Cementogenesis and Cementum Overview

Cementogenesis and Cementum

• Cementum is a thin, calcified, avascular connective tissue covering the root dentin.
• It's the least understood mineralized tissue in the body.
• Cementoblasts are the cells responsible for cementogenesis. Their origin is uncertain; they might be a specialized subset of osteoblasts or a unique cell type.
• Cementum cells (cementoblasts) possess receptors for parathyroid hormone (PTH) and parathyroid hormone-related protein (PTHrP), responding similarly to factors regulating osteoblast activity.
• Cementum thickness varies, thickest at the root apex and interradicular areas of multi-rooted teeth, and thinner towards the cervix.
• Cementum firmly adheres to the dentin and the periodontal ligament (P.D.L.) fibers.
• A primary function is attaching to collagen fibers of the P.D.L., maintaining proper tooth position and integrity, responding to factors promoting tooth repair and regeneration.

Cementogenesis - Matrix Formation

• Cementum formation (cementogenesis) has two major stages: matrix formation and maturation.
• Matrix formation involves the production of collagen type I and ground substance.

Cementogenesis - Maturation

• Maturation involves the deposition of hydroxyapatite crystals in the organic matrix, solidifying the cementum tissue.

Cementogenesis - Hertwig's Epithelial Root Sheath (HERS)

• Cementogenesis begins after the Hertwig epithelial root sheath (HERS) fragments.
• HERS is an epithelial collar derived from the enamel organ's apical portion.
• HERS's disintegration triggers cementoblast activation and cementogenesis.

Cementogenesis - Mineralization

• Cementum mineralization follows matrix formation, not random ion precipitation.
• Key proteins (e.g., osteocalcin, osteonectin) act as nucleators for mineralization, while other proteins (e.g., bone sialoprotein, alkaline phosphatase) promote apatite crystal growth.

Cementum Properties and Clinical Considerations

• Cementum resists resorption compared to bone, which aids in orthodontic tooth movement.
• Cementum resorption can occur from trauma, or excessive occlusal forces. The body can respond to resorption by forming new cementum to repair the previous outline/shape of the root; this is termed anatomic repair
• In cases of deeper resorption, the root outline may not recover, resulting in a "bay-like" recess. The periodontal ligament space is regained by bone formation (functional repair).

Types of Cementum

• Acellular: lacks cementocytes; found primarily on the coronal portion of the root.
• Cellular: contains cementocytes; predominant in the apical portion of the root.
• Intermediate: a transitional type, characterized by entrapped epithelial cells and often found in premolars and molars.

Cementum Structure

• Cementum has a specific structure, involving cementocytes and cementoid layer.

Cementum - Chemical Composition

• Cementum has a 45-50% inorganic component (hydroxyapatite crystals) and a 50-55% organic component (collagen, polysaccharides, trace elements).
• It has the highest fluoride concentration among mineralized tissues.

Cemento-Enamel Junction

• The cemento-enamel junction (CEJ) varies across different teeth: sharp and well-defined in permanent teeth; scalloped in deciduous teeth.

Incremental Lines of Salter

• These lines are hypermineralized areas in cementum with less collagen and more ground substance. They are parallel to the surface in acellular cementum and appear as annuli in cellular cementum.

Functions of Cementum

• Serves as a medium for collagen fiber (Sharpey's fibers) attachment to the periodontal ligament (PDL).
• Continuous cementum formation maintains the PDL attachment apparatus integrity.
• Cementum deposition compensates for tooth wear (attrition).
• It’s essential for root repair in case of fractures or resorption.

Hypercementosis

• Hypercementosis is an abnormal thickening of cementum.
• It can be diffuse or localized.
• If hypertrophy is functional, it's termed cementum hypertrophy.
• If not functionally significant, it's hyperplasia.

Clinical Considerations, Summary

• Cementum's resistance to resorption is crucial for orthodontic tooth movement.
• Cemental resorption may follow trauma or excessive occlusal force. -There are distinct types - acellular, cellular, intermiedate, and afibrillar-
• There is both an anatomic and functional repair mechanism in response to root resorption.