Hertwig's sheath in the rat incisor.

Abstract

A study was undertaken to reveal the histomorphologic nature of Hertwig's epithelial root sheath in the mandibular incisor of the young Sprague‐Dawley rat. Hertwig's epithelial sheath was found to be composed of three distinct cell layers: (1) inner dental epithelium, (2) stellate reticulum, and (3) outer dental epithelium. The inner dental epithelium and outer dental epithelium were simple cuboidal to low columnar cell layers whereas the stellate reticulum was a stratified squamous layer. As one proceeded incisally from the basal loop, the three cell layer diminished to two with the disappearance of the stellate reticulum. Further forward, the two cell layer became a single layer with the absence of the outer dental epithelium. The remaining inner dental epithelium eventually became discontinuous and was replaced by connective tissue elements. The inner dental epithelium and outer dental epithelium of the intact sheath were separated from the adjacent connective tissue by a distinct non‐metachromatic, PAS‐alcian blue positive basement membrane. The membrane next to the inner dental epithelium was followed incisally onto the external surface of the dentin. Epithelial rests were not identifiable in the periodontal ligament. In other words, an island of epithelial cells surrounded by a distinct basement membrane was not observed.