Two categories of insult that most commonly cause endodontic disease are bacterial infection and dental trauma.
Bacteria can also enter the endodontic system of a non-traumatized tooth through extension of periodontal disease. If the periodontal epithelial attachment migrates apically to an endodontic vascular entrance such as a lateral canal, furcation communication, or the apical foramen or delta, then the pulp could become infected. This is referred to as a primary periodontal lesion with secondary endodontic involvement (it has also been referred to as a “perio-endo lesion”). Apical and radicular LEOs ?can dissect coronally along the side of the root to exit in the sulcus, creating a primary endodontic lesion with secondary periodontal disease (has also been referred to as an “endo-perio lesion”). The bony defects around a tooth with primary endodontic disease and concurrent but unrelated periodontal disease can meet to form a combined periodontal and endodontic lesion.
Pulp inflammation and necrosis can also result from deep dental caries with extension of the bacterial infection to the pulp.
Blunt trauma can cause pulp haemorrhage and endodontic disease even when the tooth crown does not fracture. Although the pulp has some ability to heal after mild trauma, the most common result of pulp trauma is irreversible pulpitis even when there is no bacterial contamination of the pulp.
Radiographic signs depend on the pulp response: arrested development of a tooth (wide pulp with thin dentin), pulp calcification, internal resorption, external resorption, wide periodontal ligament space, periradicular radiolucencies, discontinuous lamina dura, root fractures.