These can be unpredictable. Teeth with deep periodontal probings on teeth with mesial and distal roots in close proximity can have those probings as a result of periodontal disease. They can also have those probings as a result of endodontic pathosis. Really, the best way to determine if its endodontic origin, is to initiate endodontics and monitor the probings over time. If the probings resolve, as they did in this case, then the cause is endodontic in nature. Unfortunately, if its periodontal in nature the prognosis is usually poor. After a few months in CaOH2, we had our answer, as the probings dropped to 3mm and then we finished the case. Managing the case in this way makes things predictable. The one year followup shows complete healing in 2D.
-Trudeau