Effect Of Dentin Demineralization Processed By Solution With Ethylenediamine Tetraacetic Acid

AIM:1.To evaluate the decalcifying power of solution with different concentrations of ethylenediamine tetraacetic acid (EDTA) at the differ-ent portions of human root canal in one week.2. To evaluate the effect of solution with different concentrations of EDTA on the microhardness and the surface morphology of human root canal dentin after one week.METHODS:1.The root canals of twenty human premolars were cut into three 3 mm-thick parts including the coronal, middle and apical third. Each slice was sectioned into two equal parts longitudinally, which were exposed the dentine area of 3 mm×l mm except the apical third. Specimens were assigned to one of five groups with three subgroups(n=8) for immersion in 5 mL of 5% EDTA,10% EDTA,15% EDTA,20% EDTA or deionized water at 37℃for one week. The concentration of Ca2+ extracted from the dentine was measured by atomic absorption spectrophometry (ABS) every 24 hours. The amount of calcium extracted was analyzed using the Kruskal-Wallis test for global comparisons and the Mann-Whitney test for pairwise comparisons. 2.Forty-five extracted human premolars with wax fixing root tips were extirpated of pulp, injected with 5% EDTA,10% EDTA,15% EDTA,20% EDTA or deionized water to the dentinoenamel junction and obturated with Ceivitron at 37℃for one week. Five specimens of each group were used for the the surface morphology of the root canal dentine and energy spectrum analysis using field emission in-lens scanning electron microscopes (FEISEM). Forty of them were sectioned horizontally into three segments, embedded in thermal mosaic materials and were grounded flat with silicon carbide abrasive papers. The specimens of every group(n=8) were used to determine the microhardness of different depth of root canal dentine in the coronal, middle, and apical third using Vicker's micohardness tester. The data were statistically analyzed using Kruskal- Wallis test for global comparisons and the Mann-Whitney test for pairwise comparisons.RESULTS:1. In the coronal and middle third, calcium ions released by root canal dentine presented a growing trend in 168h, with rapid demineralization effect in 72h (P<0.05). In each period, the deminerali-zation capacity of EDTA increased with the concentration (P<0.05).In the apical third, it did not show the dependence law of the time and concentration. 2. EDTA solution reduced dentine microhardness less than 550μm from the pulp dentin border (P<0.05).There were significant differences between different concentrations of EDTA in the reduction of microhardness at the same depth (P<0.05). The morphology of root canal wall changed more apparently with high concentrations of EDTA, but Ca/P ratio kept same in different concentrations of EDTA solution.CONCLUSIONS:1. In the coronal and middle third, EDTA demineralized root canal dentine with concentration dependence. EDTA solution caused continuous demineralization of root canal dentin in 168h, with rapid demineralization effect in 72h.2.After action for one week, EDTA solution reduced dentine microhardness less than 550μm from the pulp dentin border. High concentration of EDTA led to small dentine microhardness.3.15% or 20% EDTA led to root canal wall erosion but didn't change the ratio of calcium and phosphorus in dentine.