Microhardness And Microstructure Of Human Fluorosed Teeth

Fluorosed teeth is a tooth malformation related to excess fluoride ingestion during tooth development,which is characterized by abnormal translucency,chalkly white opaque,staining or defects of enamel that affect tooth function and appearance. Dental fluorosis is a commom and frequently-occurring disease in china.Nowadays, the research about human dental fluorosis is mostly epidemiological investigation,but studies related to mechanical properties and microstructure are rarely reported in the literature.[Objective]To investigate relationship between severity of DF,the mechanical properties and microstructures by measuring microhardness of human dental fluorosis with different severities and observing its microstructure with:The stereomicroscope,the PLM(polarized light microscope) and the SEM(scanning electron microscope). Also to investigate the patho-mechanism of DF from structure and function,and further to provide basic data for reparation therapies.[Material and method] The severity of DF were classified by the TF index.Dental fluorosis was selected between TF1 and TF5,which devided into five groups and each group consisted of 6 teeth.The number of control teeth was 16.The teeth were split into two parts buccolingually,and defined as the surface(defect) group and profile group .After measuring microhardness, microstructure was observed by stereomicroscope ,the PLM and the SEM.[Results] 1. The microhardness values of fluorotic enamel: The microhardness values of surface fluorotic enamel(151.36±57.12KHV) were lower than that of control (271.50±26.77KHV),the former was only 55.75% of the latter.By t-test,P<0.05,with remarkably statistical significance.The microhardness values of differently deep fluorotic enamel was 1/3 of outer(158.85±47.54KHV)<1/3 of inner(193.69±8.87 KHV)<1/3 of middle(203.02±17.84 KHV),and control's is 1/3 of outer(250.03±10.92KHV)>1/3 of middle(216.08±6.44 KHV)>1/3 of inner(195.80±6.16 KHV). Pearson correlation analysis displayed that the microhardness values of outer fluorotic enamel were positively correlated with severity of dental fluorosis(r=-0.976,P<0.01, r²=0.925). There were no correlations between microhardness values of middle and inner fluorotic enamel and TFI scores.2.Microstucture of fluorotic enamel(1) The stereomicroscope displayed that chalky white opaque and staining were mostly distributed in the 1/3 of outer layer,and to some extent to 2/3 of this layer and even through all enamel to the EDJ(enamel-dentinal junction).(2)The PLM displayed that the surface of enamel was well mineralized,with extensive hypo-mineralization under the surface.(3) The SEM displayed that the porosity area of fluorotic enamel was mostly distributed into 1/3 of outer layer,and even to 2/3 or all enamel in the severe cases. The crystal structure was in a disordered arrangement and the number of crystals was reduced or even disappeared.3.Microhardness of fluorotic dentin:There were no obvious differences between microhardness of fluorotic dentin and that of the control,which distribution of microhardness were middle dentin of body > that of near EDJ>that of next to pulp.4. Microstucture of fluorotic dentin:(1)The PLM displayed that the interglobular dentin increased and an incremental line was obvious in the dentin.(2)The SEM dispayed that the number of fluorotic dentine(0.0242±0.003/mm^-2) and that of the control(0.0265±0.00285/mm^-2); but the size of fluorotic dentine(1.9361±0.2972μm) was larger than that of control(1.7543±0.1945μm).The size of tubules in fluorotic dentin was not equal and some tubules were obstructed(blocked).[Conclusion] Based on the results of this pilot study ,the mechanical properties and microstructures of dental fluorosis were affected,which was characterized by decrease of microhardness and increase of porosity in outer enamel ,and no obvious change of microhardness value in denin,with increase of the interglobular dentin, obvious incremental line and changes of tubular morphous.