Improving reline bonding in 3D-printed dentures: an experimental in vitro study

Objective: This in-vitro study aimed to evaluate the tensile bond strength of a 3D-printed denture base resin relined with conventional polymethylmethacrylate (PMMA) reline resin, following various surface treatment protocols including mechanical abrasion, monomer application, and selected commercially available adhesive systems. Methods: Ninety resin specimens were 3D printed using DentaBase resin (Asiga) and divided into nine groups: GrN: control (intact) and relined groups (Gr1-Gr8) subjected to different surface treatments including, Gr1: no surface treatment, Gr2: monomer application, Gr3: sandblasting, Gr4: sandblasting + monomer application, Gr5: sandblasting + Qu-resin, Gr6: sandblasting + Visiolink, Gr7: Sandblasting + Monobond Plus + Heliobond, Gr8: sandblasting + Lukafix bonder. Specimens underwent tensile testing at 1 mm/min and ultimate tensile strength (UTS) was calculated. Fracture patterns were examined microscopically. Data were analyzed using Kruskal-Wallis ANOVA and Dunn's post hoc test (alpha = 0.05). Results: The highest median of the ultimate tensile strength (UTS) was observed in GrN (control, 25.9 MPa), followed by Gr4 (19.7 MPa), Gr5 (18.4 MPa), and Gr6 (17.9 MPa). Gr1 (no treatment) had the lowest median UTS (11.5 MPa). Statistically significant differences were observed between GrN and Gr1 (p < 0.001), GrN and Gr2 (p = 0.002), and GrN and Gr8 (p = 0.004). No significant differences were observed among Gr3, Gr4, Gr7, and Gr6 (p > 0.05). All relined groups exhibited adhesive failures at the denture base-reline interface. Conclusion: Surface treatments improved tensile bond strength in relined 3D-printed specimens, but none restored it to control levels. Sandblasting with monomer application or with selected bonding agents produced higher bond strengths than no treatment or monomer alone.