Mechanical and optical properties are the main criteria for assessing the health of dental tissue in contemporary dentistry. Dentinal pathological changes can be detected by visuo-tactile and radiographic methods to guide clinicians in establishing a relevant diagnosis and an adapted therapy. However, such approaches cannot give information on the dentinal microstructure. Recently, laser ultrasonic techniques have been deployed to evaluate the mechanical properties of enamel [1,2] However, such techniques lack the resolution to reveal the transitions differences between tissue layers.
In this work, we used Brillouin light scattering spectroscopy as a non-contact alternative to probe mechanical changes in dentin and dentin-resin interface at GHz hypersonic frequencies. We obtained maps of the Brillouin frequency shift and linewidth that can be interpreted as maps of sound velocity and viscosity. In addition, we observed the specimens by a homemade nonlinear microscopy setup . A 730 nm wavelength Titanium-sapphire laser was used as an excitation source for two-photon excitation fluorescence microscopy (TPEF), while 1040 nm wavelengthYb:KGW laser was used for second harmonic generation (SHG).
Our results show significant changes between healthy tissues and pathological lesions. Such results can help to precisely delineate destructed dentin during clinical procedures, paving the way to minimally invasive strategies. In addition, our simultaneous analysis of Brillouin maps and nonlinear images brings valuable information on structure-related mechanical properties of dentin and dentin-resin adhesive interface.
1. Wang et al, Experimental and numerical studies for nondestructive evaluation of human enamel using laser ultrasonic technique. Appl Opt 52, 6896-6905 (2013).
2. Wang et al., Laser ultrasonic evaluation of human dental enamel during remineralisation treatment. Biomed Opt Express 2, 345-355 (2011).
3. Rabasović M et al. Nonlinear microscopy of chitin and chitinous structures: a case study of two cave-dwelling insects. J Biomed Opt 20, 016010 (2015)