I research _ working length Figs. 18a & b_RVG image of the lower molar (a) and conventional radiograph (b). Fig. 18a Fig. 18b measurements are beyond this.12 When the file is short of the radiographic apex, it is actually closer to the apical foramen than it appears radiographically.13 Radiographic WL ending 0 to 2 mm short of the radiographic apex provides a basis for unintentional over-instrumentation, more often than expected.14 Figures 16a to 17b demonstrate the way mistakes in determining WL can be corrected to finalise the case successfully. The RM depends on a few different factors, namely the surrounding structures, the angulations of the cone-beam, the visibility of the measuring file influenced by its size, and the film exposing and developing speed. In summary, radiographs are indispensable for calculating but not for determining WL and the endodontic terminus.15 The most prominent advantage of digital radiography (DR) is the ability to quantify distances with exact figures. Thanks to software programmes, images can be varied in size and contrast. But there are limitations if small size canal instruments with fine file tips, for example #8 or 10, are used. They display low contrast in their structures and affect visualisation and precision of the measuring process and hence the results. Therefore, sizes #15 and bigger are preferable. Even though there are many advantages and benefits in the use of DR, many reports emphasise that complete image quality is better with conventional radiographs (Figs. 18a & b). When conventional and DR radiographs were used for WL determination and compared to electronic locators, it was demonstrated that electronic foramen locators are superior because the RM generally gives long measurements with overinstrumentation._ Editorial note: Part II of this article will be published in roots 1/2010. A complete list of references is available from the publisher. _about the author roots Prof Vladimir Ivanovic graduated from the Faculty of Dentistry at the University of Belgrade in 1976. He obtained a M.Dent.Sc and Ph.D. with specialisation in Oral and Dental Pathology and Endodontology. He was appointed Professor in Restorative Odontology and Endodontics in 1998 at the Faculty of Dental Medicine and served as a Vice-Dean for postgraduate and undergraduate studies. He has also chaired the School Board for Dental Pathology. Prof Ivanovic conducts research at the University of Belgrade and Edinburgh Dental Institute. His main interests are maintaining vital pulp, resin-based composites and adhesive systems, and endodontology. He has attended numerous international endodontic seminars and courses to further his knowledge and skills. He has delivered over 100 lectures both nationally and internationally, published over sixty articles in national and international journals, and chapters in four dental textbooks. He is founder and President of the Serbian Endodontic Society and has been a member of the ESE since 1989. He is also country representative for the ESE General Assembly, member of the International Association for Dental Research/Continental European Division and school representative for the Association for Dental Education in Europe. He has organised over a dozen endodontic meetings in Belgrade with internationally recognised speakers. Prof Ivanovic can be contacted at vladaivanovic@hotmail.com. 36 I roots 4_ 2009