Objective: Atomic force microscopy (AFM) nanoindentation has been used to measure the surface hardness and reduced elastic modulus of deciduous and permanent enamel.
Methods: Polished enamel samples (n = 72) were prepared from deciduous molars (n = 12) and permanent premolars (n = 12). Ten indentations were performed on each sample and the hardness and elastic modulus values were calculated from the load displacement data. The data were evaluated using a one-way ANOVA at the 95% confidence level.
Results: A mean surface hardness of 4.50 GPa (SD 0.24 GPa) and a mean elastic modulus of 103.2 GPa (SD 3.2 GPa) were obtained for deciduous enamel. Permanent enamel had a mean surface hardness of 4.85 GPa (SD 0.28 GPa) and a mean elastic modulus of 108.2 GPa (SD 8.2 GPa). As a result of this study, deciduous enamel was found to be statistically significantly softer (p<0.01) and less elastic (p<0.05) than permanent enamel.
For the first time, AFM nanoindentation has been used to investigate the nanomechanical properties of deciduous and permanent enamel in a comparative study. So far, microindentation methods have been used to study the hardness of enamel. AFM nanoindentation allows the precise measurement of hardness and elastic modulus at smaller indentation depths (< 250 nm). The results of the present study are partially in agreement with previous studies employing microindentation techniques, although little attention has been paid to the investigation of the elastic modulus of deciduous enamel in the past.
Conclusion: The present study has shown that AFM nanoindentation is a useful tool to investigate the nanomechanical properties of enamel with high accuracy and a study investigating the susceptibility of deciduous and permanent enamel to erosion will be published shortly.