An Analytical Electron Microscopy Study of Iron-Rich Teeth from the Butterflyfish (Chaetodon Ornatissimus)

Iron is known to be a common constituent of vertebrate teeth, yet little is known about the form it takes or the extent to which it modifies the structural properties of the tooth. Analytical electron microscopy was used to study the iron-rich tooth cap of the butterflyfish Chaetodon ornatissimus Cuvier, 1831. Images of thin sections of the tooth cap showed three distinct layers of hydroxyapatite crystals; a densely packed cuticle, a crystallographically organized superficial enameloid and randomly oriented inner enameloid. Energy dispersive X-ray analysis (edXa) showed that iron was concentrated in the cuticular layer of the tooth cap, the concentration increasing to a maximum at the tip. Elemental analysis showed the level of calcium to be inversely related to iron concentration. An identical relationship was found for synthetic iron-doped hydroxyapatite. The implications of these results for the functional role of iron in the tooth caps are discussed.