A possible second site for hydroxyapatite dissolution in acidic media

Fawzi, Mahdi B.; Fox, Jeffrey L.; Dedhiya, Mahendra G.; Higuchi, William I.; Hefferren, John J.

doi:10.1016/0021-9797(78)90015-2

Cited by 27 publications

(9 citation statements)

References 6 publications

(19 reference statements)

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“…Dissolution procedure.-The rotating disk dissolution apparatus referred to previously (Wu et al, 1976;Fawzi et al, 1978) was used. A bovine tooth was selected and mounted in the rotating disk holder with beeswax so that only the labial surface was exposed.…”

Section: Methodsmentioning

confidence: 99%

Quantitative Study of Fluoride Transport During Subsurface Dissolution of Dental Enamel

1989

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Previous studies using bovine dental enamel as a model have shown that surface and subsurface dissolution of enamel may be governed by micro-environmental solution conditions. We have now investigated the demineralization phenomenon more rigorously with the primary objective of developing a method for deducing solution species concentration profiles as a function of time from appropriate experimental data. More specifically, in this report, a model-independent method is described for determination of the pore solution fluoride gradients in bovine enamel during subsurface demineralization. Microradiography was used to determine the mineral density profiles, and an electron microprobe technique to determine total fluoride (F) profiles associated with the enamel. In each case, matched sections of bovine enamel were exposed to partially saturated acetate buffers at pH = 4.5 containing 0.5 ppm F for various periods of time (from six to 24 hours). The treated enamel was found to have an intact surface layer and subsurface demineralization. The extent of the demineralization and the depths of the lesions increased with time in all cases. The data were first used to calculate (a) the total F gradients in the enamel at various times, and (b) the local uptake rate of F as a function of time and position. Then, by manipulation of the equations describing the uptake and transport of F, we calculated the pore diffusion rate of F and the micro-environmental solution F concentration in the aqueous pores as a function of time and of distance from the enamel surface. It was also possible to calculate an intrinsic F diffusion coefficient in the pores, which was about 1.0 X 10(-5) cm2/sec, in good agreement with reported values. 14C-sucrose uptake and release experiments with identically prepared demineralized enamel sections were also conducted to provide an independent check on the assumed dependence of porosity on mineral density. The results of this investigation, especially the outcomes relative to this new method for determination of pore solution F gradients during acid attack of the dental enamel, should be valuable in future studies of the mechanism(s) of the action of F in inhibiting dental enamel demineralization.

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Section: Methodsmentioning

confidence: 99%

Quantitative Study of Fluoride Transport During Subsurface Dissolution of Dental Enamel

1989

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“…The two-site dissolution model [45][46][47] was applied to describe HANPs dissolution kinetics under different LMWOAs in the batch experiments. Site 1 predominates when dissolution occurs under unsaturated solutions, e.g., during the initial phases of dissolution, whereas site 2 becomes active during later stages particularly when dissolution approaches equilibrium, e.g., (partial) saturation solutions.…”

Section: Data Analysesmentioning

confidence: 99%

Effects of low-molecular-weight organic acids on the dissolution of hydroxyapatite nanoparticles

Wang

Jaisi

2016

Environ. Sci.: Nano

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Roles of naturally occurring low-molecular-weight organic acids (LMWOAs) on the dissolution of hydroxyapatite nanoparticles (HANPs) were explored. Our results indicate that phosphate release during HANPs dissolution is highly dependent on the type of LMWOA, which has important implications when HANPs are used as a promising phosphorus (P) nanofertilizer in agricultural soils particularly at the rhizosphere. Furthermore, stable oxygen isotope technique was employed for the first time to accurately trace O-isotopic fractionation and evolution of phosphate during HANPs dissolution in abiotic systems. Given that the HANPs pool has distinct phosphate oxygen isotope signatures compared to soil P pools, the isotope technique could be used to identify whether plant uptake of P comes from HANPs or from soils, and thus to evaluate use efficiency of HANPs by plants in agricultural soils. ABSTRACT 25Hydroxyapatite nanoparticles (HANPs) have recently been advocated as a highly-efficient and 26 environmentally-benign 'green' phosphorus (P) nanofertilizer in modern agriculture. However, 27 knowledge on how low-molecular-weight organic acids (LMWOAs) secreted by plants in 28 agricultural soils mediate the dissolution of HANPs and release of dissolved phosphate is 29 nonexistent. Here, three most commonly occurring LMWOAs (acetic, oxalic, and citric acids) 30were evaluated for their roles on HANPs dissolution in both batch and column systems. 31Particularly, O-isotopic ratios of dissolved phosphate during HANPs dissolution were measured 32 to disentangle mechanisms controlling isotope fractionation. Our results reveal that in batch 33 system HANPs dissolution was very fast but the overall dissolution efficiency was low (≤30%), 34 unlike in column system where ~100% dissolution was achieved. The low dissolution efficiency 35 of HANPs in batch system was due predominately to rapid consumption of proton; whereas in 36 column system the HANPs were progressively dissolved by low pH LMWOAs and reaction 37 products were eluted out. Regardless of LMWOA type and experimental system, the 38 isotopically-lighter phosphate (P 16 O 4 ) was preferentially released during initial phases of 39 dissolution and dissolved phosphate became gradually P 18 O 4 -enriched with time. This 40 fractionation was less in batch (−0.3‰ to +1.1‰) than in column (−1.3‰ to +1.1‰) systems 41 due primarily to lower dissolution efficiency and higher P 16 O 4 and P 18 O 4 exchange between 42 HANPs and dissolved phosphates. The Rayleigh model well described O-isotopic fractionation 43 of dissolved phosphate under different LMWOAs. Overall, our findings provide important 44 insights into the dissolution kinetics and O-isotopic evolution of phosphate-based NPs that are 45 relevant to plant-soil systems particularly at the rhizosphere. 46 47

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“…A rotating disk dissolution apparatus was used as described previ ously [Wu et al, 1976;Fawzi et al, 1978], A human enamel slab (either lased or unlased) was mounted in the apparatus with paraffin wax. Exactly 50 ml o f the demineralization buffer solution was pipetted into a jacketed beaker at 30 °C and the sample holder and enamel slab immersed.…”

Section: Rotating Disk Dissolution Apparatus and Proceduresmentioning

confidence: 99%

Combined Effects of Laser Irradiation and Chemical Inhibitors on the Dissolution of Dental Enamel

Fox

Otsuka

et al. 1992

Caries Res

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It has previously been shown that the susceptibility of human teeth to acid dissolution can be reduced by the presence of various chemical agents in the dissolution medium or by pretreatment of the teeth with laser irradiation. Now synergism between these two approaches to improving acid resistance has been demonstrated. Extracted human teeth were irradiated with a continuous-wave carbon dioxide laser at a wavelength of 10.6 μm. Energy doses of either 65 or 130 J/cm² given over periods of 2 or 4 s, respectively, were applied and the teeth subjected to a severe acid challenge (0.1 M acetate buffer, pH 4.5, no calcium or phosphate common ion present) for 24 h. Mineral loss was assessed by measurement of mineral density profiles with quantitative microradiography. Experiments were carried out in the presence or absence of three chemical inhibitors with distinctly different mechanisms of action: ethane-1-hydroxy-ll-di-phosphonic acid, fluoride, and dodecylamine HCl. Laser irradiation alone was found to lead to increased resistance of the teeth to acid challenge, with the higher energy dose being more effective than the lower dose. Each of the chemical inhibitors was effective on both lased and unlased teeth, with the percent reduction of dissolution greater when the inhibitors were applied to teeth lased with an energy dose of 130 J/cm² which were already more resistant to acid challenge than were unlased teeth or teeth lased with a dose of 65 J/cm². Thus, the inhibitors and the higher energy laser treatment were synergistic, with the combination of laser treatment and each of the inhibitors resulting in almost complete inhibition of dissolution for the entire 24 h of acid challenge as compared with a loss of about 140 μm of enamel from the surface of the control teeth.

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A possible second site for hydroxyapatite dissolution in acidic media

Cited by 27 publications

References 6 publications

Quantitative Study of Fluoride Transport During Subsurface Dissolution of Dental Enamel

Quantitative Study of Fluoride Transport During Subsurface Dissolution of Dental Enamel

Effects of low-molecular-weight organic acids on the dissolution of hydroxyapatite nanoparticles

Combined Effects of Laser Irradiation and Chemical Inhibitors on the Dissolution of Dental Enamel

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