Arif Ali Baig

Influence of crystallite microstrain on surface complexes governing the metastable equilibrium solubility behavior of carbonated apatites.

This study was on the influence of the mineral phase crystallite microstrain (CM) on the nature of the surface complex (SC) governing the metastable equilibrium solubility (MES) behavior of carbonated apatites (CAPs) in aqueous acidic media (0.10 M acetate buffers, with and without fluoride, 0.50 M ionic strength maintained with NaCl). The MES behavior of a set of four CAPs (synthesized at 85 degrees C by a precipitation method) of increasing CM and therefore of increasing MES (CAP4 > CAP3 > CAP2 > CAP1) was quantified. The following were the findings. For CAP1 and CAP2, the SCs deduced were Ca10(PO4)6(OH)2 and Ca10(PO4)6F2 for the nonfluoride and the fluoride cases, respectively. For CAP3 and CAP4, the SCs deduced were Ca9.5(PO4)6OH or Ca9.5(HPO4)(PO4)5(OH)2 and NaCa9.5(PO4)6F2 for the nonfluoride and the fluoride cases, respectively. These results together with that from an earlier limited study show that the Ca/P ratio of the SC decreases from 1.67 to 1.58 to 1.50 with increasing CM of the CAPs; this relationship inversely correlates with the chemistry of maturation of aqueously precipitated defective apatites. Also the SCs do not appear to exist as a continuous series and only a few SCs may account for the MES behavior over a wide range of CAP preparations.

Protective effects of SnF2 – Part I. Mineral solubilisation studies on powdered apatite

PURPOSE To compare the ability of two active ingredients - sodium fluoride (NaF) and stannous fluoride (SnF2 ) - to inhibit hydroxyapatite (HAP) dissolution in buffered acidic media. METHODS Two in vitro studies were conducted. HAP powder, which is representative of tooth mineral, was pretreated with: test solutions of NaF or SnF2 , 10 g solution per 300 mg HAP powder (Study 1); or NaF or SnF2 dentifrice slurry supernatants, 20 g supernate per 200 mg HAP powder for 1 minute followed by three washes with water, then dried (Study 2). About 50 mg of pretreated HAP was exposed to 25 ml of acid dissolution media adjusted to and maintained at pH 4.5 in a Metrohn Titrino reaction cell. Exposure of HAP to the media results in dissolution and release of hydroxide ion, increasing the pH of the solution. The increase in pH is compensated for by automatic additions of acid to maintain the original pH (4.5) of the reaction cell. Total volume of titrant added after 30 minutes was used to calculate the percentage reduction in dissolution versus non-treated HAP control. RESULTS Both F sources provided protection against acid dissolution; however, in each study, SnF2 -treated HAP was significantly more acid-resistant than the NaF treated mineral. In study 1, at 280 ppm F, representing concentrations of F found in the mouth after in vivo dentifrice use, the reduction in HAP dissolution was 47.7% for NaF and 75.7% for the SnF2 -treated apatite (extrapolated). In study 2, the reduction in HAP dissolution was 61.3% for NaF and 92.8% for SnF2 -treated samples. Differences in percentage reduction were statistically significant (Paired-t test). CONCLUSIONS Results of these studies demonstrate that both of the fluoride sources tested enhance the acid resistance of tooth mineral and that resistance is significantly greater after treatment with SnF2 compared with treatment of tooth mineral with NaF.

Metastable equilibrium solubility behavior of carbonated apatite in the presence of solution strontium.

The purpose of this study was to use the concept of metastable equilibrium solubility (MES) to describe the anomalous solubility behavior of carbonated apatite (CAP) in the presence of solution strontium. A CAP sample (4.8 wt% CO3, synthesized at 70°C) was prepared by precipitation. Baseline MES distributions were determined in a series of 0.1 M acetate buffers containing only calcium and phosphate (no strontium) over a broad range of solution conditions. In order to assess the influence of strontium, MES profiles were then determined in a similar fashion with 20, 30, 40, 50, 60, 70, and 80% of the solution calcium being replaced on an equal molar basis by solution strontium. From the compositions of the equilibrating buffer solutions, ion activity products (IAPs) of the form Ca10-nSrn(PO4)6(OH)2 (n = 0–10) were calculated in an attempt to determine the correct function governing the dissolution of the CAP preparation. The results demonstrate the following important findings: (a) at high solution strontium/calcium ratios (i.e., when 60% or more of the solution calcium was replaced by strontium), the MES profiles in all the experiments were found to be essentially superimposable when the solution IAPs were calculated using the stoichiometry of Ca6Sr4(PO4)6(OH)2, and (b), at low solution strontium/calcium ratios (i.e., when 40% or less of the solution calcium was replaced by strontium), the stoichiometry yielding MES data superpositioning was found to be that of hydroxyapatite. When other stoichiometries were assumed, good superpositioning of the data was not possible.

Characterization of cornified oral mucosa for iontophoretically enhanced delivery of chlorhexidine.

Topical administration of chlorhexidine for periodontal disease can provide advantages over systemic delivery, but is limited by the permeability of the cornified oral mucosal tissue. In the present study, passive and iontophoretic transport of tetraethylammonium, salicylate, mannitol, dexamethasone, fluoride, and chlorhexidine across bovine palate was investigated to (a) determine the intrinsic barrier properties of bovine palate for its eventual use as a model of human cornified oral mucosa, (b) examine the feasibility of iontophoretically enhanced transport of chlorhexidine into and across bovine palate, and (c) identify the transport mechanisms involved in iontophoretic transport across the palate. The histology study suggests that bovine and human palates have similar cornified epithelium structures; bovine palate could be a model tissue of human hard palate for drug delivery studies. Transport study of tetraethylammonium, salicylate, and mannitol suggests that bovine palate was net negatively charged and the cornified epithelial layer was the rate-determining barrier. The direct-field effect (electrophoresis) was shown to be the dominant flux-enhancing mechanism in iontophoretic transport of ionic compounds. Electroosmosis also contributed to the iontophoretic transport of both neutral and ionic permeants. Anodal iontophoresis enhanced the delivery of chlorhexidine into and across the palate, reduced the transport lag time, and provided tissue concentration above the drug minimum inhibitory concentration, and therefore could be a promising method to assist in the treatment of periodontal disease.

Passive and Iontophoretic Transport of Fluorides across Enamel In Vitro

Passive and iontophoretic transport of fluoride from three fluoride sources, NaF, sodium monofluorophosphate (MFP), and SnF2 solutions, across bovine enamel was investigated to (1) determine the characteristics of the intrinsic barrier of enamel for ion transport, (2) examine the feasibility of iontophoretically enhanced transport of fluoride across enamel, and (3) identify the transport mechanisms involved in enamel iontophoresis. Conductivity experiments were performed with bovine enamel specimens in side-by-side diffusion cells to evaluate the electrical and barrier properties of the enamel with electrolytes of different ion sizes and under different ion concentrations and pH conditions in vitro. Transport experiments of the enamel were performed in the diffusion cells with the NaF, MFP, and SnF2 solutions. The conductivity results showed that the enamel specimens behaved as a neutral membrane or that of low pore charge density. Cathodal iontophoresis significantly enhanced the delivery of fluoride ions across the enamel from the solutions over passive transport, consistent with Nernst-Planck theory and the direct field effect (i.e., electrophoresis) as the dominant flux-enhancing mechanism. The enamel demonstrated significant transport hindrance for the ions, and the effective pore radii of the transport pathways in the enamel were found to be approximately 0.7-0.9 nm.

Chemometric evaluation of physicochemical properties of carbonated-apatitic preparations by Fourier transform infrared spectroscopy†

The purpose of this study was to develop a simple and quick method of evaluating the physicochemical properties of carbonated apatite preparations (CAP) as an index of the bioaffinity of implantable materials based on Fourier-transformed-infrared (IR) spectra by chemometrics. The wet-synthesized CAPs contained various levels of carbonate content (CO(3)), and were analyzed microstrain parameter (MS), crystallite size parameter (CP), specific surface area (Sw), CO(3), and solubility parameter (pK(HAP)) using by X-ray powder diffraction, nitrogen gas adsorption, IR, and UV absorption. The IR spectral results of CAPs suggested that the peak intensities of CAP reflected the physicochemical properties of the samples. The IR data sets were calculated to obtain calibration models evaluating the physicochemical properties of CAPs by a partial least squares regression analysis (PLS). As validation of the calibration model, physicochemical properties of CAP could be evaluated based on validation IR data sets of independent samples, and those values had sufficient accuracy. The regression vector of each calibration model suggested that the physicochemical properties of CAP, such as CO(3), Sw, MS, CP, and pK(HAP), were affected by phosphate, hydroxyl, and carbonate groups.

Mössbauer Studies of Stannous Fluoride Reactivity with Synthetic Tooth Enamel – A Model for the Tooth Cavity Protection Actions of Novel Dentifrices

SnF2 is an important toothpaste ingredient, added for the provision of clinical efficacy for hard and soft tissue diseases and in breath protection. Synthetic calcium hydroxyapatite powders were exposed to liquid supernates (25 w/w% toothpaste water slurries, centrifuged) of Crest Gum Care® (SnF2) dentifrice. One-minute treatments were followed by 3x water washing, centrifugation and lyophilization. Post treatment, powders were analyzed by Mössbauer spectroscopy with 0.5–1 gram of treated apatite powder. Results show that tooth mineral stannous fluoride interactions include: (1) formation of surface reaction products with both Sn(II) and Sn(IV) oxidation states; (2) Sn-F binding on mineral surfaces with no evidence of SnO. The surface binding is, however, not pure Sn-F but contains contributions of other ligands, probably oxygens from surface phosphates or hydroxyl groups. Results also suggest that surface reacted stannous tin is oxidized with time, even when bound as a layer on the tooth surface. This study demonstrates for the first time the presence of Sn-F on tooth enamel post treatment and the contribution of passivation to long term stannous chemistry on tooth surfaces. The study also illustrates the practical applications of the Mössbauer technique.