Effects of imaging conditions on fluorescence intensity during fluorescence-aided root canal treatment

Fluorescence-aided root canal treatment (FARCT) enables real-time visualization of protoporphyrin IX-derived red fluorescence associated with bacterial contamination during root canal treatment. However, the intensity of the detected fluorescence can vary depending on the imaging conditions. Standardization of these conditions is therefore important for reproducible fluorescence assessment. This study aimed to quantitatively evaluate the effects of magnification factor, illumination intensity, and working distance on fluorescence intensity during FARCT.

Fifteen molars exhibiting detectable red fluorescence at the root canal orifice were evaluated during root canal treatment. Fluorescence images were acquired using an EXTARO 300 FV dental operating microscope while independently varying magnification factor, illumination intensity, and working distance. Red intensity within the fluorescent canal-orifice region and green intensity from visually intact pulpal-floor dentin were quantified using ImageJ. The effects of each imaging parameter were evaluated using Bonferroni adjustment for multiple comparisons.

Both red and green intensities were significantly affected by imaging conditions. Fluorescence intensity was maintained at relatively high levels at magnification factors of 0.4-1.0, but decreased at higher magnification factors. Increasing illumination intensity progressively increased both red and green intensities, with the highest values observed at 100%. Conversely, both intensities decreased with increasing working distance and were the highest at 200 mm.

Fluorescence intensity during FARCT is strongly influenced by imaging conditions, with a magnification factor of approximately 1.0, high illumination intensity, and a short working distance providing favorable fluorescence visualization. Standardization of these parameters may improve the reproducibility of FARCT, while working distance should be balanced against clinical operability.