comparison between sodium hypochlorite and copper sulfate reducer in lightening of overexposed working length radiographs

objectives: the aims of this study were to test whether lightening of the overexposed radiographs improve determination of endodontic files length and whether lightened radiographs are comparable with ideally exposed radiographs. material and methods: four dried human skull coated with soft tissue-equivalent wax used for exposing radiographs of the upper molars. first, the endodontic file was placed in full length of the root and four series of radiographs obtained. the time to expose the first series was unchanged (standard group) but increased for the other three series.  two series of overexposed radiographs set as test groups (one lightened with copper sulfate reducer and the other lightened with sodium hypochlorite) and one series set as control group. then the endodontic file placed 2mm short in the root and four series of radiographs obtained like the former. a viewer evaluated radiographs. roc curves were obtained and areas under the curves were calculated. sensitivity, specificity and cohen's kappa was calculated. results: the average area under roc curves was 1, 0.995,1 and 0.643 for the standard, copper sulfate, sodium hypochlorite and the control group, respectively. sodium hypochlorite show a better performance in terms of sensitivity and specificity compared to copper sulfate. differences between the test radiographs and standard and control radiographs were significant (p< 0.05), but not between copper sulfate lightened radiographs and control radiographs (p=0.784). conclusion: lightening with naocl is a cheaper and less cumbersome method which need only one minute to correct the radiograph.