Physiological evidence that periodontal collagen in the rat exists as fibres prior to histological fixation.

The hypothesis that the collagen in the periodontal membrane forms a thixotropic gel in life and that the arrangement seen in histological preparations is a fixation artifact was tested by comparing the effects of various agents on the position of teeth in isolated unfixed mandibles and on the length of bundles of rat tail tendon collagen. Changing from Ringer solution to deionized water produced a reversible shortening of fibres and extrusion of teeth. Sucrose solutions produced irreversible lengthening and intrusion. Glutaraldehyde generally produced no length changes in the fibres or movements of the teeth but made both the fibres and teeth unresponsive to further changes of solution. Six mandibles in Ringer solution were heated in 5 degrees C increments to 70 degrees C. Between 60 and 65 degrees C (denaturation temperature of soft tissue collagens) the incisor extruded by 60 +/- 15 (SD) micron. This extrusion did not occur in mandibles that had been stored in formalin. These results are consistent with at least part of the periodontal collagen existing as obliquely oriented fibres before fixation. This orientation is such that contraction of the fibres could produce an eruptive force.