Maturation of periodontal connective tissue in new-born rat incisor

Abstract

The organization of collagen and ground substance in the periodontium of the rat incisor was studied during the first 12 days of postnatal life. Tissues were rapidly frozen in isopentane at −150 °C, and cut in a cryostat without decalcification. Maturation of fibres and ground substance was followed using correlated biophysical (polarization microscopy), histochemical (paS, toluidine blue and collagen immunofluorescence), and empirical (Van Gieson and silver impregnation) methods. Periodontal ligament cells contained glycoprotein granules, probably precursors of ground substance. Glycogen was prominent in young bone cells. At birth, the periodontal ligament consisted of unorganized isotropic argyrophilic fibres strongly reactive to collagen immunofluorescent staining; with further development many fibres became oriented and showed anisotropy. They were mainly disposed parallel to the tooth axis with lateral ramifications into bone. Concurrently, collagen of cementum, bone borders, and pericellular matrix of osteocytes showed intense immunofluorescence. When taken together with distinct metachromasia seen in these areas, this indicates a loose aggregation of their macromolecular constituents. Ground substance of the periodontal ligament acquired metachromasia a few days after birth. Principal fibres were subjected to heat, a variety of enzymes and one fixative. Collagenase abolished birefringence and immunofluorescence. Principal fibres were not equally stable during heating. Some fibre groups became isotropic at 62 °C ( T s ), others were unaffected or partially affected. Hyaluronidase treatment lowered T s to 57 °C, and eliminated the heat resistance of thermostable fibres. Evidently, ground substance stabilized the principal fibres. It appears that collagen-ground substance interactions affect stable-labile transformations involved in fibre remodelling, and may influence eruption.