Objectives: The aim of this study was to compare the static and fatigue fracture strength of 3-unit inlay-retained posterior FPDs, using two different CAD/CAM-manufactured zirconia frameworks (In-Ceram YZ-Cubes, Vita, Bad Säckingen, FRG and Cercon, Degudent, Hanau, FRG).

Methods: Posterior teeth (FDI 25, 27) were prepared with mesial-occlusal and occlusal-distal cavities with proximal connectors of 9 mm² and 16 mm², respectively. The teeth were cast in a cobalt-chromium alloy. 48 casts with resilient supported metal-dies were fabricated. 16 FPDs were made with connector areas of 9 mm² of In-Ceram YZ. 16 FPDs each were made with connector areas of 9 and 16 mm² of Cercon. All FPDs were cemented with a composite resin (Multilink, Ivoclar, FL). The static fracture resistance was tested in a universal testing device (Zwick, FRG) at the center of the pontic for 6 FPDs of each group. In the fatigue tests 4 FPDs of each group were cyclic loaded with 250 N using a chewing simulator (Willitec, Munich, FRG) and 6 FPDs each were cyclic loaded with 1,500 N using the universal testing device.

Results: For the static fracture strength means (In-Ceram YZ: 3,016 ± 558 N, Cercon with 9 mm²: 3,244 ± 565 N, Cercon with 16 mm²: 3,065 ± 260 N) were not significantly different for both ceramic systems (ANOVA, p>0.05). The mean of the numbers of load cycles for first fracture events at 1,500 N (In-Ceram YZ: 17,800 loading cycles, Cercon with 9 mm²: 15,900 loading cycles, Cercon with 16 mm²: 19,800 loading cycles) did not show significant differences.

Conclusions: Considering the maximum chewing forces it seems possible, to use zirconia ceramic for three-unit posterior inlay-retained FPDs, independently of a connector size between 9 mm² and 16 mm².

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