Questions: The bond strength of orthodontic brackets can be influenced by numerous factors, including pre-treatment of the tooth surface, type of the bonding system, mastication forces during treatment, and the type, size, and design of the bracket (1).
The aim of the present study was to compare the shear bond strength (SBS) and the adhesive remnant index (ARI) at the enamel-bonding interface between brackets of different base sizes, including a new very small self-ligating-bracket (MiniQuick), not yet on the market, using two different methods of enamel surface pre-treatment.
Methods: Freshly extracted bovine permanent incisors (n=360) were used in this study, which were embedded in Technovit®4004 (Kulzer GmbH, Hanau, Germany) and divided into six groups (n=60) dependent on enamel surface pre-treatment (Airflow, Rocatec) and bracket type (Sprint II, Micro Sprint, MiniQuick; Forestadent Bernhardt Förster GmbH, Pforzheim Germany). Pre-treatment included Airflow technique (Clinpro™ Prophy Powder, 3M Espe, Neuss, Germany; core size 45μm) and Rocatec technique (Aluminium oxid powder, core size 50μm), respectively, thereafter all teeth were etched with 35% phosphoric acid, followed by water spray and compressed air. Transbond™ XT light cure primer and adhesive (3M™ Unitek, Landsberg am Lech, Germany) and Valo® Cordless curing light (Ultradent Products Inc., South Jordan, UT, USA), 5s each, were used for bonding. Thus, 720 brackets were fixed with two on each tooth surface, respectively. After de-bonding (universal testing machine TIRAtest-2720, Schalkau, Germany; pressure force of 1kN maximum, testing speed of 0.5mm/min according to DIN ISO 11405/2003), SBS and ARI was evaluated in all groups. Statistics were conducted using two-way ANOVA, significance level p≤ 0.05.
Results: All groups showed a high SBS with similarly comparable high mean values. A statistically significant difference could only be detected between Sprint II and MiniQuick brackets and between Airflow and Rocatec pre-treatment. ARI score 2 and 1 revealed a high percentage in all groups.
Conclusions: MiniQuick brackets showed not only similar but also statistically significant higher mean SBS values compared to the other two bracket types, which indicates, that despite their reduced size, they are suitable for clinical use. In this context, pre-treatment with Airflow showed a positive influence on the bonding process.
Acknowledgements: This research was supported by FORESTADENT® Bernhard Förster GmbH, Pforzheim, Germany, who provided the test brackets.
Keywords: Shear bond strength, Adhesive Remnant Index, surface pre-treatment, bracket base
