Kuwait Medical Electronic Library

Sea otter dental enamel is highly resistant to chipping due to its microstructure

Charles Ziscovici 1, Peter W Lucas 2, Paul J Constantino 3, Timothy G Bromage 4, Adam van Casteren 5

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10 January 2014

doi: 10.1098/rsbl.2014.0484

Abstract

Dental enamel is prone to damage by chipping with large hard objects at forces that depend on chip size and enamel toughness. Experiments on modern human teeth have suggested that some ante-mortem chips on fossil hominin enamel were produced by bite forces near physiological maxima. Here, we show that equivalent chips in sea otter enamel require even higher forces than human enamel. Increased fracture resistance correlates with more intense enamel prism decussation, often seen also in some fossil hominins. It is possible therefore that enamel chips in such hominins may have formed at even greater forces than currently envisaged.

Keywords: chipping; dental enamel; toughness.

Figures

Figure 1. (a) Light microscopy (LM) image shows high degree of decussation in sea otter enamel. HSB extend to the tooth surface. Scale bar, 0.2 mm. (b) Enamel chip; arrow indicates measurement of h (VPSEM in SE mode: accelerating voltage 20 kV; current 300 pA; pressure 75 Pa). Scale bar, 0.5 mm. (c) LM at higher magnification showing the circular outlines of prisms in cross-section (each approx. 4 µm in diameter). Arrows indicate where cracks have entered prism edges (variable pressure scanning electron microscopy (VPSEM) in backscattered electron mode: 20 kV; 1 nA; 625 Pa). FW = 32 µm.

Figure 2. (a) Force–displacement graph to produce a chip. Scale bar 1 mm. (b) Peak force PF against chip size h for sea otter enamel (filled circles), plotted on logged scales (r2 = 0.91; p < 0.001), compared to humans (open circles), produced under identical conditions [11]. For any given chip size, PF for sea otter enamel is much higher, with average toughness of 2.8 MPa m−0.5 comparing to 1.0 MPa m−0.5 for humans. (Online version in colour.)

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KMEL References

https://pubmed.ncbi.nlm.nih.gov/