Objectives: The aim of this study was, to compare the static and fatigue fracture strength of 3-unit inlay-retained posterior FPDs, using CAD/CAM-manufactured zirconia frameworks (Cercon, Degudent, Hanau, FRG) and an lithium-disilicate based glass-ceramic (VP2563, Ivoclar, Schaan, FL). Methods: Posterior teeth (25, 27) were prepared with mesial-occlusal and occlusal-distal cavities with proximal connectors of 9 mm˛ and 16 mm˛ respectively and were cast in a cobalt-chromium alloy. Sixty-four casts with resilient supported metal-dies were fabricated. Sixteen FPDs each were made with connector areas of 9 and 16 mm˛ for both ceramic systems. All FPDs were cemented with a composite resin (Multilink, Ivoclar). The static fracture resistance was tested in a universal testing machine (Zwick, FRG) at the center of the pontic for six FPDs of each group. In the fatigue tests four FPDs of each group were treated with cyclic loading at 250 N using a chewing simulator (Willitec, Munich, FRG) and six FPDs each at 600 N using the universal testing machine. Results: For the static fracture strength means (Cercon at 9 mm˛ 3244 ± 565 N, at 16 mm˛ 3065 ± 260 N and VP2563 at 9 mm˛ 947 ± 196 N, at 16 mm˛ 1385 ± 216 N) were significantly different for both systems (ANOVA, p<0.05). Also the numbers of load cycles for first fracture events at 600 N showed significant differences. At 250 N FPDs made of Cercon did not fracture over 1,200,000 load cycles. FPDs made of VP2563 with a connector area of 9 mm˛ fractured at a mean of 986,000 loading cycles and with an area of 16 mm˛ at a mean of 1,150,000 cycles. Conclusions: Considering the maximum chewing forces it seems possible, to use Cercon for three-unit posterior inlay-retained FPDs. However usingVP2563, the connector area should have at least 16 mm˛.

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