Interaction of bio-minerals and gels with ultrafast lasers for hard tissue surface engineering

Acid-induced enamel erosion leading to dentine hypersensitivity is a growing problem for both the young and ageing population worldwide. Dentinal hypersensitivity is rising for the ageing population because of additional enamel wear. Both conditions adversely affect lifestyle and potentially can harm the systemic health of the patients. Since the loss of enamel is an irreversible process in vivo, the only way for restoring it is via exogenous means. In this work a novel route for enamel restoration using an acid-resistant, calcium phosphate based bio-mineral and ultrafast (femto-second, fs) pulsed lasers in the near IR wavelength is demonstrated. A mixture of calcium phosphate (in the form of mineral brushite) powder with a bio-mineral gel was used to coat acid eroded bovine enamel surfaces. After forming the mineral layers, the samples were irradiated with two different 100 - 200 fs pulsed lasers, one at 800 nm with 1 kHz repetition rate, and the other at 1044 nm with 1 GHz repetition rate. The laser-irradiated samples were characterized using X-ray diffraction, SEM, and Raman microscopy. It was found that irradiation with 1 GHz transformed brushite crystals to β-calcium pyrophosphate while the bio-mineral gel coating was melted and formed a homogeneous film on the enamel surface.