Fracture resistance of 3D printed resin-based permanent ceramic fixed dental prostheses after thermocycling

Objectives: Three-dimensionally (3D) printed resin-based permanent ceramics produced using additive manufacturing have recently gained considerable interest as potential restorative materials for fixed prostheses. However, limited evidence is available regarding their long-term mechanical performance following thermo cycling. The aim of this study was to evaluate the effect of different thermocycling durations on the fracture resistance of 3D-printed bar-type fixed dental prosthesis (FDP) specimens. Methods: Forty-eight bar-shaped, three-unit FDP specimens (5 × 5 × 30 mm), each containing a 4 × 4 mm² U- shaped connector, were fabricated using 3D-printed resin-based permanent ceramic. The specimens were divided into four groups according to ageing duration: unaged, 1, 3, and 12 months of thermocycling. Fracture load (N) data were analysed using non-parametric statistical methods. Group comparisons were performed using the Kruskal–Wallis test with epsilon-squared ( ε ²) effect size estimation, and the Jonckheere–Terpstra test was applied to evaluate the ordered trend across thermocycling durations. Results: Group comparisons showed no statistically significant differences in fracture load among ageing dura tions (Kruskal–Wallis, p = 0.168), with a small effect size ( ε ² = 0.047). However, the Jonckheere–Terpstra test indicated a significant decreasing trend in fracture load with an increase in thermocycling duration (Z = 2.135, p = 0.033). Conclusions: Although no statistically significant group differences were observed, effect size analysis and regression trends indicated that long-term thermocycling may gradually reduce the fracture resistance of 3D- printed resin-based permanent ceramic FDPs. Clinical significance: 3D-printed resin-based permanent ceramic FDPs can provide satisfactory initial fracture resistance; however, the mechanical strength reduction tendency following long-term ageing should be considered for clinical applications over extended durations.