Mechanical behavior of complete arch implant-supported prostheses with distal cantilevers fabricated from different digital material combinations

STATEMENT OF PROBLEM: Complete arch implant-supported prostheses (CAISPs) often require distal cantilevers; however, evidence on the influence of framework and veneering material combinations remains limited. PURPOSE: The purpose of this in vitro study was to compare the mechanical behavior of 6 digitally fabricated material configurations in CAISPs with 7.5- and 15-mm cantilevers. MATERIAL AND METHODS: Thirty screw-retained CAISPs (n=5 per group) were fabricated: cobalt chromium with feldspathic ceramic (CRCO-C), titanium alloy with high-impact polymer composite (TI-HIPC), monolithic zirconia (ZTN), veneered zirconia with porcelain (ZF-C), ceramic-filled polyetheretherketone (BioHPP) with composite resin (B-RC), and BioHPP with high-impact polymer composite veneer (B-HIPC). The specimens were thermocycled (10 000 cycles, 5 to 55 °C) and cyclic loaded (110 N, 300 000 cycles). Flexural strength testing was performed at both cantilever lengths to record maximum load (FMax), veneer fracture load (FChipping), and vertical deflection. Fracture modes were examined under optical microscopy. The data were analyzed using 2-way ANOVA, the Kruskal-Wallis test, and post hoc tests (α=.05). RESULTS: At a 7.5-mm cantilever length, all groups except B-HIPC exceeded 900 N. CRCO-C (2098 ±43.8 N) and TI-HIPC (2060 ±115.5 N) showed the highest strength, followed by ZTN (1190 ±140.9 N), B-RC (1136 ±97.9 N), and ZF-C (910.6 ±272.5 N) (P<.001). At 15 mm, strength decreased by approximately 50% for B-RC and ZF-C, 35% for the TI-HIPC group and 24% for B-HIPC, while CRCO-C remained stable. Chipping resistance was highest for CRCO-C, followed by TI-HIPC and B-HIPC; milled composite resins showed greater resistance than conventional composite resins (P=.02). Deflection at Fmax was minimal (<0.3 mm) for CRCO-C and zirconia but higher for TI-HIPC and B-HIPC, particularly at 15 mm. CONCLUSIONS: At a 7.5-mm cantilever length, most tested material-design configurations achieved clinically acceptable fracture resistance. At 15 mm, values above the clinical threshold were observed only in the CRCO-C, TI-HIPC, and ZTN configurations.