A comparison of bond strength and adhesive remnant index of 3D-printed and metal orthodontic brackets attached using different adhesives

Introduction: The aim of this in vitro study was to evaluate the shear bond strength (SBS) and adhesive remnant index (ARI) scores of two different adhesive applications of aesthetic brackets produced from permanent crown material using 3D-printing technology. Methods: Sixty maxillary premolar teeth extracted for orthodontic reasons were divided into two main groups according to the type of bracket (metal brackets n=30, 3D-printed brackets n=30) and further divided into two subgroups according to the type of adhesive (flowable composite, Tokuyama SuperLow; non-flowable composite; 3M Transbond XT). SBS and ARI score evaluations were conducted in the experimental and control subgroups (n=15). Statistical analysis was performed by a one-way analysis of variance, a post- hoc test, and Fisher's exact test. Statistical significance was accepted as P < 0.05. Results: The bond strength of the specimens was significantly affected by the type of composite and bracket type (P < 0.001). However, the SBS values were within or above the desired range for orthodontic treatment in all groups. The highest SBS value was obtained in the Metal Bracket-Transbond XT group (15.03 +/- 6.66), while the lowest SBS value was observed in the 3D-Printed Bracket-Transbond XT group (7.91 +/- 3.07). It was noted that of all materials evaluated, the most common non-enamel-damaging adhesive-cohesive fractures were in 3D-Printed Bracket Tokuyama SuperLow group (n=13). Conclusions: It is recommended that 3D-printed orthodontic brackets have sufficient and acceptable SBS levels for clinical applications and bonding using non- flowable adhesives to produce high SBS values and using flowable adhesives generating high ARI scores.