Fracture strength of prefabricated all-ceramic posterior inlay-retained fixed dental prostheses.

OBJECTIVES The purpose of this in vitro study was to compare the centric and eccentric quasi-static and fatigue fracture strength of industrially prefabricated resin-bonded three-unit inlay-retained fixed dental prostheses (IPIRFDPs). The IPIRFDPs consisted of industrial manufactured yttria-stabilized tetragonal zirconia (Y-TZP) frameworks with an industrially added microhybrid composite veneering. METHODS Identical IPIRFDP-models consisted of a second premolar, a missing first molar and a second molar (CoCrMo alloy) integrated in a low melting alloy base. Roots were covered with a soft silicone layer to simulate an artificial parodontium. Premolars had an occlusal-distal inlay-preparation and molars a mesial-occlusal inlay-preparation. Forty-two IPIRFDPs with a connector size of 9 mm(2) and a framework connector size of 4.7 mm(2) were cemented adhesively to the IPIRFDP-models. Quasi-static fracture strength was tested with centric (n=12) and eccentric (n=6) loading in a universal testing machine at a cross-head speed of 1 mm/min. Fatigue fracture strength was tested at 1200 N with centric loading (n=12) and at 600/500 N with eccentric loading (n=6) at a frequency of 0.5 Hz. Statistical comparison of groups was performed with the Mann-Whitney U test. RESULTS Quasi-static fracture strength differed significantly between centric (1749 N) and eccentric loading (880 N, p<0.001). Mean loading cycles until fracture were 4432 for centric loading at 1200 N compared to only 3 and 410 loading cycles for eccentric loading at 600 and 500 N, respectively. SIGNIFICANCE Considering the maximum chewing forces in the molar region, it seems clinically possible to use prefabricated IPIRFDPs with Y-TZP as a core material with a framework connector size of 4.7 mm(2).