Three-dimensional ultrastructural imaging and quantitative analysis of the periodontal ligament
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The periodontal ligament (PDL) is a unique connective tissue mainly comprising collagen fiber bundles and cells between the roots of teeth and inner walls of the alveolar-bone socket. PDL fiber bundles are arrayed between teeth and bone, with both ends embedded in the cementum or alveolar bone as Sharpey’s fiber. These bundles, synthesized by PDL fibroblasts (PDLFs), form several distinct groups within the PDL which has important functions besides tooth anchoring including tooth nutrition, proprioception, sensory detection, homoeostasis, and repair of damaged tissue. However, little is known about how the regular-PDL fiber bundle arrays are formed, maintained, and remodeled over large distances from cementum to alveolar bone. Recently, novel instruments and 3D-imaging methods have been developed that have been applied to the investigation of hard tissues including the PDL. Work from our laboratory has revealed the three-dimensional (3D) ultrastructure of PDLFs and PDL collagen bundles by focused ion beam/scanning electron microscope tomography. We have shown that PDLFs have a flat shape with long processes or a wing-like shape, while PDL bundles are a multiple-branched structure wrapped in thin sheets of PDLF cytoplasm. Furthermore, PDLFs form an extensive cellular network between the cementum and alveolar bone. The PDL cellular network is presumed to synchronize PDL fiber bundles and regulate arrays of PDL fiber bundles via gap junctions. In this review, we summarize and discuss our current 3D-histomorphometric studies of the PDL at the mesoscale level.
KeywordsFIB/SEM Histomorphometric analysis Imaging Morphology Periodontal ligament
The authors thank Prof. Naohisa Uchimura and Prof. Jingo Kusukawa for their support and mentoring; and Mr. Akinobu Togo, Mr. Ryuhei Higashi, Ms. Satoko Okayama, and Ms. Risa Tuneyoshi for technical assistance. This study was supported by Japan Society for the Promotion of Science (JSPS) Grant-in-Aid for Young Scientists (B) (Grant No. JP17K17090) and a JSPS Grant-in-Aid for Scientific Research (B) (Grant No. 26293040).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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