The Influence of Cells and Environment on Periodontal Healing

Objectives: Periodontal progenitor cell vitality is important for periodontal regeneration and tooth re-implantation. This study evaluates healing after transplanting periodontal progenitor cells into a connective tissue lacking periodontal components. Methods: Maxillary molars were extracted from 15 Sprague-Dawley rats and stored in sterile isotonic saline for 5 minutes, whereupon they were either transplanted into skin incisional wounds on the back of the neck (Group I), or put in fixative to provide histology corresponding to time of transplantation (Group II). Transplanted teeth were percutaneous with crown protruding through the skin and roots in cutaneous tissue. Healing was evaluated at 1, 10, and 21 days. Specimens were prepared for histometric grid-point evaluation of periodontal ligament cell and fiber characteristics. Comparisons were made between groups, time-points, and with a normal periodontium (Group III). Data was analyzed using ANOVA and multiple comparisons. Results: Normal periodontium had characteristic orientated cell and fiber attachment system [cell density 2.9 (0.4); mean (SE)]. Root surfaces after 5 extra-oral minutes and prior to transplantation (Group II) were covered by collagen fibers enmeshing periodontal cells with elongated and flattened nuclei [Density 4.5 (0.9)]. Occasional small areas of alveolar bone were also attached. At 1 day (Group I), the region between severed periodontal ligament fibers was distinct. Acellularity was present with cell density 0.8 (0.2) significantly reduced (p<0.01). At 10 days, cell repopulation was occurring [cell density 2.6 (0.3)]. Collagen fibers between tooth and cutaneous connective tissue were uniting via delicate fibrils. At 21 days, fiber attachment was established without new cementum or alveolar bone. Normal periodontium was re-established, however, in areas associated with transplanted alveolar bone. Conclusions: These preliminary findings question the innate ability of periodontal ligament progenitor cells to form cementum, ligament and alveolar bone in an alien connective tissue environment. Supported by NIDR-7061, Penn Periodontal Fund and Alpha Omega.