Influence of Surface Treatments on Properties of Zirconia Core

Objectives: This study assessed the influence of sandblasting (AB) and/or heat treatment (HT) on the flexural strength of zirconia and bond strength of porcelain to zirconia. Methods: The beam zirconia specimens were divided into four groups with different surface treatments (grinding as controls, AB, HT at 1,000°C for 10 min, and HT after SB). Porcelain-veneered zirconia specimens were also prepared. All specimens were subjected to three-point bending tests. The flexural strength was calculated and the bond strength between zirconia and porcelain was tested according to ISO 9693. XRD was used to estimate the relative amount of monoclinic phase. Means and SDs (in parenthesis) of properties are listed in Table. Data were analyzed by one-way ANOVA and identical letters at each property were not significantly different by Tukey-Kramer test (p>0.05, n=7). Results: There were no significant differences in flexural strength of zirconia. The highest amount of the monoclinic phase was found after AB. No amounts of the monoclinic phase were obtained after both HT and HT after AB. Groups for HT and HT after AB showed significantly higher bond strength of porcelain to zirconia than the other two groups. SEM showed that all specimens entirely failed cohesion in porcelain. No elements of porcelain were detected in the zirconia side at the interface using EDX. Conclusion: The present study suggests that HT after SB, which is generally performed during a laboratory procedure, may be clinically desirable. Zirconia-core veneered, all-ceramic restorations rely on the mechanical interlocking on the zirconia surface.

Group	Flexural strength in MPa (SD)	Bond strength in MPa (SD)	Relative amounts of monoclinic phase in % (SD)
Control	1169. 6 (62.5)a	26.9 (2.1)a	2.7 (0.4)b
Sandblasting (AB)	1095.4 (132. 6)a	25.4 (2.3)a	7.8 (1.0)c
Heat treatment (HT)	1056.2 (70.6)a	32. 0 (2.5)b	0a
HT after SB	1106.8 (175.3)a	33. 8 (3.2)b	0a