Fracture of tooth enamel from incipient microstructural defects

Area of Science:

• Biomaterials Science
• Dental Research
• Mechanical Engineering

Background:

• Human enamel, the hard outer layer of teeth, is susceptible to fracture.
• Internal microstructural defects, such as tufts, are implicated in tooth failure.
• Understanding enamel's fracture mechanisms is crucial for dental health and restorative treatments.

Purpose of the Study:

• To provide definitive evidence that crack growth in human enamel originates from internal defects called tufts.
• To investigate the in situ crack propagation behavior within enamel microstructures.
• To explore the role of microstructural factors, like bridging, in enamel's resistance to fracture.

Main Methods:

• Human teeth were sectioned transversely to the tooth axis.
• Enamel sections were embedded in a polycarbonate sandwich for flexural loading.
• Crack evolution was observed in situ using a video camera.
• Through-thickness crack topography was examined in translucent enamel slices.

Main Results:

• Definitive evidence was found for crack initiation and growth from internal enamel defects (tufts).
• Observations confirmed tufts as the unequivocal sources of internal tooth fracture.
• Crack segments appeared to link up below the surface, indicating a 'bridging' mechanism that offers crack resistance.
• Through-thickness observations revealed the three-dimensional nature of crack propagation.

Conclusions:

• Tufts are identified as critical origins for crack growth in human enamel.
• Microstructural features, including bridging, play a significant role in enamel's fracture resistance.
• This research provides fundamental insights into the biomechanics of tooth fracture, informing dental material science and clinical practices.