3D-printed one-piece versus two-piece orthodontic clear aligner attachments bonded with provisional crowns: A proof of concept

Objectives: This study aimed to introduce a novel technique for fabricating provisional crowns integrated as a single unit with aligner attachments. Methods: A total of 60 crowns with attachments were prepared: 20 conventional (Protemp) and 40 3D-printed (20 bonded with attachments; 20 integrated with composite attachments as a single unit) using NextDent resin. Two central incisors were scanned (once without attachments and once with attachments) to create STL files for specimen printing. Half of the specimens (30, n = 10 per group) underwent thermal cycling (5000 cycles). Shear bond strengths (MPa) were evaluated using a universal testing machine. The debonded areas and attachment failures were analyzed to determine the fracture type. Data analyses were performed using ANOVA and post hoc Tukey tests (α = 0.05). Results: The 3D-printed specimens showed higher strength values than the bonded attachments per group (P < 0.001). The 3D-printed crowns with attachments demonstrated the highest strength (12.39 ± 1.92 MPa). Thermal cycling significantly decreased the bond strength of the attachments (P < 0.001), except in the 3D-printed crowns with composite attachments as a single unit, which showed no significant change after thermal cycling (P = 0.643). In the bonded attachment groups, the adhesive type was the predominant failure mode, while in the 3D-printed groups, attachment fractures were the primary cause of failure. Conclusion: The 3D-printed provisional crowns with attachments have high strength and is clinically appropriate for orthodontic treatment when temporization of teeth is indicated. Clinical Significance: The developed technique for fabricating 3D-printed provisional restorations with orthodontics attachments as a single unit is a promising approach. The technique may be incorporated into the digital orthodontic treatment workflow when temporization is indicated.