Primary teeth, often called baby teeth, are the first set of 20 teeth that develop in humans, typically erupting in infancy. Beyond chewing food, they hold necessary space in the jaw for the permanent teeth that will follow. The natural replacement process, known as exfoliation or shedding, usually begins around age six and is complete by the early teenage years. Shedding occurs when the developing permanent tooth pushes against the primary tooth’s root, causing the root to dissolve, allowing the tooth to loosen and fall out. When this predictable sequence is disrupted, and a primary tooth remains past its expected shedding date, it is classified as an over-retained primary tooth.
Understanding Why Baby Teeth Are Retained
The failure of a primary tooth to shed is fundamentally a problem with root resorption, the natural dissolving of the tooth root. The most frequent reason for this failure is the congenital absence of the permanent successor tooth, known as hypodontia. Without the pressure and biological signaling from a permanent tooth forming beneath it, the primary tooth root has no stimulus to dissolve, allowing the tooth to remain firmly rooted in the jawbone. This absence of a permanent tooth is most commonly seen with the second premolars and the lateral incisors.
A separate cause involves a condition called ankylosis, where the primary tooth root fuses directly to the surrounding jawbone. This fusion prevents the tooth from moving vertically, locking it into the bone structure and halting the shedding process. Ankylosed teeth can sometimes appear slightly sunken compared to adjacent teeth that continue to erupt, a phenomenon known as infraocclusion.
Another common scenario is the misalignment of the permanent tooth, even when it is present in the jaw. If the permanent tooth begins to form or erupt along an abnormal path, it can miss the primary tooth’s root structure entirely. Since the permanent tooth is not positioned to exert pressure or stimulate the root to dissolve, the primary tooth remains in place, creating a barrier to the permanent tooth’s correct emergence.
Dental and Oral Health Consequences
The continued presence of a primary tooth can lead to a cascade of problems for the developing adult dentition. One of the most common issues is dental crowding, as the permanent tooth requires more space than the smaller primary tooth reserves. This space discrepancy can force other permanent teeth to erupt in rotated, crooked, or overlapping positions, resulting in a malocclusion, or improper bite.
The retained primary tooth often blocks the path of the permanent successor, leading to the impaction of the adult tooth. Impaction means the permanent tooth becomes trapped within the bone or gum tissue and is unable to emerge into the dental arch. An impacted tooth can exert pressure on the roots of neighboring permanent teeth, potentially causing damage or resorption.
If the retained primary tooth is ankylosed, it will not move as the jawbone grows, causing it to appear submerged relative to the adult teeth around it. This infraocclusion can result in an uneven biting surface, disrupting the alignment of the opposing teeth and creating abnormal forces during chewing. Such uneven pressure can cause a condition known as occlusal trauma, which may lead to wear on the other teeth or jaw joint issues over time.
The smaller size of primary teeth compared to adult teeth also creates aesthetic concerns and functional challenges. The size difference can result in noticeable gaps, or diastema, between the retained tooth and the larger permanent teeth. Retained primary teeth are also more susceptible to decay and wear over the long term, potentially compromising the health of the surrounding gum and bone tissue.
Diagnosis and Necessary Treatment
Identifying an over-retained primary tooth requires a thorough clinical examination combined with diagnostic imaging. Dentists rely heavily on dental X-rays, particularly panoramic radiographs, to visualize the entire jaw structure and confirm the presence or absence of the permanent successor. Imaging is necessary to determine the underlying cause, such as whether the tooth is ankylosed or if the permanent tooth is impacted.
Treatment planning is individualized and depends on the status of the retained tooth and the underlying cause. If the permanent tooth is missing, and the primary tooth is structurally sound, functional, and aesthetically acceptable, it may be retained and monitored for many years. Sometimes, a dental restoration may be used to modify the retained tooth’s shape or size to better match the adjacent permanent teeth.
If the primary tooth is causing crowding, is significantly ankylosed, or is structurally compromised, extraction is typically the recommended course of action. Following extraction, management shifts to addressing the resulting space and potential alignment issues. Orthodontic treatment is frequently initiated to correct crowding, move the permanent teeth into proper alignment, or create a specific space for future tooth replacement.
If the permanent tooth was congenitally absent, the space left by the extracted primary tooth must be managed with a long-term prosthetic solution. This often involves maintaining the space until the patient is old enough for a dental implant, which is generally not placed until late adolescence or adulthood when jaw growth is complete. Temporary solutions, such as a retainer with a false tooth, are used to hold the space and restore appearance and function during the waiting period.