The process of a tooth moving into its functional position in the mouth is known as eruption. This biological event happens twice: first with the 20 primary (baby) teeth, and later with the 32 permanent teeth that replace them. When a tooth fails to emerge from the gums or appears significantly later than expected, it is termed delayed eruption. This delay often causes concern but can stem from simple variations in timing or more complex underlying issues.
Understanding Normal Eruption Timelines
The timing of tooth eruption follows general guidelines, but the range considered “normal” is wide for both sets of teeth. Primary teeth typically begin to appear around six months of age, starting with the lower front teeth, with a full set usually present by age three. Permanent teeth begin their sequence around age six with the first molars, and most are in place by the early teens, excluding wisdom teeth.
Individual genetic factors heavily influence this schedule, making a delay often a matter of inherited timing. If a parent or sibling experienced late-emerging teeth, a child is likely to follow a similar pattern. A delay is generally defined as a concern only if a tooth has not appeared more than 12 months after its typical eruption age, or if a tooth on one side has erupted but its counterpart on the opposite side has not.
Physical Obstacles Blocking Growth
A frequent reason a tooth fails to grow in is a mechanical obstruction in its path, meaning the tooth is present but physically blocked. The most common barrier is an over-retained primary tooth that has failed to shed naturally. Normally, the developing permanent tooth dissolves the roots of the baby tooth, but if this process falters, the primary tooth remains rooted and blocks the underlying successor.
Another mechanical issue is impaction, which occurs when a tooth is prevented from emerging by bone, adjacent teeth, or dense gum tissue. This is common with the upper canine teeth and the third molars (wisdom teeth). Impaction can also be caused by supernumerary teeth, which are extra teeth that occupy the space needed by the permanent tooth, diverting it from its proper path. Rarely, cysts or benign tumors can develop in the jaw, acting as a physical barrier that prevents normal tooth movement.
Developmental Failure or Absence of the Tooth
In some instances, the missing tooth is not merely blocked but is absent entirely, a condition known as dental agenesis or hypodontia. This occurs when the tooth bud, the structure from which a tooth develops, never forms in the jawbone. Hypodontia is the most common developmental dental anomaly, frequently affecting the second premolars and the upper lateral incisors.
This failure of formation is often linked to genetic factors responsible for signaling the initiation of tooth development. Environmental disturbances, such as severe infection or trauma to a primary tooth, can also damage the permanent tooth bud underneath, halting its formation. More severe forms, like oligodontia (six or more missing teeth) or anodontia (complete absence of teeth), are associated with systemic conditions or genetic syndromes.
Diagnostic Tools and Treatment Options
A dental professional must evaluate any suspected case of delayed or absent tooth growth to determine the precise cause. The initial and most informative diagnostic tool is the dental radiograph, or X-ray. This imaging allows the dentist to visualize the jawbone, confirm the tooth’s presence, assess its location and angulation, and check for physical obstructions like retained roots or extra teeth.
Treatment depends entirely on the diagnosis established by the X-ray and examination. If the tooth is simply delayed with no apparent blockage, it may be monitored to allow for natural eruption. If a retained primary tooth is the cause, its extraction is often the solution to clear the eruption path. For an impacted tooth, a combined approach of minor oral surgery and orthodontics is utilized, involving a procedure called “expose and bond” to surgically uncover the tooth and attach a bracket to guide it into the dental arch.