**2.7 Interrelationship between endodontics and periodontics**

The pulp periodontal interrelationship is a unique one and consider them as a single continuous system or as one biologic unit in which there are so many paths of communication [52]. The intricacy of endo-perio lesions (EPL) throws back the intimate relationship between the periodontal complex and endodontics [53].

The EPL terminology was first instituted in 1998 in the American association of endodontic, Glossary of endodontic terms. Later on American academy of Periodontology accepted this terminology and defined EPL to be localised infection beginning from pulpal or periodontal tissue [54]. Endo perio lesions are mostly anaerobic infections and polymicrobial in nature. The aetiology of EPL lesion is due to concurrent inflammation of variable magnitude of periodontal complex and endodontics. Causative factors are mostly bacterial origin. Dental malformations, history of trauma, iatrogenic perforations, external or internal root resorptions are also responsible for the endo-perio lesion. The existence of active tooth decay, furcation defect, anatomical grooves and porcelain fused to metal crowns are regarded as liability factors in the existence of EPL.

#### *2.7.1 Pathways of EPL*

There are several pathways of communication of infectious substances from pulp to periodontal tissue and vice versa. This in combination with the existing polymicrobial anaerobic infection leads to development of EPL [55].

The apical foramina and lateral canals link the pulpo-perio complex. Deep periodontal pocket reaching beyond the apical third of tooth can be connected to endodontic system through apical foramen. Lateral canals which are found all along the root surface give out a more accessible pathway for micro-organisms to travel from one tissue to other.

Any endodontic infection in the root apex can move up through periodontal ligament reaching the marginal gingiva and can increase periodontal disease severity by increasing pocket depth. This was termed as retrograde periodontitis [56]. Inversely microorganisms and noxious irritants can invade through dentinal tubules to the pulpal complex after the gradual loss of attached periodontal tissue.


#### *2.7.2 Classification system*

Recent classification system of periodontal conditions, combined EPL are placed in the "periodontal manifestations of systemic diseases and developmental and acquired conditions" section and "other periodontal conditions" subsection.

Classification of EPLs modified from Simon et al.:



#### *Interdisciplinary Periodontics DOI: http://dx.doi.org/10.5772/intechopen.99265*

**Table 1.**

*Diagnostic examinations used to classify EPL adapted from Parolia et al. 2013 [57].*

#### *2.7.3 Treatment options*

Correct diagnosis is key to management and prognosis of EPL. The most vital parameters to be considered while planning the treatment should be pulp vitality and extent of periodontal lesion. The prognosis of primary endodontic lesion is usually good if proper irrigation protocol is followed during cleaning and shaping and they heal with proper endodontic treatment [58].

Primary periodontal lesions can be treated by periodontal therapy only. Removing entire etiologic elements that can induce or promote epithelial downgrowth followed by periodontal surgery is the best treatment modality in these cases [59].

True combined lesions are challenges that necessitate endodontic and periodontic regenerative treatment. As an initial step, true combined EPL should be treated endodontically first followed by other etiological factor management including periodontal management. If root resection or hemisection of molar teeth is planned, clinician must think of multiple factors like tooth restorability, regeneration of bone around sound root structure and concurrence of the patient. Prognosis of teeth can be ameliorated by osseous regeneration and Guided Tissue Regeneration (GTR). Endo-perio lesions are threat to dentists as multidisciplinary approach is required to acquire a positive result.
