The permanent adult dentition, which includes the standard four wisdom teeth, is the final set of teeth a person develops. A standard, second set of the four third molars is biologically impossible. However, having extra teeth beyond the normal count is a real, though rare, developmental phenomenon. This occurrence of additional molars behind the standard wisdom teeth is often what people are unknowingly referring to when they ask about having a second set.
The Standard Set of Third Molars
The teeth commonly known as wisdom teeth are scientifically designated as the third molars. A typical adult mouth contains four of these molars, with one located in each of the four quadrants: upper left, upper right, lower left, and lower right. These teeth are the last ones to erupt into the mouth, generally appearing between the ages of 17 and 25.
These molars are situated at the very back of the dental arch, positioned distally, or behind, the second molars. They complete the standard set of 32 permanent teeth, which includes incisors, canines, premolars, and all three sets of molars.
Understanding Supernumerary Teeth
The condition of having any extra teeth is formally referred to as hyperdontia, and the additional teeth themselves are called supernumerary teeth. These extra structures form beyond the normal count of 20 primary teeth. Supernumerary teeth can develop anywhere in the dental arch, though they are most frequently observed in the upper jaw.
The prevalence of hyperdontia in the permanent dentition is relatively low, affecting approximately 1% to 4% of the population. These teeth can appear as a single extra tooth. They are classified based on their location and their shape, which can range from a fully formed tooth to a rudimentary, cone-shaped structure.
Fourth Molars (Distomolars)
The specific extra molars that appear behind the wisdom teeth are known as fourth molars or distomolars. A distomolar is a type of supernumerary tooth that is positioned distal to the third molar.
These fourth molars are extremely rare, with incidence estimates generally falling between 0.02% and 2.2% of the population. Distomolars are most frequently found in the upper jaw, or maxilla, and often remain impacted, meaning they fail to fully erupt through the gum line. Their morphology can vary significantly; they may be small, conical, or tuberculated, or they might resemble a normal molar, though they are typically smaller than the third molar.
Causes and Management of Extra Molars
The exact cause of supernumerary teeth, including distomolars, is not completely understood, but current theories point toward a combination of genetic factors and developmental abnormalities. The most widely accepted hypothesis suggests the condition results from hyperactivity or horizontal proliferation of the dental lamina, which is the band of tissue responsible for forming tooth buds. This over-activity leads to the formation of an extra tooth bud.
The presence of extra molars is usually detected through routine dental X-rays, as they are often impacted or unerupted. These additional teeth can cause a range of complications, such as the displacement or crowding of adjacent teeth, delayed eruption of the standard teeth, or the formation of cysts around the tooth crown. Treatment typically involves a thorough evaluation. If the distomolar is symptomatic or poses a threat to the adjacent teeth, the standard management is surgical extraction. In asymptomatic cases that do not interfere with the dental arch, a dentist may opt for careful observation with regular follow-up.