When a tooth does not emerge as expected, it can be a source of concern. While tooth development and eruption are natural processes, various factors can disrupt this progression, leading to a tooth not growing in. Understanding the typical timeline for tooth emergence helps identify potential issues.
Understanding Normal Tooth Eruption
Tooth eruption is the process by which a tooth moves from its developmental position within the jawbone through the gum line and into the mouth. This process follows a general timeline, though variations are common. Primary, or “baby,” teeth typically appear around six months, often starting with lower central incisors. By the age of two-and-a-half to three years, most children have a full set of 20 primary teeth.
The transition to permanent teeth usually starts around age six, when the first permanent molars erupt at the back of the mouth, not replacing any baby teeth. Primary teeth then shed, making way for permanent successors. Central incisors typically emerge between ages six and eight, while lateral incisors follow from seven to nine years. Canines and premolars generally erupt between nine and thirteen years, with second molars appearing from eleven to thirteen years. Wisdom teeth (third molars) are the last to emerge, usually between 17 and 21, if at all.
When a Tooth Doesn’t Develop
Sometimes, a tooth never grows in because it never formed. This condition, known as tooth agenesis, means the tooth bud—the initial tissue from which a tooth develops—was absent from the beginning. It is a congenital condition.
Agenesis can manifest in different forms depending on the number of missing teeth. Hypodontia refers to the absence of one to five permanent teeth, excluding wisdom teeth, making it a common dental anomaly. More severe forms include oligodontia, which involves the absence of six or more permanent teeth, and anodontia, the rare complete absence of all primary and/or permanent teeth. These conditions are primarily linked to genetic factors, often involving gene mutations crucial for tooth formation. Anodontia, for instance, is frequently associated with genetic syndromes like ectodermal dysplasia, which affects multiple structures derived from the ectoderm, including teeth, hair, and nails.
When a Tooth Cannot Erupt
Even if a tooth develops, it might be unable to emerge into the mouth, known as impaction. An impacted tooth is physically blocked from breaking through the gum line, often trapped within the jawbone or soft tissue. This is a frequent occurrence, particularly with wisdom teeth, but can affect any tooth.
Several factors can cause impaction. Insufficient jaw space, known as crowding, is a common reason. Extra teeth, called supernumerary teeth, can also physically obstruct the path of normal teeth.
Growths like cysts or tumors in the jaw can create blockages. Trauma to the jaw or an existing tooth can damage the developing tooth or disrupt its eruption pathway. A tooth’s root can also fuse directly to the bone, a condition called ankylosis, preventing its movement and emergence. Additionally, abnormal tooth direction or angulation can prevent proper eruption.
Other Factors Influencing Eruption
Beyond congenital absence or physical obstruction, other factors can cause teeth to be delayed in their eruption. These are often systemic influences affecting overall development, including tooth emergence. Genetic predisposition plays a role, with familial patterns of late eruption occurring.
Nutritional deficiencies, especially severe ones affecting bone and tooth development, can contribute to delayed eruption. For example, vitamin D deficiency can impact eruption timing. Endocrine disorders, such as hypothyroidism, can slow a child’s overall growth and development, including tooth eruption. Certain medical syndromes, like Down syndrome, also feature delayed tooth eruption, indicating a broader developmental impact. Premature birth and low birth weight have been linked to slightly delayed primary tooth eruption.