Nanohardness and elastic modulus properties of enamel and dentin of primary molars in vitro, in people with various caries experiences, using a nano-indentation technique
Objective: The aim of this study was to investigate the nanohardness and elastic modulus properties of enamel and dentin in extracted human primary teeth in people with various caries experiences, using a nano-indentation technique.
Materials and Methods: Forty-five primary molar teeth were equally divided among three groups, low, moderate, and high caries experience, using the dmft/DMFT index. Non-carious and carious teeth, with intact buccal surfaces, from healthy children aged 4-12 years, were included in this study. Two-millimetre-thick specimens were prepared using two longitudinal sections. Nanohardness and elastic modulus in four zones, outer enamel, inner enamel, outer dentin and inner dentin were obtained using a nano-indentation technique. The mean nanohardness and elastic modulus between groups were analyzed and compared using two-way ANOVA at the p ≤ 0.05 level of significance.
Results: In general, both nanohardness and elastic modulus were significantly different among the four tested zones with greater values in enamel than dentin and outer than inner. Outer enamel and outer dentin in the low caries experience group had significant greater nanohardness (2.88±0.46 GPa, 0.86±0.08 GPa, respectively) than in the high caries experience group (2.37±0.56 GPa, 0.72±0.12 GPa, respectively), whereas only the outer enamel in the low caries experience group had greater elastic modulus (76.46±10.46 GPa) than that of the high caries experience group (61.29±13.33 GPa).
Conclusions: The outer enamel of the low caries experience group had greater mechanical properties than did that in the high caries experience group. This finding raises the possibility that the caries susceptibility of individuals depends on tooth mechanical properties.
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