eng Science and Education Publishing International Journal of Dental Sciences and Research 2333-1259 2015-06-02 3 4 82 86 10.12691/ijdsr-3-4-1 IJDSR2015341 article Yaparathna YMKN 1 Jayasinghe RD 2 Abeysekara WPMM 3 Fonseka MCN manilpera@gmail.com 4 Wettasinghe KA 4 Registrar in Restorative Dentistry, Faculty of Dental Sciences, University of Peradeniya, Sri Lanka Department of Oral Medicine and Periodontology, Faculty of Dental Sciences, University of Peradeniya, Sri Lanka Ministry of Health, Sri Lanka Department of Restorative Dentistry, Faculty of Dental Sciences, University of Peradeniya, Sri Lanka The mandibular first molar (MFM) is considered a vital tooth in establishing occlusion in the permanent dentition. As it is a tooth prone to caries its morphology is vital in restorative, endodontic and surgical aspects in dentistry. Accurate working length (WL) determination is considered an essential for the success of root canal therapy. Methods of WL estimation include detecting the apical constriction by tactile means (apical boundness), using a periapical radiograph or by means of an electronic apex locator (EAL). The objective of this study was to assess the accuracy of different WL assessment methods in comparison to the actual length of the tooth assessed by visualising the apical constriction of MFMs. Access cavities were prepared in 188 extracted permanent MFMs, mounted on alginate and suitable K-file was passed though each root canal to determine the apical constriction. WL was determined with a third generation apex locator with a proven accuracy (Root ZX Mini J Moritacorp. Japan). These teeth were assessed both with analog and digital radiography to assess the position of the files on the radiograph. Finally the teeth were assessed with a 2.5X magnification to visually locate the apical constriction (actual length) of each root canal. The mean actual length of mesio-buccal canal was 20.06mm, mesio-lingual canal was 19.97 mm, disto buccal canal was 19.81 mm and disto- lingual canal was 19.40 mm. Accuracy of EAL is 98.5%. There was no significant difference between the accuracies of 1st bound, film based and digital radiography. Thus the most accurate method in WL determination is the EAL. http://pubs.sciepub.com/ijdsr/3/4/1/ijdsr-3-4-1.pdf lower first molar root canal configuration digital radiography