True Three-Dimensional (3D) Morphology and Network of the Cementocytes

Objectives: Our team has developed a true 3D light microscope investigating system that can increase the magnification of a traditional microscope by 5 times without reducing the depth of field. It opens completely new horizons for transparent, true 3D qualitative and quantitative microscopic examination of cementum.
Methods: Extracted human teeth (n=15) were prepared into native or decalcified, axial and horizontal, 0.5–2 mm thick sections and cleared in triethanolamine solution. The cementum was studied using our custom-made, spatial inspection system. The stereophoto pairs were examined in our 3D stereophotogrammetry measurement application and documented with anaglyph 3D images and 3D graphical drawings.
Results: When examining cementocytes, characteristic 3D shapes of their processes are regularly seen, such as they are predominantly directed centrifugally towards the root surface and not towards the dentin, they have a series of chain-like varicose dilations and button-like widening on their tips. Some of the cementocytes are surprisingly similar to astroglial cells, while others resemble pyramidal neurons of the brain. Where cementocytes are not scattered, adjacent cell bodies are connected to each other by 1-3 apparently continuous bridge-like plasma processes. Locally connected cementocytes form wreath-like networks. Some of these networks extend from the surface through four-fifths of the cementum thickness to the cell-free zone below.
Conclusions: The spatial study of cementocyte complexes leads to a new approach to 3D understanding of their network architectures. The cell processes are principally directed towards the surface, probably due to response to nutrition or stimuli. Determining whether plasma bridges connecting adjacent cementocytes fuse without gaps requires further studies. The wreaths appear to be the functional unit that may form the basis of their putative mechanosensing, homeostasis, and mineral metabolism regulatory functions. The morphological similarities between cementocytes and neurons may be due to their common ectodermal developmental origin.