Elastic system fibers in rat incisor periodontal ligament--immunohistochemical study using sections of fresh-frozen un-demineralized tissues

Elastic fiber system evaluated in the digestive organ of rats

According to our previous reports, the intraperiodontal elastic fiber system comprises oxytalan fibers, whereas all types of elastic system fibers are present in the gingiva. Much remains to be elucidated regarding the topographic development of the elastic fiber system that constitutes the walls of the digestive organs. This study aimed to examine the topographic development of the elastic fiber system in the periodontal tissue, oral cavity and digestive tract of rats at light- and electron microscopic levels. At embryonic day 20, in situ hybridization revealed the mRNA expression of tropoelastin in the putative gingival lamina propria but not in the dental follicle. At the postnatal stage, the masticatory mucous membrane of the gingiva and hard palate comprised three different types of elastic system fibers (oxytalan, elaunin and elastic fibers). Conversely, the elastic fiber system comprised elaunin and elastic fibers in other oral mucosae and the lining mucosae of digestive tract organs (the esophagus, stomach and small intestine). The findings of our study suggest that the elastic fiber system is mainly related to tissue resistance in the periodontal ligament and tissue elasticity in the oral mucosae without masticatory mucosae and the overlying mucosa of digestive tracts and both functions in the gingiva and hard palate, respectively. The appearance of elaunin fibers in the periodontium of rats aged 14 weeks suggests the expression of tropoelastin induced by mechanical stressors such as mastication. The intraperiodontal difference in the distribution of elaunin fibers suggests heterogeneity among fibroblasts constituting the periodontium.

Immunohistochemical expression of fibrillin-1 and fibrillin-2 during tooth development

BACKGROUND AND OBJECTIVE

Oxytalan fibers are categorized as a microfibril assembly without elastin deposition, and are unique components in the periodontal ligament (PDL). However, little is known about their formation during PDL development. To clarify the mechanisms of oxytalan fiber formation in developing PDL, we performed immunohistochemical analysis to detect the direct expression of fibrillin-1 and fibrillin-2, which are major components of microfibrils.

MATERIAL AND METHODS

Frozen sections of lower molars from mice at several stages of growth were prepared without chemical fixation and decalcification using the film transfer method. Immunostaining was performed with anti-fibrillin-1 and -2, and anticytokeratin antibodies.

RESULTS

Fibrillin-1 was not expressed in the dental follicle during the crown forming stage. At postneonatal day 9, fibrillin-1 expression started with meshwork appearance between the epithelial cells from Hertwig's epithelial root sheath at the root dentin surface. Fibirillin-2 was detected much earlier than fibrillin-1 expression. Fibrillin-2 was expressed with a liner appearance, running parallel to the root axis in PDL, and was partially co-expressed with cytokeratin 14 expression in Hertwig's epithelial root sheath. Furthermore, we detected both fibrillin-1 and fibrillin-2 expression in human PDL. Fibrillin-1 was detected in fibers with a vertically oriented root axis in PDL. Fibrillin-2 was widely expressed in PDL, including around the epithelial cell rests of Malassez. Fibrillin-1 and fibrillin-2 were clearly co-expressed in thick fiber structures in human PDL.

CONCLUSION

Our results suggest that both fibrillin-1 and fibrillin-2 expression is required to form thick oxytalan fibers in PDL. Based on the expression patterns for fibrillin-1 and fibrillin-2, they have different functions during tooth root and PDL development. Early expression of fibrillin-2 may regulate dental epithelial cell behavior during root and PDL development.

The oxytalan fibre network in the periodontium and its possible mechanical function

The biomechanical character of the periodontal ligament (PDL) is crucial in its response to functional and orthodontic forces. Collagen has been the primary subject of investigations in this field. Several studies, however, indicate that oxytalan fibres, which belong to the elastic fibre family, also contribute to the biomechanical character and behaviour of the PDL. In order to elucidate this, we have evaluated the available literature on the oxytalan fibre network within the PDL and supra-alveolar tissues with respect to development, morphology and distribution, and response to mechanical stimulation. To this end, we have combined the classical histological studies with more recent in vitro studies. Oxytalan fibres develop simultaneously with the root and the vascular system within the PDL. A close association between oxytalan fibres and the vascular system also remains later in life, suggesting a role in vascular support. Mechanical loading of the PDL, through orthodontic force application, appears to induce an increase in the number, size, and length of oxytalan fibres. In line with this, in vitro stretching of PDL fibroblasts (PDLFs) results in an increased production of fibrillin, a major structural component of the microfibrils that make up oxytalan fibres. The available data suggest a mechanical function for oxytalan, but to date experimental data are limited. Further research is required to clarify their exact mechanical function and possible role in orthodontic tooth movement.