A four-rooted tooth is an anatomical variation where a tooth develops an extra root beyond its typical configuration, most often occurring in the molars. This supernumerary root represents a deviation from the standard human dental structure, which usually involves two roots in lower molars and three roots in upper molars. Understanding the prevalence of this variation is important for both dental research and clinical practice.
Statistical Rarity and Global Prevalence
A four-rooted tooth is generally considered an uncommon finding, but its prevalence varies dramatically depending on the population studied. This anatomical variation is most frequently documented in the mandibular (lower) first molar. The extra structure is known as Radix Entomolaris (RE) when located on the distolingual aspect. Global assessments place the overall prevalence of RE in mandibular first molars at around 5.6%.
In populations of Caucasian or European descent, the occurrence of this extra root is low, typically falling below 5% (0.7% to 4.2%). However, this figure shifts significantly in specific ethnic groups, particularly those of East Asian or Mongoloid heritage. In these populations, the extra root is considered a normal morphological variant due to its high frequency. Prevalence rates in regions like China and Korea often range from 22.4% to over 30%.
Four-rooted maxillary (upper) molars are exceedingly rare. Maxillary first molars usually have three roots, and the presence of a fourth root in this tooth type has been meta-analytically determined to have a global incidence of only about 0.047%.
Identifying the Specific Teeth Affected
The mandibular first molar is the tooth most characteristically associated with having four roots. Standard anatomy includes a mesial root and a distal root, but the presence of Radix Entomolaris (RE) creates a third, smaller root on the back and tongue-side of the tooth. This extra root is the primary source of the four-rooted configuration in the lower jaw.
Less frequently, the mandibular second molar may also present with an additional root. A much rarer variation known as Radix Paramolaris (RP) may also result in four roots, appearing on the mesiobuccal (front and cheek-side) aspect of the tooth.
Implications for Dental Treatment
The existence of a four-rooted molar introduces complexity that significantly impacts dental procedures. The most direct complication arises during root canal therapy (RCT), as the extra root almost always contains an extra root canal that must be located, cleaned, and sealed. Missing this curved, often smaller canal is a common cause of treatment failure because remaining tissue or bacteria can lead to persistent infection.
This anatomical deviation also presents challenges during tooth extraction. The additional root may be smaller, more curved, or fused, increasing the risk of root fracture during removal.
Specialized diagnostic techniques are employed to map the tooth’s anatomy before treatment begins. Advanced imaging, such as Cone-Beam Computed Tomography (CBCT), offers a three-dimensional view that allows dental professionals to accurately identify the number, location, and curvature of all roots and canals, preventing procedural errors.