Periodondium

Calcified tissue layer on the surface of the root that anchors the periodontal ligament, seals the ends of the dentin tubules and allows for repair at the tooth root.

Acellular cementum is the first cementum produced on the cervical two-third of the root. This mineralized tissue does not contain cells (cementocytes).

Cellular cementum is found at the apical 1/3 of the tooth root. This type of cementum contains cementocytes within the mineralized cementum and is produced throughout life in response to force or trauma.

Cementoblasts line the outer aspect of acellular and cellular cementum and produce the organic matrix, cementoid. During deposition of the cementum, these cells become incorporated into the cementoid, becoming cementocytes. Cementoblasts differentiate from ectomesenchymal stem cells of the dental follicle.

As cementoblasts secrete cementum, they become incorporated into the mineralized tissue of cellular cementum. These cells reside within lacunae and have small processes that are located in canaliculi, narrow tunnels with the cementum.

The daily deposition of cementum can be seen as vertical lines that are close together in acellular cementum and farther apart in cellular cementum.

Alveolar bone proper, directly adjacent to the periodontal ligament, is a thin layer of compact bone that lines the alveolus and anchors the fibers of the periodontal ligament.

Osteoblasts line the alveolar bone and secrete osteoid, the organic matrix of bone. These cells can become trapped in the bone matrix, becoming osteocytes.

When osteoblasts become surrounded by bone matrix, they become osteocytes.

Dentin, the first hard tissue deposited during tooth development, is produced by odontoblasts that reside in the pulp cavity throughout life. It makes up the bulk of the hard tissue of the tooth and is 70% mineralized. Dentin is not considered to be a components of the periodontium.

The periodontal ligament anchors the tooth in the socket, protects the tooth by providing a shock absorber, provides vascular supply and nutrients to the tooth, and defends the tooth against infection that would result in periodontal disease.. It consists of dense connective tissue with interstitial spaces containing blood vessels and nerves and occupies the space between the cementum and the alveolar bone. The periodontal ligament develops from the ectomesenchymal stem cells of the dental follicle during root formation.

The collagen fibers of the periodontal ligament secure the cementum of the tooth root to the alveolar bone of the alveolus. They also connect the alveolar bone and the cementum to the gingiva at the cervix of the tooth.

The interstitial spaces of the periodontal ligament are composed of loose connective tissue islands containing nerves and blood vessels that supply sensation and nutrients to the cells of the periodontal ligament.

These images were taken of a slide from the University of Michigan slide collection.