Cementum is a specialized calcified tissue that forms the outer layer of the tooth root, beginning where the enamel ends. This tissue plays a foundational role in the overall stability and long-term health of the tooth structure. Cementum is a necessary component of the periodontium, the collective term for the tissues that support the teeth. Understanding its function reveals its significance in maintaining a healthy, functional smile.
Composition and Placement on the Tooth
Cementum is a bone-like substance that covers the entire surface of the tooth root, lying directly over the dentin. It is slightly softer than dentin and is composed of about 45% to 50% inorganic material, primarily hydroxyapatite, with the rest being organic matter and water. Unlike bone, cementum is avascular; it does not contain blood vessels and receives nutrients from the nearby periodontal ligament.
The tissue meets the enamel at the cementoenamel junction, often called the neck of the tooth. It is thinnest near this junction and becomes progressively thicker toward the root’s tip, or apex, where it can reach up to 600 micrometers in thickness.
Acellular and Cellular Types
Cementum is classified into two main types based on its cellular structure. Acellular cementum is formed first, typically covering the root’s upper half closer to the crown, and does not contain cells within its matrix. Cellular cementum is found around the root’s lower half and apex. This type contains entrapped cells called cementocytes, which help with maintenance and repair.
Essential Functions in Tooth Stability
The primary role of cementum is to anchor the tooth within the jawbone. It serves as the attachment point for the thousands of collagen fibers that make up the periodontal ligament (PDL). The ends of these fibers, known as Sharpey’s fibers, are embedded directly into the cementum and the alveolar bone. This complex holds the tooth firmly in its socket while permitting slight movements necessary to absorb the forces of biting and chewing.
Cementum constantly forms new layers throughout life, allowing it to maintain attachment and repair minor surface damage. When the tooth experiences wear on its chewing surface, new layers of cementum can be deposited at the root apex to compensate for the loss and maintain the tooth’s proper height.
Cementum also acts as a protective barrier for the underlying dentin. By covering the root surface, it shields the sensitive dentin and the internal pulp from the external environment, including bacteria and temperature changes.
Implications of Cementum Damage and Disease
When cementum health is compromised, the entire tooth structure is affected. The most common cause of damage is advanced periodontal disease, where bacterial plaque leads to chronic inflammation and tissue destruction. This loss of cementum makes the root surface rough and prevents the reattachment of healthy periodontal fibers.
Loss of this covering layer often occurs with gingival recession, where the gum line pulls away from the tooth. This exposes the root surface to the oral environment, leading to rapid abrasion of the tissue. Since cementum is thinner and softer than enamel, its loss quickly exposes the underlying dentin.
The exposure of dentin tubules directly causes tooth sensitivity, often felt as a sharp, brief pain when exposed to cold, heat, or touch. In advanced cases, the destruction of cementum and supporting bone can lead to the loosening and potential loss of the tooth. Maintaining the integrity of this specialized root covering is fundamental to preventing painful dental issues.