Benign Design of Metal Free Resin Bonded Fixed Partial Dentures

Introduction: Replacing missing teeth by FPDs is a complex rehabilitation procedure, which needs consideration of abutment tooth vitality and structural integrity. FPD designs that preserve tooth structure vitality and retain restoration durability under different occlusal loads are considered to be benign. The aim of this study is to evaluate the fracture strength and mode of fracture of three conservative FPD designs compared to a traditional design. Materials and Methods: Typodont teeth were used to prepare four designs of 3-unit FPDs, consisting of a 1st premolar abutment, missing 2nd premolar and 1st molar abutment. The restoration designs were (I) traditional, (II) partial coverage of the premolar molar abutment, (III) partial occlusal coverage of the molar and (IV) inlay retained. Forty bridge units were fabricated using IPS e.max CAD blocks (lithium-disilicate glass ceramic) and Peek Optima blocks (Poly ether ether ketone) with the Cerec CAD/CAM system. These were luted to models made of polyurethane (AlphaDie MF ) with resin cement (Multilink Automix, Ivoclar-Vivadent). The cemented FPDs were loaded until failure. ANOVA two way and Tukey's test were used for data analysis. Results:The average fracture strength recorded for Peek Optima groups were:1378±210 N, 1366±322, 1178±316 and 1222±236 for design I, II, III, and IV respectively, while for IPS e.max CAD these were: 794± 214 N, 874±150, 815 ±166 and 843±241. There is a significant influence of the material type on fracture strength. At the same time there was no significant influence of the FPD designs on the fracture strength using the same material in the construction of FPDs. Fracture occurred predominantly in the area of the premolar connector. Conclusion: The more conservative designs did not result in a reduction of the structural integrity of the FPDs.