What is a perio-endo lesion?

A periodontal endodontic lesion is known as a “perio-endo” lesion. They can be of different sources in relation to either the pulp or the PDL ( the periodontal ligament). On a radiograph, a perio-endo lesion shows up as radiolucency at the apex and traveling up all the way to the CEJ ( the cement enamel junction). A probe will therefore travel down cervically down to the apex. 

The question is whether this is due to a periodontal pocket which has reached the apex OR is it a periapical infection which is so large that it is discharging through the periodontal ligament into the gingival sulcus. 

The perio-endo lesion can either be primarily of periodontal origin, of endodontic origin, or of both. 

There are 2 different kinds of pathways that might cause a perio-endo lesion:

Anatomical pathways and non-anatomical pathways. 

The anatomical pathways which  connect the pulp to the periodontal ligament are the apical foramina and the branches of the root canal system as lateral or accessory canals.

It is known that most of these lateral or accessory canals are located in the apical third of roots. When a RCT fails, always look here for unfilled canals. 30-40% of teeth have lateral or accessory canals

Another theoretical possible pathway is through the dentine tubules, which are more closely packed together  at the cervical region of the root. We know that bacteria can actually fit inside a dentinal tubule. But the pulp is resilient and does not get infected by even severe periodontal infections or infections from adjacent teeth. This has been shown by the many studies which have demonstrated that periodontal disease effects do not affect the pulp. 

Non-physiological pathways can be caused by iatrogenic perforations and vertical root fractures for example. A perforation or a root fracture opens a pathway from the pulp to the PDL. 

Similarities of the endodontic bacterial flora and the flora of periodontal pockets suggest that cross-infections are possible. However, research showed that the flora of periodontal ligament appears to be much more complex than the flora of the root canal.

Primary endodontic lesions can cause secondary periodontal lesions

An infected pulp will lead to a periapical infection because the necrotic pulp contains bacteria and toxins which cause a reaction in the periapical tissues. Accessory canals infections  can also occur at accessory root canals in the furcation or the cervical/middle part of the root. Sometimes these lesions mimic early periodontitis and the dentist gets caught out. 

Can a primary periodontal pocket cause a secondary pulpal infection?

Whether primary periodontal lesions cause secondary endodontic lesions is subject to discussion and difference of opinion but overall, most dentists would say not. One theory states that this is not possible due to the outward pressure flow in the dentinal tubules of vital teeth. 

Dentists who say it IS possible say that the types of bacteria in a necrotic pulp/PA lesion is similar to those in a periodontal pocket. These are typically spirochetes,  Actinobacillus actinomycetemcomitans, Tannerella forsythensis, Eikenella corrodens, Fusobacterium nucleatum, Porphyromonas gingivalis,  Candida albicans. If the pulp appears non-vital, bear in mind that cold and EPT testing is not 100% but 90% correct and accurate. SO treat the PERIO FIRST and wait. Don’t RCT too early. But if you know that the pulp is definitely necrotic, then do the RCT first. 

Several classification systems have been established to categorize those lesions and most widely used is the one of Simon and Glick which has 4 types. 

  1. Endodontic lesions
  2. Periodontal lesions
  3. True-combined lesions.  Both an endodontic and a periodontal lesion developing independently.
  4. Latrogenic lesions.