Effect of Speed Firing Protocol on Physical and Mechanical Properties of Cubic Phase Containing Zirconia Used as Implant Restorations

Abstract

Objectives: First part was to evaluate the surface structure, phase determination, translucency, and strength (flexural) of the zirconia (Katana STML Block and Disc) between the regular sintering (RS) and the speed sintering (SS) with and without low- temperature degradation (LTD). The second part aimed to compare the surface structure, cracks, and load-bearing capacity in zirconia screw-retained implant crowns between RS and SS protocols with and without cyclic loading (fatigue). Materials and methods: For the first part, a total of 60 zirconia discs (30 per group; RS and SS). The zirconia discs were subjected to RS and SS with and without LTD. Scanning electron microscopy (SEM) was done to characterize the zirconia specimens and the zirconia grain size. Furthermore, the zirconia specimens were analyzed for elemental analysis using energy dispersive spectroscopy (EDS) and phase identification using X-ray diffraction. The zirconia specimens were analyzed for the translucency measurements and biaxial flexural strength testing. For the second part, a total of 60 screw-retained crowns were fabricated from zirconia (Katana STML Block) by the CAD/CAM system. Then, 30 crowns were subjected to the RS protocol and 30 crowns to the SS protocol. Cyclic loading was done in half zirconia crowns (15 crowns in each group) using a chewing simulator at room temperature. SEM was done to study the surface of the crowns and the cracks in the crowns of the RS and SS protocols, with and without fatigue. Load to failure was also evaluated. Results: For the first part, the zirconia specimens with and without LTD in RS and SS presented a similar surface structure. RS showed more translucency compared to SS. Multiple comparisons of the translucency parameter were a significant difference (p value < 0.05) among various groups except for the comparison between SS and SS with LTD. The RS sintering showed bigger gain sizes and slightly more t compared to SS. The SS RS. For the second part, for the SS group, the crack surface looks more uniform, and the crack lines are present at a short distance compared to RS. It showed that the SS group showed the maximum fracture load, followed by the RS, SS with fatigue, and RS with fatigue groups. The fracture load in various groups showed significant differences. Conclusions: The RS showed a bigger grain size and slightly more t compared to SS. The SS RS. This shows that SS can be considered a suitable method of sintering zirconia. Hence, when biaxial flexural strength is required, SS can be considered; however, when better translucency is required, RS is recommended.