A comparative evaluation of fluoridated and non-fluoridated mouthrinses using a 5-day cycling enamel erosion model
ABSTRACT To assess the relative protective effect of commercial mouthrinses containing 0-450 ppm fluoride on erosion progression in enamel using a simulated 5-day in vitro cycling model with concurrent monitoring of surface microhardness (SMH) and bulk tissue loss.
Specimens were randomly assigned to six treatment groups (n=6). The model mimicked morning and evening use with rinse times (30 or 60 s) reflecting those prescribed on pack, interspersed with three cycles of demineralisation/remineralisation per simulated day. The latter comprised 1.0% citric acid monohydrate pH 3.2 for 300 s, with subsequent remineralisation in mucin-free artificial saliva pH7.0 for 120 min. SMH was determined by Vickers microindentation and bulk tissue loss using white-light interferometry.
From the end of day 1, fluoride-containing mouthrinses conferred statistically significant reductions in bulk tissue loss versus fluoride-free rinses (p<0.05), with lesion depth inversely proportional to fluoride concentration. From day 3, the mean lesion depth of specimens treated with the 450 ppm rinse were statistically significantly lower than all comparator treatment groups (p<0.05). Two distinct trends were apparent when comparing SMH changes in groups treated with fluoride-free versus fluoride-containing mouthrinses. In the latter, SMH levelled out over the final three simulated days in contrast to the former whose SMH continued to fall; differences were statistically significant at day 5 (p< 0.05).
Bulk tissue loss is inversely proportional to fluoride concentration in this cycling model. The plateau in SMH reflects stabilisation of mineral density as the study progresses and the number of fluoride binding sites and consequently uptake increases, in turn leading to enhanced lesion remineralisation.
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ABSTRACT: Firstly, determine the effect of pre-treating sound human enamel with a hydrosoluble combination polymer system (TriHydra™) comprising 0.20% carboxymethylcellulose, 0.010% xanthan gum and 0.75% copovidone, alone or in combination with fluoride, on in vitro erosion by citric acid. Secondly, investigate the effect of the polymers on fluoride uptake by incipient erosive lesions. Study 1: Sound enamel specimens were treated (60s, 20°C, 150 rpm) with either (i) deionised water, (ii) polymers in deionised water, (iii) 300 mg/L fluoride or (iv) polymers in 300 mg/L fluoride. Specimen groups (n=5) were then immersed in 1.0% citric acid (pH 3.8, 300 s, 20°C, 50 rpm) and non-contact profilometry was used to determine surface roughness (Sa) and bulk tissue loss. Study 2: Incipient erosive lesions were similarly treated with (i)-(iv). Dynamic Secondary Ion Mass Spectrometry (DSIMS) was then used to determine the fluoride depth-distribution. Study 1: Mean±SD Sa and erosion depths for treatment groups (i)-(iv) were (a)657±243, (b)358±50, (c)206±72, (d)79±16 nm and (a)19.73±8.70, (b)2.52±1.34, (b)0.49±0.34 and (b)0.31±0.21 mm respectively (matching superscripts denote statistically equivalent groups). Study 2: Lesions treated with (iii) and (iv) exhibited similar fluoride penetration depths (∼ 60 μm). Mean fluoride intensity ratios based on F/(F+P) at 1 μm for treatment groups (i)-(iv) were (a)0.010±0.004, (a)0.011±0.004, (b)0.803±0.148 and (c)0.994±0.004 respectively. The combination polymer system exhibited anti-erosion efficacy in its own right. The polymer/fluoride admixture statistically significantly reduced Sa, however suppression of bulk tissue loss was not statistically significantly different versus either treatment alone. The presence of polymer appears to promote fluoride uptake by erosive lesions most noticeably in the first 6 μm.Journal of dentistry 11/2010; 38 Suppl 3:S4-11. DOI:10.1016/S0300-5712(11)70003-3 · 2.84 Impact Factor
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ABSTRACT: In this paper, we present a generalized physical model used for simulation of photovoltaic (PV) cells, panels and arrays taking into account the direct and the reverse modes. This model is useful for power electronic systems. This model named Direct-Reverse Model is simple, fast, accurate and can help designers to study industrial systems. It is based on the basic two diodes model representing a PV cell/panel/array. It allows the investigation of the I-V and P-V characteristics at different situations such as mismatches due to the partial or global shaded PV cell at various environmental conditions by changes in PV cell surface temperature and/or solar radiation. Also the effect of the by-pass diode protection and its contributions to reduce the magnitude of the hot spots heating in a shaded PV cell are analysed. A set of experimentations on the behaviour of solar cells and solar panels have been made to validate our physical model.Energy Procedia 01/2011; 6:695-703. DOI:10.1016/j.egypro.2011.05.079
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ABSTRACT: To evaluate the effectiveness of a dentifrice with 5000ppm fluoride in preventing dental erosion by orange juice in situ in comparison to a control dentifrice with 1450ppm fluoride. This was a double-blind and randomized clinical study with a cross-over design. Sixteen subjects wore an intra-oral appliance containing two enamel disks with an exposed surface of approximately 2mm×5mm. Enamel disks in the study group were treated with a dentifrice with 5000ppm fluoride and in the control group with 1450ppm fluoride. The subjects rinsed with slurries of study dentifrices for one minute before immersing the enamel disks in 250ml orange Juice four times in an 8-h period daily. The treatment procedure was repeated for three 5-day phases for each dentifrice. Enamel erosion was measured after each 5-day treatment phase using a focus-variation 3D scanning microscopy. Medians and inter-quartile ranges (IQR) of mean erosion depth were compared between the groups. The mean erosion depths of enamel varied greatly amongst the subjects. Enamel treated with 5000ppm fluoride had less erosion (median 5.7μm, IQR 4.5μm) as compared to the control (median 12.6μm, IQR 12.3μm) after 15 days of fluoride treatment and erosive challenge cycles (p<0.05). Enamel treated with 5000ppm fluoride had significantly improved resistance to erosion by orange juice. Periodic application of 5000ppm fluoride may be beneficial in individuals at risk of acidic erosion associated with soft drink consumptions.Journal of dentistry 08/2011; 39(10):672-8. DOI:10.1016/j.jdent.2011.07.009 · 2.84 Impact Factor