Oral tissues are exposed to optical radiation during various dental treatments and diagnostic methods. However, adverse effects are seldom addressed. Hyperspectral imaging (HSI) and visible near-infrared reflection spectroscopy (VNIRS) were used to observe oral tissue changes in mice exposed to blue light with respect to erythema (erythema index; EI) and pigmentation (melanin index; MI). Pigmented mice (C57BL/6N; ngroup = 3) were exposed on the tongue and the abdominal skin for control or left unexposed. Irradiation was performed with an LED intended for photopolymerisation of dental materials (λpeaks: 409/460 nm) with irradiance ≈ 2 W/cm2 and radiant exposure ≈ 120 J/cm2. The hyperspectral measurement was performed by a camera prototype using a cooled EMCCD (1002×204 pixles; λ resolution of 4.0 nm (428-836 nm in the spectral direction); close-up lens (25 mm FOV at a working distance of 83 mm); spatial resolution at sample surface of 25 μm). The camera was scanned past the animals using a motorized translation stage. Reflectance spectra were recorded using a reflectance probe and two fiber optic spectrometers (three measurements per site per animal). MI and EI were calculated based on HSI and VNIRS reflectance spectra, and the values obtained were used to evaluate differences in tissue reflectance between the exposed and control group for each parameter immediately before exposure, immediately after (0.5 h) and ~24 h later. HIS revealed visible changes in tongue tissue scattering observed as “greying” in animals immediately after irradiation and development of condensed tissue after 24 h. Reflectance spectra obtained immediately after exposure confirmed the HSI images by changes in EI and MI of tongue tissue. Hyperspectral imaging is a promising method for assessing tissue changes after irradiation exposure, even in oral tissues of small size animals. The observed tissue damage implies that caution should be exercised when exposing oral tissue to high intensity dental blue light LEDs.

Hyperspectral imaging/reflectance spectroscopy of mouse oral tissue exposed to high intensity blue light.
Bruzell EM, Dahl JE, Milanic M, Randeberg LL.
15th Congress of the European Society for Photobiology, Liège, Belgium, 2-6 September 2013 (A)