English: Diagram showing mesio-impacted mandibular third molar tooth, with associated dental caries and pericoronitis. Captions are (A) Mesio-impacted, partially erupted mandibular third molar; (B) Dental caries and periodontal defects o both the third and second molars, caused by food packing and poor access to oral hygiene; (C) Inflamed operculum covering partially erupted lower third molar, with accumulation of food debris and bacteria underneath; (D) The upper third molar has over-erupted due lack of opposing tooth contact, and may start to traumatically occlude into the operculum over the lower third molar.