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

ObjectivesThe 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.MethodsIdentical 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 mm2 and a framework connector size of 4.7 mm2 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.ResultsQuasi-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.SignificanceConsidering 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 mm2.