Innervation of the periodontium in the monkey.

The distribution and structure of the sensory nerves and various neural endings in the periodontium were examined in adult monkeys, Macaca irus, by means of the silver nitrate technique. 1. The nerve fibers enter the periodontium passing through the bottom and the lateral wall of the bony socket. They are accompanied by blood vessels after entering the periodontium. 2. In the whole height of the periodontium, the area of richest nerve supply is the apical one third of the tooth root, while fewer nerves occur in the upper and middle third. In the apical third periodontium, nerve bundles with blood vessels are located near the alveolar bone, whereas single nerve fibers tend to occur adjacent to the cementum and surround the root of the tooth. 3. The nerve endings in the periodontium can be classified into three types by their structure. (1) Free endings or knob-like endings which, though found in the whole area of the periodontium, are concentrated near the alveolar bone. (2) Tree- or bush-like terminations located in the central part of the periodontium and near the cementum. They occasionally send out numerous branches to the cementum. (3) Specialized endings closely resembling Meissner's corpuscles. They are fairly rare. (4) Tree- or bush-like terminations localized at regular intervals as if each takes its own share of innervation territory. This type of terminals is presumed to represent periodontal mechanoreceptors.