Clinical and Microbial Factors Associated with Persistent Apical Periodontitis

Objectives: Persistence of apical periodontitis (PAP) is regarded to be sustained by bacteria that remain in root canals after treatment. In cases of adequate root-filling and coronal restoration, the origin of the microbial aetiology is not well established. As lipopolysaccharides (LPS) of Gram-negative bacteria has an etiologic role in both gingival and periapical inflammation, the present study investigates, if subgingival LPS could impact the development of PAP.
Methods: A total of 98 root-filled teeth were included. Forty-seven teeth had periapical radiographic lesions (PARLs) and 51 did not. Teeth with good coronal restorations and root fillings that were restored ≥1 year ago, with periodontal probing depths <4mm, were included. Age, gender, clinical symptoms, number of bleeding on probing (BOP) sites and other clinical variables were recorded. Subgingival plaque samples were collected by inserting 6 paper points into 6 different gingival sites per tooth. The amount of biologically active LPS per tooth was quantified using the HEK-Blue LPS Detection Kit. Ex-vivo experiments were conducted to determine if LPS could traverse from the extra-radicular environment into the root canal via dentinal tubules. Mann-Whitney U test and logistic regression were performed to identify potential risk factors at 5% significance level.
Results: LPS levels in subgingival plaque of teeth with PARLs were significantly higher than that in teeth without PARLs (p=0.016). Other risk factors of PARLs include >4 BOP sites per tooth, tenderness to percussion and palpation. Teeth with sinus tracts were found to have 1.7x higher subgingival LPS levels than teeth without sinus tract (p=0.027). LPS was found to traverse extra-radicularly into the root canal ex-vivo.
Conclusions: Findings suggest a potential contribution of subgingival LPS to PAP in teeth with adequate root-filling and coronal restoration. These results provide the basis for future prospective studies to determine the influence of subgingival LPS concentrations with periapical healing.