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The coronal pulps of four primary canines, free from radicular resorption, and of three primary teeth, with roots entirely resorbed, were prepared for electron microscopy. Mature fibroblasts, similar to those reported in the pulps of permanent teeth, were present in the pulps of the clinically mature teeth. Regression of fibroblasts, evident in the pulps of deciduous teeth at the root resorption stage, was characterized by cytoplasmic changes, modifications in the cytoskeleton and dissociation of cells and fibrils. Deciduous teeth might provide a model for studying pulp fibroblast ageing.

The lesion of microhypoplasia of an unerupted tooth was composed of small, irregularly distributed crystals, similar to those of immature and hypomineralized enamel. The lesion appeared to be a defect of crystal growth and maturation, probably involving a partial and momentary failure of the operating cycle of an ameloblast.