Tooth resorption is a pathological process where the body begins to dissolve parts of a tooth’s structure in permanent teeth. This condition involves the progressive loss of the dental hard tissues, specifically the dentin and cementum. The destruction is carried out by specialized cells known as clastic cells, or odontoclasts, which are similar to the cells that naturally resorb the roots of baby teeth. When this destructive activity is triggered in an adult tooth, it can lead to structural compromise, weakening the tooth from the inside or the outside. Early detection is important for preserving the tooth structure and function.
Classifying Tooth Resorption
Resorption is primarily classified based on the anatomical location where the process begins, separating it into internal and external categories. Internal resorption originates within the pulp space, the soft tissue core of the tooth. This type of lesion is characterized by a widening of the root canal chamber and is often discovered incidentally on routine radiographs. In some cases, internal resorption can cause a visible pink discoloration of the crown, known as a “pink tooth,” due to the highly vascularized resorptive tissue showing through the remaining thin dentin layer.
External resorption, which is the more common type, begins on the outer surface of the tooth root, often where the root is covered by cementum. This category includes several subtypes, such as external inflammatory resorption and external replacement resorption, which results in the fusion of the root to the jawbone, a condition called ankylosis. A particularly aggressive form is external cervical resorption (ECR), which starts near the gumline and progresses inward toward the pulp. ECR destroys the dentin without initially entering the pulp space. The location and pattern of this destruction are crucial factors in determining the appropriate treatment approach.
The Underlying Causes and Triggers
Pathological tooth resorption in permanent teeth requires both a breach in the protective covering of the root and a biological stimulus to activate the clastic cells. The protective layer on the inner surface is predentin, and on the outer surface, it is cementum and the periodontal ligament. Damage to these layers exposes the underlying dentin to the resorptive cells.
Dental trauma is a frequent trigger for both internal and external resorption, particularly injuries involving luxation or avulsion, where the tooth is displaced or knocked out. This physical impact can damage the periodontal ligament or the internal pulp tissue, initiating an inflammatory response. Inflammation or chronic infection within the tooth’s pulp space provides the necessary stimulus to activate the odontoclasts.
Orthodontic tooth movement is another common cause of external resorption, typically resulting in a shortening of the root tip, known as apical root resorption. The sustained pressure applied during treatment causes localized damage to the periodontal ligament, which activates the clastic cells. While some minor root shortening is expected, excessive or rapid force can lead to more severe damage.
Diagnostic Methods for Resorption
Because tooth resorption relies heavily on dental imaging for detection, as it often progresses without noticeable symptoms. Conventional periapical radiographs (X-rays) are the initial tool used to identify these lesions as dark, radiolucent areas on the root structure. However, two-dimensional X-rays often underestimate the true size of the lesion and struggle to differentiate between internal and external defects.
Cone Beam Computed Tomography (CBCT) provides a three-dimensional view and is the preferred method for accurate diagnosis and treatment planning. CBCT imaging allows the clinician to precisely locate the origin of the lesion, distinguishing if the defect is contiguous with the pulp space (internal) or separated from it by intact dentin (external). This level of detail is necessary for assessing the severity and determining the restorability of the tooth. CBCT also provides a clear assessment of the circumferential spread of external cervical lesions, which helps determine the feasibility of surgical repair.
Managing and Treating Tooth Resorption
Treatment for tooth resorption is specific to the type, location, and extent of the defect. For active internal resorption, the standard intervention is root canal therapy, which aims to remove the inflamed pulp tissue and the blood supply that sustains the clastic cells. Once the resorptive tissue is removed, the internal defect is cleaned, sterilized, and filled with a sealing material.
External resorption, particularly the aggressive external cervical type, often requires a surgical approach to access and treat the defect on the outside of the root. This procedure involves surgically raising the gum tissue to expose the lesion, removing the resorptive tissue, and then repairing the defect with specialized biocompatible filling materials, such as calcium silicate cements. The success of this repair depends on the lesion being accessible and not having spread too far circumferentially around the root.
When the resorptive process is discovered late and has caused extensive, irreparable destruction, the tooth may be deemed non-restorable. In these severe cases, the most appropriate course of action is extraction. The lost tooth structure can then be replaced using prosthetic options, such as a dental implant or a fixed bridge.