Observation Of Brushing Abrasion Of The Enamel Surface After Erosion

Objectives：To compare the effect of different enamel remineralization periods after citricacid etching on the depth of brushing abrasion.Materials and Methods:1. Ethical approval of the study was granted by the Ethics Committee.10volunteers were selected for4days experiment.2. Eighty human premolars,freshlyextracted,caries-free for orthodontic reasons, made into5mm×5mm×2mm sizeenamel.After polishing，a surface Knoop micro-hardness test was performed to select60enamels, whose microhardness values were closest to the computed mean values.3.60enamels were randomly assigned into six groups (A–F) and placed in intraoralpalatal devices.4. On the first day,palatal devices were placed in oral cavity excepteating and mouth cleaning time,to allow the formation of a salivary pellicle.On thefollowing3d, brushing experiments were made extraorally two times per day (8:00h and20:00h).The specific experimental method of brushing:first of all,covered thegroup F specimens with a film of wax,and then immersed in a cup containing50ml ofcitric acid(pH3.2)2min,subsequently,the film of wax was detached.The groups fromA to D were brushed after remineralization at the following time intervals: A,0min; B,20min;C,40min;D,60min.GroupE,acid etching and remineralization,without brushing.GroupF,remineralization,without acid etching and brushing.5. The depth of enamelabrasion was determined by a mechanical profilometer,recorded three values, took theaverage.The six groups were compared by using the Wilcoxon rank sum teststatistics,between the two groups was compared with LSD method,the test level wasP <0.05.The surface morphology of enamel blocks were observed with a scanningelectron microscope.Result:1.With the increase of enamel remineralization time after acid etching,the depth of abrasion decreased,there was statistically significant differences between groups（P＜0.05）.2.Brushing will cause abrasion to the enamel surface after acid etching,thedifference of the enamel surface wear depth was statistically significant between theexperimental groups and the control group P＜0.05）.3.Acid etching had influence on enamel surface wear,compared the experimentalgroups to the control group E,the depth of abrasion increased,the difference wasstatistically significant（P＜0.05）.4.The shorter the time of enamel remineralization after acid etching, the deeperof the surface depression in the electron microscope,and the rougher of surfacemorphology.Conclusion：1.After acid etching,brushing immediately would cause more serious abrasion tothe enamel surface.With the time increasing of the remineralization, the impact ofbrushing on the abrasion depth decreased.2.Eeven using fluoride toothpaste,brushing still have damage to the enamel aftera period of60minutes of remineralization.