Fracture strength of all-ceramic posterior inlay-retained fixed partial dentures

Objectives The purpose of this in vitro study was to compare the quasi-static (QSFS) and fatigue fracture strength of all-ceramic resin-bonded three unit inlay-retained fixed partial dentures (IRFPDs) made from a heat-pressed lithium-disilicate based glass-ceramic (LDGC) and a CAD/CAM-manufactured yttrium-oxide partially stabilized zirconia framework (YPSZ). Methods Identical IRFPD-models of the maxilla were used. They consisted of a second premolar, a missing first molar and a second molar (Co–Cr–Mo 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. Thirty-two IRFPDs were made from each ceramic using two different connector dimensions: 3 mm × 3 mm (LDGC_9, YPSZ_9); 4 mm × 4 mm (LDGC_16, YPSZ_16). All IRFPDs were cemented adhesively to the IRFPD-models, using composite resin cement. QSFS was tested in a universal-testing-machine (UTM) for six specimens. The other specimens were fatigued either with cyclic loading at 250 N (n = 4) in a chewing simulator or at 600 N (n = 6) using the UTM, and group YPSZ additionally at 1500 N. Results The medians of QSFS (N) were 960 (LDGC_9), 1316 (LDGC_16), 3180 (YPSZ_9) and 3120 (YPSZ_16). For both QSFS and cyclic loading significant differences were found between LDGC_9 and LDGC_16 (p ≤ 0.03) but not between YPSZ_9 and YPSZ_16 (p > 0.05). Differences between LDGC and YPSZ were significant for both connector sizes (p ≤ 0.001). Significance Considering the maximum chewing forces in the molar region it seems clinically possible, to use YPSZ as a core material for IRFPDs with a connector size between 9 and 16 mm2.