Role of heat and organic matrix on enamel diffusion

Objectives: Diffusion, an important mechanism involved in dental caries, is largely controlled by organic matrix (OM) network in enamel. Though heat/laser-induced retardation of enamel demineralization has been clearly characterized, the contribution of OM in this process has not been quantified yet. The purpose of this study was to investigate the changes of enamel diffusion coefficient (DC) with/without organic matrix (OM) after heat treatment. Methods: Six groups of randomly selected human sound teeth (n=7) were cut into halves and divided into normal and OM-extracted subgroups. Six sound sections were chosen from each tooth-half with five sections each heated at 100, 200, 300, 400, 500 ^oC, respectively, and one unheated section used as the control. Sections were incubated with 20 μM Fluorescein overnight and then subjected to diffusion coefficient (DC) measurement using the Fluorescence-Recovery-After-Photobleaching (FRAP) technique coupled with a laser scanning confocal microscope. Results: Factorial ANOVA was performed and significant OM and heating effects on DC were identified (p<0.001 and p=0.02, respectively). DCs of the OM-extracted subgroups were higher when compared with those of the normal subgroups. Among the normal subgroups, DCs sharply decreased at 400^oC (66.42Χ10^-8cm²/s) from 300^oC (81.46Χ10^-8 cm²/s), but among the OM-extracted subgroups, DCs dropped sharply from 200^oC (87.77Χ10^-8 cm²/s) to 300^oC (84.9Χ10^-8 cm²/s). The heat-induced DC reduction was 1.97%, 7.49%, 7.73%, 24.76%, and 28.36% for the normal subgroups heated at 100 ^oC, 200 ^oC, 300^oC, 400^oC, 500 ^oC, respectively. For the OM-extracted subgroups, it was 2.68%, 2.73%, 5.91%, 6.38%, and 18.64%, respectively. Conclusions: The observed OM effect on promoting the heat-induced DC reduction appeared to substantiate the ²OM-blocking theory² maintaining that OM has an inhibitory effect on ion diffusion and thus demineralization in enamel. The heating temperature of 300^oC to 400^oC may be promising for controlling enamel diffusion and thus preventing enamel demineralization. (This study was financially supported by Singapore BMRC Grant R-222-000-015-305)