What structures form the periodontal ligament and alveolar bone?

• A. Periodontal ligament is formed by fibroblasts from the dental follicle; alveolar bone by osteoblasts from surrounding mesenchyme.
• B. Periodontal ligament is formed by ameloblasts; alveolar bone by osteoclasts.
• C. Periodontal ligament by odontoblasts; alveolar bone by fibroblasts.
• D. Periodontal ligament by dental pulp; alveolar bone by chondrocytes.

Answer: (A)

The periodontal ligament and alveolar bone arise from different cell populations in the developing tooth’s supporting tissues. The dental follicle’s mesenchymal cells become fibroblasts that produce the fibrous connective tissue of the periodontal ligament, with collagen fibers forming Sharpey's fibers that anchor the tooth to the bone. The surrounding mesenchyme differentiates into osteoblasts that lay down osteoid and create the alveolar bone surrounding the tooth. This is why the periodontal ligament is formed by fibroblasts from the dental follicle, while the alveolar bone is formed by osteoblasts from surrounding mesenchyme. Ameloblasts form enamel, odontoblasts form dentin, osteoclasts resorb bone, and dental pulp or chondrocytes do not form the ligament or the alveolar bone.