Photothermal detection of incipient dental caries: experiment and modeling

Laser induced photothermal radiometry (PTR) was applied as a safe, non-destructive, and highly sensitive tool for the detection of early tooth surface demineralization. In the experiments, teeth were treated sequentially with an artificial demineralization gel to simulate controlled mineral loss on the enamel surface. Modulated laser light generated infrared blackbody radiation from teeth upon absorption and nonradiative energy conversion. The infrared flux emitted by the treated region of the tooth surface and sub-surface was monitored with an infrared detector twice: before and after treatment. The experiments showed very high sensitivity of the measured signal to incipient changes in the enamel structure, emphasizing the clinical capabilities of the method. In order to analyze the biothermophotonic phenomena in a sample during the photothermal excitation, a theoretical model featuring coupled diffuse-photon-density-wave and thermal-wave fields was developed. The theoretical fits based on the three-layer approach (demineralizad enamel + healthy enamel + dentin) allowed fitting thermal and optical properties of the demineralized layer. The theoretical analysis showed that the dentin layer should be taken into account in the fittings.