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The aim of this study was to evaluate the effect of grit-blasting on the color stability of zirconia ceramics following exposure to beverages. Method A total of 80 planar zirconia specimens were prepared from dense sintered zirconium blocks and were randomly allocated into four groups (n=20). Ten specimens from each group were gritblasted (GB) using aluminum trioxide powder from a distance of 10 mm. The remaining 10 specimens were used as such without grit-blasting (NGB). The grit-blasted and non-grit-blasted specimens were immersed in artificial saliva, Coffee, Red Bull, and Coca-Cola at room temperature over a 28-day test period. Color measurement (ΔE) of the zirconia specimens was performed at baseline (T0) and after seven (T1), 14 (T2), and 28 (T3) days of immersion in the beverages using the Color Eye 7000A Spectrophotometer (Gretag Macbeth, New Windsor, NY). The data were analyzed using analysis of variance (ANOVA) and the post-hoc Bonferroni test. A p-value of less than 0.05 was considered statistically significant. Result The GB specimens immersed in coffee showed the highest color changes as compared to other groups (4.47 ± 0.04) and the NGB specimens stored in saliva showed the lowest ΔE values (0.83 ± 0.03). Energy drinks and soft drinks showed similar ΔE values at the end of the 28-day study period in both the NGB and GB groups. All the specimens, irrespective of the beverages, in both groups showed increased ΔE values at different immersion periods except for NGB specimens immersed in saliva, which showed decreased ΔE values from T2 to T3. Conclusion GB specimens showed increased ΔEs compared to NGB Zirconia ceramics. Among the beverages, the coffee immersion of GB specimens showed marked color changes. The specimens immersed in the energy and acidic drinks from both groups showed perceivable color changes at the end of the 28-day study period.

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Objectives To more efficiently determine the subcritical crack growth (SCG) parameters of dental ceramics, the effects of stressing rate and choice of statistical regression model on estimates of SCG parameters were assessed. Methods Two dental ceramic materials, a veneering material having a single critical flaw population (S) and a framework material having partially concurrent flaw populations (PC), were analyzed using constant stress-rate testing, or “dynamic fatigue”, with a variety of testing protocols. For each material, 150 rectangular beam specimens were prepared and tested in four-point flexure according to ISO6872 and ASTM1368. A full-factorial study was conducted on the following factors: material, stress rate assumed vs. calculated, number of stress rates, and statistical regression method. Results The proportion of specimens for which the statistical models over-estimated reliability was not significantly different based on regression method for Material S (P = 0.96, power = 94%) and was significantly different based on regression method for Material PC (P < 0.001). The standard method resulted in SCG parameters, n and ln B, of 35.9 and -11.1 MPa2s for Material S and 12.4 and 9.61 MPa2s for Material PC. Significance The method of calculation that uses only the median strength value at each stress rate provided the most robust SCG parameter estimates. Using only two stress rates resulted in fatigue parameters comparable to those estimated using four stress rates having the same range. The stress rate of each specimen can be assumed to be the target stress rate with negligible difference in SCG parameter estimates.

The study was aimed to investigate a color indicator containing dual curing resin composite luting cement and to plot the color change to the time of solidification of the cement. In addition some physical properties were studied. Specimens were made of a dual-cure resin cement (Maxcem Elite™ Chroma, Kerr, Orange, CA, USA) and polymerized by autopolymerization only, or with light initiated polymerization. A spectrophotometer was used to quantify the color change of the cement as plotted with the curing time. The efficacy of the curing process was studied by measuring water sorption and the ultimate flexural properties of the cement. The results showed that the flexural strength of cement after autopolymerization was 27.3 MPa and after light initiated polymerization 48.1 MPa. Young’s modulus of bending was 2089.3 MPa and 3781.5 MPa respectively for the same cement samples. Water sorption after two weeks for the autopolymerization cement samples was −1.12 wt% and for the light initiated polymerization samples 0.56 wt%. Non-parametric Spearman’s correlation was measured for autopolymerized cement samples between variables for color and solidification load (N), which showed a strong correlation between curing process and color change (p < 0.05). There was a correlation between the color change and degree of monomer conversion of the dual curing resin composite luting cement which contained a color indicator system for polymerization reaction. The study also suggested that autopolymerization only resulted in suboptimal polymerization of the cement. By additional light curing considerably higher flexural properties were obtained.

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