Evaluation of Two New Veneering Techniques for Zirconia-based FDPs

Objective: To evaluate the risk of chipping and the fracture strength of two new techniques to veneer zirconia-based FDPs by CAD/CAM technology. Materials and Methods: Forty-eight standardized three-unit zirconia frames (e.max ZirCAD) for FDPs were milled with the Sirona InLab system and veneered with a lithium-disilicate glass ceramic (e.max CAD) which was also milled by CAD/CAM technology (CEREC 3). The anatomical dimensions were equal for all FDPs. Frame and veneer were joined by two different techniques: Group I (n=12): glass soldering material during the cristallization process of e.max CAD; Group II (n=12): luting technique with a self-adhesive composite (Panavia 21; group II) after acid-etching and silanization of the veneer material. Half of the FDPs were luted adhesively (Panavia 21) on PMMA abutments und submitted to a rigid dynamic eccentric loading protocol in a chewing simulator (Willytec) with simultaneous thermocycling (5°C/55°C). The FDPs were loaded on the pontic with a steel stylus (Ø 2.4mm) that moved 2 mm from the central fossa to the buccal cusp. The load was increased after each 100,000 cycles (3kg, 5kg, 9kg). The other half of the FDPs were cemented on standardized steel abutments with a glass ionomer cement and submitted to a fracture load test in a universal testing machine until failure. Results: During dynamic loading chipping has occurred in one FDP of Group I and in two FDPs of Group II. The mean fracture load of the not pre-loaded FDPs was 2179(±648) N for Group I and 1492(±257) N for Group II. One-way ANOVA revealed a statistically significant difference between both groups (p=0.003). Conclusion: The risk of chipping can be regarded as minimal and the mean fracture load was well above 1000 N. Therefore, the new techniques can be evaluated in clinical trials with an adequate safety level.