Dynamic working length determination

Accurate determination of working length is an important step in root canal instrumentation, as incorrect preparation length can lead to:

It has been shown that the working length of a canal decreases after root canal preparation.2 Therefore, constant reconfirmation of the preparation endpoint is desirable. This is normally achieved by using an ‘apex locator’ in combination with regular radiographic controls.

The ‘dynamic working length determination’ technique requires the preparation of a ligature on the endodontic handpiece using a stainless-steel orthodontic wire (Figure 1). The apex locator circuitry (the ‘file holder’ part) is directly connected to the ligature, rather than to the file, and the lip clip is connected to the patient's body to complete an electric circuit. It should be noted that this technique is not possible if the endodontic handpiece contains ceramic components, as they will interfere with the electric circuit. It is worth mentioning that some ‘apex locators’ provide delayed readings, thus these should not be used for ‘dynamic working length determination’, as there is a risk of overinstrumentation as a result of this factor.