A method for mapping submicron-scale crystallographic order/disorder applied to human tooth enamel

Area of Science:

• Biomaterials science
• Materials science
• Crystallography

Background:

• Tooth enamel is a complex biocomposite crucial for dental health.
• Understanding enamel's hierarchical structure is vital for dental caries and developmental defect research.
• Previous methods like TEM and XRD provided limited local crystallographic detail within enamel rods.

Purpose of the Study:

• To develop and validate a novel synchrotron X-ray approach for detailed crystallographic analysis of human tooth enamel.
• To measure variations in crystallographic structure across and between enamel rods.
• To correlate local crystallographic features with enamel microstructure.

Main Methods:

• Utilized a ~500-nm synchrotron X-ray beam on 1 μm thick enamel sections.
• Collected 2D X-ray diffraction patterns from small, well-separated volumes.
• Developed a quantitative metric based on azimuthal autocorrelation of diffracted intensity to assess order/disorder.

Main Results:

• Enabled population-level statistics on crystallographic features (lattice parameter, crystallite size, orientation distributions) from ~300 crystallites per pattern.
• Successfully correlated crystallographic measurements with specific locations within the enamel microstructure (rod vs. interrod regions).
• Provided the first direct measurement of crystallographic structure variations across and between enamel rods.

Conclusions:

• The developed synchrotron X-ray method offers unprecedented resolution for enamel crystallographic characterization.
• This technique advances the understanding of human enamel's complex hierarchical structure.
• Elucidating these variations can inform future research on dental caries and amelogenesis.