research _ working length I foramen in immature teeth, which leads to longer WL. The literature offers little information on this method; nevertheless, the tactile sensation technique is still advocated as very useful in the determination of apical constriction. In 1986, Dr Mirjana Vujaskovic and her mentor Prof Miroslav Pajic conducted extensive clinical research on the accuracy of the tactile sensation method controlled radiographically in relation to two reference points: 0.5 mm from the radiographic apex in patients younger than 25 and 1.0 mm in patients older than 25. The method was accurate in only 19 % of the cases, but accuracy increased to 42 % when tolerance was extended to +/- 0.5 mm. Furthermore, the researchers found significant under- and overestimations—up to 4.5 mm before and after reference points. The literature presents accuracy in a variable range of 30 to 44 % and 30 to 60 %, with wide and random distribution of measured values. An important finding for our daily practice was that pre-flaring helps in locating the apical constriction, increasing accuracy from 32 to 75 %. The paper point technique (PPT) is claimed to be the most accurate method by which to determine both WL to the very end of the canal and minimal apical foramen diameter in three dimensions. It allows the practitioner to see the cavo-surface of the apical foramen with precision in 1/4 mm. Logically, the apical patency technique is mandatory for this method. Additionally, this technique enables customisation of master gutta-percha cone three-dimensionally based on the information gained from the paper point (Fig. 14). Even though it is claimed to be the most accurate method in determining WL, neither scientific nor clinical evidence is available in the literature. In spite of being advocated by many endodontic experts, PPT lacks to the ability to determine morphological details and pathological states within the root canal and in the peri-apical tissues. However, it is a fairly simple method and can be helpful in establishing and confirming final WL since it is non-aggressive and therefore does not injure periodontal tissues or endanger apical wound healing. The radiographic method (RM) is probably still the most widely used method for determining WL. It reveals many important details and is useful in every endodontic procedure. However, it also has limitations and often provides an illusory image. There are three matters to be noted when determining WL with RM. First, it is mandatory to produce preoperative, diagnostically accurate radiographs. Second, the radiographic apex and the anatomical apex do not (always) coincide, but in most textbooks and articles these terms are used interchangeably. Third, the apical foramen cannot (always) be visualised on a radiograph, which is a significant handicap. Fig. 16a Fig. 16b In 1986, Dr Vujaskovic, Prof Pajic and I conducted a long-term clinical study on the accuracy of RM in determining WL. The same methodology was applied as described for the tactile sensation method. The RM was accurate in 51 % of cases, strictly respecting reference points on a radiograph (0.5 mm from the radiographic apex in patients younger than 25 and 1.0 mm in patients older than 25). When the range of tolerance was extended to a clinically acceptable +/- 0.5 mm from the reference points, accuracy increased to 68 %. It further increased to 88 % when tolerance was extended to +/- 1.0 mm. Underand overestimations were not over 2 mm, compared to 4.5 mm with the tactile sensation method. Similar findings were confirmed in other studies. Figures 15a and b show that the measuring file is longer than it appears radiographically. When the instrument is short of the radiographic apex, it is beyond the apical foramen in 43 % of all cases. If the apical constriction is 0.5 mm before the apex, then 66 % of all Figs. 16a & b_Clinical situation with instrument beyond the apex (a), which was later corrected by obturating the canal approximately 0.8 mm short of the radiographic apex (b). Figs. 17a & b_Correction of a treatment mistake in determining WL (a) and the more or less successful end result (b). Fig. 17a Fig. 17b roots 4 _ 2009 I 35