The Effect of Preceramic Soldering on Fracture Resistance of 4-Unit Zirconia Fixed Dental Prostheses

Purpose Preceramic soldering of zirconia may deliver better fitting restorations. However, there is not sufficient evidence regarding the influence of preceramic soldering of zirconia restorations on mechanical strength. The aim of this study was to evaluate the effect of preceramic soldering on the fracture load of 4-unit zirconia fixed dental prostheses (FDPs). Materials and methods Eighty samples of 4-unit FDPs between maxillary right first premolar and maxillary right second molar were prepared and two restorative materials were used as a framework (Z) and monolithic restoration (M). The samples were divided into two subgroups as control (C) and study (S). The restorations of study groups (S) were divided into two pieces and soldered with a bonding material (DCM HotBond Zirkon). The groups were divided into two subgroups for thermal cycle (T) application. After soldering and thermal cycling application, 4-point bending test was applied to the samples at a cross-head speed of 1 mm/min in a universal testing machine and the fracture load was recorded. The data was analyzed statistically, and the level of significance was set at alpha = 0.001. Results Statistically significant differences were found among the groups, based on the results of maximum failure loads (p < 0.001). The highest mean failure load was observed in the ZCT(-) group (1094.1 + 139.77 N), while the lowest mean failure load was obtained in the ZST(+) group (627.7 + 82.14 N). No significant difference was found among the groups MC and MS, MC, and ZC groups (p > 0.001). Thermal aging application caused lower fracture resistance in control and soldering groups (p < 0.001). Conclusions The preceramic soldering applications affected zirconia group negatively. However, the values were above the clinically acceptable static load bearing capacity for posterior teeth. Soldering did not cause a statistically significant difference for the fracture strengths of monolithic zirconia groups. Thermal cycling affected the fracture strength of zirconia and monolithic zirconia restorations negatively.