Decay at the gum line, often called cervical or root caries, is a distinct and challenging form of dental decay. This area marks the boundary where the crown meets the root, making it naturally difficult to clean effectively. Unlike decay on chewing surfaces, gum line decay can be hidden by gum tissue or appear as a subtle change in color along the tooth’s neck. This unique position makes the area highly vulnerable to the rapid development of cavities.
The Primary Role of Plaque and Acid Accumulation
The immediate cause of all dental decay is the sticky, colorless film known as plaque, a complex biofilm of bacteria. At the gum line, the gingival sulcus—the shallow groove between the tooth and the gum—creates a sheltered zone where this biofilm flourishes. Specific types of acid-producing bacteria thrive here, primarily Streptococcus mutans and various Lactobacillus species.
These organisms metabolize fermentable carbohydrates, such as sugars from the diet, into organic acids, most notably lactic acid. This localized acid production drastically lowers the pH level directly against the tooth surface, causing the loss of minerals from the tooth structure, a process called demineralization. Since the gum line is less exposed to the sweeping action of the tongue and neutralizing saliva flow, the acid remains in sustained contact with the tooth, accelerating mineral dissolution. Streptococcus mutans is particularly damaging because it is aciduric, meaning it continues to produce acid even in highly acidic conditions.
Structural Vulnerability of Exposed Root Surfaces
The tooth’s anatomy changes dramatically at the gum line, greatly increasing the risk of decay when the gums recede. The crown is protected by enamel, the hardest and most highly mineralized substance in the body. In contrast, the root surface is covered by cementum, a much softer and thinner protective layer.
Cementum has a lower mineral content and is significantly less durable than enamel. When gum recession occurs, the root surface is exposed, bypassing the enamel’s robust protection. The cementum and underlying dentin are far more susceptible to acid attack, often dissolving at a higher pH than enamel. Consequently, decay that starts on the exposed root surface can progress up to 2.5 times faster than decay limited to the crown’s enamel.
Contributing Mechanical and Environmental Factors
Several external forces and systemic conditions accelerate gum line decay. Aggressive horizontal brushing, particularly with a hard-bristled toothbrush, causes mechanical abrasion. This forceful action wears away the thin cementum layer and contributes to gum tissue recession, directly exposing the vulnerable root surface to the acidic environment.
Xerostomia, commonly known as dry mouth, is another factor, often resulting from certain medications or systemic diseases. Saliva plays a role as a natural buffer, helping to neutralize acids and wash away food debris and bacteria. A reduction in saliva flow significantly compromises this protective mechanism, leaving the gum line area without its primary defense. Frequent consumption of acidic beverages or sticky, sugary foods also provides a constant supply of fermentable carbohydrates and corrosive agents that linger near the gum margin, compounding the problem.