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Topic

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Cementum

Cementum is a specialized mineralized connective tissue that covers the root surface of the tooth, extending from the cementoenamel junction (CEJ) to the root apex. It plays a critical role in anchoring the tooth to the alveolar bone by providing attachment for the periodontal ligament (PDL) fibers (Sharpey fibers).

Unlike enamel, cementum is avascular, non-innervated, and capable of limited repair and deposition throughout life. It is similar in composition to bone but lacks Haversian systems. Cementum thickness increases toward the root apex and adapts to occlusal stress and tooth movement.

Synonyms

  • Root cementum

  • Dental cementum

  • Cemental layer of tooth

Location and Structure

  • Location: Covers the entire root surface of the tooth

  • Extent: From cementoenamel junction (CEJ) to root apex

  • Thickness:

    • Thin near CEJ

    • Thicker toward apical third and furcation areas

  • Composition:

    • Inorganic: hydroxyapatite crystals

    • Organic: collagen fibers and ground substance

  • Types:

    • Acellular cementum (coronal portion, primary attachment)

    • Cellular cementum (apical portion, adaptive and reparative role)

Relations

  • Externally: Periodontal ligament

  • Internally: Dentin of tooth root

  • Superiorly: Cementoenamel junction (junction with enamel)

  • Inferiorly: Root apex and apical foramen

  • Laterally: Alveolar bone via periodontal ligament space

Attachments

  • Periodontal ligament fibers: Sharpey fibers insert into cementum, anchoring tooth to alveolar bone

  • Root surface interface: Firmly bound to underlying dentin

  • Functional unit: Forms part of the cementum–PDL–alveolar bone complex

Function

  • Tooth anchorage: Provides attachment site for periodontal ligament fibers

  • Force distribution: Transmits occlusal forces to alveolar bone

  • Root protection: Covers and protects root dentin

  • Adaptive growth: Allows minor adjustments during tooth eruption and orthodontic movement

  • Repair: Can be deposited throughout life to compensate for wear or trauma

Clinical Significance

  • Essential for periodontal stability and tooth retention

  • Involved in orthodontic tooth movement dynamics

  • Landmark for assessing cementoenamel junction integrity

  • Important in dental implant planning and periodontal evaluation

MRI Appearance

T1-weighted images:

  • Cementum appears as a very low signal (dark) thin layer covering the tooth root

  • Dentin and enamel are also low signal, with cementum indistinguishable as a separate layer

  • Surrounding marrow of alveolar bone shows bright signal

  • Periodontal ligament space appears as a thin low-signal line

T2-weighted images:

  • Cementum remains low signal (dark) due to dense mineralization

  • Tooth root appears uniformly hypointense

  • Periodontal ligament space may appear slightly brighter than cementum

  • Alveolar marrow shows intermediate-to-bright signal

STIR:

  • Cementum remains dark

  • Periodontal ligament and surrounding soft tissues show intermediate signal

  • Alveolar marrow signal suppressed compared to T2

  • Useful for distinguishing mineralized tooth structures from adjacent soft tissues

CT Appearance (Non-Contrast)

  • Cementum appears as a high-attenuation thin layer along the tooth root

  • Density is slightly less than enamel and similar to dentin

  • Best appreciated on high-resolution dental or cone-beam CT

  • Clearly delineates:

    • Root contour

    • Cementoenamel junction

    • Relationship with alveolar bone and periodontal ligament space

  • Periodontal ligament space appears as a thin radiolucent line between cementum and bone

Dental X-Ray Appearance

  • Cementum is not distinctly separable from dentin on routine radiographs

  • Tooth root appears as a uniform radiopaque structure

  • Cementum contributes to overall root radiopacity

  • Periodontal ligament space seen as a thin radiolucent line around the root

X ray image

Cementum