Commentary

One problem that clinicians face in endodontics is how to accurately identify and maintain the biological length of the root canal systems. It has been established that the junction of the dentin and the cementum (CDJ) is the landmark that determines the end of this biological length,1, 2 from a starting point on the coronal side of the tooth (reference point, or area), which must be measured to achieve maximum success during nonsurgical root canal treatment. The variations in anatomy of tooth apices, both by age and tooth type, and the electric properties of each root canal according to its pathological status,3 make the task of determining the exact location of the apical constriction all the more challenging.

Methods for studying the accuracy of EAL have varied between in-vitro, in-vivo and radiographic. The former use electroconductive materials to simulate the clinical situation, alginate, gelatine, agar or saline media all giving predictable results with apex locators when compared with tooth length.4 Some of these media can leak through the apical foramen and cause premature readings although, in contrast, some in-vitro experimental models can in fact give greater accuracy than can be achieved clinically.

In-vivo studies are more representative of the true accuracy of a given apex locator.5 Studies that use apex locators to find the working length, cement the file in place, extract the tooth and locate the file under magnification in the root canal emulate what happens in clinical practice. When extraction of the tooth has not been possible, studies have used radiographs to verify the canal length. Problems associated with this are the need to work in two dimensions, with anatomic variation and distortions.6

This current study addresses which of the chosen EAL work better under random clinical situations, which in turn provides a superior method to the in-vitro assessments. There are, however, several clinical parameters that might have affected the overall accuracy of the study. First, the endodontic file size 15 was used for all tested root canals in vivo, for all types of teeth. The size of the endodontic file should be proportional to the size of the canal for maximum predictability of the measurement process. For example if a no.15 file is inserted into a larger distal canal or palatal canal of a molar it may give inaccurate readings; this could be prevented by using larger file size. Secondly, the authors also did not carry out pre-flaring on the canals tested although several studies have shown that pre-flaring allows working-length files to reach the apical foramen more consistently, in turn increasing the efficacy of the EAL.7 Finally, the study did not look into the probability of having a file at the CDJ, even though the EAL would give false readings (long or short) as the file was removed after the in-vivo reading and was re-inserted in-vitro,leading to measurement error.

Practice point

The study confirms the reliability of the chosen EAL to determine endodontic working length.