Occurrence of Fourth Molars (Distomolars) in South Indian Population – A Descriptive Retrospective Study

Aim: To determine the total prevalence of fourth molars/distomolars occurring in South Indian ethnic population using panoramic radiographs.

Methods: Orthopantomograph radiographs of patients who visited the hospital during the period from January 2023 to December 2023 were retrospectively collected and examined for the presence of fourth molars. The gender, symmetry, age, arch involved, laterality and frequencies of occurrence of fourth molars, associated anomalies were compared and the data obtained was subjected to statistical analysis using descriptive statistics.

Results: A total of 392 panoramic radiographs of patients were examined for presence of fourth molars. Fourth molars were found in five patients (1.27%) including 2 males and 3 females. Three cases were found in the maxilla (0.76%), two in the mandible (0.51%). There was no statistically significant difference observed in gender evaluation (P > 0.05). Four cases occurred on right side (1.02%) with one on left side (0.25%) with no bilateral occurrence.

Conclusion: Approximately 1.27%% of Indian population had fourth molars. Although the frequency of occurrence is low, clinicians should be aware of its existence in Indian people to arrive at early diagnosis, to provide appropriate treatment and to minimize or prevent complications.

Keywords: Distomolars, Fourth molars, Indian population, Orthopantomograph, Prevalence, Supernumerary molars

Different dental anomalies involving either crown or root part of the tooth are sometimes encountered during clinical practice [1-5]. There are 32 permanent teeth and 20 primary teeth in an individual. Teeth which exceed normal number in the dental arch either in primary or permanent teeth are termed as supernumerary tooth. Supernumerary teeth can involve any teeth including incisors, canines, premolars and molars. Supernumerary tooth is classified in different ways based on their location and shape. According to location they are categorised as mesiodens, parapremolars and distomolars and paramolars. Mesiodens are the teeth located between two central incisors and seen most commonly in the dental midline. Parapremolars are seen either buccal or lingual/palatal to the normal premolars [2]. Distomolars are also called as ‘fourth molars’ or ‘distodens’ or ‘hypergenetic molars’ and are positioned distally to the third molars. Paramolars develop buccaly or lingually/palatally to any molar teeth most commonly first and second molars. All supernumerary teeth may occur either in the maxilla or mandible, unilateral or bilateral, or can be observed as erupted or remain impacted and may be found associated with syndromes, other anomalies or isolated [2].

Distomolars or supernumerary molars are rarely reported in the dental literature. Although one or few case presentations can be read pertaining to distomolars but their true prevalence is not exactly studied. Therefore, the aim of this research article is to evaluate the total prevalence of fourth molars occurring in Indian ethnic population using retrospective data.

A total of 392 panoramic radiographs of patients were retrospectively collected who visited the Dental wing, Karnataka ENT Hospital and Research centre, Chitradurga during the period from January 2023 to December 2023. The age of the patients ranged from 18 to 65 years. There were 198 males and 194 females. The images were prescribed by the dentist to examine the condition of third molars associated with pain or dental caries. Radiographs taken for the treatment of other teeth or other purpose were also included in the study. Those cases where there was absence of third molar or was extracted was not included in the study. Radiographs were taken in standardized technique to reduce the error and to obtain images with adequate quality. Blurred or inaccurate radiographs or images with artifacts were excluded to avoid radiographic misinterpretation. Prior to the study patient consent was obtained to use radiographs for the purpose of research or study. The author of the paper examined radiographs in a well illuminated x-ray viewer. In this investigation, the supernumerary molar was defined as presence of a well demarcated radiopaque toothlike structure located distally to the third molar having both crown and root portion. Regardless of size, any extra molar present distally to the third molar and with aforementioned criteria was considered as a fourth molar. The total prevalence, prevalence of unilateral or bilateral presence, maxillary or mandibular, left or right-side placement of fourth molar, their morphology, associated anomalies and their gender predilection was examined.

Statistical analysis

The data obtained was subjected to statistical analysis using descriptive statistics. P values of < 0.05 were considered as statistical significance.

Out of 392 patients examined, fourth molars were observed in five patients and hence the prevalence recorded was 1.27% (5/392) (Table 1). Three cases were detected in females (0.76%) and two in males (0.51%) (Table 2). Among five cases, two were noticed in the mandibular arch and three in the maxillary arch (Table 3). All cases occurred unilateral with no bilateral occurrence (Table 4). Among unilateral cases, four occurred on right side (1.02%), with only one on left side (0.25%) (Table 4).

Table 1: Total prevalence of Fourth molars

Table 2: Gender wise distribution of Fourth molars

Table 3: Arch-wise distribution of Fourth molars

Table 4: Distribution of Fourth molars based on laterality

Figure 1: Radiograph showing fourth molar in the maxillary left quadrant (red arrow)

Figure 2: Orthopantomograph showing distomolar in the mandibular left quadrant (yellow arrow). Distomolar is placed in mesioangular position and almost in the ramus of the mandible.

Figure 3: Panoramic radiograph showing distomolar in the maxillary left quadrant (yellow arrow)

Supernumerary molars are divided into two types, depending on their location as distomolars and paramolars. Distomolars are also referred as “fourth molars” or “distodens” or “dens distomolar” or “hypergenetic molars” are located distally to the third molars [6-10]. The phenomenon behind occurrence of distomolars is interesting especially considering the fact that in modern man, missing third molars are becoming a common finding. These are usually diagnosed as a coincidental radiological finding without any associated pathology. Literature shows scarcity of data regarding the prevalence of fourth molars among different population.

Shahzad et al (2012) in Japan evaluated the prevalence of fourth molars among Japanese population using panoramic radiographs. Authors found a prevalence of 2.2% and reported more commonly in black patients (6.4%) compared to whites (0.9%) [6]. The prevalence was slightly less in females (2.1%) compared to males (2.2%). They encountered more in the maxilla (78%) than in the mandible (22%) but not with a statistically significant difference. Maximum of fourth molars occurred unilaterally in this population (55%) [6]. Another Japanese study found a prevalence of 0.32% (87 fourth molars) among the 26,721 cases evaluated during a 5-year period using both conventional and CBCT images. The mean age observed with fourth molars was 30.43 years and the male to female ratio was 1:098. The majority of cases occurred in the maxilla (92%) and exhibited normal shapes (89%) and most cases were found impacted (82%). Authors also studied the shape of fourth molars and reported that among 87 cases found, all 78 fourth molars were in normal shape and remaining only nine were in abnormal shape [9].

In the present study out of 392 patients examined, fourth molars were observed in five patients and hence the prevalence recorded was 1.27%. Three cases were detected in females (0.76%) and two in males (0.51%) showing similar observation found in other studies [9,11]. Among five cases, two were found in the mandibular arch and three in the maxillary arch. All cases occurred unilateral with no bilateral occurrence. Among unilateral cases, four occurred on right side (1.02%), with only one on left side (0.25%). When the eruption status was evaluated, four fourth molars were erupted into the oral cavity and one was impacted. Evaluation of shape and size revealed that four fourth molars including both maxillary and mandibular appeared smaller than normal third molars with only one appeared extremely small. All fourth molars had crown and root portion. Four distomolars were placed in normal vertical position with one in horizontal position (mesioangular position). Assessment of treatment modality resulted that no extraction was performed as these distomolars were asymptomatic.

Turkish study performed by Kaya et al [11] found a prevalence of 0.26% distomolars among Turkish population. In total, 30 distomolars were observed in 26 patients. 0.29% were found in males and 0.23% were noticed in female patients. Out of 30 distomolars, 25 were impacted and five were erupted. Maxillary distomolars were more frequently found compared to mandibular arch distomolars and bilateral distomolars were detected in three male patients. A Spanish study found a prevalence of 0.96% supernumerary molars including both distomolars and paramolars (130 patients) among the 13,557 Spanish patients evaluated. Among these, 137 were categorized as distomolars and remaining 36 as paramolars [12]. In 28% cases, mechanical-obstructive pathology was observed whereas enlargement of the follicular sack bigger than 3 mm was present in 16.2% of the sample [12].

Case reports with bilateral occurrence of fourth molars have also been reported. Cases of all fourth molars which occur both in maxilla and mandible are also extremely rare. Cavalcanti et al presented an occurrence of bilateral fourth molars both in the maxilla and mandible in 2011 [7]. Recently an Indian case report showed occurrence of four fourth molars in both maxilla and mandible along with an impacted permanent canine [10]. In the maxillary arch, bilateral fourth molars erupted normally and in mandible both were impacted. Therefore, authors in this case removed mandibular both fourth molars.  Recently in 2024, Nagaveni NB reported an occurrence of distomolar in the mandibular right quadrant along with another anomaly like congenital agenesis of all four second premolars in an Indian female patient [13]. In this case the fourth molar appeared similar to the third molar in morphology except for the size (smaller size). The same author published another case of fourth molar occurring in the maxillary arch observed in an Indian male patient [14]. The fourth molar appeared small and had conical shaped crown with short single root which was erupted in vertical position. In addition to this other anomaly observed were rhyzomicroly or short root anomaly involving mandibular first, second and third molars with 1:1 crown root ratio along with pyramidal, single rooted maxillary right and left second molars [14].

Most of the time, maxillary fourth molars appear rudimentary and conical shape whereas mandibular one appears similar to third molars but slightly smaller to it. The same observation was found in the previous retrospective studies and case reports [6-10, 13,14]. While extracting these molars the decision to remove should consider the risk or benefits associated with them. Sometimes distomolars are found with some congenital dental anomalies like supernumerary teeth, short root anomaly, root dilaceration, agenesis of tooth and pyramidal molars. Literature shows occurrence of different dental anomalies or conditions occurring in Indian population which is highly essential for increasing the richness of the existing literature [15-18].

Although the frequency of occurrence of distomolars/fourth molars in south Indian population is low, clinicians should be aware of its existence in Indian people to arrive at early diagnosis, to provide appropriate treatment and to minimize or prevent complications.