Indian Journal of Dental Sciences

: 2020  |  Volume : 12  |  Issue : 2  |  Page : 103--108

Distomolars – Exploring the known entity

Dinesh Chand Patidar1, Deepika Patidar2,  
1 Department of Oral and Maxillofacial Surgery, College of Dental Science and Hospital, Indore, Madhya Pradesh, India
2 Department of Pediatric and Preventive Dentistry, College of Dental Science and Hospital, Indore, Madhya Pradesh, India

Correspondence Address:
Deepika Patidar
Department of Pediatric and Preventive Dentistry, College of Dental Science and Hospital, Rau, Indore, Madhya Pradesh


A supernumerary tooth is one that is additional to the normal series and can be found in any region of the dental arch. A distomolar, also called as “fourth molars,” is a supernumerary tooth that is positioned distal to third molars. Distomolar can be found completely erupted in the dental arch, or it could be partially or entirely impacted. This literature review attempts to highlight the prevalence, etiology, morphology, complications, and diagnosis of distomolars. Various literatures reveal that supernumerary teeth are more frequently seen in the maxilla with a male predilection and their prevalence in the permanent dentition has been approximated to range from 0.1% to 3.6%. A distomolar may have a normal morphology or have a much smaller dimension than adjacent third molars. Molariform (tuberculated) shape is most frequently observed by various authors in their studies. Distomolars are usually found impacted within the jaws and may lead to several complications. Even though the frequency of distomolars is low, dental surgeons should always be aware of the presence of distomolars during radiographic or clinical examinations. A thorough knowledge and information about this supernumerary entity may definitely provide a hope for an early detection and appropriated treatment planning so as to prevent or minimize any complications created by them.

How to cite this article:
Patidar DC, Patidar D. Distomolars – Exploring the known entity.Indian J Dent Sci 2020;12:103-108

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Patidar DC, Patidar D. Distomolars – Exploring the known entity. Indian J Dent Sci [serial online] 2020 [cited 2020 Jul 12 ];12:103-108
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A supernumerary tooth is one that is additional to the normal series and can be found in any region of the dental arch.[1] Supernumerary teeth can be classified on the basis of their location in the dental arches and morphology. Based on the location, they are mesiodens, parapremolar, paramolar, and distomolar. Morphologically, they can be rudimentary or supplemental.[1],[2]

Exact etiology of supernumerary teeth is not well known. Most of the authors indicate phylogenetic aspects, specifically hyperactivity within the dental lamina, as causing the appearance of additional tooth buds. Hereditary and environmental factors are also considered as important etiological factors.[3],[4],[5],[6],[7],[8] Various literatures reveal that supernumerary teeth are more frequently seen in the maxilla with a male predilection and their prevalence in the permanent dentition has been approximated to range from 0.1% to 3.6%.[9],[10],[11],[12],[13],[14],[15],[16],[17],[18],[19] The prevalence of supernumerary molars has been reported as being approximately 75% among all the supernumerary teeth in the maxilla.[20],[21]

A distomolar, also called as “fourth molars,” is a supernumerary tooth that is positioned distal to third molars following the line of dental arch or with a slight palatal or lingual offset. The fourth molars are considered as the second or third more common group of supernumerary teeth. A distomolar may have a regular morphology or may vary from its standard morphology. Distomolars can be found completely erupted in the dental arch, or it could be partially or entirely impacted.[1],[9],[20]

In embryonic sections, the formation of an epithelial outline behind the follicle of the third molar can be examined, which usually undergoes a regression until it disappears eventually; however, sometimes, this outline continues its evolution, forming the distomolar.[9] This study attempts to review various literatures highlighting distomolar and the related findings.


In various studies, the prevalence of distomolar among the studied population varies from 0.03% to 2.1%.[9],[10],[11],[12],[13],[14] It has been noted that maxilla has a higher incidence of supernumerary teeth than the mandible.[9],[10],[11],[12],[13],[14] A major percentage of distomolar has been observed with a male predilection by several authors in their research.[5],[9],[11],[12],[13],[14],[15] The higher prevalence might be due to the association of supernumerary teeth with the autosomal recessive gene, which has a greater penetration in males.[21] Many literatures report that prevalence varies according to the population studied by authors in their studies. The difference seen in the prevalence could be due to the racial difference among the studied populations.

In Caucasian population, the estimated prevalence of supernumerary teeth varies between 0.1% and 3.8%.[19] However, Anibor et al.[22] found a higher prevalence of 12.7% for Nigerian population in their study. Jose et al.[9] found a prevalence of 0.96% of supernumerary molars in 130 Spanish patients, out of which 87.3% were impacted, 79.2% alone represented distomolars, and 63.6% found in the maxillary arch. Mitsea et al.[15] conducted a retrospective study on 859 orthopantomograms (OPGs) of Greek Caucasian individuals and analyzed a low prevalence of distomolar 0.95%–0.1%, which was more frequently seen in the maxilla. Cassetta et al.[21] did an epidemiological study on 25,186 Italian Caucasian populations and found 13 distomolar teeth with higher proportions found in the maxilla and erupted as well. On the contrary, Arandi et al.[1] and Jaiyeoba et al.[23] noticed all impacted distomolars in their case studies [Table 1] and [Table 2].{Table 1}{Table 2}

In Asian population, the estimated prevalence of supernumerary teeth is higher between 2.7% and 3.4%.[18] In a research study done by Rani et al.[24] on 1025 OPGs of a North Indian population, the percentage of 0.4 was found (n = 4), of which three cases exhibited left distomolar and one case revealed bilateral distomolar, and all were detected in the maxillary arch. Gopakumar et al.[10] estimated a value of 0.03% of distomolars in 11,141 individuals in Kerala, South Indian population, whereas Dara et al.[25] assessed 14 (12.5%) of distomolars out of 112 supernumerary teeth in Chennai, South Indian population. In addition, Thomas et al.[12] in their study analyzed that distomolars were more common in the maxillary arch on the right side, whereas in the mandibular arch, an equal frequency of occurrence was observed for both the sides and found 33% bilateral distribution of distomolars. Similarly, Arslan et al.[11] found distomolars more common in the maxillary arch and most often impacted. Out of 4023 Turkish patients, the existence of distomolars was 0.57%. Correspondingly, Kaya et al.[13] found a prevalence of 0.26% and too reported the more frequent occurrence of distomolars in the maxilla, with majority being impacted. Kurt et al.[14] reported 9 out of 14250 Turkish individuals to have maxillary bilateral distomolars (0.063%) and no case in the mandible. In addition to this, Bereket et al.[17] found (204) 23.97% of distomolars out of 1100 supernumerary teeth in their study. According to researchers, the prevalence of supernumerary teeth for Southern Chinese population was reported as 2.4%.[26]

The presence of four distomolar teeth situated in each quadrant of the same patient is a rare finding. Arslan et al.[11] and Jaiyeoba et al.[23] both examined distomolars in all four quadrants in one case in their study on Turkish and Nigerian population, respectively. Interestingly, Rao et al.[27] demonstrated a rare case with six distomolars in a 19-year-old Indian female. Although a male predilection of distomolar is observed in several research studies all over the world,[5],[9],[11],[12],[13],[14],[15] Gopakumar et al.,[10] Martinez et al.,[16] and Rani et al.[24] examined a higher proportion of distomolar in females in their studies [Table 1] and [Table 2].


Several theories have been proposed to describe the occurrence of supernumerary teeth: phylogenetic theory, dichotomy theory, and dental lamina hyperactivity theory. The phylogenetic suggests that the development of supernumerary teeth is due to phylogenetic reversion to extinct primates with three pairs of incisors or teeth that exist in primitive time and lost in the current time period. The dichotomy theory put forward a dichotomy or separation of the tooth bud, resulting in two equal or unequal sized parts, leading to the formation of two teeth of equal size, or one normal and one dysmorphic tooth. The widely accepted one is the dental lamina hyperactivity theory which suggests that local, independent, conditioned hyperactivity of the dental lamina where the remnants of the dental lamina are responsible for the development of an extra tooth bud. None of these theories alone present a satisfactory explanation for this phenomenon. However, complex interactions among various environmental and genetic factors have also been postulated.[3],[4],[5],[6],[7],[8],[13]

 Morphological Characteristics

A distomolar may have a normal morphology with a completely developed crown, single root, and distinct from the adjacent third molar, or it may vary from its standard morphology. Distomolars can erupt fully and align themselves in the dental arch, or they can be partially or completely impacted.[1],[20]

 Crown Morphology

Distomolars are either eumorphic or dysmorphic in shape (i.e., conoid, tubercular, or mixed).[1],[2],[12],[13],[14] They may have a rudimentary shape and are usually found as solitary and impacted teeth.[28] The crown morphology of distomolar is generally poor when located in the maxilla, with many being peg shaped, whereas in the mandible, distomolars are found to be similar to regular molars in configuration.[29],[30] Arslan et al.[11] reported three different types of distomolars: a premolar shape with one root, a premolar shape with only a crown and no root, and a rudimentary conical shape. Moreover, molariform (tuberculated) shape is most frequently observed shape by various authors in their studies.[12],[17],[21] Tuberculated form demonstrates more than one cusp and is barrel shaped. Due to its big coronal portion along with the absence of adequate space in the arch, it may lead to the tooth impaction [Table 2].[21]

Stafne et al.[30] examined blunt, multicuspid, and much smaller distomolars than adjacent third molars in their study. Accordingly, Kaya et al.[13] found conical and miniature distomolars in higher proportions in their study. On the other hand, Kokten et al.[31] found slightly smaller distomolar than adjacent third molars but with standard tooth morphology in their study. Ohata H et al.[29] found dwarfed maxillary molars in their case study. The maxillary distomolars are likely to be dwarfed as compared to the mandibular one. This could be due to the less bone mass in the posterior maxillary tuberosity region of the third molars, while in the mandible, comparatively more bone mass in the ramus area makes easier for the tooth to develop but could also leave the tooth more prone to impaction [Table 2].[29]

 Root Morphology

Most of the researchers have pointed out a single root in distomolars in their studies.[11],[29],[31] Ohata H et al.[29] in their case study with distomolar found two incomplete roots in one case, one incomplete root in second case whereas a single complete root was observed in the third case. Arslan et al.[11] reported a premolar-shaped distomolar with one root, while rootless distomolars were also noted in their study. Accordingly, Itro et al.[32] too reported bilateral mandibular distomolars without root in a case study done on adult Caucasian male.


In general, the presence of fourth molars is detected coincidentally on radiographic examinations, and these supernumerary molars are usually found impacted. The ratio of erupted distomolars to impacted ones is 1:5.[31] The high percentage of impacted fourth molars can be attributed to the fact that the development of these hypergenetic teeth is somewhat delayed as compared to their “normal” predecessors.[9] Most often unnoticed distomolar does not create any problem within the dental arch; however, impacted distomolars may lead to several complications such as impaction, root resorption or pulp necrosis of the adjacent tooth, infection, pain in the molar region, follicular cyst due to degeneration of follicular sac, neoplasms, and compression of trigeminal nerve causing neuralgias.[1] Nazif et al.[33] estimated a 30% incidence of pathologies associated with impacted distomolars in their study. Daguci et al.[19] noticed interference in the eruption of third molars by most of the impacted fourth molars in their study, which is in agreement with the study conducted by Kaya et al.,[13] in which most of the distomolars were found impacted and were seen as blocking the eruption of third molars by creating a physical barrier; however, no cyst was observed in their study. In a study done by Menardia et al.,[34] an incidence of 40% distomolars affecting the eruption of adjacent third molars was found. They also noted complications such as pain in the retromolar region, odontogenic follicular cyst, and odontogenic sinusitis in their case study. Comparatively, Thomas et al.[12] found majority of them (66.6%) obstructing the eruption of adjacent third molars while no associated cyst and follicular enlargement was seen in their study. On the contrary, Stafne et al.[30] found a 6% incidence of follicular cyst in their study. Moreover, Arandi et al.[1] found one impacted distomolar compromising the periodontal health of the adjacent third molar in their research [Table 2].

In case they erupt and become clinically evident, they may cause malocclusion, retention or ectopic eruption, delayed eruption of the adjacent teeth, mandibular disorders, dental caries, and periodontal diseases.[1] Kaya et al.[13] noticed dental caries and periodontal problem associated with one of the erupted distomolars in their study. Distomolars may cause localized periodontitis and traumatic bite or cheek bite when erupted buccally causing injury to the buccal mucosa and neuralgic pains.[35]


Clinical evaluation and radiographic assessment are the key factors for the diagnosis of supernumerary teeth. Radiographs are the most reliable and definite method for the diagnosis of an unerupted supernumerary teeth. The most frequently used radiographs are panoramic, periapical, and occlusal radiographs.[12] A panoramic radiography is the most valuable diagnostic approach for this purpose, as both the dental arches can be visualized in a single radiograph. Since the conventional radiographs provide two-dimensional images of three-dimensional structures limiting the optimal treatment planning, a comprehensive and widespread interpretation of each film is required so as to avoid various diagnostic errors. New advanced imaging techniques such as DentaScan, computed tomography scans, and cone-beam computed tomography (CBCT) are more specific and are used nowadays to detect these anomalies. CBCT is a valuable tool to easily detect the accurate location of these teeth and their relation with adjacent anatomical structures, inclination, and the assessment of surrounding bone thickness as well. It is indicated when the extraction of supernumerary teeth is decided.[15],[21],[28]


It is well known that distomolar presented a clear male predilection and is most frequently located in the maxilla in both the genders. They may erupt normally or remain in an ectopic position. A variety of complications are associated with distomolars. Even though the frequency of distomolars is low, dental surgeons should always be aware of the presence of distomolars in the radiographs or clinically. Further research works are needed to identify the prevalence and characteristics of fourth molars among different populations.

Clinical significance

A thorough knowledge and update of this supernumerary entity may definitely provide a hope for an early detection and appropriated treatment planning so as to prevent or minimize any complications created by them.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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