A. Boyde, David Mills
By the commonly accepted rules of nomenclature, cells forming hard tissue which become incorporated within the inter- and extra-cellular tissue mass which they secrete are called '-cytes': the spaces in which these cells sit are called lacunae. Hence, osteoblasts become osteocytes in osteocytic lacunae, chondroblasts become chondrocytes, cementoblasts cementocytes, even odontoblasts become odontocytes in some mammalian species. We provide evidence that enamel spindles are cell bodies of ameloblasts which have become entrapped and buried in the enamel matrix produced by the surrounding cells, to produce amelocytic lacunae: it is no life for a cell in a rigid, dense and dead tissue, and we do not suppose that amelocytes live once they are set on that route. Spindles, normally only found at the enamel-dentine junction, are absent when the enamel at the junction is free of prisms, i.e., the ameloblasts had no Tomes' processes. Spindles have an organic content, the amelocyte residue which can be stained - and removed by bleach, after which the spindle space no longer stains. Spindles are extensions of enamel tubules which result from the extension of a fine ameloblastic process [from the major Tomes' process] which unites with an odontoblast process. In marsupial mammals, the spindle-like ends of the enamel tubules are commonly located well within the enamel. Spindles/amelocytes may form at the neonatal line in human deciduous teeth in cases of severe neonatal stress, and these features simply represent encapsulation of moribund ameloblasts. The frequency of spindles at the enamel dentine junction is greater in cases where the tooth germ is severely deformed by growth pressure from the forming root of a neighbouring tooth.