Structural and functional characterization of enamel pigmentation in shrews

Area of Science:

• Zoology
• Materials Science
• Biomineralization

Background:

• Pigmented tooth enamel, characterized by orange to red coloration, is observed across diverse vertebrate groups, including mammals and fish.
• While an iron compound is known to cause this pigmentation, its precise chemical and structural nature within enamel remains uncharacterized.

Purpose of the Study:

• To elucidate the chemical composition and structural organization of the iron compound responsible for pigmented tooth enamel in the northern short-tailed shrew (Blarina brevicauda).
• To investigate the impact of this iron pigmentation on the biomechanical properties, specifically the hardness, of the enamel.

Main Methods:

• Utilized a combination of advanced characterization techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), and synchrotron X-ray diffraction.
• Employed nanoindentation measurements to assess the mechanical properties of the pigmented enamel.

Main Results:

• Identified the pigment as a near-amorphous magnetite phase, comprising approximately 8wt% of the enamel.
• Demonstrated that this magnetite phase is deposited around nanoscale enamel crystals.
• Quantified the influence of the iron pigmentation on enamel hardness through nanoindentation.

Conclusions:

• The study reveals that pigmented enamel in Blarina brevicauda is due to the deposition of amorphous magnetite nanoparticles within the enamel structure.
• The findings provide insights into the biomechanical function and evolutionary context of iron-based tooth pigmentation in vertebrates.