Protoporphyrin IX fluorescence for real-time visualization of bacterial persistence during root canal treatment

Apical periodontitis (AP) results from microbial infection within the root canal system. Although mechanical and chemical debridement techniques have advanced, real-time intraoperative visualization of bacterial persistence remains limited. This study evaluated whether fluorescence-aided root canal treatment (FARCT) using protoporphyrin IX fluorescence (PpIX-FL) could assist clinicians in visualizing bacterial persistence in real time during routine endodontic procedures.

Fifty patients (23 initial treatments, 27 retreatments) underwent root canal treatment. PpIX-FL was visualized in real time under 405-nm excitation using a dental operating microscope. Fluorescent areas were documented, and multivariate logistic regression analysis was performed to assess associations with clinical factors. Histological examination and confocal microscopy were conducted to verify bacterial presence corresponding to PpIX-FL.

PpIX-FL was detected in 56.0% of cases, particularly in isthmuses, fins, and contaminated gutta-percha. Fluorescence was significantly more prevalent in retreatment cases (OR=8.32; p = 0.05) and teeth with periapical lesions ≥2 mm (OR=61.06; p = 0.005). Confocal imaging and Gram staining confirmed that red autofluorescence areas corresponded with Gram-positive bacterial infiltration into dentinal tubules.

PpIX-FL enables reagent-free, real-time visualization of bacterial contamination within the root canal system. FARCT should be regarded as an adjunctive visualization approach rather than a stand-alone diagnostic or therapeutic modality. The present findings demonstrate the clinical feasibility of PpIX-based autofluorescence for fluorescence-guided visualization in endodontic retreatment and anatomically complex cases.