Topical fluoride treatment prevents dental caries. However, the resulting calcium-fluoride-like deposits are soft and have poor wear resistance; therefore, frequent treatment is required. Lasers quickly heat surfaces and can be made portable and suitable for oral remedies. We examined the morphology, nanohardness, elastic modulus, nanowear, and fluoride uptake of fluoride-treated enamel followed by CO2 laser irradiation for 5 and 10 sec, respectively. We found that laser treatments significantly increased the mechanical properties of the calcium-fluoride-like deposits. The wear resistance of the calcium-fluoride-like deposits improved about 34% after laser irradiation for 5 sec and about 40% following irradiation for 10 sec. We also found that laser treatments increased fluoride uptake by at least 23%. Overall, laser treatment significantly improved fluoride incorporation into dental tissue and the wear resistance of the protective calcium-fluoride layer.
Metal rubber (MR) is a damping material with a space-disordered network interpenetrating structure. The fretting wear and fracture of its internal spiral turn caused by mutual extrusion and friction are the main reasons for its fatigue failure. However, the research on fretting wear of metal wire with curvature inside metal rubber is rarely reported, and the in uence of curvature on the fretting wear of spiral metal wire is unclear. In order to deeply explore the fretting wear characteristics of metal wires with curvature, the fretting wear evolution model of metal wires with curvature was deduced and constructed in this work.Combined with nite element simulation and tribological test, the difference of fretting wear between metal wire with curvature and metal wire without curvature was analyzed. The results show that the fretting wear model of metal wire with curvature can accurately predict the wear degree of metal wire with curvature. The prediction accuracy error is within 10% under all working conditions. There are apparent differences between the metal wire with curvature and the metal wire without curvature under the same working conditions. In particular, when the metal wire contacts at a slight angle, the difference in the wear degree between them is extensive, and the error decreases with the increase of contact angle. The fretting wear evolution model of metal wire with curvature is more suitable for predicting fretting wear of metal wire contact pairs, which abound in MR in the form of low contact angle and high curvature.
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