Analysis of an Immediate Diagnostic Technique for Detecting Root Canal Bacteria Using Light-induced Fluorescence

Purpose: The decision to perform a root canal filling is influenced by many factors including subjective symptoms and clinical signs. Sterility of the root canal before filling is usually confirmed using the bacterial culture method. However, the outcome of this method is not known for about 24 to 48 hours, and it is associated with a risk of technical contamination, which may affect the results. Therefore, we investigated the possibility of evaluating sterility inside the root canal using blue light of wavelength of approximately 405 nm. Materials and Methods: A total of 31 root canals were investigated. After checking subjective symptoms and clinical signs, one drop of sterile water was introduced into the root canal. The water was absorbed 30 seconds later by inserting two sterilized paper points into the root canal. One paper point was used for the bacterial culture test and the outcome was evaluated after 48 hours. The other was analyzed with the high-sensitivity fluorescence-induced test using 406-nm wavelength excitation light and the resulting waveform of the fluorescence spectrum obtained using the microscope multi-photometry system was recorded. Results: Clinical signs indicated that performing a root canal filling was not appropriate in 10 cases. These 10 cases had positive results with both the bacterial culture test and the fluorescence test. Of the remaining 21 cases, 16 had negative results for both tests, while the bacterial culture test was positive in the other 5 cases. Three of these 5 cases had negative fluorescence test results, indicating technical contamination; the other 2 cases had positive fluorescence test results, indicating bacterial infection. Conclusion: Light-induced fluorescence analysis may be able to evaluate the bacterial state in the root canal, and could replace the simple bacterial culture test in the analysis of root canal bacteria.