Comparison of nerve fibers in the deciduous first and second molar teeth: an in vitro study

Sensory nerves of the tooth pulp have been evolved in both deciduous and permanent teeth for conducting possible damages to the teeth. Although it has been reported that the deciduous tooth's pulp is histologically similar to permanent teeth, the difference in the density of nerves between the first and second deciduous molars has been reported in no studies.

The aim of the study was to investigate the histological assay of pulpal nerves and assess the relationship between diameter and density of nerve fibres in the first and second deciduous molar teeth.

In this in vitro study, 15 deciduous first and 16 deciduous second extracted from molar teeth belonging to children aged from 5 to 8 years were studied. After fixation, the decalcified teeth were sectioned and then stained with silver solution and calcitonin gene-related peptide (CGRP) antibody. The mean diameter of myelinated fibres, un-myelinated fibres, and density of peripheral network fibres of dental pulp were examined.

The results showed that the mean diameter of myelinated and non-myelinated fibres and density of nerve fibres were significantly more in the second molars (4.269, 2.328 µm, 2.6 fibres per unit area) compared to the first molar teeth (3.793, 2.093 µm, 1.8 fibres per unit area) (P < 0.032, 0.019, 0.003, respectively). An important finding in this study, which is reported for the first time, is the presence of fatty cells (adipocytes) in pulp tissue of some of the first deciduous molars as well as the second molars.

Based on the results of the current study, differences between nerve fibres of first and second molar teeth are significant. It could be concluded that the less sensitivity to pain of the first deciduous molars compared with the second deciduous molars, is due to the lower nerve density of this tooth.