Cementing zirconia: effect of cement types, polymerization mode, cement space, and air particle abrasion
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OBJECTIVES: To evaluate various cements in vitro for adhesion to zirconia, light curing vs. self-curing, the effect of particle abrasion (APA) on the zirconia intaglio for maximizing retention, the effect of thermocycling, and the effect of cement space. METHODS: The tested cements included: Ceramir C&B (Doxa) Panavia F2.0 (Kuraray); Multilink Automix (Ivoclar); Theracem (Bisco); Duolink (Bisco); Bifix (Shofu); CemEZ (Zest Dental). For testing cements retention, custom made zirconia rings 12.5 mm outer diameter, 5.5 mm height and 6.147 mm inner diameter were used to emulate crowns. Round steel rods (McMaster) were manufactured to fit into the zirconia rings allowing a cement space of 50 Microns or 100 Microns. A cementing jig was used to keep the rods at the center of the zirconia rings. Cements were tested using light curing and self-curing (n=10 per each test). Groups of zirconia rings were air braded with 100 Microns aluminum oxide particles for 10 Sec. Half the specimens were stored in water for 24 hours at 37o C in dark environment or thermocycled for 5000 cycles. A ‘push-out’ test using an Instron universal machine at a crosshead speed of 0.5mm/min. Loads to failure were recorded to calculate cements retention. RESULTS: Statistical analysis was performed using JMP Pro 13 software. Data were analyzed using one way ANOVA, multiple t-test, and Tukey-Kramer HSD. For self curing method without APA, retention strength ranking for tested cements were: Ceramir C&B ≥ Theracem > Panavia F2.0 ≥ Duolink ≥ Multilink Automix ≥ Bifix. For light curing method without APA, retention strength ranking for tested cements were: CemEZ ≥ Theracem ≥ Multilink Automix ≥ Duolink ≥ Bifix ≥ Panavia F2.0. There was a significant influence in retention strength for light cured cements compared to self-curing method except for Theracem and Panavia F2.0. For the self-curing method with APA, retention strength ranking for tested cements were: Theracem > Duolink ≥ Panavia F2.0 ≥ Multilink Automix ≥ Bifix > Ceramir C&B. For the light curing method with APA, retention strength ranking for tested cements were: Theracem ≥ Multilink Automix ≥ CemEZ ≥ Duolink ≥ Panavia F.0 ≥ Bifix. A significant increase in retention strength with APA compared to self-curing method with APA. There was no significant effect of thermocycling treatment on retention strength of the cements tested. There was no significant effect of different cement spaces on retention strength except for Ceramir C&B without APA and Multilink Automix with and without APA (P < 0.0001). CONCLUSIONS: 1- There was a significant difference in retention strength to zirconia among tested cements in self and light curing methods. 2- Light curing resin cements influenced retention strength to zirconia for the tested cements. 3- APA influenced the retention strength to zirconia for tested cements except for Ceramir C&B. 4- Increasing the cement space from 50μm to 100μm had no significant difference in retention strength to zirconia except for Ceramir C&B without APA and Multilink Automix with and without APA. 5- Thermocycling had no significant effect of on retention strength to zirconia for the tested cements.