High Contrast Reflectance Imaging of Enamel Demineralization and Remineralization at 1950‐nm for the Assessment of Lesion Activity

Background and Objectives Previous studies have shown that large changes in the diffuse reflectivity of caries lesions during drying with air can be used to assess lesion activity. The largest changes occur at short wavelength infrared (SWIR) wavelengths coincident with high water absorption. The strongest water absorption in the SWIR occurs at 1950 nm. In this study changes in the reflectivity of simulated lesions with varying degrees of remineralization was measured at 1500–2340 nm and at 1950 nm as the samples were dried with air. Study Design/Materials and Methods Twenty bovine enamel surfaces each with five treatment windows were exposed to two demineralization/remineralization regimens to produce simulated lesions of varying depth, severity, and mineral gradients. An extended range tungsten‐halogen lamp with a long pass filter (1500–2340 nm) and a broadband amplified spontaneous emission source centered near the peak of the water‐absorption band at 1950‐nm were used as light sources and an extended range InGaAs camera (1000–2340 nm) was used to acquire reflected light images as the samples were dried with air. Lesions were also assessed using digital microscopy, polarized light microscopy, optical coherence tomography, and transverse microradiography. Results Both wavelength ranges showed extremely high lesion contrast (>0.9) for all six lesion treatment windows in both models. The change in contrast (Δ I ) was significantly higher for the 1950 nm broadband source for all the intact lesion windows compared with the 1500–2340 nm wavelength range. Conclusion SWIR light at 1950 nm yields extremely high contrast of demineralization and appears to be the optimum wavelength for the assessment of lesion activity on tooth coronal surfaces. Lasers Surg. Med. 00:00–00, 2020. © 2020 Wiley Periodicals LLC