The third molars, commonly known as wisdom teeth, are the final set of teeth to develop in the human mouth. They typically begin to emerge between the ages of 17 and 25. These teeth can stop growing at any stage. This developmental halt can occur for two primary reasons: either the tooth never forms due to genetic factors, or its physical progression is obstructed mid-development.
Standard Developmental Stages of Third Molars
The normal development of a wisdom tooth begins deep within the jawbone with the formation of the tooth germ, or tooth bud, observable as early as six to nine years of age. Following this, the tooth undergoes mineralization, where calcium and other minerals harden the crown structure.
The crown of the third molar is fully formed and hardened by the time an individual is around 14 to 15 years old. Once the crown is complete, the tooth begins its slow, gradual path toward eruption into the oral cavity. Root development continues during this eruption phase, with the final root length and closure of the apex often not completed until around age 22, though this timing is highly variable.
Genetic Absence: When Wisdom Teeth Never Form
A wisdom tooth stops growing by never starting, a condition known as dental agenesis or hypodontia. This occurs when the initial tooth bud fails to form in the jaw entirely, meaning the tooth is congenitally missing. Genetic factors play a substantial role in this phenomenon, with specific genes like MSX1 and PAX9 being linked to the failure of tooth development.
Third molars are the teeth most frequently affected by agenesis; up to 23% of the population is missing at least one wisdom tooth. A dentist confirms this absence through a panoramic X-ray, which visualizes the entire jaw structure. If a radiograph taken after the age of 14 shows no sign of the developing tooth germ, it is considered conclusive that the tooth will not form or grow.
Physical Obstruction: Why Growth Halts Mid-Development
The most common reason for a mid-development halt is physical obstruction, leading to a condition called impaction. Impaction occurs when the fully formed tooth crown is prevented from erupting into its functional position in the mouth. This issue is attributed to a mismatch between jaw size and tooth size.
When there is insufficient space at the back of the dental arch, the third molar’s eruptive force is met with resistance from the bone, gum tissue, or the adjacent second molar. The tooth ceases its vertical eruption and becomes trapped in the jawbone or beneath the gumline. Impaction is classified by the angle of the trapped tooth, such as mesial impaction, where the tooth is tilted forward toward the second molar, or horizontal impaction, where it lies completely on its side. The physical barrier effectively stops the growth and eruption process.
Clinical Monitoring of Non-Erupting Molars
For wisdom teeth that have stopped growing due to impaction or non-formation, clinical monitoring is a necessary part of long-term dental care. Dentists rely on periodic panoramic X-rays to visualize the position of the molar and assess surrounding structures. The decision to intervene is based on the risk of future complications, not simply the tooth’s presence.
An impacted tooth completely encased in bone and asymptomatic may be monitored through surveillance, especially if the risk of surgical complications outweighs the risk of retention. Intervention is required if the tooth is partially erupted, creating a gum flap that traps bacteria and causes chronic infection, or if it poses a risk of decay or bone loss to the adjacent second molar. An impacted tooth can also lead to the formation of cysts or tumors, necessitating proactive removal.