Nanoindentation, enamel mechanical

This chapter describes the results of an ongoing study we are conducting into the nanoscale mechanical properties, chemical composition and structure of healthy enamel, carious lesions and the acquired salivary pellicle layer. A variety of material characterization techniques are being used, including nanoindentation, scanning electron microscopy (SEM), electron microprobe analysis (EMPA), scanning acoustic microscopy, atomic force microscopy (AFM) and time-of-flight secondary ion mass spectroscopy (TOF SIMS). 

Fig. 1. Young s modulus, E, (a) and hardness, H, (b) for the enamel of the mesial half of a maxillary 2nd molar as determined by nanoindentation. The standard deviations for these averages range from 0.2 to 0.3 GPa for hardness and from 2 to 5 GPa for modulus. Note the wide variation in mechanical properties between the enamel surface and the EDJ. Average values of H and E that have been reported earlier by other researchers are included for comparison. 

Figure 1 also includes previously reported values for H and E for comparison with the mechanical property maps of Cuy et al. [12]. It is clear that nanoindentation is able to sense a much wider variation in these properties than previously observed. This is at least partially because the past investigations of mechanical properties yielded mainly average values of H and E that correspond to the values for the interior enamel. Many of these previous studies did not show the extreme local variations that can be measured with nanoindentation. Only the earlier nanoindentation studies have shown any evidence for the highest E and El found by Cuy et al. [12] using nanoindentation. Willems et al. [3] reported E = 90.59 16.13 GPa and Mahoney et al. [21] reported H = 4.88 0.35 GPa. 

Preliminary nanoindentation results on other teeth (premolars, incisors and canines) indicate variations in mechanical properties as large as those discussed for molars [unpubl. data]. In each case the exact distribution of mechanical properties within the enamel appears to correlate with the extent of mechanical loading experienced by the tooth during mastication. However, there appears to be an increase in the viscoelasticity (loss modulus) for the enamel of anterior teeth when compared to posterior teeth, again this may be related to their function. 

Cuy JL, Mann AB, Livi KJ, Teaford MF, Weihs TP Nanoindentation mapping of the mechanical properties of human molar tooth enamel. Arch Oral Biol 2002 47 281-291. 

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