The purpose of this study was to investigate the effect of Er,Cr:YSGG, diode laser and a combination of diluted hydrofluoric acid and diode laser on the flexural strength, surface topography and crystalline phase of 3Y-TZP.
Partially stabilized zirconia powder was compressed in a 25mm diameter silicone mold at 300 MPa using a cold isostatic press for 10 minutes. The cylindrical blanks were sintered at 1500°C for 2 hours at a heating rate of 5°C/min and furnace-cooled. A total of 120 samples (1.8 mm thick) were randomly assigned into four different groups (n=30 per group). Extreme clinically relevant conditions were applied with Er,Cr:YGSS, and diode laser to the samples for a total of 2 minutes. A third group had a surface graphite coating applied and a solution of diluted hydrofluoric acid prior to diode laser treatment. The root mean squared surface roughness (Rrms) was measured on atomic force micrographs before and after the various laser treatments. Scanning Electron Microscopy (SEM) was done in order to confirm change in roughness for the etched and diode laser group. The biaxial flexural strength was tested using a ball-on-ring-of-balls fixture on a Universal Testing Machine. Crystalline phases were analyzed by x-ray diffraction (XRD). Statistically significant differences between groups were assessed by ANOVA and Tukey’s test (p≤.05). The biaxial flexural strength data was analyzed using Weibull statistics.
Results showed no significant difference in flexural strength and surface roughness between laser treatment groups and the control. The experimental group showed a significant difference in flexural strength and surface roughness, this indicates that the combination of graphite, acidic solution and diode laser has detrimental effects on physical and mechanical properties of 3Y-TZP. No crystalline phase transformation was detected for any of the groups. In conclusion under extreme clinically applicable conditions, the use of Er,Cr:YSGG and Diode Lasers is safe to use intraorally for routine dental procedures in the presence of zirconia. Diode/HF treatment would be precluded for any clinical application due to low Weibull modulus and possibility of high flaw population.