Assessment of the remineralization of artificial lesions via dehydration with thermal and near-IR reflectance imaging

Objectives: Previous studies have demonstrated that the optical changes that accompany the loss of water from porous lesions could be exploited to assess lesion severity with QLF, thermal and near-IR imaging. Since arrested lesions are less permeable to water due to highly mineralized surface layer, the rate of water loss can be investigated for lesion activity. The purpose of this study was to investigate whether the rate of water loss correlates with the lesion activity and whether that rate can be measured using thermal and multispectral near-IR reflectance imaging.
Methods: Artificial enamel lesions were prepared on thirty bovine enamel blocks (15 per group) using a demineralization solution at two periods (8 and 24 hours) and they were subsequently placed in an acidic remineralization solution at different periods (0, 4, 8 and 12 days) to produce varying degrees of remineralization. The samples were dehydrated using an air spray for 30 seconds and imaged via thermal and reflectance imaging at 1300-1700 nm wavelengths.
Results: The area enclosed by the time-temperature curve, ΔQ, from thermal imaging showed significant differences between the lesion window and other windows. Near-IR reflectance intensity differences, ΔI, before and after dehydration decreased with longer periods of remineralization. Near-IR wavelengths longer than 1400 nm are likely to be best suited for assessment of remineralization.
Conclusions: The highly mineralized surface layer plays an important role in the dehydration process of remineralized enamel lesions. This study demonstrated that both the thermal and near-IR reflectance imaging were suitable for detection of remineralization in simulated caries lesions, but only near-IR reflectance imaging was capable of detecting differences between different periods of remineralization.