Digital Tactile Sense

An experienced clinician may detect an increase in resistance as the file approaches the apical 2 to 3 mm provided the coronal portion of the canal is not constricted. This detection is by tactile sense. In this region, the canal frequently constricts (minor diameter) before exiting the root. There is also a tendency for the canal to deviate from the radiographic apex in this region.

However, you should be aware that this method, by itself, is often inaccurate. It is ineffective in root canals with an immature apex and is highly inaccurate if the canal is constricted throughout its entire length or if the canal has excessive curvature. This method should be considered as supplementary to high-quality, carefully aligned, parallel, working length radiographs and/or an apex locator.