Attenuation behavior of blue (laser) light in dentin: A literature-based evaluation regarding the validity of the Bouguer-Beer-Lambert law for dental applications

Background Knowledge about light propagation in dental hard tissue is indispensable in aesthetic dentistry and therapeutic applications of lasers. Since the blue (laser) wavelength is suitable for oral surgery, reducing bacteria in dentinal structures and light curing of composite resin fillings, this study aims to examine the attenuation properties for the wavelength of approx. 450 nm in dentin and to determine a clinically relevant attenuation coefficient. Material and Methods As a basis to evaluate an optical attenuation coefficient in coronal human dentin it was necessary to compare the optical transmittance of our own measurement for dentin thicknesses of 0.5 and 1 mm with transmittance values from studies with similar experimental setups. PubMed, Web of Science, Cochrane, Google Scholar and Scopus served as databases for data acquisition. 11 studies using various blue light sources (tungsten halogen, LED, diode laser, xenon and standard illuminants) around the spectral region 450 nm were gathered to determine optical transmittance values. Data (n=30) in the thickness range of 0.2 mm up to 6 mm dentin were investigated regarding a possible applicability of the Bouguer-Beer-Lambert law for describing the attenuation behavior of anisotropic dentin in interaction with light of blue wavelength. Results The distribution of the extinction values of all the cited studies illustrates a linear rising trend with increasing dentin thicknesses with the result of applicability of the BBL-law in a first approximation. Based on the transmittance values, a mean attenuation coefficient of 1.22 mm -1 was determined, which corresponds to an attenuation of approx. 70%. This allows the determination of an apparent optical penetration depth of 0.8 mm for light in the blue wavelength range in coronal dentin. Conclusions The results show that, despite the inhomogeneous structure of the dentin, the Bouguer-Beer-Lambert law provides a reliable order of magnitude for determining the optical penetration depth of blue light in dentin. Clinical significance Clinical laser applications require an understanding of the light propagation of defined wavelengths in biological tissues to protect adjacent structures, amongst other things. The established therapeutically relevant mean attenuation coefficient of 1.22 mm -1 for the blue wavelength of approx. 450 nm in dentin is a further step towards ensuring the safe use of photonic technologies in dentistry.