Precise working length determination is one of the prerequisites for successful endodontic treatment. At present there is an improved way of verifying working length. The fourth generation of electronic apexlocators has already been developed to specify this so important action of endodontic treatment. In our study we tried to verify accuracy of working length determination with the Ray-Pex 4, the fourth generation group device. Evaluation of the quality of the electronic measurement approach was based on the distance from file tip to anatomical apical foramen. Measurement was accomplished on a digital image of sectioned apical region with instrument inserted in root canal. One milimeter distance maximum from file tip to anatomical apical foramen was considered as a correct measurement. Results were satisfactory in 95 % (37 of 39 root canals). Statistical comparison of single- and multi-canal root group didn’t show any difference. On the basis of results of this study and our experiences acquired during time of this experiment we finally recommend a rational way of using apex locator Ray- Pex 4.

        Key words: endodontic – apex locator – Ray-Pex 4 – root length determination