Meeting Abstract
The periodontal ligament (PDL) is a network of unmineralized collagen fibers that connects teeth to alveolar bone, the innervation of which transformed teeth into multimodal sensory structures that transduce and integrate sensations of pressure, vibration, pain, and temperature to the cortex. This evolutionary innovation occurred in concert with other dramatic changes in the orofacial skeleton such as the emergence of heterodont dentition and expanding brain. The metatherian opossum, Didelphis virginiana, is a key phylogenetic comparison to the well-studied eutherians because it is an omnivore, heterodont, and retains a PDL. Here we identify and map individual nerve types and locations in the lower first molar of D. virginiana using immunofluorescence. Glial and glial-related cells that surround neurons were immunolabeled with S100, SMI 312 and NF-M, and PGP 9.5 and imaged with a confocal microscope. PDL collagens were quantified using picrosirius Red (PSR). PSR revealed that the majority of collagen fibers are oriented in a dorsomedial “sling”. Immunolabels showed neurons running dorsoventrally (DV) in neurovascular bundles and parallel to both the alveolar socket and tooth root. Other nerve bundles appear to be Golgi-Mazzoni corpuscles, very thin corpuscles, and free nerve endings. Innervation of the PDL in opossums shows a DV organization more analogous to nerves seen in eutherian carnivoran incisors than in the molars of their omnivorous counterparts. This suggests the last common ancestor of Eutheria and Metatheria, ~150 million years ago, had a conserved PDL structure and DV organized neurovascular structure, the function of which we will be testing in future research.
