Ultrastructural study of experimental cementum regeneration in rats.

Abstract

The present study examined two phases of experimental cementum regeneration at the ultrastructural level. Small fenestration wounds (1 mm in diameter) were made on the mesial root of mandibular first molars in 20 Lewis strain rats to remove cementum and periodontal ligament. The wounds were covered with sheets of Nucleopre filter, before replacing the extraorat flaps, to allow population of denuded roots by cells arising mainly from the adjacent periodontal ligament. The rats were sacrificed in two batches of 10 each to provide observation periods of 2 and 4 weeks. The specimens were processed for transmission electron microscopy. At 2 wk, fibroblasts exhibiting ultrastructural features suggestive of various stages of synthetic activity were seen in the wound and adjacent to denuded root surfaces which appeared irregular. At 4 wk, cementoid regeneration was seen with bundles of oriented collagen fibrils inserting into the cementoid matrix. A consistent finding at both observation periods was the presence of an electron‐dense, granular zone between the cementum/collagen matrix and the denuded root surface. Contrary to previous reports, the electron‐dense zone appeared bi‐layered with collagen fibrils and filamentous material in the superficial layer. At both observation periods, synthetic activity and matrix organization were more advanced in areas away from the root surface (fibrillogenesis) compared to areas adjacent to the root surface (cementogenesis). The present findings suggest that some important cellular and molecular events, possibly regulatory in nature, occur during the early stages of cementum regeneration in rats.