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A radical new methodology for the exogenous mineralization of hard tissues is demonstrated in the context of laser-biomaterials interaction. The proposed approach is based on the use of femtosecond pulsed lasers (fs) and Fe 3+ -doped calcium phosphate minerals (specifically in this work fluorapatite powder containing Fe 2 O 3 nanoparticles (NP)). A layer of the synthetic powder is applied to the surface of eroded bovine enamel and is irradiated with a fs laser (1040 nm wavelength, 1 GHz repetition rate, 150 fs pulse duration and 0.4 W average power). The Fe 2 O 3 NPs absorb the light and may act as thermal antennae, dissipating energy to the vicinal mineral phase. Such a photothermal process triggers the sintering and densification of the surrounding calcium phosphate crystals thereby forming a new, dense layer of typically ∼20 μm in thickness, which is bonded to the underlying surface of the natural enamel. The dispersed iron oxide NPs, ensure the localization of temperature excursion, minimizing collateral thermal damage to the surrounding natural tissue during laser irradiation. Simulated brushing trials (pH cycle and mechanical force) on the synthetic layer show that the sintered material is more acid resistant than the natural mineral of enamel. Furthermore, nano-indentation confirms that the hardness and Young’s modulus of the new layers are significantly more closely matched to enamel than current restorative materials used in clinical dentistry. Although the results presented herein are exemplified in the context of bovine enamel restoration, the methodology may be more widely applicable to human enamel and other hard-tissue regenerative engineering. Statement of significance In this work we provide a new methodology for the mineralisation of dental hard tissues using femtosecond lasers and iron doped biomaterials. In particular, we demonstrate selective laser sintering of an iron doped fluorapatite on the surface of eroded enamel under low average power and mid-IR wavelength and the formation of a new layer to substitute the removed material. The new layer is evaluated through simulated brushing trials and nano-indentation. From the results we can conclude that is more acid resistant than natural enamel while, its mechanical properties are superior to that of current restorative materials. To the best of our knowledge this is the first time that someone demonstrated, laser sintering and bonding of calcium phosphate biomaterials on hard tissues. Although we here we discuss the case of dental enamel, similar approach can be adopted for other hard tissues, leading to new strategies for the fixation of bone/tooth defects. [ABSTRACT FROM AUTHOR]

The aim of this in vitro single blind study was to investigate the dose response of fluoride in milk on enamel demineralisation and remineralisation under pH cycling using transverse microradiography (TMR). Enamel slabs (n = 11) with caries-like lesions were exposed to milk containing 6 different fluoride concentrations (0, 0.25, 0.5, 1.0, 5.0 and 10.0 ppm F). On each of the 14 days of the cycling period the lesions were exposed to five 2-minute periods of cariogenic challenge (1.5 mM CaCl2, 0.9 mM KH2PO4 and 50 mM acetic acid at pH 5.0) and two 5-min periods in milk plus 10 min in a milk/saliva (1:3) slurry. The slabs were stored at 37°C in artificial saliva throughout the cycling period and demineralisation and remineralisation was assessed by TMR using dedicated image software. Remineralisation (ΔZ) was observed in all fluoride groups in contrast to demineralisation in the non-fluoride control. Remineralisation was significant (p < 0.05) for all concentrations above 1.0 ppm F. The results showed that fluoride concentration in milk exhibited a clear dose dependency and that the presence of fluoride even at low concentrations promoted remineralisation in this pH-cycling model. Copyright © 2012 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Abstract: Objectives: This study investigated the effect of two concentrations of fluoride in milk, 2.5 and 5.0ppm, on the prevention of demineralisation with a cariogenic challenge compared with milk with 0ppm F. Methods: In a controlled, randomised, cross-over, double-blind in situ study, 23 subjects wore a lower removable appliance with 2 enamel slabs for 21days during each study arm. Subjects used F-free toothpaste and the cariogenic challenge comprised of five 2min dippings per day in 12% sucrose. The slabs were dipped in 50ml of milk with 0ppm, 2.5ppm or 5.0ppm F twice daily for 5min. Subjects drank 100ml twice per day of the same milk. Slabs were analysed with Knoop microhardness to assess changes in mineralisation. Results: Results showed that enamel was softened in all groups but the extent of enamel softness was reduced with an increasing concentration of F in milk, being highly significant for both F groups compared to the control (p <0.0001). 5.0ppm F group showed a trend towards less softening compared to the 2.5ppm F but was not statistically significant. Conclusions: In our in situ model, 2.5 and 5.0ppm F in milk significantly protected enamel from demineralisation. [Copyright &y& Elsevier]