Electron Microscope Studies of the Submicroscopic Structure of the Dentinal Matrix

Abstract

DENTIN is generally referred to as a fibrillar calcified matrix permeated by dentinal tubules containing the process of odontoblasts. 1 2 The dentinal tubules and the fibrils in the matrix have been the subject of histologic studies with the electron microscope,3^but the calcified matrix has not been given the same attention. It has been described as a homogeneous calcified cementing substance7 or a cement composed of inorganic salts and an organic material sensitive to the action of papain.8 For this paper, the dentin matrix is defined as that region in dentin occupied by the mineral salts hydroxyapatite, and will include not only the intertubular region but also the outer calcified sheaths of the dentinal tubules.3 Since prevailing histologic concepts of the fine structure of dentinal matrix are not clear, the present investigation was necessary to determine the microstructure of sheep's teeth as part of a programme being carried out to find the cause of the excessive wear when the sheep feed on certain improved pastures.9 A comparison with human dentin was of interest and a sperm whale tooth was chosen to see if the largest mammal had identical dentin microstructure. MATERIALS AND TECHNICSThe sheep teeth were central incisors of various ages and most were fixed in ethanol immediately after extraction. Some teeth, however, were fixed in osmic acid-Veronal buffer solution"' and others were left unfixed and packed in ice until they could be prepared at the laboratory the following day.The human teeth were premolars extracted for orthodontic reasons, and they were fixed in a similar manner to the sheep teeth. The sperm whale tooth, however, had been kept in a dry and unpreserved state for a period of two years. Most of the teeth were ground and polished with optical polishing powder, followed by fine powdered common salt in a saturated aqueous solution, to obtain flat dentin surfaces, and two-stage collodion carbon replicas were made of each surface, both before and after etching with selective reagents. Replicas were also made of the dentin surfaces of teeth which had been cleaved with a sharp chisel. After removing the collodion with amyl acetate, the carbon replicas were shadowed with uranium and then examined in a Metropolitan Vickers electron microscope, type EM2/1M.