the effect of porcelain firing and type of finish line on the marginal fit of zirconia copings

statement of the problem: although all-ceramic restorations are broadly used, there is a lack of information concerning how their fit is affected by fabrication procedure and marginal configuration. purpose: the purpose of this study was to evaluate the marginal fit of zirconia cad/cam ceramic crowns before and after porcelain firing. the influence of finish line configuration on the marginal fit was also evaluated. materials and method: twenty standardized zirconia cad/cam copings were fabricated for chamfer and shoulder finish line designs (n=10). the marginal fit of specimens was measured on 18 points, marked on the master metal die by using a digital microscope. after the crowns were finalized by porcelain veneering, the measurements of marginal fit were performed again. the means and standard deviations were calculated and data were analyzed using student’s t-test and paired t-test (α=0.05). results: there were significant differences between marginal fit of chamfer and shoulder finish line groups before and after porcelain firing ( p = 0.014 and p = 0.000, respectively). the marginal gap of copings with shoulder finish line was significantly smaller than those with chamfer configuration ( p = 0.000), but there were no significant differences between the two marginal designs, after porcelain firing ( p = 0.341). conclusion: porcelain veneering was found to have a statistically significant influence on the marginal fit of zirconia cad/cam crowns. both margin configurations showed marginal gaps that were within a reported clinically acceptable range of marginal discrepancy.