New findings in the degenerating tissues of the periodontal ligament during experimental tooth movement.

The degenerating tissues found in rat periodontal ligaments during tooth movement were examined morphologically, histochemically, and elementally, with decalcified and unfixed, undecalcified frozen sections. There were two types of degenerating tissues found in the compressed periodontal ligaments: One (type A tissue) was stained differently from collagen and the other (type B tissue) showed the same color as collagen. Type A tissue also showed the deposition of fibrin in Martius scalet blue and Weigert stain. The electron micrograph also showed the deposition of fibrin in type A tissue. No collagen fibers with typical bandings were seen in either tissue. The digestion experiment showed that type A tissue was digested by trypsin but not type B, whereas most of type B tissue was digested by collagenase but not type A. The backscattered electron image by scanning electron microscopy of type A tissue of the unfixed undecalcified frozen sections showed the presence of many small pieces. The elemental analysis of the pieces showed high peaks of phosphorous and calcium. These results indicate that collagen degradation, fibrin deposition, and calcification occurred in the degenerating tissues, especially in type A tissue during the experimental tooth movement.