FRACTURE OF TOOTH ENAMEL FROM INCIPIENT MICROSTRUCTURAL DEFECTS
H Chai, James J. Lee, Brian R. Lawn
We present definitive evidence for crack growth from internal defects called 'tufts' in human enamel. Side walls of slices sawn from extracted human teeth are observed during loading to 'failure'. 'Longitudinal' and 'transverse' slices (parallel and normal to tooth axis, respectively) are tested in simple loading configurations, and the evolution of ensuing cracks across the enamel sections viewed by video camera. These observations unequivocally identify tufts as the sources of tooth fracture. In sufficiently thin slices the enamel becomes translucent, thereby allowing for observations of the subsurface crack topography. Crack segments which appear to be disjointed on a section surface link up into a contiguous primary crack below the surface, suggesting some crack resistance by 'bridging' behind the advancing crack tip, although the enamel remains barely less brittle than glass. The role of these and other microstructural factors in determining the resilience of tooth structures is considered.
Journal of the Mechanical Behavior of Biomedical Materials