Cementum
Dental Anatomy · Core Clinical Science
TL;DR
Cementum is the mineralized connective tissue covering the root surface of teeth. It anchors the periodontal ligament (PDL) to the tooth and plays a critical role in tooth support, repair, and adaptation to occlusal forces.
- Covers the root dentin from the cemento-enamel junction (CEJ) to the root apex
- Approximately 45–50% inorganic mineral (hydroxyapatite) — softer than both enamel and dentin
- Two main types: acellular (primary) and cellular (secondary) cementum
- Anchors Sharpey’s fibers of the periodontal ligament into the root surface
- Unlike enamel, cementum can be continuously deposited throughout life (apical and cellular types)
Key Facts
What Is It?
Cementum is a specialized, calcified connective tissue that covers the anatomical root of a tooth. It is one of the four principal components of the periodontium — the attachment apparatus that anchors teeth within the alveolar bone. The other three periodontal components are the periodontal ligament (PDL), alveolar bone, and gingiva.
Cementum is produced by cementoblasts, which are derived from ectomesenchymal cells of the dental follicle during tooth development. These cells deposit a matrix of collagen and non-collagenous proteins that subsequently mineralizes with hydroxyapatite crystals. Unlike enamel, which is formed entirely before tooth eruption and cannot regenerate, cementum is capable of ongoing deposition throughout the life of the tooth — a property that has significant clinical implications.
In terms of composition, cementum closely resembles bone, with approximately 45–50% inorganic mineral content and 50–55% organic matrix and water. However, it lacks blood vessels, lymphatics, and nerves, and it does not undergo physiological resorption and remodeling in the same cyclical fashion as bone.
Why It Matters
Cementum is the structural anchor of the tooth. Without a healthy cementum layer, the periodontal ligament has no root surface in which to embed its collagen fibers, and tooth support is lost. Understanding cementum biology is essential for interpreting periodontal disease, planning surgical procedures, and understanding the limits of tooth movement in orthodontics.
Clinical Relevance
Cementum is relevant to clinicians in several key areas:
- Periodontal disease: In periodontitis, the attachment apparatus is progressively destroyed. Scaling and root planing aims to remove calculus and contaminated cementum from exposed root surfaces to allow periodontal reattachment.
- Root sensitivity: When cementum is lost due to gingival recession or root planing, the underlying dentin — with its open tubules — is exposed, leading to dentinal hypersensitivity.
- Orthodontic treatment: Heavy or prolonged orthodontic forces can cause root resorption, which begins at the cementum. Monitoring for resorption is part of responsible orthodontic care.
- Endodontics: The apical foramen — where the root canal communicates with the periapical tissues — is typically located slightly lateral to the anatomical apex, within the cementum. Root canal obturation should ideally stop at the cementodentinal junction.
Types of Cementum
Cementum is not homogeneous across the entire root surface. It is classified into distinct types based on the presence of cells and the origin of its matrix fibers.
| Type | Also Called | Location | Key Features |
|---|---|---|---|
| Acellular Extrinsic Fiber Cementum (AEFC) | Primary cementum | Cervical one-third of root | No cells; densely packed Sharpey’s fibers; primary attachment zone; formed first |
| Cellular Intrinsic Fiber Cementum (CIFC) | Secondary cementum | Apical and furcation areas | Contains cementocytes; intrinsic fibers only; adapts to occlusal changes; thicker deposits |
| Cellular Mixed Stratified Cementum (CMSC) | Mixed cementum | Apical third and furcation | Combination of AEFC and CIFC layers; contains both cementocytes and Sharpey’s fibers |
| Acellular Afibrillar Cementum (AAC) | — | Cervical enamel (coronal to CEJ) | Thin; no cells; no extrinsic fibers; found on enamel in 60% of teeth; no attachment function |
The Cemento-Enamel Junction (CEJ)
The CEJ is the anatomical boundary where the enamel of the crown meets the cementum of the root. It is a critical clinical landmark for measuring periodontal attachment levels and determining bone loss on radiographs.
The relationship between cementum and enamel at the CEJ follows one of three patterns, with frequency varying among individuals:
- Cementum overlaps enamel (60–65%): The most common pattern; a thin layer of cementum extends coronally over the apical enamel.
- Butt-joint relationship (30%): Cementum and enamel meet edge-to-edge with no overlap.
- Gap (5–10%): Cementum and enamel fail to meet, leaving a zone of exposed dentin at the CEJ — a site of potential sensitivity and attachment vulnerability.
Clinical Considerations
Cementum behavior in health and disease has direct implications for several clinical procedures.
- Root caries: When cementum is exposed due to recession, it is highly susceptible to carious attack. Cementum is softer than dentin and enamel, demineralizes at a higher pH (approximately 6.7), and lacks the protective effect of the overlying gingiva. Fluoride application and oral hygiene instruction are especially important in this population.
- Hypercementosis: Excessive cementum deposition (hypercementosis) can occur as a response to occlusal stress, periapical inflammation, or Paget’s disease. It can complicate tooth extraction and endodontic treatment by creating bulbous root ends.
- Cementum regeneration: Guided tissue regeneration (GTR) procedures aim to stimulate new cementum, PDL, and alveolar bone formation on previously diseased root surfaces. New cementum with functionally oriented fiber insertion is the gold standard outcome of periodontal regenerative therapy.
- Cementodentinal junction (CDJ): In endodontics, the CDJ is considered the ideal apical limit of root canal preparation and obturation. It typically lies 0.5–1.0 mm from the radiographic root apex.
Common Mistakes & Misconceptions
Cementum is one of the less-discussed dental hard tissues, and several misconceptions arise from confusing it with bone or with dentin.
-
Misconception: “Cementum is just like bone and undergoes the same remodeling cycle.”
Correction: While cementum resembles bone histologically, it does not undergo the same cyclical resorption and apposition. Cementum is far more resistant to resorption — this is why teeth can be moved orthodontically while the alveolar bone remodels without the roots being resorbed (in normal circumstances). -
Misconception: “Removing cementum during scaling has no lasting consequences.”
Correction: Excessive removal of cementum during root planing destroys the attachment of Sharpey’s fibers and can lead to permanent loss of attachment, root sensitivity, and increased root caries susceptibility. -
Misconception: “Cementum is only found on the root.”
Correction: Acellular afibrillar cementum (AAC) can be found on the cervical enamel in approximately 60% of teeth, extending a short distance coronal to the CEJ. While it has no attachment function, it is a normal anatomical variant.
Related Topics
Cementum is inseparable from its role within the broader periodontium and its relationship to adjacent dental tissues.
References & Sources
The following sources provide authoritative coverage of cementum biology and clinical significance.
- Nanci A, 2013. Ten Cate’s Oral Histology: Development, Structure, and Function. 8th ed. Elsevier Mosby.
- Bosshardt DD, Selvig KA, 1997. Dental cementum: the dynamic tissue covering of the root. Periodontology 2000, 13(1):41–75.
- Lindhe J, Lang NP, Karring T, 2008. Clinical Periodontology and Implant Dentistry. 5th ed. Blackwell Munksgaard.
- Diekwisch TGH, 2001. The developmental biology of cementum. International Journal of Developmental Biology, 45(5–6):695–706.
Summary
Cementum is the mineralized tissue that covers the tooth root and provides the structural foundation for periodontal attachment. Though thin and often overlooked compared to enamel and dentin, cementum is indispensable — it anchors Sharpey’s fibers, adapts continuously to functional demands, and is a key target tissue in periodontal disease and therapy. Its unique biology, distinct from both bone and dentin, makes it a fascinating and clinically important tissue in its own right.
Key Takeaways
- Root covering: Cementum covers the root surface from the CEJ to the apex, varying in thickness from cervical (~20–50 µm) to apical (~150–200 µm).
- Two primary types: Acellular (primary) cementum anchors the PDL in the cervical area; cellular (secondary) cementum adapts at the apex and furcations.
- Sharpey’s fibers: The collagen fibers of the PDL insert into cementum as Sharpey’s fibers — the physical link that suspends the tooth in the socket.
- Susceptible to root caries: Exposed cementum demineralizes at pH ~6.7, making it far more vulnerable to carious attack than enamel (pH 5.5).
- Regeneration is possible: Unlike enamel, cementum can regenerate through guided tissue regeneration — new cementum formation is the hallmark of true periodontal regeneration.
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