Image-guided Ablation of Occlusal Lesions Using Near-Infrared Transillumination

Objectives: A CO₂ laser operating at 9.3µm is ideally suited for the image-guided ablation of carious lesions. Previous studies have shown that near-IR transillumination at 1300-nm can be used to image deep occlusal lesions with high contrast. The purpose of this study was to use near-IR transillumination images to guide a CO₂ laser for removal of natural occlusal lesions on extracted teeth.
Methods: Extracted human teeth (n=10) with natural occlusal lesions were imaged using NIR transillumination. Digital images were acquired using a 3D surface profilometry system at 25x and 50x magnification respectively. NIR transillumination images were acquired using an InGaAs camera and tungsten halogen source in the spectral region of 1340nm to 1420nm. Areas with the higher contrast were selected for removal. A CO₂ laser operating at 9.3µm with pulse duration of 15µs and a water spray that delivered 10mL/sec over a 5cm² area was used to ablate the lesions defined by the near-IR images. Optical coherence tomography (OCT) was used to confirm lesion presence and serial scans were used to assess ablation selectivity. Polarized light microscopy was used to confirm lesion removal.
Results: The mean contrast in the NIR transillumination images between the lesions and the sound enamel was 0.362±0.045. The contrast did not change significantly (p>0.05) as tissue above the lesion was ablated by the laser. As the depth of ablation increased, OCT images revealed the extent of the subsurface lesion area. 47 lesions were identified from the OCT images. 21 lesions were either completely or partially removed.
Conclusions: NIR transillumination images are can be used for guiding the laser ablation of deep occlusal lesions.