Evidence for rapid multipolar and slow unipolar production of human cellular and acellular cementum matrix with intrinsic fibers.

The genesis of root cementum has been studied infrequently in animal models, e.g., in mice, rats and dogs, but rarely in the human. The present study was based on 8 premolars (4 maxillary and 4 mandibular, 7 first and 1 second) selected from a large collection of freshly extracted human teeth. All teeth were free of disease and presented with roots developed to about 50-80% of their length. After decalcification in EDTA, the apical half of the roots was divided axially into mesial and distal portions. The latter were subdivided into 4 slices cut in the corono-apical direction. These slices were Epon-embedded and cut for examination in the light- and transmission electron microscope. It was found that 2 basically different modes of cementum matrix production occurred at or near the advancing root edge. These 2 modes, i.e., the multipolar versus unipolar matrix production, resulted in either cellular (CIFC) or acellular intrinsic fibre cementum (AIFC). Both varieties did not contain fibres of Sharpey and were restricted to regions of the root usually covered with cellular mixed stratified cementum (CMSC). By comparison with recently published data on the rate of cementum apposition, it is suggested that the multipolar mode is a rapid form, whereas the unipolar mode is a slow-rate form of producing intrinsic fibre cementum.