Dissolution Of Calcium Hydroxyapatite Research Articles

Calcium and Inorganic Phosphorous Levels in Stimulated and Unstimulated Saliva in Early Childhood Caries – A Comparative Study

Introduction: Saliva, a chief player in the oral cavity, is determined by its secretion rate and quality to aid either in the development of caries, or its remineralization.6 The ability for saliva to function as a source of calcium and phosphate increases its supportive properties as it influences the precipitation or dissolution of calcium hydroxyapatite (HAP), the principal inorganic component of dental hard tissue. Materials & Methods: 30 healthy children, aged between 3 and 6 years old were screened and recruited for the study at the Department of Pedodontics and Preventive Dentistry of the A.B Shetty Memorial Institute of Dental Sciences, a constituent of Nitte University. The subjects were clinically examined and scored based on their decayed, missing (due to caries) and filled surfaces (dfs) and were further categorized into two equal groups of 15. Result: In the subjects with Early Childhood Caries (ECC), the mean calcium concentration in samples of unstimulated saliva was 4.2383 ± 0.8594 and in samples of stimulated saliva was 4.1965 ± 0.6240. While, the mean inorganic phosphorous concentration in samples of unstimulated saliva was 3.219 ± 0.8540and in samples of stimulated saliva was 3.0634 ± 0.5470. Conclusion: From this study, we obtained a relationship between calcium, saliva and the caries status of children with the calcium concentration decreasing with increase in the caries status, as well as on stimulation of saliva.

Kinetics of growth and dissolution of calcium hydroxyapatite in suspensions with variable calcium to phosphate ratio

Kinetics of growth and dissolution of calcium hydroxyapatite at constant pH (6.0 and 7.2), and with variable values of the calcium to phosphate mole ratio in solution (0.1<Ca/P<20) are reported. Both processes are shown to be controlled by the polynuclear surface mechanism in which nucleation is expressed as a function of mean-ion activity. For dissolution, the lateral growth rate of nuclei is proportional to the difference between the total concentration of calcium ions in a saturated solution and in the solution, and the rate constant is related to the frequency for a calcium ion to make a diffusion jump into a kink and simultaneously, partially dehydrate. For growth, a newly developed model for the lateral growth rate is applied. This model takes into account that hydroxyl ions are formed at hydroxyl sites slightly below the growing surface by dissociation of trapped water molecules. In this way the lateral growth rate consists of two consecutive reactions, the process of calcium ions entering calcium sites, accompanied by phosphate ions, being delayed by the relatively slow production of hydroxyl ions at hydroxyl sites. The frequency for ion integration is found to be within a factor of 2 of the expected value, 1.6×10 5/s, for both growth and dissolution, both values of pH and all values of Ca/P studied. As this frequency is practically constant, the frequency for a calcium ion to leave a kink decreases as the saturation concentration of calcium decreases. This reflects important changes in the dynamics of the crystal surface. Kinetically determined values for the surface tension are for growth σ=100 mJ/m 2 and for dissolution σ=40 mJ/m 2.

Mechanism and Kinetics for the Dissolution of Apatitic Materials in Acid Solutions

Abstract - This work concerns the study of the digestion step in the production process of phosphoric acid. Some qualitative experiments indicate that the difference between the pH at the surface of the phosphate and that in the bulk of the solution is negligible and that the dissolution is controlled by diffusion of products away from the phosphate particle. In further experiments, to isolate the dissolution phenomenon from the formation of calcium sulfate, the sulfuric acid normally used industrially is replaced by hydrochloric acid. The phosphate material used in our experiments is a model apatitic material: synthetic hydroxyapatite (HAP). The dissolution of calcium hydroxyapatite was studied with increasing amounts of calcium and phosphate at different temperatures. A simple method was developed for this observation based on the time required for complete dissolution of the HAP powder. The results confirm that the dissolution is controlled by a diffusional process through an interface of calcium and phosphate ions released from the solid surface. A kinetic model for the dissolution of apatitic materials is proposed which assumes a shrinking particle behaviour controlled by diffusion of calcium ions. The experimental results are fitted to this model to determine the mass transfer constant for HAP dissolution in acid solutions. The activation energy of the reaction is about 14kJ/mol. This study was carried on in conditions similar to the industrial ones for the production of phosphoric acid by the dihydrate-process

Diffusion coefficients for the ternary system Ca(OH)2–H3PO4–water

A conductimetric method has been used to measure the ternary diffusion coefficients of calcium hydroxide–phosphoric acid in dilute aqueous solution at 25 °C. Diffusion coefficients for concentrated solutions of the electrolytes are evaluated from previously reported Gouy optical data for the related system Ca(H2PO4)2–H3PO4–water. The experimental results indicate strong electrostatic coupling between diffusive flows of aqueous Ca(OH)2 and H3PO4. The implications for dissolution of calcium hydroxyapatite, the main constituent of bone and teeth, are discussed.