The tooth is composed of three main anatomical divisions: the crown (visible above the gum line), the root (anchored within the jawbone), and the neck. The neck acts as the transition zone between the two, forming a narrow, slightly constricted area. This transition area is where the protective layers of the crown and root meet, and it is normally shielded by the gum tissue.
Defining the Cervical Region
The neck of the tooth is technically known by the anatomical term “cervical region” or “cervix dentis.” This area is the constricted portion situated between the exposed crown and the root embedded in the jawbone. In a healthy mouth, the neck is located just below the edge of the gum tissue, or gingiva. The gingiva forms a tight seal around the tooth, creating a biological barrier against bacteria. The cervical region is a static landmark used by dental professionals for measuring gum recession and other periodontal health indicators.
The Cementoenamel Junction
The neck is structurally defined by an internal boundary called the Cementoenamel Junction (CEJ). This junction is the meeting point where the highly mineralized enamel covering the crown ends and the cementum covering the root begins. The CEJ is typically a scalloped line that extends around the entire circumference of the tooth. Beneath the enamel and cementum lies the dentin, a softer layer that forms the bulk of the tooth structure. The relationship between the cementum and enamel at the CEJ is variable, affecting the region’s vulnerability: they usually overlap (60%) or meet edge-to-edge (30%), but sometimes a gap exists, leaving the underlying dentin exposed.
Clinical Vulnerabilities of the Neck
The cervical region becomes vulnerable when gum tissue recedes, which can happen due to factors like aggressive toothbrushing or periodontal disease. When the gums pull back, the softer cementum covering the neck is exposed to the harsh oral environment, leading to two primary clinical concerns. The first is an increased risk of decay, known as cervical or root caries. Cementum is significantly less mineralized than enamel, making it highly susceptible to acid erosion and bacterial decay once exposed. The second concern is dentin hypersensitivity, which presents as a short, sharp pain in response to cold, hot, or sweet stimuli. This sensitivity occurs because the exposed cementum wears away, uncovering microscopic tubules within the underlying dentin. These tubules lead directly to the tooth’s nerve, causing a painful sensation when external stimuli cause the fluid within them to shift.