Complex index of refraction of dental enamel at CO_2 laser wavelengths

Abstract

The reflectance vs angle of incidence method was used to determine the refractive index and absorption coefficient of dental enamel at CO(2) laser wavelengths. A strong wavelength dependence of the optical constants was observed in this spectral region which corresponds to a well-known absorption band of hydroxyapatite, the main constitutent of dental enamel. A directional dependence of the optical constants of dental enamel was also observed. The absorption coefficient reaches a maximum between 9.75 and 10 microm. This particularity may be important for the main CO(2) laser treatments proposed in dentistry up to now: surface treatment of teeth and fusion of dental materials.

Permanent and transient changes in the reflectance of CO2 laser-irradiated dental hard tissues at λ = 9.3, 9.6, 10.3, and 10.6 μm and at fluences of 1–20 J/cm2

“…The combined specular and diffuse reflectance values of ten polished sections from extracted, unerupted human third molars and ex- tracted bovine incisors were measured at 9.3, 9.6, 10.3, and 10.6 m and are listed in Table 2. Our measured values for bovine and human enamel are similar to those published by Duplain et al [15] for bovine enamel. The reflectance of human dentin is considerably lower than that of human enamel.…”

“…Furthermore, our fluences were lower and would therefore be expected to lead to a much smaller plume. The low-fluence reflectance measurements tabulated in Table 2 indicate that the low-intensity reflectance of human and bovine enamel varies strongly over the wavelength range of the CO 2 laser, exceeding 49% at 9.6 m. These results are consistent with earlier results obtained by Duplain et al [15] on bovine enamel. Because the reflectance is primarily due to the phosphate absorption, it is directly related to the mineral content of the tissue (Table 3).…”

“…However, when k is very large, this measurement is difficult. Duplain et al [15] estimated the optical constants of bovine enamel at various CO 2 laser wavelengths (9-11 m) from angularly resolved, polarized reflectance data using the Lorentz model to interpret the data. If the surface of the irradiated tissue is heated sufficiently, the optical constants may change significantly both temporarily and permanently.…”

Near-IR imaging of thermal changes in enamel during laser ablation

“…Although this can be explained as a purely geometrical effect leading to decreasing fluence as the conical crater develops over repeated laser pulses, it appears worse for the 9.3 and 9.6-µm wavelengths that manifest high reflectance. The imaginary component of the refractive index at those wavelengths gives rise to reflectance values approaching 50% (10,11). …”

Оптические постоянные монокристалла апатита в ИК области 6-28 mum

“…Для средней ИК об-ласти информация по оптическим постоянным апатита практически отсутствует, за исключением работы [21], в которой данные, полученные методом классического дисперсионного анализа, представлены в виде парамет-ров осцилляторов, с помощью которых описывалась спектральная кривая коэффициента отражения R(ν). Од-нако имеются числовые данные, касающиеся измерений на эмали дентина зуба, применительно к длинам волн 9.6, 10.3 и 10.6 µm СО 2 -лазера [22,23]. Поскольку эмаль дентина состоит на 98% из апатита [14], эти данные можно сопоставить с измерениями для апатита.…”