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The PDL is formed by different cell types. The fibroblasts are the most abundant as they are responsible for the metabolism of the extracellular components. Within this heterogeneous population of fibroblasts within the PDL, osteoblast-like fibroblasts are also present, and these are rich in alkaline phosphatase.^6,7 In addition, the PDL contains stem cells, epithelial cell rests of Malassez, cells from the blood vessels, and cells associated with the immune and nervous systems.

The extracellular matrix of the PDL consists of collagenous and noncollagenous proteins. Collagen type I is the most abundant, and it is also the primary constituent of the Sharpey fibers, together with collagen II, V, VI, XII, and XIV.⁸ Other noncollagenous proteins present in the PDL are tenascin, fibronectin, vitronectin, elastin, and glycoproteins. In addition, hyaluronate, heparan sulfate, chondroitin sulfate, and dermatan sulfate are the glycosaminoglycans identified in the PDL. Dermatan sulfate is the principal glycosaminoglycan, while versican and decorin are the main proteoglycans.^8,9