Carabelli Trait in Primary Tooth - A Case Report

ABSTRACT

The Carabelli cusp (Cusp of Carabelli) is a tubercle or the extra fifth cusp found on the mesiopalatal cusp of the maxillary permanent and deciduous molars. It is nonfunctional but it can be used to distinguish populations and is also used in forensic and anthropological studies. This condition is uncommon on deciduous teeth. In this case report, we present a rare case of unilateral presence of cusp of Carabelli in deciduous dentition.

INTRODUCTION

The cusp of Carabelli is the fifth supplemental cusp found along with two lingual cusps and two buccal cusps on the palatal surface of the permanent maxillary first molar and the primary maxillary second molar. It is located approximately 2 mm below the mesiopalatal cusp, at the junction of the middle and occlusal thirds of the crown. It was originally described by Carabelli more than a century ago. This fifth cusp, or traces of it, can be used as a reliable identification mark in determining the identity of the maxillary first molar.[1,2]

It is also known as the “Carabelli’s trait, Carabelli tubercle, fifth cusp, or tuberculum Carabelli.”[3] The frequency of occurrence of this fifth cusp has been recognized to vary depending upon racial population.[4,5]

The etiology is unknown but it could be due to genetic or exogenous factors or due to overactivity of the dental lamina. Most studies agree that the cusp has a genetically determined phenotype.[6] The paired box 9 and Msh homeobox 1 are the dominant genes that cause abnormal cuspal morphology.[7]

This article describes an incidental dental finding of unilateral accessory cusps in primary maxillary second molars which is a rare presentation.

CASE REPORT

A 10-year-old male patient was accompanied by his parents to visit the dental clinic for a routine dental checkup. On intraoral examination, the patient had mixed dentition, with permanent maxillary central incisor, lateral incisors, and permanent maxillary molars erupted, the first premolar erupting, and deciduous maxillary second molars present. The presence of the fifth cusp, the Cusp of Carabelli, in the mesiopalatal cusp of the deciduous maxillary second molar was observed on the right side deciduous second molar [Figure 1]. As per Dahlberg’s (1963) scale for determining the degree and expression of Carabelli cusps, it is of type 6, which has a broad base outline with moderate tubercles [Table 1].

Figure 1.

Clinical presentation of Cusp of Carabelli in the right side deciduous second molar.

Table 1.

Dahlberg’s classification is the most commonly applied method for determining the degree and expression of Carabelli cusps

Degree	Expression
0	Smooth mesiolingual crown surface
1	Small vertical ridge and groove
2	Small pit with minor grooves diverging from depression
3	Double vertical ridges or slight and incomplete cusp outline
4	Y form
5	Small tubercle
6	Broad cusp outline with moderate tubercle
7	Large tubercle with a free apex

DISCUSSION

Teeth are frequently the most abundant skeletal system remnant in the archaeological and fossil record. They can provide valuable information about the nature and inculcate diversity among human populations, thereby acting as a potential forensic tool.[8] The crown of the tooth shows variations in the morphologic traits and is traditionally used to compare human populations and to identify their geographical distributions. This is useful in the forensic field for postmortem profiling and to infer human migratory patterns and population affinities.[9] This is because size and shape of the tooth, number of tooth, frequency of occurrence, and their morphology have a strong genetic basis and can be used as variables to have a deeper insight into microevolutionary trends and to assess biological relationships.[10]

The Carabelli trait was discovered in early hominin species and is more common in European races than in Asian races. Although it is a nonfunctional cusp, it can be used to differentiate populations and is also used in forensic and anthropological studies. The groove separating the cusps may be prone to caries and may cause problems with orthodontic band placement.[11]

Mavrodisz, K et al. (2007).[12] As per Kamatham et al.,[9] Carabelli trait was classified into absent, positive, and negative expressions (positive trait shows a definite cusp form and negative trait shows a pit or groove form). The expression of positive trait was found in 27.6% and the expression of negative trait was found in 62.2% of primary second molars. The trait was found to be absent in 10.2% of deciduous second molars, whereas 6.5% shows unilateral occurrence, as seen in our case report.

As per the study conducted by Smita et al.,[10] Type 3 (Dahlberg classification) was the one that was most frequently expressed, while Type 6 was least frequently expressed and both the types were expressed in Islamic groups. In 90% of the groups surveyed, bilateral trait expression was noted. In the study by Shethri et al.,[11] the bilateral occurence of cusp of Carabelli was 70.71%.

Numerous studies have been conducted on various countries, races, and populations and there is no perfect prevalence on percentage of occurrence in primary maxillary molars. The prevalence varies depending on the country and ethnicity. The majority of studies show that this cuspal trait and not triat is bilateral.[9-13]

In this case report, unilateral trait was seen with a Carabelli cusp configuration of Type 6.

CONCLUSIONS

Cusp of Carabelli presentation in the primary second molar is reported in a 10-year-old male subject unilaterally on right side. The cusp was described initially by Carabelli and the classification by Dahlberg is employed. This fifth extra cusp expressed unilaterally in the right deciduous second molar is rare to find and this nonfunctional cusp aids as a forensic tool.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.