Comparison of shear bond strength of metallic orthodontic brackets bonded to zirconia models underwent different surface conditioning methods and different primer systems

Objectives: This study aimed to compare the shear bond strength (SBS) of metal brackets bonded to zirconia models with different surface treatment methods and two types of primers and to determine the adhesive remnant index (ARI). With the increase in demand for orthodontic treatment by adults and most adult patients having acrylic resin, amalgams, gold, composite resin, zirconia, or porcelain restorations, bonding of orthodontic braces to these surfaces is now a necessity. Brackets bonding to zirconia prostheses are a challenge in orthodontics because they need special surface conditioning. Material and Methods: In this in vitro study, 60 zirconia models were divided randomly into two groups of 30 models according to the primer material used (Assure ® Plus and Transbond ™ XT). The labial surface of each model was subjected to one of the following three surface preparation: No surface treatment (control group), sandblasting with 50 µm aluminum oxide (Al2O3) particles, and acid etching with 9.6% hydrofluoric acid (HF). Metal orthodontic brackets (Dentaurum) were bonded to zirconia models using Assure ® Plus or Transbond ™ XT adhesives. The SBS was measured using a universal testing machine at a crosshead speed of o.5 mm/min. The labial surfaces of models were inspected under a stereomicroscope, and the ARI scores were determined. Raw data were analyzed using Statistical Package for the Social Sciences program through analysis of variance and the Kruskal–Wallis test ( P ≤ 0.05). Results: The Al2O3 air abrasion with the Assure ® Plus group had the highest mean of SBS values, while HF groups with Transbond ™ XT adhesive or Assure ® Plus gave rise a significantly lower SBS values than that obtained for the Al2O3 group. A significant difference was noted among the groups in the ARI scores. In Al2O3 group bonded with Transbond ™ XT had scores 1 and 2, which was designated as a mix-type failure, indicating a favorable failure mode. Conclusion: This study showed that air abrasion of zirconia models had a significant effect on the SBS of metal brackets bonded to zirconia surface, and the Transbond ™ XT adhesive is a suitable primer material.