Abstract
The present study investigated the numbers, ratios, types and microstructures of myelinated and unmyelinated nerve fibers in human normal primary and immatured permanent teeth from the standpoint of neural development using an electron microscope. The root pulp of human normal primary canies and immatured premolars was used in this study. The root pulp was embedded in Epon 812 with the usual method. The specimens were sliced in 1-2 um and in 50-70nm thicknesses respectively with a microtome for examination with an optical and electron microscope. The numbers and diameters of the myelinated and unmyelinated nerve fibers were measured and calculated using the Image Analysis System (NHI image 1.49) in the computer.
The results in this study were as follows:
1) It was indicated that the numbers of nerve fiber on the root pulp in immatured permanent premolars were significantly higher than that of the primary canines. The apparent increasing tendency of the nerve fibers was seen in conjunction with the forming root apex formation in immatured permanent premolars. The average ratio of the myelinated and unmyelinated axons was 1: 9.998and 1: 6.706 in primary canines and immatured premolars respectively.
2) The average diameter of the myelinated and unmyelinated axons and G-values (ratio axon diameter/total fiber diameter) of the myelinated axons showed no significant statistical difference between primary canines and immatured premolars.
3) The total myelinated axons of which the diameter is over 5 gm, contained 24.621 % and 35.339% axons respectively in primary canines and immatured premolars.
4) The various kinds of structures were observed on the unmyelinated axons with the electron microscope.
Based on the above results, the numbers of the nerve fibers specifically content of the myelinated axons in them were thought to be one of the factors in which each tooth has his different sensibility. Furthermore, according to the differences of the axon structures this would suggest that the nerve fibers have different functions apart from mediation of pain transmission.
