fracture resistance of zirconia restorations with a modified framework design

Objectives: chipping is one of the concerns related to zirconia crowns. the reasons of chipping have not been completely understood. this in-vitro study aimed to assess the effect of coping design on the fracture resistance of all-ceramic single crowns with zirconia frameworks. materials and methods: two types of zirconia copings were designed (n=12): (1) a standard coping (sc) with a 0.5mm uniform thickness and (2) a modified coping (mc) consisted of a lingual margin of 1mm thickness and 2mm height connected to a proximal strut of 4mm height and a 0.3mm-wide facial collar. after veneer porcelain firing, the crowns were cemented to metal dies. afterwards, a static vertical load was applied until failure. the modes of failure were determined. data were calculated and statistically analyzed by independent samples t-test. p<0.05 was considered statistically significant. results: the mean and standard deviation (sd) of the final fracture resistance equaled to 3519.42±1154.96 n and 3570.01±1224.33 n in sc and mc groups, respectively; the difference was not statistically significant (p=0.9). also, the mean and sd of the initial fracture resistance equaled to 3345.34±1190.93 n and 3471.52±1228.93 n in sc and mc groups, respectively (p=0.8). most of the specimens in both groups showed the mixed failure mode. conclusions: based on the results, the modified core design may not significantly improve the fracture resistance.