Sang-Won Myoung, James J. Lee, Paul Constantino, Peter Lucas, Brian R. Lawn
Teeth are remarkable biological structures, brittle but resilient. Here we examine the inter-relation between enamel morphology and crack resistance by sectioning human molar teeth after loading to fracture. The sections reveal that many cracks start from tufts, hypocalcified defects at the enamel dentin junction, and grow longitudinally around the enamel coat to produce failure. Microindentation corner cracks placed next to the tufts in the sections deflect along the tuft interfaces and occasionally penetrate into the adjacent enamel. Although they constitute weak interfaces, the tufts are nevertheless filled with dense matter, and appear to be stabilized against easy extension by self-healing, mutual stress-shielding, and decussation, accounting at least in part for the capacity of tooth enamel to survive high functional forces.