The indifferent fiber plexus and its relationship to principal fibers of the periodontium

Scanning electron micrographs demonstrate the presence of an indifferent fiber plexus as an integral part of periodontia in the rat, dog, armadillo and man. Individual fibers measure 1400 Å in diameter in scanning electron micrographs. The indifferent fibers course in every direction throughout the area between bone and cementum without particular orientation. They anastomose extensively with the principal fibers to form a continuous fibrous matrix. Anastomoses with principal fibers begin adjacent to bone or cementum and increase until the indifferent fiber plexus reaches maximum density a short distance from the mineralized matrix. At this point a principal fiber may lose its structural identity as it blends with the profusion of indifferent fibers. This phenomenon occurs in all species studied but is more evident in the relatively unstressed teeth of armadillos. In the dog, principal fibers may extend from cementum to bone as highly compact structures. Anastomoses between principal and indifferent fibers often occur via fibers of intermediate size. The latter fibers become more oriented as their fiber diameters increase. Gingival fibers of the rat, in contrast to principal fibers of the alveolodental ligament, rarely consist of compact fiber bundles. Instead, fibers of indifferent and intermediate size aggregate to form gingival cords in which component fibers are readily distinguishable.