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Effect of Repeated Firings on Color Stability of Repaired Zirconia

Emre Tokar and Serdar Polat

Aim: The goal of this study was to investigate effect of repeated firings on color stability of repaired zirconia restorations. Materials and Methods: Eighty disc shaped (dimensions: 2 mm x 5 mm) zirconia samples were fabricated using CAD/CAM technology. The samples were randomly divided into two groups for two different intraoral porcelain repair kits (Ceramic Repair N and Clearfil Repair). Four subgroups (n=10) were set at these groups according to number of firing (1, 3, 5 and 7). L*a*b* values of the specimens were recorded and firing were performed in a porcelain furnace. After the firing process, specimens of each subgroup were repaired using a teflon mold (dimensions: 2 mm x 2 mm) with a porcelain repair kit that was related to major group and a compatible composite resin. L*a*b* values of the fired and repaired specimens were recorded. ΔE values and translucency parameters (ΔTP) were calculated using initial and final recorded data. The acquired data was analyzed using two-way ANOVA. Results: Mean ΔE values of the groups were compared to clinical acceptability threshold (ΔE=5.5) and clinical detection threshold (ΔE=3.7). Group K1 (1 firing and Clearfil Repair) showed that lowest mean ΔE value (ΔE=3.57) and this was within the clinical detection level. Other Clearfil Repair applied groups illustrated that clinically acceptable results related to clinical acceptability threshold. Mean ΔE value of Ceramic Repair N applied groups were higher than clinically detection and acceptable levels. Highest mean ΔE value (ΔE=6.24) was found at Group K7 among the tested groups. Translucency parameters (ΔTP) decreased while firing number increased. Conclusion: Color of the repaired zirconia restorations might be affected by multiple firings and intraoral porcelain repair systems. Color differences of the groups that repaired using Clearfil Repair kit were clinically acceptable. Besides, if firing number of zirconia framework increases, color and translucency differences will be high after the repair.