A Comparison of Themarginal and Internal Fit of Cobalt- Chromium Copings Fabricated By Two Different Cad/Camsystems (Cad/ Milling, Cad/ Ceramill Sintron)

Statement of the problem: marginal fitness is the most important criteria for evaluation of the clinical acceptability of a cast restoration. marginal gap which is due to cement solubility and plaque retention is potentially detrimental to both tooth and periodontal tissues. purpose: this in vitro study aimed to evaluate the marginal and internal fit of cobaltchromium (co-cr) copings fabricated by two different cad/cam systems: (cad/ milling and cad/ ceramill sintron). materials and method: we prepared one machined standard stainless steel master model with following dimensions: 7 mm height, 5mm diameter, 90˚ shoulder marginal finish line with 1 mm width, 10˚ convergence angle and anti-rotational surface on the buccal aspect of the die. there were 10 copings produced from hard presintered co-cr blocks according to cad/ milling technique and ten copings from soft non- presintered co-cr blocks according to cad/ ceramill sintron technique. marginal and internal accuracies of copings were documented by the replica technique. replicas were examined at ten reference points under a digital microscope (230x). the student's ttest was used for statistical analysis. p< 0.001 was considered significant. results: statistically significant differences existed between the groups (p< 0.001). the cad/milling group (hard copings) had a mean marginal discrepancy (md) of 104 μm, axial discrepancy (ad) of 23 μm and occlusal discrepancy of 130 μm. for cad/ ceramill sintron group, these values were 195 μm (md), 46 μm (ad), and 232 μm (od). internal total discrepancy (itd) for the cad/milling group was 77 μm, whereas for the cad/ceramill sintron group was 143 μm. conclusion: hard presintered co-cr copings had significantly higher marginal and internal accuracies compared to the soft non-presintered copings.