Effect of different design preparations on the flexural and fracture strength of fiber-reinforced composite fixed partial dentures: an in vitro study.

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To determine and compare the flexural and fracture strength of three-unit fiber-reinforced composite (FRC) fixed partial dentures (FPDs) using three abutment design preparations. The flexural and fracture strength of three-unit FRC FPDs were evaluated using three design preparations of the abutments (conventional full crown [group A], box-shaped [group B], and tub-shaped [group C]). Thirty three-unit FRC FPDs were fabricated (10 specimens per group) for the replacement of missing mandibular first molars and were adhesively luted to extracted human teeth. The flexural and fracture strength were determined using a universal testing machine with a steel loading pin of 20 mm diameter with a 3-mm-diameter hardened circular tip. Each specimen was evaluated under SEM to determine mode of failure. Mean fracture strength for group A was 820.00 ± 56.51 N, group B was 536.94 ± 65.62 N, and group C was 501.24 ± 66.71 N. The highest mean flexural strength was found in group A (68.33 ± 4.71 MPa), followed by group B (44.74 ± 5.46 MPa) and lowest in group C (41.77 ± 5.56 MPa). The SEM evaluation showed partial or complete debonding of veneering composite from fiber framework, leaving intact fiber frameworks in all the specimens. Full-coverage design had significantly higher flexural and fracture strengths than box and tub-shaped designs. Since both values were noted to be in the order of masticatory stresses, the full coverage design is a good alternative for the replacement of missing molar teeth; however, the framework veneering composite interface was the weakest phase of FRC FPDs, thus indicating that further improvement in veneering composite or fiber framework is needed to improve the compatibility of veneering composite with that of fiber framework for long-term clinical implications.