Statement of Problem: Determiningthe appropriate Working Length (WL) is an important factor in the success of root canal therapy. Several methods are available for this purpose but radiography is the mostly used one.
Purpose: The aim of this study was to compare the conventional and self -developing films with a Gold standard in estimation of the working length.
Materials and Method: In this descriptive study, radiographs were obtained with conventional and self-developing films from 45 mesiobuccal maxillary molar root canals which were mounted on a phantom head. Conventional films were processed automatically and self-developing films manually in accordance with manufacturer’s instructions. The radiographs were examined by three endodontologists and one oral and maxillofacial radiologist under double-blind conditions. Actual working lengths were measured on each tooth (Gold standard) and then measurements from each film type were compared together and against the Gold Standard. The data were analyzed using t-test and paired t-test.                                                                                      
Results: The average difference in WL between the conventional and self-developing films measured against the Gold standard was 0.33 mm and 0.14 mm, respectively. No significant difference was found between these two types of films and the Gold standard ( p =0.06 and p =0.7, respectively). Also, there was no significant difference between these two types of filmsfor estimation of the working length ( p =0.4).
Conclusion: Althoughthere was no significant difference between these two types of films, the assessment shows that self-developing films produced more accurate results in estimation of the working length. It is concluded that in the absence of dark room and processing solutions, self-developing films can be suitably used instead of conventional films.