|Year : 2013 | Volume
| Issue : 1 | Page : 12-15
Prevalence of the carabelli trait in Iranian adolescents
Department of Prosthodontics, Isfahan University of Medical Sciences, Hezar-Jarib Ave, Isfahan, Iran
|Date of Web Publication||22-Aug-2013|
Department of Prosthodontics, Dental Material Research Center, School of Dentistry, Isfahan University of Medical Sciences, Isfahan
Aim: The study of dental morphological features is important in anthropological researches, because it can provide information on the dental variations within a specific population. The aim of this study was to evaluate the prevalence of Carabelli trait in Iranian adolescents. Subjects and Methods: In this descriptive study, 500 individuals (aged 15-49 years) were examined. Direct intraoral examination was done, morphological details of the crown, and sex of the subjects were recorded and Dahlberg classification system was used. Hydrocolloid impressions were taken and the study was repeated on the dental casts. The resultant data were compared with the clinical data. Descriptive statistics and Chi-square tests were used for data analysis (α = 0.05). Results: The prevalence of the trait was 96.6%, with significantly different distribution between males and females. Class 6 was the most frequent configuration (28.4%) and Class 1 was the least frequent (6.2%). Conclusions: The frequency of the trait was higher than that in other reports, but nearly similar to that of European groups.
Keywords: Carabelli anomaly, classification, prevalence, tooth abnormalities
|How to cite this article:|
Mosharraf R. Prevalence of the carabelli trait in Iranian adolescents. SRM J Res Dent Sci 2013;4:12-5
| Introduction|| |
The study of dental morphological characteristics is important in anthropological research, because it can provide information on the phylogenetic relationship between species and variations within a population. , All human populations have some degree of dental morphological variations. Dental anatomical characteristics provide useful information for phylogenic and genetic studies and understanding variations within and among human populations.  It is commonly accepted that dental characteristics, such as size, shape, presence, number of cusps, and also the size of the dental arches, are genetically determined. , Therefore, the above-mentioned characteristics differ among races and can constantly alter due to natural selection and genetic changes.  The most commonly detected dental characteristic is the Carabelli cusp that can be used to determine the degree of intercourse between different populations. 
Tubercle of Carabelli is a dental morphologic trait found on the mesio-palatal surface of maxillary deciduous second molar and maxillary permanent first molar crowns. , It is rarely present on the upper first primary molars, or on the second or third upper permanent molars. This nonfunctioning mini cusp is present symmetrically on both sides of the maxillary arch.  Although it is said that this cusp is not clinically important, it has some importance in dental industries (for manufacturing dental instruments), forensic odontology, and anthropology. The orthodontic molar bands have no compensation for this cusp. As a result, the space between the band and the tooth is filled by food debris, and it results in early caries and periodontal diseases. Furthermore, the Carabelli groove is a sensitive area for dental caries. This needs to be kept in mind during pit and fissure sealing. Even the molar extraction forceps have no accommodation for this cusp and may therefore result in fracture of the molar teeth. 
The etiology of a Carabelli cusp remains unknown. Both genetic and exogenous factors have been proposed. Most studies agree that the phenotypical appearance of the cusp is genetically determined.  There must be a dominant gene responsible for the presence of the cusp. 
This cusp was first described in 1842 by Carabelli.  Since that time, many studies have evaluated the morphology of this cusp and its anthropological features. Carabelli's cusp has been detected and studied in non-hybridized ethnical groups, especially Eastern and Central American groups, in which the evaluation of heritability and sex distribution is easier.  The incidence and degree of expression differ among species; therefore, it compares different populations.  According to Bermúdez De Castro,  Carabelli's trait can be useful in establishing phylogenic relationships among closely related populations. The cusp may rival the main cusps in size, whereas other related forms, including a small ridge, pit, or furrow may have a specific feature.  A similar structure, the cingulum, is found among apes and gibbons. , A Carabelli cusp has been seen in Australopithecus and Neanderthal man as only a simple groove. Thus, Carabelli's cusp has evolved from a simple groove to a well-developed cusp. 
Carabelli cusp is expressed in several degrees and different frequencies between different populations.  For example, this cusp is more rarely present in Caucasian peoples  and its occurrence is influenced by race.  Some authors claim that bilateral occurrence of Carabelli cusp was originally an inherited character in the molar region, but that the character was inhibited during the process of evolution of the masticatory system and regression of the molar dentition. 
The aim of this study was to evaluate the prevalence, expression, and left-right asymmetry of trait of Carabelli in permanent dentition of Iranian adolescents.
| Subjects and Methods|| |
This descriptive investigation was undertaken in some dental clinics of Isfahan city, Iran. The samples (n = 500) were carefully screened and only Iranian individuals (aged 15-49 years) with erupted maxillary first and second molars bilaterally were selected. Individuals with mixed parentage up to three generation were excluded from the study. Direct intraoral examination was done carefully and morphological details of the crown, namely, the number of teeth cusps, presence or absence of Carabelli cusp, and sex of the subjects were recorded on prepared forms. Interview, examination, and recording of the data were done by a single examiner to eliminate inter-observer variability. Data were excluded from the investigation in cases where the teeth were restored, worn, or heavily broken down. After that, hydrocolloid impressions were taken and dental casts were immediately made. Alginate (Alginoplast; Heraeus Kulzer, Hanau, Germany) was the impression material used and the casts were made of dental stone type III (Mold stone, Pars dandan Co., Tehran, Iran). The study was repeated on the dental casts and the resultant data were compared with clinical data for each subject. If there was any difference, the examination of that subject was done again.
Dahlberg classification system [Figure 1] was used for the study and descriptive statistics and Chi-square tests were used for data analysis (α =0.05).
|Figure 1: Dahlberg's (1963) scale for the determination of degree and expression of Carabelli cusps|
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| Results|| |
Of the 500 individuals examined, 223 (44.6%) were males and 277 (55.4%) were females. In this population, we examined 1000 teeth (500 × 2), in which Class 6 was the most frequent Carabelli cusp configuration (28.4%) and Class 1 was the least frequent one (6.2%) [Table 1].
|Table 1: Total degree and expression of a Carabelli cusp in this population according to the scale of Dahlberg (1963) |
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Chi-square analysis revealed significant differences between all 8 groups in both sides (P < 0.001), and the predominant Carabelli cusp configuration was Class 6 (32.4%) in left side and Class 5 (29.6%) in the right side [Table 2].
Most cases (300/500; 60%) had bilaterally same configuration [Table 3]. Only 12 cases (2.4%) did not have Carabelli cusp bilaterally.
Chi-square analysis revealed significant differences between males and females in all 8 groups (P < 0.001). Chi-square analysis also revealed significantly difference between males and females in the group of bilaterally same configurations (P = 0.04).
| Discussion|| |
The frequency of the Carabelli trait varies from population to population or within the population groups. , The findings of the present study showed an overall prevalence of 96.6% in the surveyed group, which is higher than that in previous reports. Mavrodisz reported a "European average" of about 65.34% for the frequency of this cusp.  Carbonell reported that this trait is of low prevalence in Mongoloids (Chinese and Japanese), but of high prevalence in white Caucasians.  Scott,  Alvesalo et al.,  and Kieser , reported high frequencies for the trait in white Caucasian populations. In Malaysian children, the frequency of Carabelli cusp on the maxillary first molars was 54.2%.  Among Indians, 52.77% of maxillary first permanent molars displayed a Carabelli tubercle.  Hassanali  showed that Carabelli's trait was present in 26-27% of Asian school children. Caucasoid populations differ from Mongoloids by having a high prevalence of Carabelli's trait.  In a study in Saudi Arabia, the prevalence of the trait was 58.7% with almost similar distribution between males and females. The frequency of the trait in Negroids was comparatively low.  It has been concluded that the frequency of Carabelli cusp is high in Europeans (70-90%), but low in oriental races.  However, Stamfelj  stated that positive expressions of this trait were found in 10.1% of the subjects, which was surprisingly lower than in Europeans. However, we can conclude that the highest frequency of Carabelli cusp has been seen in Europeans  and Iranian population. This morphological similarity between Iranian and European populations had been showed in other dental characteristics such as occlusal morphology of mandibular premolars. 
Dahlberg's classification is the most commonly applied method for determining the degree and expression of Carabelli cusps. , In this population, Class 6 was the most frequent Carabelli cusp configuration (28.4%) and Class 1 was the least frequent (6.2%). In the study of Mavrodisz et al.,  Class 0 was the most frequent Carabelli cusp configuration with a 34.6% frequency. Other investigations used some other methods for classification of Carabelli cusp configuration. ,,
Few researchers stated that Carabelli's tubercle is invariably bilateral; but, the majority describes it as usually bilateral. ,,, In the present study, most cases (300/500; 60%) had bilaterally same configuration and only 12 cases (2.4%) did not have Carabelli cusp, bilaterally. Only 8 cases (1.6%) did not have Carabelli cusp, unilaterally. Therefore, we can say that, in our study, Carabelli's tubercle was invariably bilateral.
In the present study, there was no sexual preference in the overall prevalence of the trait . Bilateral occurrence of this cusp was significantly higher in females than in males (P = 0.040). In the study by Harris,  males had cusp of Carabelli more than females, but there was no sex difference in the morphological expression of Carabelli's trait in his study sample. Salako et al.,  reported higher incidence of this cusp in females (53.5%) than in males (46.5%).
In this type of studies, some researchers used intra-oral examination, ,, some of them studied dental casts, ,,,, and some used both the methods. , Intra oral examination has the advantages of accurate recording, proper identification of teeth, and follow-up of the patients when needed. It ensures racial and sexual identification.  A sample of extracted teeth would be less than ideal. , For more precise results, we used both methods (intra-oral and cast examinations) in the present study.
In future, it would be better to arrange a same study comparing monozygote and heterozygote twins using the genealogical tree in their parents and close relatives.
| Conclusion|| |
In this Iranian population, the prevalence of Carabelli trait was 96.6% with significantly different distribution between males and females. According to Dahlberg's scale, Class 6 was most frequent and Class 1 was least frequent. The frequency of the trait was higher than that in other reports, but nearly similar to that of European groups.
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[Table 1], [Table 2], [Table 3]