Study Of Nanomechanical Properties Of Premature Tooth Enamel

Natural biological hard tissues, such as tooth enamel and bone, have been attractingmaterial scientists’ interest due to their specific mechanical properties and micro-structure. Todate, some models have been proposed to explain the fundamental of their excellent mechanicalproperties. Understanding the mechanism of mechanical properties also plays a key role indeveloping biomimetic biomaterials to substitute damaged human hard tissues.This thesis studied the nanoindentation creep behavior of premature porcine2ndmolartooth enamel. Four different kind of enamel samples were employed, including wet, lyophilized,heat treated and PMMAembedded enamels. Creep, reduced elastic modulus (Ec) and hardness(H) of premature enamel were compared with mature1stmolar enamel to figure out theinfluences of composition and micro-structures on the mechanical properties. Furthermore,mathematical analysis was conducted in order to discuss the impact of structures on mechanicalproperties.The results demonstrate that, comparing with mature enamel, premature2ndmolar enamelin wet, lyophilized and heat treatment state have3to15times more creep under certain loadfor120s. This is mainly due to the differences of composition. Lyophilization slightly increasescreep of all enamel samples. While after heat treatment, creep of all enamels significantlydecrease. Composition analysis shows that water and organics exist within premature enamel,which may lead to structure defects such as gaps between HAp crystallites. XRD analysisdemonstrates that crystal growth happened after heat treatment. This may promote the decreaseof creep. After treating premature enamel with sodium hypochlorite, gaps within enamelcrystallites are further filled with PMMA infiltrations as proved by Raman spectrum.Nanoindentation creep test demonstrates that after embedding, creep extent is2times less thanbefore, while Ecand H increase by about2times. Based on the results above, current model forenamel mechanical property is modified with the consideration of structural element.