Fracture resistance of zirkonia, inlay-retained fixed partial dentures

Objectives:Evaluation of the suitability of inlays as a bridgeretainer. Additionally, the fracture resistences of all-ceramic, as well as composite veneered inlay-retained FPD’s were investigated for different gaps. Material and methods: Inlay preparation were performed on a first premolar and a second molar. Preparation dimensions:2mm in width and 4mm in height. Replicas from the prepared abutment teeth were casted with a CoCr-alloy and fixed PMMA models.In each case 8 ZrO FPDs were manufactured using a CAD/CAM-system and veneered with a heat press ceramic (Ivoclar/ Vivadent/ Lichtenstein). Additionally 32 FPDs were manufactured using a prefabricated ZrO frame veneered with Artglass. In 16 FPDs the frame was localized in the upper occlusal part of the box inlay cavity and in 16 FPDs the frame was localized in the lower occlusal/approximal part of the box inlay cavity. All FPDs were conditioned with Rocatec (Espe) prior to veneering and cemented with Variolink II (Ivoclar). All FPDs underwent 10.000 thermal cycles (between 6,5° and 60°C) and were additionally loaded with 50 N for 600.000 cycles. Results: None of the FPDs debonded. Fractures could be observed predominantly in the veneering material. Using Artglass for veneering ZrO frames, the mean fracture loads ranged from 727,6 N / 626,06 for the molar FPDs to 451,01N / 597,98 N for the premolar + molar FPDs. Neither the localization nor the span length had a significant influence of the fracture resistance (p=0,083). FPDs veneered with a heat press ceramic showed a significant greater fracture resistance (p<0,001) than the frames veneered with Artglass. Conclusion: The results of this in-vitro study indicate that inlay retained ZrO fixed partial dentures veneered with a heat pressed ceramic seems to withstand the clinical mastication loads and offer sufficient stability for clinical use. The fracture resistance of ZrO fixed partial dentures veneered with Artglass need further investigations.