| Background Caries has been listed as one of the three diseases, which do great harm to the human health by WHO. Dental plaque as the most important cariogenic factor has been researched in the decades and has been achieved advanced evolvement on the role in caries pathogenesis. There have, however, a lot of arguments needed to be affirmed. Calcium (Ca) and phosphorus (P) are the chief element constituted the dental hard tissue. Fluoride (F) plays a important role in the prevention of dental caries. The content level and dynamical changes of Ca, P and F of dental plaque, which are indispensable micro-ecological environment in caries progress, have close relation within the occurrence and development of dental caries. But the exact action mechanism quite concerned in recent years has not been solved completely. That deeply discusses the specialty of Ca, P and F ion in dental plaque, and researches the dynamic change under cariogenic factors and the impact on the enamel demineralization will be important meaning to clear the pathogenesis of caries, and effectively process the forecast, prevent and therapy of caries. Objective In our study, by using spectrophotometer and fluoride ion selective electrode methods, we evaluate the relation between the content of Ca, P and F of dental plaque and caries history. And then, to measure the effect of frequent sucrose exposure on the content of Ca, P and F of dental plaque and enamel demineralization. Meanwhile, we also evaluate the relation between the content of mineral of dental plaque substratum and that of plaque fluid, and to measure the effect of different DSEN as driving forces similar to those found in dental plaque fluid on the enamel demineralization and ultrastructure of surface layer. What carried out will deeply clarify caries pathogenesis, and to provide the new reliable experimental data for promoting caries prevention. Materials and Methods 1. Twelve subjects with free caries(DMFS=0), high caries(DMFS≥12) were selected. All the volunteers were refrained from oral hygiene for 48h to allow for sufficient plaque formation and to collect fast plaque with the exception of subanterior teeth in the 3rd morning. Treated with acid in order to extract all mineral from plaque, sample was detected by using atom spectrophotometer for Ca, ultraviolet spectrophotometer for P and fluoride ion selective electrode for F. To evaluate the difference of content of dental plaque mineral between subjects with free caries and high caries. 2. An acrylic resin appliance containing 3 human enamel and 3 resin blocks (4 mm×4 mm×1 mm) was constructed for each volunteer (total 10). A 20% sucrose solution was dripped onto the enamel blocks with 0～8 times/d in 7 days. After 7 days, by using prior same detecting method, evaluate and compare the content of Ca, P, F, weight of enamel-based and resin-based dental plaque, and enamel demineralization. 3. The test was designed two phase to carry out. In phase 1, as control group, nine volunteers were requested to refrain from oral hygiene for 3d. On the 4th morning, half mouth supragingvial plaque was gathered before and at 7 min after sucrose rinse. In phase 2, as test group, the same volunteers refrained from oral hygiene for 3d, simultaneously, rinsing 20% sucrose solution for 3 min and 8 times/d. After the phase, the plaque was gathered similar to phase 1 method. Plaque fluid was isolated by refrigerated centrifuge. The concentrations of Ca, P and F in dental plaque fluid and residue after centrifuged was determined by using the prior method, to contrast the difference of plaque residues mineral concentrations between phase 1 and 2 and the plaque fluid. 4. The sections of human enamel were exposed to lactic acid solutions with DSEN(0.1～0.5) and DSFA(1.08～5.37) for 96 hours at 25℃, using the deionized water as control in the same conditions. Enamel demineralization was monitored by using SEM and confocal laser scanning microscopy (CLSM). Results 1. The concentration of free caries group significantly(Ca, P, p﹤0.05, F, p﹤0.01) high compared with high caries. The evident relation between Ca-P or Ca-F of free caries plaque can be found. However, only can the relation of Ca-P be found in high caries plaque, andthe level of relation was lower than the former. 2. The proximately same trend of content changes of Ca, P and F in enamel-and resin-based plaque can be found. The content of Ca, P in dental plaque decreased significantly from 0～8 times/d, but F concentration only decreased significantly in 8 times/d comparing the baseline, and the wet weight of dental plaque increased sharply. (p<0.01). Enamel demineralization can be found from 4～8 times/d. In contrast with the mineral content changes of enamel-and resin-based under increasing sucrose exposure frequency, the mineral content of resin-based plaque continually reduced, but the mineral content of enamel-based plaque have silght increased in the 8 times/d comparing with 4 times/d. 3. Following sucrose exposure within group-control or -test respectively, at 7 min, the concentrations of Ca, P and F of plaque residue were significantly lower in compared with before exposured to sucrose (p﹤0.05), and only the concentration of Ca in plaque fluid significantly higher than before exposured to sucrose (p﹤0.05). Following sucrose rinse of 8 times/d frequency in 3 days, the concentration of Ca of plaque residue of control-test before sucrose significantly lower than the counterpart of group-control(p﹤0.05). The others can not be found significantly difference. 4. Only was enamel subsurface demineralization detected in solutions with group 1～3 (DSEN, 0.1 ～0.3). Enamel mineral loss and micropores of surface layer decreased significantly with increasing DSEN and DSFA values(p﹤0.001). However, no mineral loss and micropores of surface layer was observed in sections of enamel exposed to solutions with group 4, 5(DSEN,0.4 0.5) and control. The enamels of group 4 and 5 were covered with homogeneous remineralization layer. Conclusions 1. There have significantly negative correlation between the content of Ca, P and F of adult plaque and DMFS. The lower content mineral of plaque of Caries-high reduced the buffer capability while the bacteria produce acid following metabolism, and reinforced the cariogenicity of plaque. 2. Frequent sucrose exposure reduced the mineral content and buffer capacity of dentalplaque, and increased cariogenicity of dental plaque which resulted in enamel demineraliza-tion. The cariogenic factor caused the same trend in enamel and resin-based plaque. 3. That short-period frequency sucrose exposure only reduced the content of Ca of plaque indicates that the attenuation of mineral content of plaque is a gradual pattern following time accumulated under certain sucrose exposure frequency. After one sucrose exposure, the mineral content of plaque has effect on the concentrations of mineral, and therefore on the degree of saturation with respect to minerals in plaque fluid. It do not have evident impact on mineral of control group's plaque fluid that there have slight changes of mineral content of plaque after 3 days short-period frequency sucrose exposure . 4. The demineralization driving forces similar to dental plaque fluid under different DSEN and DSFA have significantly effect on the surface layer of enamel, furthermore, on the subsurface demineralization process. |
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