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

Abstract

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 (ΔI) 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

Dynamic SWIR imaging near the 1950-nm water absorption band for caries lesion diagnosis

“…In this study, there was no significant difference in ΔI between the active and arrested lesions at 1950 nm or for most of the other wavelengths, with only 1300 nm showing a significant difference. This result conflicts with previous studies, including the recent study on bovine enamel blocks 21 where ΔI was significantly higher for active lesions. In this study, the lesions were chosen based on microCT data and are much deeper than the lesions that were chosen for previous investigation that utilized measurements with optical coherence tomography, which has a more limited imaging depth.…”

“…The high contrast of demineralization and the high sensitivity to water absorption suggests that 1950 nm should be ideal for SWIR reflectance dehydration measurements and recent studies of simulated lesions on bovine enamel blocks support this hypothesis. 21 That study also found that the change in contrast after drying (ΔI) was significantly higher at the 1950-nm broadband source than at other wavelengths in the 1500 to 2340-nm wavelength range. 21 The purpose of this study is to investigate the use of SWIR reflectance dehydration measurements at 1950 nm to assess the activity of naturally formed caries lesions on extracted teeth.…”

“…21 That study also found that the change in contrast after drying (ΔI) was significantly higher at the 1950-nm broadband source than at other wavelengths in the 1500 to 2340-nm wavelength range. 21 The purpose of this study is to investigate the use of SWIR reflectance dehydration measurements at 1950 nm to assess the activity of naturally formed caries lesions on extracted teeth.…”

“…When dry, the contrast is markedly higher from the lesion areas at 1950 nm compared with other wavelengths, which is consistent with what has been observed in other recent studies. [20][21][22] Dehydration curves for the SWIR wavelengths investigated in this study are plotted in Fig. 4 for an arrested lesion and an active lesion along with best-fit curves using Eq.…”

“…19 Recent studies at wavelengths beyond 1700-nm show that the contrast of demineralization on tooth surfaces continues to increase with increasing wavelength due to decreasing scattering in sound enamel and increasing water absorption. [20][21][22] Contrast is particularly high near the strong water absorption band at 1950 nm. The high contrast of demineralization and the high sensitivity to water absorption suggests that 1950 nm should be ideal for SWIR reflectance dehydration measurements and recent studies of simulated lesions on bovine enamel blocks support this hypothesis.…”