Intertwined Sharpey fibers in human acellular cementum.

We had carried out a detailed morphological study on the human acellular extrinsic fiber cementum (AEFC) in order to support the exclusively extrinsic origin of matrix collagen bundles. Mesial and distal cervical third of fresh premolars from young individuals were examined. Semi-thin and thin section clearly show the Sharpey fibres entering in the cementum at right-angle to the root surface and coursing throughout the cementum to the cemento-dentinal junction. On their way to the dentin the Sharpey fibres divide into smaller bundles which, coursing obliquely or tangentially, intersect with others deriving from neighbouring Sharpey fibres. Both de-proteinated and decalcified samples observed at SEM present Sharpey fibres along the fractured surfaces entering and running trough the cementum perpendicularly to the root surface. Fibril bundles are seen branching out from the main body of a single Sharpey fibre and coursing obliquely or perpendicularly to the original fibre. These morphological evidences obtained both at TEM and SEM further confirm that in AEFC fibril bundles running parallel or obliquely to the root surface are branches of Sharpey fibres and not intrinsic cementum fibres.