Quantitative Analysis of Incipient Dental Mineral Loss

Objectives: Laser induced photothermal radiometry (PTR) was applied as a safe, non-destructive, and highly sensitive tool for the optical and thermal evaluation of tooth properties before and after demineralization treatment.

Methods: In the experiments, teeth were treated sequentially with an artificial demineralization gel to simulate controlled mineral loss on the enamel surface. During the experiments, frequency scans were performed at the treatment location. The samples were mounted on LEGO bricks, which ensured their accurate placement in the holders for scanning, and controlled by precision micro-stages. The experimental setup included a semiconductor laser (659 nm, 80mW) as a source of the PTR signal. 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 was monitored with an infrared detector before and after treatment. The output signal was acquired automatically using instrument control software, so no operator input influenced the results. 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.

Results: The experiments showed very high sensitivity of the measured signal to incipient changes in the enamel structure. 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 results were compared to the simplified two-layer (demineralizad enamel + healthy enamel) approach.

Conclusions: The thermal and optical properties of the demineralized tooth layers were calculated using best fits to the theory. Theoretical analysis showed that the dentin layer should be taken into account in the fittings. The PTR technique coupled with the multilayer theoretical model was shown to be a promising non-ionizing alternative to radiographic methods for the characterization of early tooth demineralization.