Fluoride remineralization of demineralized bovine tooth enamel and hydroxyapatite pellets

Quantitative remineralization evolution kinetics of artificially demineralized human enamel using photothermal radiometry and modulated luminescence

Human molars were subjected to demineralization in acid gel followed by incubation in remineralization solutions without or with fluoride (1 or 1000 ppm). Photothermal radiometry (PTR) and modulated luminescence (LUM) frequency scans were performed prior to and during de/remineralization treatments. Transverse Micro-Radiography (TMR) analysis followed at treatment conclusion to determine mineral loss and lesion depth. The remineralization process illustrated a complex interplay between surface and subsurface mineral deposition, confining the thermal-wave centroid toward the dominating layer. Experimental amplitudes and phases were fitted to a coupled diffuse-photon-density-wave and thermal-wave theoretical model used to quantitatively evaluate evolving changes in thermal and optical properties of de/remineralized enamel lesions. Additional information obtained from the LUM data corroborated the remineralization kinetics affecting the PTR signals. The results pointed to enhanced effectiveness of subsurface lesion remineralization in the presence of fluoride.

Electron probe micro-analysis for subsurface demineralization and remineralization of dental enamel

A quantitative study of fluoride distribution profile changes in dental enamel was conducted by means of electron probe micro-analysis (EPMA). Fluoride-deposited hydroxyapatite powders were chosen as fluoride standards, and analytical conditions were optimized. The lower limit of detection for fluoride was estimated to be 270 ppm, with an accelerating voltage of 5 kV, a specimen current of 40 nA, and a counting time of 40 seconds. Fluoride profiles in fluoride-treated dental enamel, which exhibited intact surface layers and subsurface demineralization, were determined. The results were also compared with those of an acid-abrasion method, and reasonable consistency was found between these two methods, although the acid-abrasion procedure yielded a slightly lower fluoride content in the initial layers, followed by a higher content of fluoride in the deeper layers. The precision of fluoride profile data obtained from EPMA permits further studies to be conducted on the kinetics of subsurface demineralization and intact surface layer formation ("white spot" formation) which is observed during the acid challenge of dental enamel.

Effect of acid type on kinetics and mechanism of dental enamel demineralization

The influence of acid type (pKa effects) of weak organic acid buffers on dissolution kinetics of dental enamel was critically examined for rigorous testing of the behavioral validity of the physical model of Patel et al. (1987). Quantitative evaluation of this model indicated that monitoring initial dissolution rates was a viable approach to critical testing of the model. Initial dissolution rates were determined in 0.1 mol/L acetate (pKa = 4.77), benzoate (pKa = 4.20), and salicylate (pKa = 2.98) buffers (pH = 4.50, mu = 0.50), with ground bovine enamel blocks of known surface area mounted in a rotating disk apparatus. The Levich theory was used to study dependence of dissolution rates on stirring rates in these buffers. The experimental data were analyzed by the physical model which includes pKa effects, complexation of the buffer anion with the other ions, surface kinetics, simultaneous diffusion and equilibrium of all species in enamel pores, diffusion layer thickness, and bulk solution composition. The KIAP (formula: see text) governing the dissolution reaction and the surface resistance factor were deduced from the model. Dissolution kinetics was also followed in these buffers in the presence of calcium or phosphate common ions. In effect, by conducting both the stirring rate studies and common ion experiments, we derived the driving force function independently by these two techniques. The results obtained in this study were consistent with the model, indicating that pKa effects on the dissolution of dental enamel can be accounted for quantitatively by the model, and it was found that weak acids do not influence either the apparent solubility or the surface reaction process of bovine dental enamel.

Quantitative microradiographic study of simultaneous demineralization/remineralization of dental enamel in weak acid buffers

The remineralization behavior of weak acid-treated bovine tooth enamel has been investigated using a recently developed quantitative microradiographic method. Acetate buffer solutions at pH 4.5 containing calcium, phosphate, and 10 ppm fluoride were used in this study. When the solution ion activity product ( KFAP = a10CA a6PO4 a2F ) was 1 X 10(-108), the remineralization of the demineralized region was relatively uniform and complete. On the other hand, when the KFAP was approximately less than or equal to 1 X 10(-112), remineralization of the outer 10-20 micron was incomplete. In addition, for the smaller KFAP solutions there was significant demineralization in the deeper recesses of the originally demineralized region. These results agree with a recent chemical kinetics study in which it was proposed that KFAP = 1 X 10(-112) demarcated the region of solution conditions in which remineralization only occurs from that in which simultaneous demineralization/remineralization takes place. A model consistent with all of the data is proposed.

Solution activity product (KFAP) and simultaneous demineralization-remineralization in bovine tooth enamel and hydroxyapatite pellets

The effects of changing the ion activity product of the remineralization solution at pH 4.5 (pKFAP 108-118) on the remineralization behavior of demineralized bovine tooth enamel and hydroxyapatite pellets have been studied. Solutions containing calcium-4.5, phosphate, and fluoride in acetate buffers were used. The 45Ca/F molar ratios indicated the formation of fluoridated hydroxyapatite in the enamel or the pellet when the pKFAP values for remineralizing solutions were less than 112. When the pKFAP values were greater than 112, the 45Ca/F ratios were found to be much less than 5. Also, when the pKFAP values were large (greater than 112), the remineralization patterns based on the fluoride distribution in the tooth (or pellet) were found to be different than when the pKFAP values were small (less than 112). The hypothesis that a pKFAP value of 112 is the demarcation between remineralization only and simultaneous dissolution-remineralization has been proposed based on these results.