Effects of different surface treatments and artificial aging on the repair bond strength of additively manufactured resin materials for permanent restorations

Aim: The aim of this study was to evaluate the effect of six different surface treatments on the shear bond strength (SBS) of two 3D-printed resins [NextDent C&B MFH and Saremco Print Crowntec] repaired with a nanofilled composite [Filtek Ultimate Universal Restorative] after thermal cycling. Material and Method: A total of 240 specimens fabricated from 3D printing resins underwent thermal cycling and were subjected to six surface treatments (Control, Silane, Sandblasting, Sandblasting+Silane, Hydrofluoric acid, and Hydrofluoric acid+Silane). The specimens were repaired with nanofilled composite and divided into 24 subgroups (n=10); half received additional thermal cycling. SBS tests were performed for all specimens, and failure types were examined under a stereomicroscope. Statistical analyses included the Shapiro–Wilk, Fisher's Exact, Mann–Whitney U, Bonferroni-adjusted Z tests, and three-way Robust ANOVA. Surface roughness values were analyzed using Generalized Linear Models with Bonferroni correction. Results: A statistically significant interaction among surface treatment, resin type, and thermal cycling on SBS was found (p<0.05). The highest SBS was observed in the sandblasting group of C&B resin without additional thermal cycling, while the lowest values were in control groups. Surface roughness in the Sandblasting group (0.96±0.51) was significantly higher than in the Control (0.37±0.12) and Hydrofluoric acid (0.33±0.06) groups (p<0.05). Most failures were cohesive. SEM and roughness analyses revealed distinct surface morphology differences among groups. Conclusions: Surface treatments significantly increased SBS. Sandblasting and hydrofluoric acid groups showed higher SBS than the Silane group. Both 3D-printed resins demonstrated clinically acceptable SBS with no significant difference between them. Appropriate surface treatments can enhance the repair performance of 3D-printed resins.