Axonal transport of fluorescent carbocyanine dyes allows mapping of peripheral nerve territories in gingiva

Animal models of orofacial pain

Pain is one of the most common reasons for which patients seek dental and medical care. Orofacial pain conditions consist of a wide range of disorders including odontalgia (toothache), temporomandibular disorders, trigeminal neuralgia and others. Most of these conditions are either inflammatory or neuropathic in nature. This chapter provides an overview of the commonly used models to study inflammatory and neuropathic orofacial pain.

Identification and neuropeptide content of trigeminal neurons innervating the rat gingivomucosal tissue

OBJECTIVES

The purpose of this study was to identify and characterise the neuropeptide content and the size of trigeminal ganglion (TG) neurons innervating the rat gingivomucosal tissue.

DESIGN

Retrograde nerve tracer Fluorogold (FG) was injected into the gingiva (group 1, n=5) or applied into the gingival sulcus (group 2, n=5) of the first right maxillary molar. After 10 days, the ganglia were dissected and FG fluorescence was observed under UV light microscope. Expression of calcitonin gene-related peptide (CGRP) and substance P (SP) in FG-labelled neurons was investigated by immunohistochemistry. Cross-sectional areas of neuron cell bodies containing FG were determined. As a control group, approximately 1000 neuron cell bodies representing the entire TG neuron population was evaluated in five trigeminal ganglia.

RESULTS

In group 1, the percentages of neurons containing CGRP (median 63%, range 48-72%) and SP (median 64%, range 54-64%) were significantly greater than in the control group (CGRP: median 43%, range 42-47% and SP: median 23%, range 21-27%). In group 2, only the percentage of neurons containing SP (median 50%, range 40-56%) was significantly greater than in the control group. FG-labelled neurons were predominantly small or medium sized (less than 1200 microm2). The neurons in the group 1 were significantly smaller than in group 2. In both experimental groups, immunopositive neurons were significantly smaller than immunonegative neurons.

CONCLUSIONS

The majority of neurons in TG that innervate the rat gingivomucosa are small or medium sized and contain CGRP and SP.

Cementum onSmilodon sabers

The maxillary canines of Smilodon californicus Bovard, 1907 have a deeply curved cementoenamel junction. The gingiva of modern cats is attached to the tooth at the cementoenamel junction and provides tactile and other dental information to the animal. The presence of cementum at the cervix of the maxillary canines, also called sabers, would indicate that the gingiva in Smilodon was attached in this region. Such an attachment would be advantageous, providing stability and sensory input for the large tooth. Also, gingiva at the cervix would impact the manner in which the teeth were used. Previous study using scanning electron microscopy of dental casts was indirect. The purpose of this study was to confirm by direct methods the presence of cementum at the cervix of Smilodon californicus sabers. Parts of three Smilodon californicus sabers were sectioned and examined with light and scanning electron microscopy (EDS). In addition, percent weight of calcium and phosphorus was measured in enamel, dentin, and cementum using electron dispersive spectroscopy. Cementum was identified in the cervical region of each saber. Spectroscopy confirmed that the tissue is calcified and the mineral is hydroxyapatite. Percent calcium and percent phosphorus of individual tissues were highly variable between specimens. However, the ratios of calcium to phosphorus were not significantly different from the hydroxyapatite standard. In the future, bite models will have to take the presence of soft tissues into account.