Background and Aim: Radiography has extensive applications in root canal treatment and the developer age plays an important role in making a definite diagnosis. The present study examined the effect of developer age on the diagnostic accuracy of endodontic file length measurement using D-speed, E-speed and E/F-speed films.

Materials and Methods: In this diagnostic study, radiographs were processed weekly by a developer aged for up to 6 weeks. Radiographs were viewed by 5 postgraduate students of endodontics and oral radiology. They determined the file tip position using a 3-point confidence scale. The area under the curve (Az) was calculated and used as a diagnostic accuracy scale. The effects of film type and endodontic file size were analyzed by one-way ANOVA, Tukey’s post hoc test and Student’s t test.

Results: E-speed and D-speed films had similar diagnostic accuracy higher than that of E/F speed film (p<0.0001). The Az values of D, E and E/F speed films were 0.5882, 0.5538 and 0.3578, in fresh developer, 0.5782, 0.5718 and 0.3498 in 2-week old develop-er and 0.6196, 0.6724 and 0.2080, in 4-week old developer solution, respectively. Devel-oper age did not decrease the diagnostic accuracy of D and E-speed films but decreased that of E/F films at 4 weeks. Radiographs processed with 6 weeks old developer were not readable. All observers showed higher diagnostic accuracy determining the size of file # 15 than 10 (p<0.0001). The mean Az values for endodontic file sizes 10 and 15 using fresh, 2-week and 4-week old developers were 0.3984 and 0.6016, 0.3732, and 0.6268 and 0.2774 and 0.7226, respectively.

Conclusion: The developer aged for up to 4 weeks did not significantly affect the diag-nostic accuracy of D-speed and E-speed films. E/F speed films cannot be used with de-velopers older than 2 weeks and their usage was associated with lower accuracy compared to E and D-speed films.