The shedding of primary teeth is a predictable biological process signaling the transition to adult dentition. Children typically begin losing their front teeth, the central incisors, around age six or seven, though this timeline can vary. This process is regulated by the permanent tooth developing directly underneath the primary tooth. The presence of the successor tooth triggers the root of the primary tooth to dissolve, allowing it to loosen and fall out naturally.
When the Permanent Tooth Misses the Mark
The primary signal for a baby tooth to exfoliate is the biological interaction with the developing permanent tooth underneath. Specialized cells, called odontoclasts, are activated to break down the primary tooth’s root structure through root resorption. This cellular activity is regulated by signaling molecules released by the dental follicle surrounding the crown of the permanent tooth.
If the permanent tooth begins to erupt at an unusual angle, it may be directed away from the baby tooth’s root, failing to stimulate complete resorption. This misalignment leaves the root intact, anchoring the baby tooth firmly in place while the permanent tooth emerges elsewhere. When the permanent tooth erupts behind the retained baby tooth, it results in a double row of teeth, commonly referred to as “shark teeth.”
Another common reason for the lack of shedding is the complete absence of the permanent successor tooth, known as congenital absence or hypodontia. Without the underlying permanent tooth, the biological trigger for root resorption is missing, and the primary tooth root does not dissolve.
Structural Issues That Keep Baby Teeth Stuck
Structural problems inherent to the baby tooth or surrounding jawbone can also cause retention, regardless of the permanent tooth’s position. The most prominent example is dental ankylosis, an abnormal fusion of the tooth root directly to the jawbone. This fusion occurs when the periodontal ligament, the fibrous tissue between the tooth and the bone, is damaged and replaced by bone cells.
This direct connection prevents natural movement and stops the root from dissolving completely. The ankylosed tooth cannot move upward with the growing jawbone and appears “sunken” or lower than adjacent teeth, a condition called infra-occlusion. Ankylosis most commonly affects the primary molars, which can complicate the eruption of the permanent premolars.
Trauma to the mouth, such as a hard blow received earlier in childhood, can damage the periodontal ligament or surrounding bone tissue. This injury can trigger an inflammatory response that encourages the bone to fuse with the tooth, and prior physical injury is frequently implicated in secondary ankylosis.
When to See a Dentist and What Happens Next
Parents should seek a dental consultation if a permanent tooth has begun to erupt but the corresponding baby tooth has not fallen out, or if the expected shedding time has passed by about one year. Early assessment is recommended because retained primary teeth can lead to crowding and misalignment of adjacent permanent teeth.
After a clinical examination, the dentist’s first step is to obtain a dental X-ray of the area. This imaging is necessary to determine the underlying cause, as it clearly shows the presence or absence of the permanent tooth and its exact position. The X-ray also allows the dentist to assess the degree of root resorption and check for signs of ankylosis, such as the lack of a visible periodontal ligament space.
In many cases, especially when the permanent tooth is misaligned, the most straightforward treatment is the simple extraction of the retained baby tooth. Removing the obstruction clears the path and often allows the permanent tooth to drift into its correct position over time. If a baby tooth is ankylosed, extraction may be necessary to prevent interference with normal jaw development and the eruption of neighboring teeth.