The Intermediate Plexus of the Periodontal Ligament: History and Further Observations

¹ Department of Anatomy, Colleges of Medicine and Dentistry, University of Kentucky, Lexington, Kentucky

A study of the periodontal ligament of mouse molars supported the concept of the continuity of the principal fibers across the periodontal space. No intermediate plexus was found. The principal fibers, imbedded in the alveolar bone passed to the cellular or acellular cementum without an interruption in their continuity. Shortly after passing from the alveolar septum the closely packed fibers became more loosely arranged and the individual fibers took separate courses joining a few adjacent fibers to become attached to the cementum. A greater number of bundles containing fewer fibers were attached to the cementum in contrast to a lesser number of bundles containing more fibers attached to the alveolar septum. This arrangement greatly enhanced the compressibility and strength of the periodontal ligament during normal tooth movements.

Evidence of distal physiological drifting was observed. Principal fiber bundles were found deeply imbedded in the alveolar septum on the mesial aspect of the teeth and not so deeply imbedded on the distal aspect. Distal drifting was accomplished by resorption of alveolar bone distal to the teeth and deposition of bone mesial to the teeth with little apparent change in the principal fibers of the periodontal ligament.

From the observations of the arrangement of the principal fibers and the evidence of distal drifting, it was believed that the fibers were continuous from the alveolar bone to the cementum in teeth of limited growth. No intermediate plexus was found in the periodontal ligament of the molar teeth of the mouse. However, no conclusion refuting or establishing the existence of an intermediate plexus in continuously erupting teeth could be made from the present study.