Retained Primary Tooth: Causes, Treatments, and Outlook

A retained primary tooth occurs when a baby tooth remains beyond the typical age of loss, potentially causing alignment issues, bite problems, or complications with permanent teeth development. While some cases pose no immediate concern, others require intervention to prevent long-term dental issues.

Contributing Factors And Prevalence

Several factors contribute to a primary tooth remaining in place beyond the expected time frame. Genetic predisposition, jaw structure variations, and disruptions in the normal exfoliation process all play a role in this dental anomaly.

Genetic Variations

Inherited traits significantly influence the retention of primary teeth. Dental development patterns, including the timing of tooth eruption and exfoliation, often follow familial trends. A 2021 review in the European Journal of Orthodontics highlighted that genetic factors affect the agenesis (absence) of permanent successors, a key reason for primary teeth persisting. When a permanent tooth fails to develop due to genetic mutations affecting odontogenesis, the corresponding primary tooth may remain indefinitely.

Certain syndromes, such as cleidocranial dysplasia and hypodontia, are strongly associated with retained primary teeth. Individuals with these conditions often exhibit delayed or missing permanent dentition, leading to prolonged retention of baby teeth. Variations in genes responsible for enamel and dentin formation, such as MSX1 and PAX9, have been linked to anomalies in tooth development. Genetic screening in families with a history of dental agenesis can sometimes help predict the likelihood of retained primary teeth in younger generations.

Jaw Structure Differences

The size and shape of the jaw influence how teeth emerge and align. A smaller jaw may lack sufficient space for permanent teeth to erupt, leading to prolonged retention of primary teeth. Research published in The Angle Orthodontist (2022) found that individuals with micrognathia, an underdeveloped lower jaw, were more likely to experience delayed exfoliation due to crowding and impaction of permanent successors.

Malocclusion, or improper alignment of teeth, can also contribute. If a primary tooth remains too long, it may prevent the normal eruption of adjacent or opposing permanent teeth. In some cases, an abnormal eruption path causes the permanent tooth to emerge incorrectly, leading to further complications. Discrepancies in alveolar bone density may also affect root resorption, prolonging primary tooth retention.

Early Or Delayed Loss Of Primary Teeth

The timing of primary tooth loss significantly affects the transition to permanent dentition. Premature loss, often due to trauma or decay, can disrupt the natural eruption sequence, sometimes leading to retained primary teeth. A 2020 study in the Journal of Clinical Pediatric Dentistry found that early extraction of primary molars increases the risk of space loss, potentially preventing permanent teeth from emerging correctly.

Delayed exfoliation can occur when root resorption is incomplete or when the underlying permanent tooth fails to erupt on schedule. Conditions such as hypothyroidism have been linked to delayed tooth eruption. Additionally, ankylosis, where the primary tooth fuses to the surrounding bone, can prevent normal shedding and require intervention.

Routine dental examinations help identify retained primary teeth early and determine if intervention is necessary to maintain proper alignment.

Physical Signs And Dental Assessments

A retained primary tooth is often identified by its prolonged presence beyond the expected age of exfoliation, typically between 6 and 12 years old. These teeth tend to appear smaller than adjacent permanent teeth, creating a noticeable size discrepancy within the dental arch. Discoloration or excessive wear may also occur, particularly if the tooth has been subjected to prolonged chewing forces without a permanent successor.

Functional concerns may arise, including occlusal misalignment, where the bite does not fit together properly due to the absence or improper positioning of permanent teeth. This can lead to difficulties in chewing, uneven pressure distribution, and, in some cases, temporomandibular joint discomfort. A retained primary molar, for instance, may lack the durability for long-term function, increasing susceptibility to fractures.

Dentists diagnose retained primary teeth using clinical examinations and imaging techniques. Intraoral exams assess tooth mobility, gingival health, and signs of ankylosis, where the tooth is fused to the alveolar bone and lacks normal movement. Percussion testing, which involves tapping the tooth, can help confirm ankylosis, as affected teeth produce a dull sound due to direct bone attachment.

Radiographic imaging determines whether a permanent successor is present beneath the retained tooth. Panoramic and periapical X-rays provide insight into root morphology and bone integration. Cone-beam computed tomography (CBCT) offers a more detailed three-dimensional view, particularly useful in assessing root resorption patterns or planning interventions. If a permanent tooth is missing, the retained primary tooth may be preserved as a functional alternative if it remains structurally sound and does not impede adjacent dental development.

Root Resorption Patterns

Root resorption determines whether a primary tooth will exfoliate as expected or remain in place. Normally, resorption begins when the permanent successor exerts pressure on the primary tooth’s root, triggering osteoclast activity that gradually breaks it down. This allows the baby tooth to loosen and be replaced. However, incomplete or absent resorption can lead to retention.

Variability in resorption patterns often stems from differences in the presence, position, or development of the underlying permanent tooth. If a successor fails to form, the absence of eruptive pressure may result in little to no resorption, leaving the primary tooth intact but potentially misaligned. In some cases, partial resorption causes the retained tooth to tilt or sink lower than surrounding teeth, creating occlusal discrepancies.

Ankylosis further complicates resorption by preventing natural root breakdown. This occurs when the primary tooth fuses directly to the surrounding bone, eliminating the periodontal ligament that normally facilitates movement. Ankylosed teeth often appear submerged relative to neighboring teeth as surrounding bone continues to develop while the retained tooth remains static. This condition is more common in primary molars and can be identified through radiographic imaging, where a lack of visible periodontal space confirms fusion to the bone.

Orthodontic Correction Options

Orthodontic treatment for a retained primary tooth depends on its position, structural integrity, and the presence of a permanent successor. If a retained tooth disrupts alignment or occlusion, orthodontic strategies can help guide surrounding teeth into a more functional arrangement.

When a permanent tooth is present but impacted—often due to obstruction by the retained primary tooth—orthodontists may use braces or clear aligners to create space and encourage proper eruption. In some cases, orthodontic traction is employed, where a small attachment is bonded to the impacted tooth and connected to braces via elastic forces, gradually guiding it into position.

Prosthetic Solutions

When a retained primary tooth lacks a permanent successor and is structurally compromised, prosthetic options can restore function and aesthetics. Retained primary molars may wear down over time, reducing chewing efficiency and increasing the risk of fractures. A dental crown can reinforce the structure and extend the tooth’s longevity, distributing occlusal forces more evenly.

If extraction is necessary, prosthetic replacements such as dental bridges or implants provide viable solutions. A fixed dental bridge uses adjacent teeth for support, filling the gap left by the extracted primary tooth. However, this option requires modifying neighboring teeth, which may not be ideal for younger patients. Dental implants offer a more permanent alternative, particularly for individuals who have reached skeletal maturity. Titanium implants integrate with the jawbone, providing long-term stability and preventing bone resorption after tooth loss.

For pediatric or adolescent patients where implant placement is not immediately feasible, a removable partial denture or space maintainer can preserve alignment until a definitive solution is possible.

Surgical Treatments

When orthodontic or prosthetic interventions are insufficient, surgical procedures may be necessary, particularly in cases of ankylosis or impacted permanent successors. If a retained tooth is fused to the bone and fails to exfoliate naturally, surgical extraction may be required to prevent complications such as infraocclusion, where the tooth appears submerged due to continued bone growth. Infraoccluded teeth can affect adjacent dentition and may require bone grafting if significant resorption occurs after extraction.

For impacted permanent teeth obstructed by a retained primary tooth, an uncovering procedure followed by orthodontic traction can facilitate proper eruption. This involves removing soft and hard tissues to expose the impacted tooth, allowing it to be guided into position using orthodontic appliances. If the permanent tooth remains unerupted despite intervention, surgical repositioning or autotransplantation may be considered. Autotransplantation involves relocating a donor tooth—often a premolar—to the site of the missing permanent tooth, with careful attention to root development and periodontal integration. While requiring precise planning, long-term studies have shown favorable outcomes in maintaining functional dentition.