Nanomechanical characterization of exfoliated and retained deciduous incisors

OBJECTIVES: The anisotropic natures of dental tissues result in variable properties from one point to the other within the same tooth. The aim of this study was to analyze deciduous incisors enamel and dentin for elastic modulus and hardness. In addition, retained deciduous incisors were assessed to compare properties with exfoliated teeth. METHODS: Deciduous mandibular incisors either exfoliated at physiological age or retained were included in this study. Samples were prepared by dissecting teeth in transverse sections and surfaces under investigation were prepared and polished for nanoindentation. Nanoindentation was performed at multiple sites using Hysitron [TI 725 Ubi] testing instrument. Data analysis was performed using SPSS software (version 20) to calculate absolute hardness and elastic modulus. The statistical significance was calculated using the t-test. RESULTS: The hardness of human deciduous incisor varies between 0.01-7 GPa. The highest value of hardness was observed for the incisal edge (5.09 ± 0.64 GPa) followed by mid-surface enamel and cervical enamel. The hardness of mantle dentin was (0.56 ± 0.19 GPa) and the inner dentin was (0.34 ± 0.12 GPa). CONCLUSIONS: The average hardness of primary teeth enamel is lower than permanent teeth enamel. The hardness of retained teeth enamel is greater than exfoliated teeth however lower than permanent teeth enamel of the equivalent region.