Primary teeth, often called baby teeth, serve as natural guides for the permanent teeth that follow. These 20 temporary teeth are important for proper chewing, speech development, and maintaining space in the jaw. The natural process of a primary tooth falling out is exfoliation, which occurs as the root is gradually dissolved by the erupting permanent tooth below it. When a primary tooth remains in the mouth past the expected time for its shedding, it is considered retained. This retention is a dental anomaly that requires professional evaluation to prevent potential complications with the developing adult dentition.
Why Primary Teeth Fail to Shed
The retention of a primary tooth occurs because the natural mechanism responsible for root dissolution and shedding is interrupted. The most common reason is the congenital absence of the permanent successor tooth, a condition known as agenesis or hypodontia. If there is no developing permanent tooth to exert pressure and initiate the breakdown of the primary tooth’s root structure, the baby tooth often remains firmly in place. Hypodontia, the absence of one to five permanent teeth, affects between 2% and 8% of the population, making it a frequent factor in retention.
Another significant cause is ankylosis, where the root of the primary tooth fuses directly to the surrounding jawbone. This fusion eliminates the periodontal ligament, which is the soft tissue necessary for the tooth’s normal movement and eventual shedding. Ankylosis prevents the tooth from rising with the growing jaw and resists the forces of the permanent tooth, effectively locking the primary tooth into the bone.
The third category involves a physical obstruction in the permanent tooth’s eruption path. This can be due to the permanent tooth being severely misaligned, impacted against another tooth, or blocked by a supernumerary (extra) tooth. In these cases, the permanent tooth fails to make the necessary contact to dissolve the primary root.
Structural Problems Caused by Retention
When a primary tooth fails to exfoliate, the most immediate consequence is often an alteration in the alignment of the permanent teeth. The adult tooth, unable to erupt into its correct position, may be forced to emerge outside the dental arch, leading to an ectopic eruption. This results in dental crowding, as the retained tooth occupies the space intended for the larger permanent tooth. If the permanent tooth cannot erupt at all, it remains impacted within the jawbone.
Retained primary teeth can also create issues with the overall bite, a condition known as malocclusion. A common issue is infraocclusion, where the retained tooth appears to sink below the level of the adjacent permanent teeth. Since the jaw continues to grow around the retained tooth, it may not maintain the correct height relative to the neighboring teeth, causing an uneven bite plane. This can lead to abnormal wear on opposing teeth or place excessive force on certain teeth, resulting in trauma to the tooth structure or supporting bone.
Long-term retention also poses risks to the health of the surrounding bone and gums. The presence of a primary tooth past its expected lifespan may lead to localized bone loss around its root, complicating future treatment options. Furthermore, the size difference between a retained primary tooth and its permanent neighbors can result in gaps, known as diastema, or create areas that are difficult to clean. These areas may increase the risk of periodontal inflammation or decay in both the retained tooth and the adjacent adult teeth.
Professional Diagnosis and Treatment Options
A dental professional relies on a clinical examination combined with diagnostic imaging to accurately assess a retained primary tooth. Radiographs, or X-rays, are the primary tool, allowing the dentist to visualize the unerupted permanent tooth and the condition of the primary tooth’s root. The X-ray confirms whether the permanent successor is present, its exact position, and whether the primary tooth is ankylosed or has a resorbed root.
Treatment is entirely dependent on the underlying cause identified through this diagnostic process. If the permanent tooth is present but blocked by the primary tooth, the usual course of action is the extraction of the retained tooth. This removal clears the path and often allows the permanent tooth to move into its correct position naturally, though orthodontic monitoring may be needed to ensure proper alignment.
When the permanent tooth is congenitally missing, the treatment plan focuses on the long-term prognosis of the retained primary tooth. If the baby tooth is healthy, functional, and aesthetically acceptable, it may be retained, sometimes well into adulthood. If a retained primary tooth is healthy but undersized, it can be modified with tooth-colored filling materials or a crown to better match the adjacent permanent teeth. If the retained tooth is compromised or significantly infra-occluded, extraction is recommended. This is followed by space maintenance until the patient is old enough for a definitive prosthetic solution, such as a bridge or a dental implant, typically placed after bone growth is complete.