Effect of metal framework design on the fracture resistance of implant-supported metal-ceramic crowns fabricated by selective laser melting.

PURPOSE: To evaluate the fracture resistance of implant-supported metal-ceramic crowns fabricated using selective laser melting (SLM), according to the metal support height around the screw access hole (SAH) and the substructure design. MATERIALS AND METHODS: Metal-ceramic crowns and rectangular bilayer specimens were fabricated using SLM in two independent experimental series. In the SAH design series, the substructure design was kept constant while the metal support height around the SAH was varied (none, half, and complete metal support; n = 12 per group). In the substructure design series, the SAH configuration was held constant (complete metal support), and the metal substructure design was varied (uniform cut-back, lingual support, and circumferential ring support; n = 12 per group). Crown specimens underwent thermomechanical aging (50 N, 100,000 cycles, 2 Hz, 5°C-55°C), followed by fracture resistance testing, Weibull analysis, failure mode classification, and fractographic analysis. Rectangular bilayer specimens representing each framework design were used for edge-chipping evaluation. Statistical analyses used one-way ANOVA and Tukey HSD tests (α = 0.05). RESULTS: The complete metal support SAH design showed significantly greater fracture resistance than the other SAH configurations (p < 0.05). However, in the corresponding rectangular bilayer specimens, this design showed the lowest edge-chipping resistance among the SAH configurations. Fractographic analysis showed that fractures originated at the occlusal loading site and propagated toward the crown margin. Among substructure designs, the circumferential ring design exhibited significantly greater fracture resistance and superior edge-chipping resistance compared with other designs (p < 0.05). CONCLUSIONS: Complete metal support around the SAH improved fracture resistance. Loading close to the SAH may increase susceptibility to veneering ceramic chipping under the tested conditions. A circumferential ring design providing uniform ceramic support enhanced overall mechanical performance.