The objective of this investigation is to explore the region-dependent damage behavior of enamel, as well as to develop a good understanding of the deformation mech- anisms of enamel with numerical modeling. Nanoinden- tation experiments have been performed to investigate the load-penetration depth responses for outer and inner enamel. Results show that the unloading curve does not follow the loading curve, and degradation of stiffness in the unloading curve is observed. Based on the experimental data, a physi- cal quantity, the chain density in protein, has been introduced to the Drucker-Prager plastic model. Numerical simulations show that the simulated load-penetration depth curves agree with the experiments, and the stiffness degradation behav- iors of outer and inner enamel are captured by the numerical model. The region-dependent damage behavior of enamel could be revealed by the numerical model. The micro dam- age affected area at inner enamel is larger than that at outer enamel, indicating that the inner enamel experiences more micro damage than the outer one. Compared with its outer counterpart, the inner enamel which is rich in organic protein could break more internal protein chains to dissipate energy and to enhance its resistance to fracture accordingly.
Bing-Bing AnRao-Rao Wang .Dong-Sheng ZhangRao-Rao WangDong-Sheng Zhang
There is an increase in the mineral content of human dentin with aging. Due to the consequent changes in the mineral to the collagen ratio, this process may influence the degree of hydrogen bonding that occurs with the loss of water and the extent of shrinkage as a result of dehydration. Thus, the objective of this investigation is to quantify the differences in the dehydration shrinkage of human dentin with patient age. Specimens of coronal dentin are prepared from the molars of young （23 ~〈 age 34） and old （52 ~ age ~〈 62） patients, and then maintained in storage solutions of water or hanks balanced salt solutions （HBSS）. Dimensional changes of the dentin specimens occurring over periods of free convection are evaluated by using the microscopic digital image correlation （DIC）. The results distinguish that the shrinkage of the young dentin is significantly larger than that of the old dentin, regardless of the orientation and period of the storage. The strains parallel to the tubules increase with proximity to the dentin enamel junction （DE J）, whereas the shrinkage largest in the deep dentin （i.e., near the pulp）. increases from the pulp to the DE J, and is the strains in the transverse direction axe the The degree of anisotropy in the shrinkage largest in the young dentin.
