A tooth that fails to come out, whether it is a primary (baby) tooth that stays too long or a permanent tooth that never fully emerges, can be confusing. This issue stems from distinct causes related to either the primary or permanent dentition. Understanding why a tooth remains in place is the first step toward finding the appropriate solution for maintaining a healthy mouth. Both scenarios involve a disruption in the natural process of tooth eruption and require professional dental assessment.
Causes of Primary Tooth Retention
When a primary tooth remains in the jaw past its expected shedding date, it is considered over-retained. The normal process involves the underlying permanent tooth slowly dissolving the primary tooth’s root through a biological process called root resorption. This resorption weakens the tooth’s support until it becomes loose and falls out naturally.
One frequent reason this process fails is the complete absence of a permanent successor tooth, a condition known as hypodontia or tooth agenesis. Without the developing permanent tooth to exert pressure and trigger root resorption, the primary tooth’s root structure remains intact, keeping it anchored in the jawbone.
Another cause is dental ankylosis, where the root of the primary tooth fuses directly to the surrounding jawbone. This fusion prevents the tooth from moving, making it impossible for the normal shedding process to occur.
The permanent tooth may also be present but erupting along an abnormal path, failing to make contact with the primary tooth’s root to initiate resorption. Additionally, the primary tooth’s root may only partially resorb, leaving enough structure to physically block the path of the permanent tooth. In some instances, a cyst or tumor beneath the primary tooth can impede the development and eruption of the permanent tooth, leading to the tooth’s retention.
Causes of Permanent Tooth Impaction
A permanent tooth is considered impacted when it fails to fully erupt through the gum line into its functional position by the expected time. This condition is most commonly associated with the third molars (wisdom teeth), but it can also affect other teeth, particularly the maxillary canines. Impaction often occurs due to a lack of sufficient space in the jawbone, which can result from a jaw too small for all the teeth.
Severe dental crowding means there is not enough room for the tooth to emerge properly, forcing it to remain trapped in the bone or gum tissue. The tooth may grow at an incorrect angle, such as horizontally or at an extreme slant, which pushes against the roots of neighboring teeth and prevents eruption. Sometimes, the tooth bud itself is simply misplaced, developing in a position far from its normal eruption track.
Physical obstructions can also block a permanent tooth’s path, including a benign cyst, a tumor, or the presence of supernumerary (extra) teeth. When the tooth is blocked, it can remain fully embedded in the jawbone (full bony impaction) or partially emerge through the bone but not the gum tissue (soft tissue impaction).
Dental Diagnosis and Treatment Options
Determining why a tooth will not come out requires a professional dental examination beyond a visual check. The dentist will take X-rays, such as panoramic radiographs, which capture a single image of the entire mouth and jaw structures. These images visualize the exact position of the retained or impacted tooth, its relationship to surrounding nerves, and the presence of any underlying pathology like cysts.
The treatment strategy depends upon the cause, location, and potential complications identified in the diagnostic images. For minor issues or in young patients, the initial approach may be non-invasive, involving a period of observation and monitoring to see if the tooth corrects its path naturally.
If the primary tooth is retained and the permanent tooth is blocked, the primary tooth is typically extracted to create an open pathway for the successor. In cases of permanent tooth impaction, surgical intervention is often required, ranging from a simple extraction to a complex surgical procedure. Surgical exposure, where the dentist uncovers the impacted tooth and attaches an orthodontic bracket, is common for impacted canines, allowing the orthodontist to guide the tooth into position.
If a retained primary tooth is healthy and has no permanent successor, it may be monitored and kept to serve as a natural placeholder, often with a crown or other restoration to match the size of the adult teeth.