The cementoenamel junction is the specific line around the tooth's perimeter, where the enamel covering the crown of the tooth meets the cementum protecting the root. In most cases, the cementum overlaps the enamel around the tooth. Still, in some people, this area contains a thin band of exposed dentin. At this location, the hard, mineralized enamel stops, and the less-mineralized root covering begins.
The CEJ acts as a covering of connective tissue. Think of it as a tight turtleneck around the tooth's neck, keeping the less-mineralized root surface warm and protected from bacteria and acids. Patients may feel sensitivity to hot and cold foods when the CEJ is exposed. This exposure is known as gum recession, the gum's process of coming away from the tooth's neck and shrinking down.
To confirm this is the cause of your discomfort, a dental professional will measure the gum recession to determine the degree of CEJ exposure. When probing the gum tissue, your dental professional will place a small measuring ruler called a periodontal probe in the space along the CEJ. In completing this process, dental professionals can evaluate whether the attachment fibers between the teeth and the bone are healthy or if the patient is at risk for periodontal infections, inflammation, or future recession.