| Description |
This research was aimed at examining a novel systematic approach for gaining insight and understanding of how fluoride (F) may influence the demineralization and remineralization behavior of dental enamel. Bovine enamel was selected for this study and experiments were conducted involving different situations in which enamel interactions with F occurred. Total F concentration and mineral density profiles were determined in enamel as functions of both time and position. These data were converted into local microenvironmental aqueous concentrations of pore solution F as a function of time using a new model-independent computational technique. From this information, thermodynamic ion activity products (lAPs) in the pore solution phase of the enamel were calculated and correlated to the demineralization and remineralization patterns. Several applications of this new approach were made in the understanding of the role of F on the demineralization and remineralization behavior of dental enamel. In the first study, a general method was developed that permitted the computation of the pore solution F concentration and lAPs in the pore solution phase from experimental data of mineral density and total F concentration profiles in bovine enamel. A subsurface lesion with an intact surface layer was formed by dissolution treatment of the bovine enamel in a partially saturated acetate buffer (KHAP = aCa[10]aPO4[6]aOH[2]= 10[-124.0], KFAP = aCa[10]aPO4[6]aF[2] = 10[-114.5], and pH = 4.50) containing 0.5 ppm of solution F. Mineral density profiles were determined microradiographically, and an electron microprobe technique was used to determine total F profiles. A computational technique was developed for quantitatively determining local microenvironmental concentrations of calcium, phosphate, fluoride, and other relevant ions as well as pH as a function of time and position within the enamel matrix. The local demineralization rate of the enamel was shown to be directly related to the local pore solution composition. Calculated solution lAPs correlated with local instantaneous dissolution rate within the enamel matrix. The analysis supported the hypothesis that, when F was present in the system, the local enamel dissolution rate was a function of the microenvironmental solution IAP, KFAP = aCa[10]aPO4[6]aF[2] when F was absent, the local dissolution rate was a function of the IAP, KHAP = aCa[10]aPO4[6]aOH[2]. Dissolution occurred only when both the KFAP value was less than 10[-115±1.0 and the KHAP was less than around 10-118.0±0.5. The same approach was used to investigate the subsequent dissolution behavior of bovine enamel previously demineralized in F containing partially saturated acetate buffer. Again the experimental data were converted by the computation program into IAPs of the pore solution phase in the dental enamel and an attempt was made to compare these IAPs to the local dissolution behavior of dental enamel. The outcome of this study was consistent with the first study, i.e., the dissolution or nondissolution in the bovine enamel as a function of time was correlated with lAPs, KHAP or KFAP, of the pore solution phase. The intact surface layer remained undissolved as long as the calculated lAP of KFAP remained larger than 10[-115.0±1.0]; during the later stages of the experiment the intact surface layer dissolved and this correlated with the calculated KFAP decreasing to values below 10-115.0±1.0. This study, furthermore, suggests that it is not the bound F that preserves the surface layer during acid dissolution, but rather the maintenance of enough F in the pore solution phase to keep the microenvironmental solution IAP, KFAP, high enough to inhibit dissolution. In a final study, the remineralization of previously demineralized bovine enamel in a remineralizing solution was investigated. The data showed that simultaneous demineralization and remineralization took place during the early stages of the treatment. Both remineralization and demineralization correlated with the lAPs of KFAP or KFAP in the dental enamel. Remineralization occurred rapidly in the region of KFAP between 10[-112.0] and 10[-108.0], and was much slower at the lower KFAP values. Demineralization occurred only at early times in the deeper regions of the lesion where both KHAP and KFAP were unsaturated to 10[-118.0±0.5 and 10[-115±i1.0, respectively. |
