Near-Infrared Image Guided Laser Ablation of Root Surface Lesions

Objectives: Near-Infrared (NIR) reflectance at wavelengths above 1500-nm is used to distinguish between sound and demineralized tooth structure. Cross polarized optical coherence tomography (CP-OCT) can be used to measure the depth of such lesions. Previous studies have shown that these imaging modalities, combined with a CO₂-laser, can effectively remove coronal lesions, but its use in removing root surface lesions needs to be further investigated. This study evaluates whether simultaneously scanned NIR and CO₂-laser can be used to selectively remove root surface lesions.
Methods: Samples with natural root surface lesions were selected by verifying demineralization via NIR reflectance at 1500-1700-nm, and digital microscopy. Next, CP-OCT images were taken across sample lesions. Samples were then scanned using a NIR fiber laser to identify the region of demineralization. This image was used to selectively guide the CO₂-laser in removal of the lesion. Two groups were investigated, one with and one without dynamic focusing, i.e. changing the z-axis position of the tooth prior to imaging between ablation steps. Initial and final CP-OCT images were generated to analyze change in lesion depth. Initial and final NIR images were analyzed to assess the area of selective lesion removal.
Results: CP-OCT indicated that the laser removed 53% of the depth of the root surface lesions (n=9) without dynamic focusing, while it removed a significantly higher percentage, 86%, of the depth of root lesions (n=8) with dynamic focusing. CP-OCT images displayed a clear reduction in lesion depth, while NIR reflectance images corroborated the removal of demineralized areas on root surfaces.

Conclusions: NIR imaging modalities have proved capable of obtaining high contrast images of demineralized root surfaces. The findings indicate that the use of an image guided approach can be utilized in selectively removing lesions from root surfaces.