| Objective: The objective of this in vitro study is to analyze the effect of surface polishing and overglazing on the fractural strength of two all ceramic restorative materials, the IPS Empress CAD fabricated with a computer aided design-computer aided manufacturing system (CAD-CAM) and IPS Empress Esthetic with pressing technique.;Materials and Methods: A total of 80 IPS Empress Esthetic and CEREC 3D IPS Empress CAD ceramic disks (12 mm x 1.5 mm) were used in this study, 40 disks per each material. The 80 disks were divided into two major groups (group A and group B). Group A consists of IPS Empress Esthetic and group B consists of IPS Empress CAD. After disk preparation, each group was divided into five subgroups: A1, A2, A3, A4, and A5 (eight samples per subgroup) which were the control (unpolished, unoverglazed), polished only, overglazed only, overglazed-adjusted-polished, and overglazed-adjusted-reoverglazed subgroups, respectively. The subgroups B1, B2, B3, B4, and B5 (eight samples per subgroup) which were categorized the same as group A, respectively. Forty IPS Empress Esthetic ingots (12 mm width x 10 mm height) were pressed into a disc shape with a pressing technique. Forty IPS empress CAD blocks (12 mm width x 15 mm height) were milled into a disc shape using the CEREC inLab software version 3.83 and the inlab MCX milling unit. Overlazing was done using the IPS Empress Universal Glazing Paste and IPS Empress Universal Glaze and Stain Liquid and was conventionally oven-glazed based on manufacturer recommendation. The prepared disk surfaces were polished with an Optrafine polishing kit and Optrafine polishing paste (1 ml). All disks were loaded until they experienced a catastrophic fracture.;Results: The comparison of mean values of biaxial flexural strength across the five types of IPS Empress Esthetic disks and five types of IPS Empress CAD disks both showed highly statistical significance (F= 38.65 and F=38.50, respectively at p <0.0001), in which the mean value of the subgroups A3 and B3 followed by the mean value of A5 and B5 were significantly higher than the mean values of the other subgroups (A1, A2, A4, B1, B2, and B4). There was no statistically significant difference in the mean values of these three subgroups for both materials (A1, A2, A4, B1, B2, and B4). The comparison of mean values of fractural strength across the five types of IPS Empress Esthetic disks and five types of IPS Empress CAD disks showed highly statistical significance (F= 40.37 and F = 39.91, respectively, p <0.0001), in which the mean value of the subgroups A3 and B3 followed by the mean value of A5 and B5 were significantly higher than the mean values of other three subgroups for both materials. There was no statistically significant difference in the mean values of these three subgroups for both materials. The biaxial flexural and fractural strengths of IPS Empress Esthetic material showed highly statistical significance in the mean value of the subgroup A3 (t = 4.28, p =0.0008 and t = 4.34, p = 0.0007 respectively) compared to B3 of IPS Empress CAD material. The mean values of the biaxial flexural and fractural strengths of the subgroup A5 of IPS empress esthetic material which were statistically significantly (t = 2.63, p =0.019 and t = 2.52, p = 0.025 respectively) higher than B5 of IPS empress CAD material. In contrast there was no statistically significant difference between the mean values of biaxial flexural and fractural strengths of the other three subgroups for these two materials.;Conclusions: The biaxial flexural and fractural strengths of IPS Empress Esthetic and IPS Empress CAD of the subgroups A3, A5, B3, and B5 mean values were statistically significantly higher than the mean values of the other subgroups (A1, A2, A4, B1, B2 and B4). The biaxial flexural and fractural strengths of the subgroup A3 of IPS Empress Esthetic material were statistically significantly higher than the mean value of IPS Empress CAD material. |
