| Dental caries is a common and high-incidence disease, and it can be cured with remineralization and prevented from further deterioration by early detection. Generally, traditional caries detection methods(i.e. visual examination, dental explorer and X-ray imaging et.al.) have being of less sensitive to early caries, so that the detection method which has the merit of being more sensitive and more specific to early caries has a very significant effect on dental caries prevention and treatment. Photothermal radiometry(PTR) is a new non-destructive testing technique, which has the advantages of nondestructive, non-contractive and high resolution for nondestructive inspection and evaluation in practical application. One-dimensional thermal-wave model for tooth issue induced by modulated laser was investigated, PTR experimental system was developed, and then it was used for experimental research on PTR frequency-domain response and location scan imaging. As consequence, thermophotonic lock-in imaging(TPLI) for dental tissue was preliminarily researched.Firstly, one-dimensional thermal-wave model for three layers tooth tissue induced by modulated laser was developed in combined one-dimensional diffusion approximation of radiative transfer theory into one-dimensional heat conduction equation. Numerical simulations of PTR frequency-domain responses were carried out to analyze the effect of caries characteristic parameters(i.e. optical scattering coefficient, absorption coefficient, the thermal diffusivity coefficient and the caries layer thickness et.al.) on the PTR signal.Secondly, PTR frequency-domain scanning and location scanning imaging systems were developed, which included the building of hardware and the programming of software based on Lab VIEW & Matlab. The PTR amplitude and phase are effectively collected, recorded and analyzed by this software system. The PTR system stability was verified by using comparison analysis of PTR responses at the different laser peak power stimulation.Thirdly, PTR frequency-domain scanning and location scanning imaging experiments were carried out, and the caries characteristic parameters were obtained by multi-parameters statistic best-fit. The inhomogeneous characteristic of health tooth was investigated by PTR frequency-domain scanning. Simultaneously, the relationship between the caries levels and the corresponding characteristic parameters was analyzed by PTR frequency-domain scanning and location scanning imaging of artificially created demineralization tooth. Furthermore, the validity of simulation analysis was studied.Finally, thermophotonic lock-in imaging(TPLI) for dental tissue inspection was preliminarily investigated in compared to X-ray radiography, the results show that TPLI has the merit of high contrast and difference to tissue inhomogeneous and dental caries. Furthermore, TPLI was used for inspection the artificially created demineralization tooth with changing caries time, and the results show that TPLI has being more sensitive to dental caries position and caries level. |
