Effect of surface treatment conditions of zirconia on the shear bond strength of orthodontic metal bracket

Abstract

The purpose of this study was to examine the effects of various surface treatments of zirconia on the shear bond strength of orthodontic metal brackets after thermal cycling process. Zirconia specimens were fabricated as a cuboids (8 × 8 × 9 mm³) and divided into 8 groups depending on the surface treatments and thermal cycling process after bonding of metal brackets: 1) Polishing (P group), 2) 110 ㎛ A1₂O₃ blasting (B group), 3) 110 ㎛ A1₂O₃ blasting + Silane primer (BS group), 4) 110 ㎛ A1₂O₃ blasting + MDP/Silane primer (BSM group), 5-8) Thermal cycling process (5-55℃, 5000 cycles) after the surface treatments (PT, BT, BST, and BSMT groups). Specimens were measured the changes in surface roughness after surface treatments. Specimens were bonded to metal brackets using resin cement, and shear bond strength was measured by a universal testing machine. After mechanical test, the zirconia and metal bracket surfaces were observed by SEM and optical microscopy. After thermal cycling, surface roughness of the B, BS, BSM groups were significantly higher than P group (p0.05). The averages of shear bond strength in groups were recorded as following order: P B BS BSM. After the thermal cycling process, all groups were significantly decreased in shear bond strength (p0.05). From observations of zirconia and metal bracket surfaces, failure modes of P, PT, B, BT, and BST groups showed adhesive failures, BS group showed a mixed failure (adhesive failure + cohesive failure), meanwhile BSM and BSMT groups showed cohesive failures. All of the results taken together suggest that the 110 ㎛ A1₂O₃ blasting + MDP/Silane primer treatment was suitable for use in clinics due to its high bonding strength even after the thermal cycling treatment.