Influence of design and mode of loading on the fracture strength of all-ceramic resin-bonded fixed partial dentures: an in vitro study in a dual-axis chewing simulator.
STATEMENT OF PROBLEM: In a clinical study, all-ceramic resin-bonded fixed partial dentures showed a high rate of fractures within the first years of service but remained in function as cantilevered restorations. No data are available on the fracture strength of such cantilevered restorations. PURPOSE: This in vitro study evaluated the influence of design and mode of loading on the fracture strength of all-ceramic resin-bonded fixed partial dentures. MATERIAL AND METHODS: Forty-eight frameworks were copy milled using the aluminum-oxide ceramic In-Ceram, glass-infiltrated, and circularly veneered with feldspathic porcelain to replace a maxillary incisor on a test cast. The airborne particle-abraded restorations were bonded to acid-etched human abutments using composite. Twenty-four restorations used a conventional 2-retainer design and another 24 restorations used a cantilevered single-retainer design. Subgroups of 8 specimens were subjected to a quasi-static load in the direction of the long axis of the abutments (0 degrees) or in an angle of 45 degrees. Additional subgroups were subjected to dynamic loading under 45 degrees with either 50 or 25 N in a dual-axis chewing simulator until fracture. RESULTS: Mean fracture strengths, under 45-degree quasi-static loading, were between 134 and 174 N and under 0-degree loading about 233 N. Samples subjected to dynamic loading fractured after 25 to over 200,000 loading cycles. CONCLUSION: Direction of loading exhibited a significant influence on the fracture strength, regardless of the retainer design. The applied dynamic loading force, regardless of the retainer design, had a significant influence on the loading cycles until fracture.