Influence Of Surface And Heat Treatments On Properties Of Zirconia

Method: Sixty sintered zirconia bar specimens were divided into three groups (n=20): control, air abrasion and grinding. The roughness of the specimens was evaluated using a profilometer and microscope analysis was performed. Then, each group was divided into 2 groups and submitted to multiple firings (2 or 10 times). After firing cycle, monoclinic content of zirconia was analyzed by X-ray diffraction (XRD) analyses. Flexural strength measurements of the bars were performed by using a 3-point flexural strength test. The data for the surface roughness Ra (µm) were compared by one-way ANOVA and Duncan’s tests. The results of relative amount of the monoclinic phase and biaxial flexural strength, were statistically analyzed by two-way ANOVA and Tukey’s HSD tests (p=0.05).

Result: Surface-treated specimens were rougher than the control group (p<0.001) and they had higher monoclinic content than control specimens (p<0.05). However, neither surface treatments nor firing cycles significantly affected the flexural strength of zirconia.

Conclusion: Although multiple firings did not affect the flexural strength of zirconia, some monoclinic remained on the surface after firing procedure and rougher surfaces had higher monoclinic content than control specimens. Therefore, clinician should be careful when working with zirconia. 

Table 1. Results of the statistical analysis of surface roughness values (Ra, micrometre)

Table 2. Mean and standard deviations of monoclinic content and flexural strength for zirconia after surface treatments and repeated firings.