Phosphoric acid activated surface modification of tooth dentine by 9.45 μm transversely excited atmosphere $CO2$ laser

Tuning a laser wavelength to the stretching vibration of specific biomolecules has some advantages in ablating hard tissue and for surface modification induced by the photothermal or the photomechanical interaction. A tunable pulsed transversely excited atmosphere $CO2$ laser was tuned to 9.45 μm, which is the stretching vibration of phosphoric acid in hydroxyapatite. Dried cow dentine was irradiated at 36 W/cm². The infrared absorption spectra of the bovine dentine sample were measured using a microscopic Fourier-transform infrared (FTIR). After laser irradiation, x-ray fluorescence of elements contained in a $300 μm×300 μm$ irradiated area was measured by energy dispersive x ray (EMAX-5770). This laser irradiation reduced the peak wavelength of the dentine surface from 9.76 to 8.93 μm. The atomic ratio of Ca/P was changed from 1.4 to 1.9 as measured with x-ray diffraction. These results show the potential for application of a 9.45μm $CO2$ laser to ablation and modification of the dentine surface as measured by FTIR absorption microscopy.