Abstract
1. The quantitative and somatotopic aspects of
periodontal/gingival and pulpal afferent connections of
the mandibular and maxillary incisors, canines and molar
teeth to the mesencephalic nucleus of trigeminal nerve
and the trigeminal ganglion have been investigated in the
vervet monkey and olive baboon using horseradish
peroxidase (HRP) retrograde axonal tracing method.
2. It has been demonstrated that the periodontal
proprioceptive afferent neurons of incisors, canines and
molars are found predominantly in the ipsilateral caudal
part of the trigeminal mesencephalic nucleus extending
from the level of inferior colliculi to the trigeminal
motor nucleus in pons. The incisors have
K significantly more mesencephalic neural connections than
canines and molars. No HRP labelled pulpal mesencephalic
neurons have been observed. Faintly labelled neurons
have been observed bilaterally, presumably in the
supratrigeminal nuclei.
3. It has been shown that the incisors and canines have
a large and preponderantly ipsilateral representation in
the trigeminal ganglion compared to the molars which have
a sparse ipsilateral representation. The discrete
periodontal/gingival and pulpal HRP labelled afferent
neurons innervating mandibular teeth are found in the
postero-lateral aspect of the ganglion and those of the
maxillary teeth are found in the middle, along the
dorso-ventral extent of the ganglion.
4. Present study shows that about 10% to 15% of the
mesencephalic neurons (unilaterally) and 0.32% to 0.58%
of trigeminal ganglion neurons have afferent connections
with the periodontium of incisors, canines and molars in
the monkey and baboon. The stereological analysis and
cell counts in stratified serial paraffin wax sections
has shown that there are bilaterally 1379-2674 and
1620-2816 mesencephalic neurons; 98073-101178 and
137250-153555 ganglion neurons in the monkey and baboon
respectively.
5. The periodontal proprioceptive mesencephalic
afferent connections of the anterior and posterior teeth
suggest that they are involved in the modulation of the
reflex effects on the jaw-opening and jaw-closing motor
neurons and are thus important in the regulation of
masticatory jaw movements. Moreover, a cluster of
mesencephalic neurons may form a functional unit for
synchronizing jaw movements during mastication. The
numerous trigeminal ganglion afferent connections of the
anterior teeth suggest that they have a major sensory
role particularly in perception of the food bolus.
Furthermore, the afferent connections of the anterior
teeth may serve to regulate the jaw movement by providing
anterior guidance during the occlusal phase of chewing.
It is concluded that the connections of teeth to the
ipsilateral trigeminal mesencephalic nucleus and
ganglion; the connections to the interneurons of the
supratrigeminal and the sensory nuclei are involved in
the reflex modulation and bilateral control of jaw
movements and the perception of stimulation of the teeth.
