Erdal Eroğlu

Change of shade by light polymerization in a resin cement polymerized beneath a ceramic restoration

OBJECTIVES The aim of this in vitro study was to examine the effect of the color changes of a resin cement material (Variolink II) polymerized beneath a simulated ceramic restoration (IPS Empress II) by two different light polymerizing units. METHODS A conventional halogen light and a light emitting diode unit were used to polymerize resin cement with catalyst. A pressable ceramic block (10mm in diameter, 2 or 1mm in height) was used as an interface between the polymerizing light tip and resin cement. Colorimetric values of the specimens before and after polymerization were measured using a spectrophotometer (Easy Shade). The CIE L*a*b color system was used for the determination of the color difference. Differences between measurements were calculated as delta E*(ab). Repeated measurements analysis of variance (ANOVA) was used to analyze the data (polymerization of resin cement, polymerizing unit and ceramic thickness) for significant differences. The Tukey HSD test and paired two-tailed tests were used to perform multiple comparisons (alpha=.05). RESULTS L*a*b values of ceramic system were affected by the polymerization of resin cement (before and after) (P<.01). The a* value was affected by polymerization unit (P<.05), however L* and b* values were not affected by the light polymerization unit (P>.05). The b* value was affected by ceramic thickness (1 or 2mm) (P<.05), but L* and a* values were not affected by ceramic thickness (P>.05). The specimens polymerized beneath 1mm ceramic thickness with conventional halogen light induced a significantly higher color changes than any other specimen (P<.05). CONCLUSIONS The results of this in vitro study suggest that light polymerization of the resin cement (Variolink II) used in this study is an important factor for the color of the definitive restoration and should be considered during shade selection and fabrication.

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 × 12 × 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 Tukeys honestly significant differences (HSD) tests (α=.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.

Effects of coloring procedures on zirconia/veneer ceramics bond strength

PURPOSE The most common failure seen in restorations with a zirconia core is total or layered delamination of the ceramic veneer. In the present study, the shear bond strengths between veneering ceramics and colored zirconia oxide core materials were evaluated. MATERIALS AND METHODS Zirconia discs (15 × 12 × 1.6 mm) were divided into 11 groups of 12 discs each. Groups were colored according to the Vita Classic scale: A3, B1, C4, D2, and D4. Each group was treated with the recommended shading time for 3 s, or with prolonged shading for 60 s, except for the control group. Samples were veneered with 3 mm thick and 3.5 mm in diameter translucent ceramic and subjected to shear test in a universal testing machine with a crosshead speed of 1 mm/min. One-way analysis of variance (ANOVA) and Tukeys HSD tests were used for comparisons of the groups having the same shading times. A paired t-test was used for groups of the same color (3 s/60 s). RESULTS Among the 11 groups investigated C4 (3 s) had the highest bond strength with a value of 36.40 MPa, while A3 (3 s) showed the lowest bond strength with a value of 29.47 MPa. CONCLUSION Coloring procedures can affect zirconia/ceramic bond strength. However, the results also showed that bond strengths of all the investigated groups were clinically acceptable.