What Is Cementum and Its Primary Functions in Teeth?

Cementum is a specialized, calcified tissue that covers the exterior surface of a tooth’s root. It is one of the four main tissues that form a tooth, along with enamel, dentin, and pulp. Using a tree as an analogy, enamel is the hard bark on the visible part of the tree, while cementum is the bark covering the roots. This layer begins where the crown’s enamel stops and plays a role in securing the tooth within the jaw, making it integral to the tooth’s stability.

Anatomy and Composition of Cementum

Cementum is a component of the periodontium, the group of specialized tissues that surround and support the teeth. It forms a thin, pale yellow layer over the root’s dentin, starting at the neck of the tooth. The thickness of this layer varies, being thinnest near the crown (about 10-15 micrometers) and becoming progressively thicker towards the root’s tip, or apex, where it can be 50-200 micrometers.

The composition of cementum is similar to bone, consisting of about 45-50% inorganic material (hydroxyapatite crystals) and 50-55% organic matter and water. The organic part is mostly collagen, which provides a flexible scaffold. A primary difference from bone is that cementum is avascular, meaning it contains no blood vessels. It receives nutrients from the adjacent periodontal ligament, the fibrous tissue connecting the tooth root to the jawbone.

There are two main types of cementum. Acellular cementum is the first to form and covers the upper portion of the root. It is formed before the tooth erupts and does not contain cells. Cellular cementum develops after the tooth is in its functional position and covers the lower half and tip of the root. This type contains cells called cementocytes, which are trapped within the cementum as it forms.

The Primary Functions of Cementum

The primary function of cementum is to anchor the tooth in its socket. This is achieved through its connection with the periodontal ligament, a network of collagen fibers. One end of these fibers embeds into the cementum, while the other end embeds into the jaw’s alveolar bone. This strong, yet flexible, connection allows the tooth to withstand the immense forces of biting and chewing.

Cementum also serves to protect the underlying dentin of the root. Dentin is a sensitive tissue, and by covering it, cementum acts as a protective barrier, similar to how enamel protects the dentin in the crown.

Cementum also plays an adaptive role. As teeth wear down from use, a process known as attrition, they can slowly erupt further to maintain proper contact with opposing teeth. This movement is compensated for by the continuous deposition of new cellular cementum at the root’s apex, which maintains the tooth’s dimensions and position.

Common Issues Affecting Cementum

A frequent problem is cementum exposure from gum recession. When gum tissue pulls away from the teeth, it leaves the root surface and its thin cementum layer unprotected. Because cementum is much softer than enamel, it wears away quickly from toothbrushing and is more susceptible to decay. This loss can expose the underlying dentin, leading to tooth sensitivity to hot, cold, or sweet stimuli.

A less common condition is hypercementosis, the excessive formation of cementum on the tooth roots. This can be a response to chronic inflammation or trauma, though it sometimes occurs without a clear cause. While often harmless, an extensive buildup can complicate tooth extraction by fusing the root to the jawbone, a condition known as ankylosis.

Cementum can also be lost through resorption, where the body breaks down the tissue. While this is normal for shedding baby teeth, it is problematic in permanent teeth. External root resorption can be triggered by orthodontic pressure, trauma, or chronic infections. This erosion of the root surface weakens the tooth’s foundation and can lead to tooth loss.

Cementum Repair and Regeneration

Unlike enamel, which cannot regenerate, cementum has a limited capacity for self-repair due to the cementocytes within cellular cementum. When minor damage occurs, new layers of cementum can be deposited by cementoblasts, the cells that form it. This natural repair process is slow and cannot restore large areas of cementum lost to gum recession or extensive decay.

When damage from advanced periodontal (gum) disease has occurred, natural repair is insufficient. In these cases, dental procedures can encourage the regeneration of lost tissues. One technique is guided tissue regeneration (GTR), a surgical procedure that places a barrier membrane between the gum and the damaged root.

This membrane prevents faster-growing gum cells from covering the root. This creates a space where cells that form new cementum, periodontal ligament, and bone have a chance to repopulate the area. While not always completely predictable, these techniques represent a significant advancement in treating periodontal defects. They aim to rebuild the tooth’s natural support structures, restoring function and improving the long-term outlook for a compromised tooth.

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