The typical adult mouth contains four wisdom teeth, also known as third molars, which are the last teeth to emerge, usually between the ages of 17 and 25. These teeth are positioned at the very back of the dental arches, one in each quadrant. The presence of a fifth molar is a surprising finding and represents a developmental anomaly. While most people have a full set of 32 permanent teeth, an extra tooth beyond the standard count is a recognized dental variation.
Defining Supernumerary Teeth
The medical term for having extra teeth is hyperdontia, and the additional teeth are called supernumerary teeth. These structures can develop anywhere in the mouth, but they are classified by their location relative to the standard dentition. A fifth wisdom tooth is a supernumerary molar, typically referred to as a distomolar or a paramolar. A distomolar is a fourth molar positioned directly behind the third molar (wisdom tooth). A paramolar grows adjacent to one of the molars, often toward the cheek or tongue side.
Prevalence and Underlying Causes
The prevalence of hyperdontia in the permanent dentition affects between 0.1% and 3.8% of the general population. Having a fifth wisdom tooth, or a distomolar, is less common than other forms of supernumerary teeth, such as a mesiodens, which appears between the two upper front incisors. Distomolars are considered the second most frequent type of extra tooth. The occurrence of these extra molars is considered a rare event.
The development of supernumerary teeth is not fully understood, but it is influenced by genetic and developmental factors. One leading theory involves the hyperactivity of the dental lamina, the tissue responsible for initiating tooth formation. An overgrowth or persistence of this tissue could lead to the formation of an extra tooth bud. Genetic factors are also implicated, as hyperdontia often demonstrates a familial tendency, suggesting it can be inherited.
Specific systemic conditions and genetic syndromes are known to be associated with hyperdontia. These include Cleidocranial dysplasia, a disorder affecting bone and tooth development, and Gardner syndrome, a rare genetic disorder that causes growths in various parts of the body. Studies have suggested a higher prevalence of these fourth molars in certain ethnic groups. The majority of cases, however, occur sporadically without any clear connection to a syndrome.
Clinical Management of Extra Wisdom Teeth
The diagnosis of a fifth wisdom tooth, which may be impacted or unerupted, is made using dental imaging like panoramic X-rays. If the extra tooth is positioned unusually or near sensitive anatomical structures, a three-dimensional cone-beam computed tomography (CBCT) scan may be necessary for precise surgical planning. The management decision depends on whether the extra tooth is causing or is likely to cause complications.
The presence of a distomolar can lead to various complications, similar to those associated with a regular impacted wisdom tooth. These issues include the crowding and misalignment of adjacent teeth due to pressure. The extra tooth can also lead to the formation of follicular cysts, fluid-filled sacs that can damage the surrounding jawbone and roots of neighboring teeth.
If the extra molar is fully erupted, asymptomatic, and does not interfere with chewing or oral hygiene, a “watch and wait” approach involving regular monitoring may be adopted. Extraction is recommended if the tooth is impacted, causing pain, contributing to infection, or posing a risk to the health of adjacent teeth. The surgical removal process is similar to a standard wisdom tooth extraction. However, the unusual positioning of a distomolar at the very back of the jaw may require a more complex surgical approach.