Introduction to Cementum

Introduction to Cementum

• Cementum is a mineralized dental tissue that covers the roots of human teeth.
• It begins at the cementoenamel junction and extends to the apex of the tooth.
• It provides a medium for collagen fibers anchoring the tooth to surrounding structures.
• It enables the teeth to function correctly.

Physical Characteristics of Cementum

• Cementum is softer than dentin.
• It's a light yellow color.
• It lacks the luster of enamel and is darker.
• It's semi-permeable to various materials.

Chemical Composition of Cementum

• Cementum comprises 45-50% inorganic substances and 50-55% organic material and water.
• It has the highest fluoride content among mineralized tissues.
• Its organic component primarily consists of type I collagen and protein polysaccharides (proteoglycans).

Types of Cementum

• Cementum is classified as acellular and cellular cementum.
• Acellular cementum lacks cementocytes.
• Acellular cementum is primarily found in the coronal portion.
• Cellular cementum contains cementocytes.
• Cellular cementum is found in the apical portion.

Cementum Classification (Schroeder's)

• Acellular afibrillar cementum: Lacks cells and collagen fibers (except for mineralized ground substance). Found coronally.
• Acellular extrinsic fiber cementum: Primarily densely packed Sharpey's fibers. Found in the cervical region of tooth roots.
• Cellular mixed stratified cementum: Contains both extrinsic and intrinsic fibers and may include cells. Found in the apical region of tooth roots and furcations.
• Cellular intrinsic fiber cementum: Contains cells but lacks extrinsic collagen fibers. Fills resorption lacunae.
• Intermediate cementum: A poorly defined region near the cementodentinal junction with cellular remnants of Hertwig's root sheath.

Cementocytes

• Cementocytes are cells residing in cementum.
• These cells are either degenerating or marginally active.

Cementoblasts

• Cementoblasts create cementum.
• These cells produce collagen and protein polysaccharides, forming cementum's organic matrix.
• Cementoblasts possess many mitochondria, a well-developed Golgi apparatus, and significant granular endoplasmic reticulum.

Cemento-dentinal Junction

• This section shows the interfacing of cementum and dentin.
• Permanent teeth have a smooth cemento-dentinal junction, whereas deciduous teeth have a scalloped junction.
• An intermediate cementum layer separates dentin and cementum.
• This layer is most noticeable in the apical two-thirds of molar and premolar roots.

Cemento-enamel Junction

• In 60% of teeth, cementum overlaps enamel, with a short distance between them.
• In 30% of teeth, cementum meets enamel in a sharp line edge-to-edge.
• In 10% of teeth, there's no contact between enamel and cementum.

Clinical Considerations

• Cementum is more resistant to resorption than bone, facilitating orthodontic tooth movement.
• This difference stems from cementum's avascular nature in contrast to bone's rich vascularization.
• Cementum resorption can follow trauma or excessive occlusal forces.

Repair and Resorption

• Cementum's primary objective in the repair process is to restore the root surface contour to its initial form.
• Functional repair occurs if only a thin layer of cementum is laid down on resorption, leading to a bay-like region in the root.
• A more robust repair, known as anatomic repair, strives to entirely restore the original outline.

Hypercementosis

• Hypercementosis is an abnormal thickening of cementum.
• It can affect all or some part of the dentition and may manifest in part(s) of a single tooth.
• If the overgrowth enhances cementum's functional capacities, it is called hypertrophy.
• If overgrowth lacks correlation with functional improvement, it is termed hyperplasia.