Thermophotonic lock-in imaging: A novel early caries detection and imaging modality

Using photothermal wave principles and as an extension to the frequency-domain photothermal radiometry, a novel dental imaging modality, thermophotonic lock-in imaging (TPLI), is introduced. In order to assess the capabilities of the proposed methodology samples with natural and artificially-generated caries were examined and the results were compared with the destructive transverse microradiography density profiles. It was found that the increased light scattering and absorption within early carious lesions increases the thermal-wave amplitude and shifts the thermal-wave centroid, producing contrast between the carious lesion and the intact enamel in both amplitude and phase images. Phase images are emissivity normalized and therefore insensitive to the presence of stain. Amplitude images provide integrated information from deeper enamel regions. It was concluded that the results of our non-invasive, non-contacting imaging methodology exhibit significantly higher sensitivity to very early demineralization than dental radiographs and are in agreement with the destructive transverse microradiography mineral density profiles.