CELLULAR-ORIGINS AND DIFFERENTIATION CONTROL MECHANISMS DURING PERIODONTAL DEVELOPMENT AND WOUND-HEALING

In the context of cellular origins, ondotogenic epithelium and oral ep ithelium are the sources for junctional epithelium during development and duringwound healing respectively. In contrast, both odontogenic an d non-odontogenic mesenchyme contain the progenitors for gingival fibr oblasts in developing tissues while in wounded tissues, gingival fibro blasts are derived from gingival connective tissues and comprise a het erogeneous population of cells with diverse properties and functions. Periodontal ligament, bone and cementum cell populations apparently or iginate from dental follicle progenitor cells during development, but during wound healing derive from ancestral cells in periodontal ligame nt and bone. Cellular differentiation in developing periodontium is go verned in part by epithelial-mesenchymal interactions that generate sp ecific signals which regulate selective cell populations in time and s pace. On the other hand, differentiation during wound healing and rege neration is regulated by a vast array of extracellular matrix informat ional molecules and by cytokines that induce both selective and non-se lective responses in the different cell lineages and their precursors, Further, several important signalling systems are irretrievably lost after development is complete. Thus, in the context of cellular origin s and differentiation, developing and wounded periodontal tissues exhi bit fundamental differences. Future prospects for improved healing and regeneration of periodontal tissues may derive from identification an d isolation of informational molecules that are stored in connective t issue matrices. These molecules and elucidation of their functions may open new perspectives in our understanding of the biology of periodon tal wound healing and may provide novel approaches to periodontal rege neration.