Study On The Properties Of Human Tooth Enamel Materials In Different Ages

As one of the most important tissues and organs in the human mouth,teeth are an important function of chewing food and providing energy for the human body.In this process,teeth inevitably suffer from friction and wear.The enamel,the outermost part of the tooth,exhibits extremely excellent performance against this damage.With the growth of age,due to the changing oral environment,the microstructure and chemical components of enamel will constantly change,which will lead to the change of enamel performance,the research on enamel performance of age will be of great significance,but also for different age groups of dental hygiene and clinical prevention.In this thesis,in vitro simulation experiment was used to study enamel of different age groups.The teeth collected were divided into four groups according to age: deciduous teeth(9～12 years old),juvenile permanent teeth(14 ～ 20 years old),young adult permanent teeth(25～45 years old),and elderly permanent teeth(over 60 years old).In this thesis,the surface mechanical properties,indentation morphology,surface morphology and chemical composition of enamel of different age groups were compared and analyzed by various analysis methods.On this basis,the mechanical properties and the thickness of the softening layer of enamel before and after acid erosion were compared with citric acid erosion medium to reveal the difference of the resistance to acid erosion of enamel in different ages.The main work and conclusions are as follows:(1)There are significant differences in mechanical properties,microstructure and chemical composition of enamel in different ages.Under the same load,the young adult permanent teeth have the highest Vickers hardness of enamel,followed by the elderly permanent teeth,then the juvenile permanent teeth,and the deciduous teeth have the lowest Vickers hardness of enamel.Under 5N loading,the indentation depth,crack propagation length and indentation debris accumulation of enamel of different ages were significantly different.Under the same load,the fracture toughness of deciduous teeth enamel was the highest,followed by young adult enamel,then juvenile enamel,and the elderly enamel had the lowest fracture toughness.The microstructure and chemical composition of enamel surface change with age,and cause the change of enamel mechanical properties at different ages.(2)Under the same conditions of acid erosion,the thickness of the softening layer of deciduous teeth was the largest,The influence of acid erosion on the vickers hardness and fracture toughness of deciduous enamel is much greater than that of permanent enamel.Deciduous teeth had the worst resistance to acid erosion,followed by elderly permanent teeth and juvenile permanent teeth,and young adult permanent teeth had the best resistance to acid erosion.The mineral content in human enamel is the highest in young adults,while the mineralization degree of children deciduous teeth is not mature enough,which is more likely to cause the loss of hydroxyapatite inorganic minerals in the process of acid erosion.The increase of mineral loss leads to the increase of vacancies in the surface structure of tooth enamel and the deterioration of surface densiveness.With the extension of acid erosion time,the mechanical properties of tooth enamel surface further decline.