Linear measurements to determine working length of curved canals with fine files: conventional versus digital radiography.

This in vitro study compared conventional and digital radiographic linear measurements to determine the working length (WL) of curved canals with fine endodontic files. In total, 30 mesiobuccal root canals in molars were measured with a #06 K-file to a length 1 mm short of the apical foramen (WL1). Teeth were mounted in plastic blocks and standardized periapical radiographs were obtained by conventional and digital (Digora Optime) radiographic methods with #06, #08 and #10 K-files positioned in WL1. Two independent and calibrated examiners performed the conventional measurements with a millimeter ruler, from the file stop to the file tip (WL2). For the digital images, examiners used the linear measurement tool on the Digora software, in original mode (WL3). For comparison of WL1, WL2 and WL3, the Wilcoxon test (P < 0.05) was applied and the reproducibility of the measurements was assessed. There was no statistically significant difference between Wl2 and Wl3 for #06, #08 and #10 K-files (P = 0.341, 0.641 and 0.232, respectively), with an acceptable level of interexaminer agreement. The measurements of Wl2 and Wl3 were significantly (P < 0.05) larger than those of WL1. No difference was observed among the linear measures obtained with either radiographic method, which showed higher WL values than the direct measurements.