The Effect of Combining Opaquing Powders with Feldspathic Porcelain

Objectives: The aim of the study was to investigate the effects of combining metal oxide opaquing powders with a dental porcelain. This may be beneficial when providing porcelain laminate veneers for discolured teeth. Methods: Cerium oxide (CeO2) and zirconium oxide (ZrO2) were incorporated into the opacious dentine powder of the feldspathic porcelain Vitadur Alpha at 5%, 10% and 20% concentrations by wt (n=10 per group). The colour (CIEL*a*b*) and reflectance (Y) of the specimens were measured over white and black backgrounds using a colorimeter (Minolta CS-100) under artificial daylight. To determine the masking ability (δE1), contrast ratio (CR) and colour shift compared to the control (δE0) were determined. Biaxial flexural strength test was also performed on 20%-CeO2 and 20%-ZrO2 test powders and compared to the control (n = 20). Results: ANOVA showed a significant difference of the dE1 and CR for all test groups compared to the control (p<0.001). Tukey's post hoc test showed significant differences between test groups (p<0.001) with increasing masking ability (δE1) and CR observed in the order: control < 5%-ZrO2 and 10%-ZrO2 < 20%-ZrO2 and 5%-CeO2 < 10%-CeO2 < 20%-CeO2 (groups with underscore = p>0.05). CeO2 had a greater CR and masking ability than ZrO2 groups compared to the control (p<0.05). Only the colour shift of the 20%-CeO2 and 20%-ZrO2 test porcelains was considered to be greater than or nearly close to the threshold value (dE=5); 20%-CeO2 δE0=5.83±2.0 and 20%-ZrO2 δE0=4.94±1.80. There was no significant difference (p>0.05) in the mean flexural strength (MPa): control 55.2±3.9, 20%-CeO2 58.5±8.0, 20%-ZrO2 59.6±6.4. Conclusions: Increasing concentrations of opaquing powders have greater CR and masking ability, however, the higher concentrations may be associated with an undesirable colour shift. There appears to be no observable effect on the flexural strength of the test groups compared to the control.