Evaluation of translucency of monolithic zirconia and framework zirconia materials

PURPOSE: The opacity of zirconia is an esthetic disadvantage that hinders achieving natural and shade-matched restorations. The aim of this study was to evaluate the translucency of non-colored and colored framework zirconia and monolithic zirconia. MATERIALS AND METHODS: The three groups tested were: non-colored framework zirconia, colored framework zirconia with the A3 shade according to Vita Classic Scale, and monolithic zirconia (n=5). The specimens were fabricated in the dimensions of 15×12×0.5 mm. A spectrophotometer was used to measure the contrast ratio, which is indicative of translucency. Three measurements were made to obtain the contrast ratios of the materials over a white background (L*w) and a black background (L*b). The data were analyzed using the one-way analysis of variance and Tukey HSD tests. One specimen from each group was chosen for scanning electron microscope analysis. The determined areas of the SEM images were divided by the number of grains in order to calculate the mean grain size. RESULTS: Statistically significant differences were observed among all groups (P<.05). Non-colored zirconia had the highest translucency with a contrast ratio of 0.75, while monolithic zirconia had the lowest translucency with a contrast ratio of 0.8. The mean grain sizes of the non-colored, colored, and monolithic zirconia were 233, 256, and 361 nm, respectively. CONCLUSION: The translucency of the zirconia was affected by the coloring procedure and the grain size. Although monolithic zirconia may not be the best esthetic material for the anterior region, it may serve as an alternative in the posterior region for the bilayered zirconia restorations.

Evaluation of the bond strength between aged composite cores and luting agent

PURPOSE: The aim of this study was to evaluate effect of different surface treatment methods on the bond strength between aged composite-resin core and luting agent. MATERIALS AND METHODS: Seventy-five resin composites and also seventy-five zirconia ceramic discs were prepared. 60 composite samples were exposed to thermal aging (10,000 cycles, 5 to 55degrees C) and different surface treatment. All specimens were separated into 5 groups (n=15): 1) Intact specimens 2) Thermal aging-air polishing 3) Thermal aging- Er:YAG laser irradiation 4) Thermal aging- acid etching 5) Thermal-aging. All specimens were bonded to the zirconia discs with resin cement and fixed to universal testing machine and bond strength testing loaded to failure with a crosshead speed of 0.5 mm/min. The fractured surface was classified as adhesive failure, cohesive failure and adhesive-cohesive failure. The bond strength data was statistically compared by the Kruskal-Wallis method complemented by the Bonferroni correction Mann-Whitney U test. The probability level for statistical significance was set at alpha=.05. RESULTS: Thermal aging and different surface treatment methods have significant effect on the bond strength between composite-resin cores and luting-agent (P<.05). The mean baseline bond strength values ranged between 7.07 +/- 2.11 and 26.05 +/- 6.53 N. The highest bond strength of 26.05 +/- 6.53 N was obtained with Group 3. Group 5 showed the lowest value of bond strength. CONCLUSION: Appropriate surface treatment method should be applied to aged composite resin cores or aged-composites restorations should be replaced for the optimal bond strength and the clinical success.

Evaluation of the bond strength between aged composite cores and luting agent

PURPOSE: The aim of this study was to evaluate effect of different surface treatment methods on the bond strength between aged composite-resin core and luting agent. MATERIALS AND METHODS: Seventy-five resin composites and also seventy-five zirconia ceramic discs were prepared. 60 composite samples were exposed to thermal aging (10,000 cycles, 5 to 55degrees C) and different surface treatment. All specimens were separated into 5 groups (n=15): 1) Intact specimens 2) Thermal aging-air polishing 3) Thermal aging- Er:YAG laser irradiation 4) Thermal aging- acid etching 5) Thermal-aging. All specimens were bonded to the zirconia discs with resin cement and fixed to universal testing machine and bond strength testing loaded to failure with a crosshead speed of 0.5 mm/min. The fractured surface was classified as adhesive failure, cohesive failure and adhesive-cohesive failure. The bond strength data was statistically compared by the Kruskal-Wallis method complemented by the Bonferroni correction Mann-Whitney U test. The probability level for statistical significance was set at alpha=.05. RESULTS: Thermal aging and different surface treatment methods have significant effect on the bond strength between composite-resin cores and luting-agent (P<.05). The mean baseline bond strength values ranged between 7.07 +/- 2.11 and 26.05 +/- 6.53 N. The highest bond strength of 26.05 +/- 6.53 N was obtained with Group 3. Group 5 showed the lowest value of bond strength. CONCLUSION: Appropriate surface treatment method should be applied to aged composite resin cores or aged-composites restorations should be replaced for the optimal bond strength and the clinical success.

The effect of coloring liquids on the translucency of zirconia framework

PURPOSE: Translucency of all-ceramic restorations is an important factor which affects the final appearance and esthetic outcome of the restoration. The aim of this study was to evaluate the effect of the shade of coloring liquid on the translucency of zirconia framework. MATERIALS AND METHODS: Thirty zirconium oxide core plate (15 x 12 x 0.5 mm) were divided into 6 groups of 5 plates each. Each group was classified according to the shade of coloring liquid based on Vita Classic Scale (A2, A3, B1, C2, and D2), and each sample was immersed in coloring liquid for 3 seconds as recommended by the manufacturer, except for the control group. Contrast ratio, as a translucency parameter, was calculated using a spectrophotometer and the data were analyzed with oneway analysis of variance (ANOVA) and Tukey's honestly significant differences (HSD) tests (alpha=.05). RESULTS: Significant differences in translucency among the control and test groups, and the B1 shaded group and other shades was observed. There were no significant differences among A2, A3, C2, and D2 shaded groups. CONCLUSION: The translucency of the zirconium oxide cores was affected by the coloring procedure and significant differences in the translucency measurements were identified between specific shades.