Pulpal perio relations

Classification of perio-endo lesions
There are four types of perio-endo lesions and they are classified due to their pathogenesis.

Endodontic lesions: an inflammatory process in the periodontal tissues resulting from noxious agents present in the root canal system of the tooth.
Periodontal lesions: an inflammatory process in the pulpal tissues resulting from accumulation of dental plaque on the external root surfaces.
True-combined lesions: both an endodontic and periodontal lesion developing independently and progressing concurrently which meet and merge at a point along the root surface.
Iatrogenic lesions: usually endodontic lesions produced as a result of treatment modalities.
Pathogenesis
A. Endodontic lesions
When the pulp becomes inflamed/infected, it elicits an inflammatory response of the periodontal ligament at the apical foramen and/or adjacent to openings of accessory canals. These inflammatory lesions cause localized oedema and a resulting increase in intra-pulpal pressure and cell death.5 Increased damage associated with an inflammatory exudate cause local collapse of the venous part of the local microvasculature. This causes local tissue hypoxia and anoxia resulting in localized necrosis, the chemical mediators of which cause further localized oedema, completing the cycle.35

Carious lesions or any direct exposure to the oral cavity of dentine or pulp may ingress bacteria to contaminate an otherwise sterile lesion. This is predominantly a mixed anaerobic infection.6 Endodontic lesions are most frequently initiated and sustained by the apical foramen, followed by accessory and lateral canals, and most infrequently by dentinal tubules. A periapical lesion may perforate the cortical bone close to the apex, elevate the periosteum and overlying soft tissues, and drain into the gingival sulcus,36 and form pseudopockets that simulate periodontal disease without necessarily permanent damaging of the cementum and its fibres.15 If the acute periapical drainage becomes chronic and drainage through the gingival sulcus continues a downgrowth of epithelium along the tract can result in a periodontal pocket in which secondary periodontal disease may complicate the lesion.37 Simon, Glick and Frank38 further categorized endodontic lesions into two sub-categories: 1. primary endodontic lesions, when a sinus tract has formed to establish drainage, and 2. primary endodontic lesions with secondary periodontal involvement, when plaque formation occurring in the sinus tract with progression to periodontitis and associated calculus formation.

B. Periodontal lesions
Plaque and calculus initiate periodontal lesions. Inflammatory mediators cause destruction of gingival connective tissue, periodontal ligament and alveolar bone. Alteration of the root surface occurs by loss of the outer cementoblast layer and results in shallow resorptive lesions of cementum. Endotoxins produced by plaque bacteria also have an irritant effect on overlying soft tissue, preventing repair.39 Although periodontal disease has been shown to have a cumulative damaging effect on the pulp tissue, total disintegration of the pulp will only be a certainty if bacterial plaque involves the main apical foramina, compromising the vascular supply.15,36 The presence of an intact cementum layer is important for the protection of the pulp from pathogenic agents produced by the plaque bacteria.36 Therefore, the exposure of dentinal tubules by the removal of cementum due to rigorous scaling and root-planning for the treatment of periodontal disease will allow bacterial invasion of the tubules. This would increase the likelihood of cumulative damage to the pulp.15 Results from microbiological and immunological studies support the suggestion that the source of endodontic infection in perio-endo lesions with periodontal origin is the periodontal pocket bacteria.