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-axischewing simulator

Statement of problem. In a clinical study, all-ceramic resin-bonded fixed p artial dentures showed a high rate of fractures within the first years of s ervice but remained in function as cantilevered restorations. No data are a vailable oil 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 alu minum-oxide ceramic In-Ceram, glass-infiltrated, and circularly veneered wi th feldspathic porcelain to replace a maxillary incisor on a test cast. The airborne particle-abraded restorations were bonded to acid-etched human ab utments using composite. Twenty-four restorations used a conventional 2-ret ainer design and another 24 restorations used a cantilevered single-retaine r design. Subgroups of 8 specimens were subjected to a quasi-static load in the direction of the longs asis of the abutments (0 degrees) or in an angl e of 45 degrees. Additional al subgroups were subjected to dynamic loading under 45 degrees with either 50 or 25 N in a dual-axis chewing simulator un til fracture. Results. Mean fracture strengths, under 45-degree quasi-static loading, wer e between 134 and 174 N and. under 0-degree loadings about 233 N. Samples s ubjected tu dynamic loading fractured after 25 to over 200,000 loading cycl es. Conclusion. Direction of loading exhibited a significant influence on the f racture strength, regardless of the retainer design. The applied dynamic lo ading force, regardless of the retainer design, had a significant influence on the loading cycles until fracture.