Combined periodontic-endodontic lesions take the form of
abscesses and can originate from either or both of two distinct locations[1] and may be informally subclassified as follows:[citation needed]
Endo-Perio: infection from the pulp tissue within a tooth may spread into the bone immediately surrounding the tip, or apex, or the tooth root, forming a
periapical abscess. This infection may then proliferate
coronally to communicate with the margin of the
alveolar bone and the
oral cavity by spreading through the
periodontal ligament.
Perio-Endo: infection from a
periodontal pocket may proliferate via
accessory canals into the root canal of the affected tooth, leading to pulpal inflammation. Accessory canals may not be big enough to allow bacterial penetration, periodontal disease must reach the apex to induce an endodontic lesion.
Neither the
prognosis, treatment nor expected treatment outcome depend on the source of the infection.[2]
A combined lesion may also be the result of a fractured tooth.