| dc.description.abstract | The periodontal ligament of humans is a unique organ, a thin membrane of non-ossified connective tissue sandwiched between two active mineralization fronts. Factors such as oral hygiene, tobacco smoking, and pathogenic microflora are considered etiologic factors for periodontitis, but these are considered the proximate causes in evolutionary medicine. To properly approach the problems of the periodontal ligament, it must be understood why Homo sapiens even has one in the first place; this is a search for the ultimate cause.
The case of an extinct marine lizard, the Globidens phosphaticus is considered to document the sudden appearance of a periodontal ligament in the fossil record through the use of µCT radiography, thin-section histology, and isotope analysis. The results are compared to other related squamates in a phylogenetic series to document other characters that developed concurrently, and to relate these to the paleoenvironmental condition of the late Cretaceous Era. These characters are then related to some of the same characters that convergently developed in mammals due to the same environmental influences.
Analysis is then made of the nature of the occlusal wear, alveolar bone, and the root surface of the fossilized remains and it was determined the non-mineralized PDL of G. phosphaticus was indeed homologous to what is seen in thecodont mammalian tooth attachment tissues. To answer the question of how a tripartite attachment consisting of alveolar bone, PDL, and cementum arose from a simpler homogenous tissue, examination was made of the µCT radiographs of extant reptiles and mammals and found that craniofacial sutures are contiguous with the tooth attachment tissues. Using a transgenic mouse model, great similarities of the unmineralized PDL and the similarly non-mineralized craniofacial sutures could be seen, the lack of ossification presumably due to an inhibition of Wnt signaling. Using a transgenic mouse overexpressing β-catenin, root deformities resembling the mosasaur root were observed.
Finally, to test the effect of direct application of occlusal force to bone without intervening PDL, dental implants consisting of titanium or zirconia were tested in a novel mouse model with sinus augmentation. In this case, superior osseous integration of titanium implants was found, despite an early delay in healing. | en |
