Near-infrared endoscopic imaging of deep artificial approximal lesions in extracted teeth

Near-infrared (NIR) dental imaging using scanning fiber endoscope (SFE) is being developed with advantages of miniature size (1.6mm), flexible shaft, video frame rate (7Hz), and expandable field of view (60 degrees). Using 1310, 1460, and 1550 nm laser diodes, the multispectral NIR SFE provides high contrast of lesion with transparency of stained and non-calcified plaque. However, capabilities of scanned NIR imaging remain unknown. Artificial interproximal lesions are created in extracted human posterior teeth by preparing a cavitation on the mesial or distal surface and then the cavitated artificial lesions were filled with hydroxyapatite powder and sealed with cyanoacrylate resin. Lesions are prepared at different occlusal-gingival depths from marginal ridges, lesion drilling depths and lesion size. Endoscopic reflectance images were acquired and compared to micro-CT scans and 1310 nm OCT images of the lesions to evaluate performance of the nirSFE. Results show that NIR SFE can image deep lesions under sound enamel with thickness of ≤4mm. All three wavelengths can detect deep lesions through the occlusal enamel which are not visible by naked-eye. 1460 nm has the highest contrast between lesion and sound enamel while 1310nm more clearly shows the contrast between enamel and dentin. Our nirSFE system can detect artificial interproximal lesions less than 4 mm below the occlusal surface, distinguish different drilling depth both in enamel and in dentin layer. Furthermore, the nirSFE realtime imaging and video functionality renders better lesion contrast and helps distinguish specular reflection and lesion signal. In conclusion, the NIR SFE has the potential to measure volume of these lesions due to the many viewing angles achievable by the miniature and flexible probe tip.