Shear bond strength of metallic orthodontic brackets to zirconium crowns treated by sandblasting compared to enamel using a universal adhesive: An in vitro study

Objectives > Orthodontic brackets are increasingly bonded to the surface of zirconium crowns due to the growing aesthetic demands in adults' restorations. Therefore, providing a reliable bond between these substrates is of great importance. This study aimed at investigating the shear bond strength (SBS) of orthodontic metal brackets bonded to zirconium treated by sandblasting. In addition, the value was compared with SBS between metal brackets and enamel. Materials and methods > Samples were divided into three groups including first premolar enamel specimens (n = 20), untreated zirconium blocks (n = 20) and sandblasted zirconium blocks (n = 20). Enamel specimens underwent etching and bonding procedures using 37% phosphoric acid and 3 MTM ScotchbondTM Universal adhesive. Zirconium blocks were randomly allocated to two groups. The first group was prepared by sandblasting with 50 mm aluminium oxide particles (Al2O3) under 4 bars pressure followed by bonding brackets with 3 MTM ScotchbondTM Universal adhesive. Metal brackets were also bonded to the untreated zirconium group using the same adhesive. All samples underwent thermocycling, and SBS was calculated using a universal testing machine with a crosshead speed of 1 mm/min. Data were analysed using One-way Anova and Tukey's tests. Results > The highest SBS was recorded in sandblasted zirconium group (26.17 +/- 8.22 MPa) followed by enamel group (23.667 +/- 7.00 MPa) and untreated zirconium group (11.49 +/- 7.00 MPa). There was a significant difference between the SBS of untreated zirconium and that of two other groups. Conclusion > Perfect SBS was achieved by sandblasting pre-treatment, comparable to that of enamel. Therefore, sandblasting of zirconium crowns is recommended prior to bonding orthodon-tic brackets.