Electron microscopic quantitations of feline primary and permanent incisor innervation

Abstract

Axons from pulps of fully developed primary and permanent teeth were processed for electron microscopy, counted and measured for cross-sectional area and circumference. These measurements were totalled for each specimen and experimental groups were compared statistically. Permanent teeth contained a significantly greater myelinated and unmyelinated innervation. However, primary teeth contained a higher proportion of unmyelinated axons. Considering the tooth weight as an indication of the amount of tissue innervated, no significant differences were found in amount of innervation between primary and permanent teeth. Therefore, innervation density appears the same, while relative proportions of fibre types are not. Fibre-size analyses suggested that myelinated axons in permanent tooth pulps were more irregular in shape. It is concluded that differences exist between the innervation patterns of primary and permanent teeth. These differences may be relevant to tooth sensitivity. A significant positive linear correlation was found between amounts of myelinated and unmyelinated innervation in primary teeth. This suggests predictability of unmyelinated innervation quantities from more easily determined myelinated innervation quantities.