The Dissolution Kinetics of Hydroxyapatite in the Presence of Kink Poisons

Abstract

Le addition de phosphates exerceva nulle influentia super le rapiditate del dissolution. Sub conditiones de un vigorose convection fortiate, le emanation de iones ab sitos de defectos superficial pareva restringer le intensitate del dissolution. Alora le addition de phosphates organic e inorganic reduceva le rapiditate del dissolution per un factor de inter 2 e 8, e iste phenomenon esseva attribute a absorption a sitos de defectos superfical.Phenomenologically, tooth decay is simply the dissolution of enamel in saliva. The inorganic structural component of human dental enamel, which constitutes about 95 per cent by weight of this layer, is predominantly hydroxyapatite.J Thus, the various process consists essentially of the dissolution of hydroxyapatite in an aqueous solvent. The influences exerted by different substances on this dissolution step are relevant to the consideration of possible mechanisms whereby cariostatic agents exert their activity.Studies of the rate of dissolution of human dental enamel in acidic solutions, both in the presence and in the absence of additives, have previously been reported. 2-Interpretation of the results of these studies was, however, complicated by three factors: by the presence of the organic matrix1 in the enamel; by the failure to differentiate clearly between changes in equilibrium solubility and changes in dissolution rate; and by the performance of experiments in poorly defined hydrodynamic situations.Less equivocal information7 can be derived from studies of the dissolution kinetics of synthetic hydroxyapatite pellets both in the presence and in the absence of additives. Such studies, which are themselves of intrinsic interest, have not apparently been reported in detail previously. Materials and MethodsAll chemicals were of A.R. grade unless otherwise stated, and all solutions were prepared in double-distilled water.Hydroxyapatite was prepared by a modification of the method of McCann.5 To an alkaline boiling solution of 1.5M ammonium nitrate (1.5 1.), solutions of 0.20M calcium acetate (500 ml.) and 0. 12M ammonium dihydrogen phosphate (500 ml.) were added separately, but at equal rates, over a period of 3 hours. The resulting slurry was refluxed for a further 24 hours, the product being then separated, washed, and dried. The yield was about 95 per cent.

Effect of Carbonate and Fluoride on the Dissolution Behaviour of Synthetic Apatites

“…How ever, fluoride present in the buffer solu tion at I ug/ml did reduce the dissolution rate by 20-30%, and this is consistent with numerous reports in the literature [Napper and Smythe, 1966;Forward, 1977;AponteMerced and Feagin, 1979;Grenby and Bull, 1980]. Tung el al., [1981] recently de monstrated exchange of F" for OH" at the surface sites of apatite, and this is consist ent with the observations and mechanism proposed here.…”

“…Other workers have suggested that the dissolu tion of non-carbonated hydroxyapatite and dental enamel is diffusion controlled [StralJ'ors, 1958;Gray. 1962;Napper and Smythe. 1966;Higuchi et al, 1969;Linge and Nancollas, 1973;White and Nancollas, 1977].…”

A New Method of Measuring Hydroxyapatite Dissolution Rate

“…3, 4) although no categorical statement on the rate orders could be made it appeared to be first for calcium and sec ond for phosphorus with respect to undersa turation. Napper and Smythe [1966], how ever, using a porous disc found the dissolu tion of hydroxyapatite as measured by weight to be second order.…”

Characterization and identification of mixed-metal phosphates in soils: the application of Raman spectroscopy

“…Attempts to synthesize mixed-metal hydroxylapatites in the binary series Ca -Cd, Ca -Pb, Ca -Sr and Cd -Pb followed a method adapted from that of Valsami-Jones et al (1998) and Napper and Smythe (1966). A 300 ml solution of 1.3 M ammonium acetate was prepared, heated in a water-bath to 90ºC and the pH adjusted to 7.5 using ammonia solution.…”