Cementum: Composition, Structure, and Function

Intended Learning Outcomes

• Students should be able to describe the composition and structure of cementum.
• Students should be able to distinguish between the two main types of cementum and their distribution.
• Students should be able to describe how the structure of cementum relates to its function.
• Students should be able to apply the knowledge to interpret the clinical significance of cementum in health and disease.

Cementum Definition

• Cementum supports the junction between the tooth root and the alveolar bone.
• Key part of the periodontium and thus attachment.

Why Study Cementum?

• Its important for general dental health
• Cementum is affected by root caries
• Affected by Periodontal Disease
• Cementum is used in prevention treatments

Cementum Composition

• Inorganic Content: 45-50% hydroxyapatite crystal, with a critical pH of 6.7.
• Organic Content: 50-55%, composed mainly of type I collagen fibers and minor quantities of other types (III, V, VI, XII, XIV), non-collagenous matrix proteins, and water.

Structural features of cementum

• Cell presence determines if it's acellular or cellular.
• Fiber type determines if it's extrinsic (Sharpey's fibers) or afibrillar (no fibers)
• Time of formation determines if it's primary or secondary

Acellular cementum

• Also known as primary cementum.
• Covers the cervical and middle third of the root (40-70% of root surface).
• It is the first-formed cementum, adjacent to the dentine, creating the dento-cementum junction (CDJ).
• Development is slow
• It contains collagen fibers (extrinsic) and non-collagenous matrix proteins.
• No cells are present.
• There are two types, acellular afibrillar cementum (AAC) which contains no collagen fibers, and acellular extrinsic fibers cementum (AEFC) which has a key function in support and anchorage

Acellular cementum functions

• As part of the periodontium, cementum supports the tooth's position within the alveolar socket.
• Extrinsic fibers form the attachment with the periodontal ligament fiber bundles known as Sharpey's fibers, formed by fibroblasts, and the alveolar bone.
• These fibers are oriented perpendicular to the root surface.

Cellular Cementum

• Also known as secondary cementum.
• Contains cemetocytes.
• Formation is quick
• A layer of cementoid (unmineralized matrix or pre-cementum) is found at the periphery of cellular cementum.
• Cellular mixed stratified cementum (CMSC) is a subcategory of this.
• Over time, CMSC makes up the bulk of cellular cementum.
• It contains intrinsic fibers that are parallel to the root surface.
• It also contains extrinsic fibers over time.
• Cellular intrinsic fiber cementum (CIFC) is found in the apical third of the roots and inter-radicular regions of posterior teeth.
• CIFC is often absent in single-rooted teeth.

Cellular Cementum Cells

• Cementoblasts form cementum via cementogenesis and originate from the dental sac.
• Cementocytes are found in cellular cementum and originate from cementoblasts trapped in the matrix due to the speed of deposition.

Cellular cementum functions:

• Adaption occurs via reshaping of the root to adjust for movement of the tooth, such as drifting after tooth extraction.
• Deposition of cementum at the apex to maintain occlusion and compensate for occlusal wear, with thicker cementum in posterior teeth (post-eruptive movement)
• Cellular cementum can anatomically repair resorbed or fractured root surfaces to some degree.
• It can also functionally repair periodontal disease healing, maintaining the width of the PDL.

Distribution of Cementum

• Acellular cementum (AEFC) is found towards the cervical of the roots, while cellular cementum (CMSC) is found towards the apical region.
• Molar teeth undergo heavier occlusal loads than incisors, leading to a difference in thickness.

Cementum Over the Lifespan

• Cementogenesis takes place continuously.
• Thickness, hardness, and mineral content increase with age.
• Cementum thickness increases in two steps from the cementum enamel junction (CEJ) to the root apex regions.

Cemento-Enamel Junction (CEJ) Variation

• The relationship between cementum and enamel varies at the CEJ.
• In 60-65% of cases, cementum and enamel overlap.
• In 10% of cases, there is a gap between cementum and enamel.
• In 25-30% of cases, cementum and enamel meet.

Structural Abnormalities involving Cementum

• Hypercementosis: Excessive deposition of cementum towards the apex, resulting in thicker roots.
• Aetiology inlcudes local factors such as trauma or inflammation, systemic factors such as Paget's disease, or idiopathic (unknown) causes
• Hypercementosis may affect single or multiple teeth and is often asymptomatic, but may cause problems for extractions.

Explore the composition, structure, and function of cementum, a vital component of the periodontium. Learn about the two main types of cementum and their roles in tooth support and attachment. Understand the clinical importance of cementum in maintaining dental health and its implications in root caries and periodontal disease.