Experimental Study Of The Effect Of Silica On Demineralization And Remineralization Of The Human Premolars Enamel In Vitro

Objective:To investigate the effect of silica on demineralization and remineralization of the human permanent premolars enamel in vitro and to compare the demineralizing effect and demineralizing ability of silica and fluoride in order to explore silica on resistance to early enamel caries. Methods:Samples preparation:Freshly clinically caries-free human premolars extracted for orthodontic reasons were used for the experiments The premolars had never been exposed to topical fluoride application or fluoride mouth rinses or fluoride dentifrices. By interviewing each patient, the information about the usage of fluoride was confirmed. The teeth were stored in distilled water containing 0.05% thymol at 4°C until required in both experiments 1 and 2.Before use . the enamel surfaces were examined under a stereomicroscope( × 10) to exclude the samples with defect, physical damage or crack on surfaces. After removal of the root, the crown was then cut vertically into two halves with a water-cooled diamond wafering blade. The buccal pieces were rinsed with distilled water and air-dried Finally, Enamel samples were painted with two layers of nail varnish leaving a 3 mm×4mm window on the buccal middle part of the natural enamelThe hollow cavities (pulp chamber) in the specimens were filled with blue dental inlay wax.Experiment 1Total of 123 enamel blocks were divided randomly into three groups with 41 specimens in each group as follows:1. control group, treated with distilled water;2. F group, treated with 1ppm NaF ;3. Si group, treated with 1ppm NaSiO3.The different groups were immersed in above three solutions for 8 hours at 37℃ respectively, and then each enamel block was exposured in 10ml Acid gel (0.1M lactic acid solution was produced, the pH was raised to 4.1 with 5M NaOH, and 3%w/v hydroxyethylcellulose) for 168 hours.The calium contents in the acid gel at regular time interals( 1,8,12,24,48,72 and 168 hours) were determined and the configuration variations were investigated by SEM.Experiment 2All specimens were ground and polished.And perfectly flat and intact surfaces were presented. Indenter penetration measurements were made using a hardness testing machine with a 25g load. Knoop hardness measurements were determined by the extent of the indenter lengths. 32 specimens that had no significant differences in the indentation length were selected. Acid resistant nail varnish was used to cover all sides of the specimen except the polished surfaces.The area of the selected surface was 3mm ×4mm.Carious lesions representing the preliminary stage of subsurface enamel demineralization were produced by each enamel specimen immerging into 10 ml of 0.1 M lactic acid at pH 4.1 for 168 hours. After creating the lesion, specimens wererinsed with de-ionized water for 1 mm and then were divided randomly into four groups decontrol group,F group,Si group and F/Si group) with 8 samples of each. The control samples were immersed in basic remineralizing solutions(10ml per sample) containing 30mM Ca, 1.SmM P and the experiment samples were exposed into three different remineralizing solutions adding 1ppm F, 1ppm Si and 1ppm F/Si into 30mM Ca,1.8mM P remineralizing solutions respectively for 14 days at pH7.0,37℃.The potential remineralizing effect and ability of different remineralization solution were evaluated by SEM and Surface Microhardness.Data Analysis:Results obtained on calium released from acidic solutions and microhardnessdetermination were analyzed by a one-way ANOVA test. The differences among meanvalues were compared by Student-Newman-Keuls multiple comparison test.Results:1 .Pretreatment with silica had no significant influence on the calcium release in the lactic acid buffer solution compared with that of the control group (P>0.05), although the calium released in the silica group was slight elevated.2.In the fluoride group, a reduced calcium loss was observed; the total calium release in the control and the silica groups was significantly(P<0.05) higher than that in the fluoride group.3.No evident morphological differences were observed in the type of enamel demineralized patterns between the control and the silica groups.However, In the specimens treated with lppm NaF(24h),the prism core material was partially removed leaving the prism peripheries intact, and the specimens treated with lppm Si and distill water(24h) preferentially removed the prism core material.4.In the second experiment,the addition of silica ,fluoride,or both significantly improve the rehardening of surface-softened enamel compared with that of the control group. No significant difference(P=047) was obsered between the effects ofthe addition of fluoride(F) and the addition of silica(Si).5.The combination of both elements(F/Si) did not result in a supplementary decrease of the indentation length.6.The Si , F/ Si and F of remineralization groups had a similar effect on the micromorphology of the enamels surfaces and cross-sections. However, the particles on enamel surfaces and cross-sections of the specimens in the three experimental groups were more and bigger in diameter than that in the control group.Conclusion:1.The pre-treatment with 1ppm silica don't prevent the demineralition of enamel in vitro. Pretreatment with lppm fluoride can prevent the demineralition of enamel significantly.2.The prism core material has been preferentially removed in the specimens treated with lppm Si for 24 hours. The prism peripheries are not intact and lots of minerals are deposited on the specimens'surface treated with lppm Si for 168 hours. The prism core material is partially removed leaving the prism peripheries intact in the specimens treated with lppm NaF for 24 hours,and after 168 hours the prism core material is partially removed and less minerals than Si group(168h) are deposited on the specimens'surface.3.Silica has a rehardening capacity comparable with that of fluoride.Lots of particles are deposited on the specimens'surface and cross-section,but the surfaces of specimens treated with adding lppm Si into basic remineralization solution are more smooth than treated with adding 1 ppm F into basic remineralization solution.4.This study shows that silica and fluoride used together have the same effect of remineralization as F group in the human enamel in vitro. Whether silica and fluoride have synergistic anticariogenic effect and the optimum concentration should to be further studied.