Evaluation of Translucency and its Measurements, in Monolithic Zirconia Materials

Objectives: To explore the standardization of the quantification of translucency in dental ceramics by comparing various optical property measurements including Transmission (T), Contrast Ratio (CR), Translucency Parameter (TP), Gloss and Surface Roughness and by investigating the relationship between thickness, polish grade and translucency.
Methods: Four monolithic zirconia materials were used as discs in this study; VITA-YZ Translucent, High Translucent, Super Translucent and Extra Translucent. IPS e.max CAD HT was used as a control. 10 specimens from each of these materials were prepared in 125 µm, 70 µm, 15 µm, and 0.5 µm polished surface in the following thicknesses 1.00 mm, 0.75 mm, 0.50 mm and 0.35 mm. The following tests were completed: T, CR and TP using a X-rite Ci7600 spectrophotometer, surface roughness by Mitutoyo SJ-201 Profilomer, and gloss index by a Rhopoint Novo-Curve glossmeter. Data were analyzed by using two-way ANOVA for different groups and Tukey’s for paired groups. Coefficient of absorption and loss of reflectance ratio were calculated by linear regression.
Results: Material type, thickness and polishing grade have statistically significant effect (p < .0001) on translucency. The highest mean for transmission was 70.64 ± 0.84 for E.max in 0.35 mm in thickness and polished to 0.5 µm and the lowest mean was 26.99 ± 0.71. A strong linear correlation was observed between transmission and TP (r=-0.99), and between T and CR (r=0.99) as shown in the figure.
Conclusions: E.max HT is significantly more translucent than zirconia. Transmission is viable to be used as a standardized measurement for translucency with material settings of 1mm thickness and optical polishing. Standardizing translucency can help clinicians to make informed decisions in choosing the most optimum dental materials, increasing the aesthetic success of prostheses.