Fracture strength of repaired 3D-printed interim fixed dental prostheses: In vitro comparison of repair material type and surface treatment

Purpose: To date, no evidence exists regarding the optimal technique/material to repair three-dimensional (3D) printed interim fixed dental prostheses (IFDPs). This study aimed to investigate different repair techniques/materials and compare their impact on the fracture strength of repaired 3D-printed IFDPs. Materials and Methods: A total of 208 3-unit IFDP specimens (n = 8) were printed using two materials (NextDent or ASIGA). One group had no surface treatment (control), while the other two groups were treated with alumina blasting and etch-primer (EP) and then repaired using flowable composite resin or Multilink in a customized putty index. Repaired specimens were thermocycled (5000 cycles) and then loaded onto a universal testing machine until fracture, and the fracture strength was recorded in newtons (N). ANOVA with Tukey's post hoc test and t-test were used for data analysis (α = 0.05). Results: All repaired 3D-printed IFDPs exhibited lower fracture loads compared to intact specimens (p < 0.001). Repairs made with composite resin resulted in a superior fracture load than Multilink (p < 0.001). Alumina-blasting and EP treatment surface treatments significantly increased the fracture strength of repaired NextDent IFDPs compared with untreated groups (p < 0.001). EP surface treatment did not influence the repair of ASIGA specimens (p > 0.05). Conclusion: The type of repair material significantly influences the repair strength. Repair using a composite showed the highest strength. Surface treatment (mechanical or chemical) increased repair strength for NextDent specimens. ASIGA specimens were not affected by chemical surface treatment, while mechanical treatment positively influenced repair strength.