be statistically significantly higher after glaze and after thermo cycle (p<0.05). Microhardness level after glazing was statistically significantly higher than after Thermo cycle (p<0.05). When evaluating the surface of Empress material; initial surface roughness was found to be statistically significantly higher after glaze and after thermo cycle (p<0.05). There was no statistically significant difference between microhardness levels after glazing and after thermo cycle (p:0.074; p>0.05). When evaluating the surface of Cerec material; initial surface roughness was found to be statistically significantly higher after glaze and after thermo cycle (p<0.05). There was no statistically significant difference between microhardness levels after glazing and after thermo cycle (p>0.05) When glaze is not applied to the surface, the initial microhardness of the Emax group was significantly higher than that of the CS, Empress and Cerec groups (p<0.05). When glaze is not applied to the surface, the post-thermo-cycle microhardness of the Emax group was significantly higher than that of the CS, Empress and Cerec groups (p<0.05). When evaluating surface of CS material; microhardness after thermo cycle was found to be statistically significantly lower from baseline (p:0.000; p<0.05). When evaluating surface of Empress material; microhardness after thermo cycle was found to be statistically significantly lower from baseline (p<0.05). When evaluating surface of Emax material; microhardness after thermo cycle was found to be statistically significantly lower from baseline (p<0.05). Conclusion: It was concluded that application of the glazed layer on the surface of the samples significantly affects the surface roughness values of all samples. Reduction of the surface roughness values lead to increase the smoothness of the surfaces. Glazing decreases the surface roughness and microhardness values of CAD/CAM milled laminate veneer samples. Compared to glass ceramics, composite CAD/CAM material is more prone to increase of surface roughness values after aging. Thermocycling has more influence on surface roughness values than microhardness values. This study was conducted for researchers and clinicians to better understand the surface quality and properties of CAD/CAM materials to be used in clinics. This study was conducted to enable clinicians and researchers to evaluate the surface properties of materials to be used in CAD/CAM systems and to produce better quality, healthier and longer lasting restorations. Key Words: CAD/CAM; Surface roughness; Microhardness; Glaze; Thermocycling