Apical Periodontal Sensitivity

If an instrument is advanced in the canal toward inflamed tissue, the hydrostatic pressure developed inside the canal may cause moderate to severe, instantaneous pain. At the onset of the pain, the instrument tip may still be several millimetres short of the apical constriction. When pain is inflicted in this manner, little useful information is gained by the clinician, and considerable damage is done to the patient’s trust.

When the canal contents are totally necrotic, however, the passage of an instrument into the canal and past the apical constriction may evoke only a mild awareness or possibly no reaction at all. The latter is common when a peri-radicular lesion is present because the tissue is not richly innervated. It would appear that any response from the patient, even an eye squint or wrinkling of the forehead, calls for reconfirmation of working length by other methods available and/or profound supplementary anesthesia.