Effect Of Dentine Layer And The Surface Topography Of Dental Crown On The Mechanical And Tribological Properties Of Human Teeth

A majority of natural biological tissues exhibit remarkable mechanical and tribological properties due to their individual structure and surface topography. Human tooth which mainly consists of enamel, dentine and pulp has close relevance to masticatory possess, pronunciation, breathing and facial appearance. Enamel, the outer layer of tooth, has high hardness and excellent wear resistance, while dentine, the inner layer of tooth, contains more organic substances and then has lower hardness. Human tooth is divided into three parts, crown, neck and root from its appearance, and masticatory possess occurs mainly on the surface of dental crown. In order to achieve mastication function, the crown generally has complex surface topography. Given that tooth wear is irreversible, the surface topography of dental crown changes with aging. For most people, their teeth can achieve mastication function throughout their lives. It seems that human teeth have excellent mechanical properties, which may be closely associated with the unique structure and surface topography. Therefore, it is necessary to study the effect of tooth structure and surface topography on the mechanical and tribological properties of human teeth. Results would be helpful to the development of new dental materials and the clinical treatments for dental lesions.In this thesis, the effects of tooth structure and surface topography on the mechanical and tribological properties of teeth were investigated using in vitro testing and finite element analysis (FEA), respectively. The main results and conclusions were as follows:1. Dentine layer has no obvious effect on the microhardness and sliding wear resistance of enamel. For a tooth, the surface fracture toughness decreased after the dentine layer was removed. And this phenomenon became increasingly obvious along with the indentation load increasing. Nanoscratch testing results showed that the dentine layer had no significant influence on the sliding wear behavior of the tooth. However, with the dentine layer being removed, the impact wear behavior of the tooth changed obviously. For the tooth sample without dentine layer, the wear volume increased and some arcuate cracks appeared on the wear surface in comparison with the tooth sample with dentine layer. That is, the resistance against impact wear of human teeth decreased after the dentine layer was removed..2. The stress distribution within a tooth changed with the surface topography of dental crown. Stress concentration appeared in dental groove and neck region when no dentine was exposed on the crown. Once the dentine was exposed on the crown as a result of severe tooth wear, stress concentration transferred from dental groove to the region of the enamel near the exposed dentine. This phenomenon became increasingly obvious and the stress in dental neck increased with the wear extent on the dental crown. It seems that the exposure of the dentine could aggravate the lesions of crown surface and neck.3. When masticatory force was applied on the surface of tooth, the stress in the EDJ zone was increased gradually from the enamel to the dentine.