Mechanical behavior of enamel rods under micro-compression

Area of Science:

• Biomaterials Science
• Mechanical Engineering
• Materials Science

Background:

• Dental enamel exhibits a complex hierarchical structure crucial for its mechanical properties.
• Previous research focused on fracture toughness, but stiffness and strength effects of hierarchy remain debated.
• Enamel's structure involves hydroxyapatite nanofibers (level-1), enamel rods (level-2), and bands (level-3).

Purpose of the Study:

• To determine the stiffness and strength of isolated enamel rods (level-2) using micro-compression.
• To investigate the influence of hierarchical structuring on enamel's mechanical properties.
• To compare experimental findings with existing data for other hierarchical levels and bulk enamel.

Main Methods:

• Micro-compression testing of isolated enamel rods (level-2).
• Testing rods in parallel, perpendicular, and oblique orientations to the loading direction.
• Development of an analytical model to verify experimental findings and extend to higher hierarchical levels.

Main Results:

• The highest stress level withstood before fracture was approximately 1500 MPa in the perpendicular orientation.
• Elastic modulus was approximately 60 GPa and showed stiffness isotropy across orientations.
• Oblique loading resulted in shearing failure and damage-tolerant deformation due to interrod sheet interactions.
• Level-2 rod properties were comparable to reported values for level-1 and bulk enamel.

Conclusions:

• Hierarchical structuring appears to have a minor influence on the compressive properties of dental enamel.
• Stiffness isotropy in enamel rods is attributed to inter-rod mineral contacts.
• The study provides valuable insights into the mechanical behavior of dental enamel at the rod level.