Effects of Surface Pretreatment and Repair Composite Type on Bond Strength of a 3D-Printed Permanent Resin

Objectives: To evaluate the effects of surface pretreatment and repair composite type on microtensile repair bond strength (μTBS) to an aged 3D-printed permanent crown resin, with explicit consideration of the printing/post-curing workflow used.Methods: Sixty resin blocks (6 × 6 × 6 mm) were printed from Saremco Crowntec using an Asiga Max printer at 50-μm layer thickness, cleaned with 96% alcohol, and post-cured with Signum HiLite Power for 2 × 180 s before thermocycling (5,000 cycles). Blocks were assigned to three pretreatments: diamond bur roughening plus phosphoric acid cleaning, 53-μm aluminum oxide airborne-particle abrasion, or 30-μm tribochemical silica coating. Each pretreatment was repaired with either a highly filled flowable composite or a conventional microhybrid composite using silane and a self-cured universal adhesive. After an additional 5,000 thermocycles, specimens were sectioned into approximately 1-mm² sticks and tested in tension at 1 mm/min. The printed block was the experimental unit.Results: Bur-treated groups showed the lowest μTBS values (19.88-25.26 MPa). Airborne-particle abrasion groups showed higher values (36.24-42.19 MPa), and surface pretreatment had a significant effect (p < .001). Within the same pretreatment, μTBS did not differ between the highly filled flowable and microhybrid repair composites.Conclusion: Airborne-particle abrasion with aluminum oxide or tribochemical silica coating improved repair bond strength of the tested 3D-printed permanent resin compared with bur roughening. Under the conditions of this study, the highly filled flowable composite performed similarly to the conventional microhybrid composite. These findings are specific to the tested resin-printer-cleaning-post-curing workflow and should not be generalized to other permanent printed resins or post-curing units without further validation.