Cementum

Location and borders of cementum

Cementum covers the outer surface of the root (radix dentis) and the cervix of the tooth (cervix dentis). It is part of the periodontium — the complex of tissues surrounding the tooth.

• Border with enamel: In the cervical region (contact zone), cementum meets the enamel. There are four possible variants of their junction: end-to-end alignment; enamel overlapping cementum; cementum overlapping enamel; or a gap between enamel and cementum leaving an exposed area of dentin.
• Border in the root canal: Cementum may extend into the root canal as far as the physiological apex (apical constriction), where the cementodentinal junction is formed.
• Connection with the periodontium: The periodontium (periodontium) lies external to the cementum, which is a dense connective tissue situated between the root and the alveolar bone.

Classification: types of cementum

Depending on its structure and localization, cementum is divided into two types:

• - Acellular (primary) cementum: lies directly against the dentin and covers the lateral surfaces of the root.
• - Cellular (secondary) cementum: covers the apical third of the root and the furcation area (root bifurcation) of multirooted teeth. As a rule, it is located superficial to acellular cementum, but sometimes it may lie directly against the dentin.

Histological structure

Cementum is formed continuously throughout life by cells on its outer surface. Cellular cementum consists of cellular elements and intercellular substance:

• - Cementoblasts: active cells ("builders") that provide rhythmic deposition of new layers of cementum. During the formation of acellular cementum, they move outward, whereas during the formation of cellular cementum, they become entrapped within it.
• - Cementocytes: cells located in specialized cavities (lacunae). They are derived from entrapped cementoblasts and are structurally similar to osteocytes.
• - Intercellular substance: consists of ground substance and fibers running in various directions. Some fibers run longitudinally, parallel to the surface. Most fibers run in a radial direction; these are Sharpey's fibers. Other fibers are embedded at one end into the dentin and at the other into the periodontal fibers.

Main functions

• - Supportive: participation in forming the tooth-supporting apparatus. Cementum provides attachment of periodontal fibers to the root and cervix of the tooth.
• - Protective: safeguards root dentin from damaging influences.
• - Reparative: participation in healing processes (e.g., in root fractures or during periodontitis treatment).

Clinical significance and pathologies

When the root portion adjacent to the crown becomes exposed, the dimensions of the clinical root decrease relative to the anatomic root. With age, as areas of the tooth not covered by enamel become exposed, the clinical crown becomes larger than the anatomic crown.

A benign tumor known as a cementoma may develop from odontogenic connective tissue differentiating into cementum. It is typically tightly fused to the tooth roots and may consist of fibroblastic tissue incorporating dense calcified cementum-like masses that can merge into large conglomerates as they grow. Several forms of cementomas are distinguished: benign cementoblastoma (true cementoma, macroscopically appearing as a yellowish-white tissue of varying density), cementifying fibroma, periapical cemental dysplasia, and gigantiform cementoma.

Class and exam questions

What else to study on this topic

• Dentyn (dentinum)
• Periodontium (periodontium)
• Enamel (enamelum)
• Dental pulp (pulpa dentis)

Other topics in the "Anatomical Structures" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.