Iron Deposition and Ferritin Heavy Chain (Fth) Localization in Rodent Teeth

Sagittal sections of 4-week old rat incisors showed a gradual increase in iron level in the enamel organ from secretory to maturation stages. In addition, iron was detected in ameloblasts of erupting third molars of 4-week old rats, suggesting iron plays a role in both incisor and molar development. In odontoblasts, the presence of iron was demonstrated, and this is consistent with iron’s role in collagen synthesis. Using postnatal 3-, 6-, 9-day old mice, the spatial and temporal expression of Fth in tooth development again indicated the presence of iron in mature ameloblasts and odontoblasts.While these data do not explain what functional role iron has in tooth formation, it does highlight a significant molecular activity associated with the formation of the rodent dentition.Rodent incisors are characterized by yellowish pigmentation at labial side due to the presence of iron, with an iron content of about 0.030% in the whole upper incisors and 0.027% in the whole lower incisors [1]. Electron microscopy has shown that iron is found only in the region of the enamel organ associated with maturation [2]. The function of iron in enamel is not understood. A quantitative analysis on butterflyfish Chaetodon miliaris teeth found that those feed on harder prey have more iron than those that feed on softer-bodied prey, suggesting that iron serves as a strengthening agent to resist abrasion and cracking [3], and this is equally feasible in rodent incisor teeth. Furthermore, the iron concentration is inversely related to the level of calcium in the lingual edge of the tooth cap of butterflyfish [4], consistent with earlier observations that rats with a diet high in calcium showed decreased iron pigmentation in enamel [5] while incisors of iron deficient rats showed higher calcium content in outer enamel [6]. This also suggests that iron and calcium may be able to reversibly substitute for each other in hydroxyapatite. It has also been proposed that iron can decrease the solubi