What is APICAL PERIODONTITIS ? Apical periodontitis is inflammation around the end of the root (apex ) of a tooth So even more simply inflammatory fluid (swelling) under the root It can be the result of a patient clenching on a tooth and causing swelling in the PdL but we know it as inflammation under the root as a result of a bacterial over load (infection ) within the root canal system which leads to the production of fluid under the root - unfortunately unlike our skin which can swell and str