An in vitro study of orthodontic brackets bonded to transition dental zirconia: Shear bond strength, adhesive remnant index, and surface irregularities.

Purpose: Orthodontic treatment often involves bonding brackets to teeth, and the protocols for natural enamel differ from those for prosthodontically restored teeth. With the rising number of adult orthodontic patients, many present with zirconia crowns. This study aimed to evaluate the shear bond strength (SBS) of ceramic orthodontic brackets bonded to transition dental zirconia, which combines 3Y-TZP and 5Y-TZP powders.

Methods: Ninety zirconia substrates were divided into three groups (n=30) based on transition zirconia brands (3M ESPE Lava™ Plus, Cercon® ht ML, and Katana™ Zirconia UTML) and bonded with ceramic brackets (CHIC Ceramic Roth Maxillary and Symetri Clear) using 3M™ Transbond™ XT. A control group used traditional zirconia and metal brackets. Surface treatments included 50-micron aluminium oxide abrasion and Z-Prime™ Plus application. SBS was tested post-thermocycling. Adhesive Resin Index (ARI) was scored and surface roughness was evaluated pre- and post-bonding.

Results: Group 1 (3M ESPE Lava™ Plus with CHIC Ceramic Roth Maxillary brackets) had a significantly lower SBS (mean 13.27MPa) compared to the other groups, which all had SBS values above 18.80MPa (P≤.023). Group 2 (3M ESPE Lava™ Plus with Symetri™ Clear) demonstrated a significantly higher mean ARI compared to the control group (Cercon® XT with Victory Series™ Roth), (P=.027). Additionally, significant changes in surface roughness were observed in Groups B (Cercon® ht ML) (P=.008) and C (Katana™ Zirconia UTML) (P=.016).

Conclusion: This study determined that the shear bond strength of various transitional zirconia substrates with ceramic brackets exceeded the clinically acceptable SBS levels. The combination of 3M ESPE Lava™ Plus and Symetri™ Clear exhibited significant variation in ARI. Additionally, significant surface irregularities were observed in 3M ESPE Lava™ Plus and Cercon® ht ML following air abrasion, compared to other transitional zirconia brands.