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Renukaradhya, S., and Rao:

Occlusal groove patterns and cusp number in permanent mandibular first and second molar among Indian population - A pilot study

Sindhu Nair, Vijayalakshmi S. Kotrashetti, Ramakant Nayak, Jagadish Hosmani

Department of Oral Pathology and Microbiology, Maratha Mandal’s NGH Institute of Dental Sciences, Belgaum, Karnataka, India

Correspondence: Dr. Vijayalakshmi Kotrashetti, Department of Oral Pathology and Microbiology, Maratha Mandal’s NGH Institute of Dental Sciences, Belgaum – 590 010, Karnataka, India. Fax.: (0831)-2479323. E-mail: drviju18@yahoo.com
Received: 02 May 2018;
Accepted: 22 June 2018
doi: 10.15713/ins.jcri.225

Abstract

Background: The study of the origin and variations of the human dentition is called dental anthropology. It can be used as an effective tool to identify geographic or racial affinities. Dental anthropology includes metric and non-metric analysis. Non-metric analysis includes studying the morphology of teeth. Morphological analyses on extra cusp, shoveling of incisor, and Carabelli’s trait have been studied extensively in Indian population, but cusp number variation and variation in groove morphology are lacking. Thus, the aim is to determine the frequency of occlusal groove pattern and cusp number in permanent mandibular first and second molar among Indian population.

Materials and Methods: A total of 150 subjects of Indian origin were considered (75 males and 75 females) in the age group of 18–25 years. Exclusion criteria included caries, restorations, and attrition of teeth. After obtaining consent, impression was obtained using alginate impression material and cast made using dental stone. Mandibular first and second molar was analyzed for occlusal groove pattern and cusp number based on Arizona State University - Dentoanthropological System of State University of Arizona criteria.

Results: The most frequent pattern in 36 and 46 was 5Y followed by 4+ and 6X. In 37 and 47, 4+ pattern was more frequent followed by 4X. Significant difference was observed in distribution of patterns between 36 and 37 and 46 and 47, respectively (P < 0.01) and between males and females significant difference was observed with respect to 37 and 47.

Conclusion: The mandibular first molar showed 5Y pattern more frequently indicating a more conservative trend while the second molar showed 4+ pattern depicting a high evolutionary trend. There was a significant difference in the distribution of patterns between males and females with respect to the second molar.

Keywords Forensic odontology, groove, indian population, mandibular molars, occlusal cusp


Introduction

The study of the origin and variations of the human dentition is called dental anthropology. It can be used as an effective tool to identify geographic or racial affinities. Dental anthropologic studies include metric and non-metric traits. The former includes number of teeth, individual tooth measurement, cusp size, and number, and the latter includes parameters such as location of cusps, occlusal pattern, and root configuration.[1] The patterns of occlusal surfaces of molars can occur during the final stages of molar growth, which results in terminal deposition of enamel and are suggested to be polygenically conditioned and which are determined by the combination of allele on two or more sites/loci.[2]

In anthropology, variations in occlusal surfaces of mandibular molars are described by morphological categories. In 1928, various occlusal surface patterns were outlined and their frequency was discussed in different population groups by Hellman. The original classification of Hellman was based on number of cusps and groove patterns established between the occlusal surfaces of lower molars. Y5 type is the basic pattern which is termed as “dryopithecoid,” where the “5” refers to the main cusps which are homologous with the major cusps of previous tooth forms in phylogeny. In the four-cusped class, all these cusps are included except the hypoconulid on the distal aspect, which is the most variable one. The number 4 or 5 is combined with the letter Y or a plus sign (+) which indicates the arrangement of the grooves between these cusps. While the 5Y pattern is considered to be the most conservative and of the ancestral variety, the 4+ pattern represents the evolutionary advanced type. It has been depicted that in modern tooth forms there is a generalized reduction in the dental components, which is supported by the fact that the 4+ tooth is much smaller than the 5Y tooth Jorgensen in 1955 added an additional groove confirmation called the X form.[3] At present, the X form is considered to be the most evolved form.

Studies determining the cusp number and groove patterns have been conducted in different populations such as Iranian, Croatian, and Alaskan populations. However, on literature search, such studies have not been done with regard to the Indian population.

Thus, the aim of this study was to determine the frequency of occlusal groove pattern and cusp number in permanent mandibular first and second molar among Indian population.

Materials And Methods

The study was conducted at the department of oral pathology. A total of 150 subjects were considered (75 males and 75 females) in the age group of 18–25 years. Before commencement of the study, written consent was obtained and a detailed history of the patient was recorded to determine their Indian origin. There are a total of 28 states in India, subjects for this study belonged to 20 states of India. The exclusion criteria included caries, restorations, and attrition of the teeth that were to be studied. Impressions were obtained using alginate impression material and cast was poured using dental stone. Occlusal groove pattern was determined on the cast by delineating the groove using a sharp tip lead pencil. Classifications of the characteristics of the occlusal surfaces of the molars were determined according to the standards for characterization of morphological variants of permanent teeth of Arizona State University (ASU) (ASU - Dentoanthropological System of the State University of Arizona).

Classification of the groove pattern on the mandibular first (M1), second (M2), and third (M3) molars:

  • Y - Contact of the second and third cusps.

  • + - Contact of cusps from one to four.

  • X - Contact of the first and fourth cusps.

The groove pattern was calculated by means of loupe at x magnification.

Classification of the number of cusps on the mandibular first (M1), second (M2), and the third (M3) molars:

  • 4 - The presence of cusps 1–4 (1 - protoconid, 2 - metaconid, 3 - hypoconid, and 4 - entoconid).

  • 5 - The presence of 5 cusps (hypoconulid)

  • 6 - The presence of 6 cusps (entoconulid).

The following parameters were observed:

  1. The number of cusps on the teeth

  2. The groove pattern on the teeth

  3. Variations in groove pattern and cusp number between mandibular first and second molar

  4. Variations in groove pattern and cusp number between males and females

  5. Variations in groove pattern and cusp number in subjects belonging to different parts of India.

The results were tabulated and statistically analyzed using Chi-square test and tests of significance were done to observe any correlation between the above-mentioned parameters.

Results

Table 1 shows the general distribution of patterns in 150 subjects. The most frequent pattern in 36 was the 5Y form (80%) followed by 4+ (12%), 6X (6%), 4X (1.33%), and 6Y (0.66%). In 46, the most frequent pattern was 5Y (79.33%) followed by 4+ (13.33%), 6X (6%), and 4X and 6Y (0.66% each). With respect to the mandibular second molars, both 37 and 47 exhibited 4+ (90%) as the most frequent pattern, followed by 4X (5.33%), 5Y(4%), and 6X (0.66%) [Figures 1-4]. Tables 2 and 3 show the distribution of patterns in males and females. Significant difference was found in the distribution of patterns between the first and second molars [Table 4] and with respect to the second molar between males and females [Table 5].

Table 1: General distribution of patterns

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Figure 1: Cast showing mandibular 1st molar showing 5Y pattern and mandibular second molar showing 4+ pattern

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Figure 2: Cast showing mandibular 1st molar showing 4+ pattern and mandibular second molar showing 4+ pattern

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Figure 3: Cast showing mandibular 1st molar showing 5Y pattern and mandibular second molar showing 4X pattern

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Figure 4: Cast showing mandibular 1st molar showing 6X pattern and mandibular second molar showing 5Y pattern

Table 2: Distribution in males - (total - 75)

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Table 3: Distribution in females (total - 75)

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Table 4: Comparison of cusp and groove patterns between teeth

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Table 5: Comparison of cusp and groove patterns between males and females

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DISCUSSION

Evolutionary changes have been observed in the dentition of modern humans, some up to the present day. In general, it is observed that both the dentition and jaw have become smaller. Through the ages, studies have shown that tooth size has been decreased on an average by about 1% every 2000 years. From then, presently, the rate of decrease in jaw size/tooth size has doubled to 1% every 1000 years. The main reasons for the above have been attributed to changes in the diet, preparation of food, and emerging technology which are, in turn, dependent on human behavior and their development. These factors often cause an abrupt change in the way the human dentition has been evolving. Therefore, clarifying and evaluating size and pattern of permanent lower molar teeth help in predicting the general evolutionary trends occurring in the of modern hominid populations.[4]

According to McCollum and Sharpe (2001) tooth shapes, cusp patterns and their arrangement in a dental pattern are species specific.[5] In a study conducted by Macesic et al. on a sample of Croatian population, + groove pattern was most frequently found, followed by X shape pattern.[2] A similar study was conducted in Iranian adolescents by Mosharraf et al. on mandibular second molars and + 4 form was the most frequent occlusal configuration.[1] Hasund and Bang (1985) studied the same in Alaskan Eskimos and Y5 was predominant pattern in the mandibular first molars, while +5 and +4 were dominating patterns for the second molar. In the mandibular third molar, majority of cases were +5. They concluded that men showed a stronger tendency toward a conservative pattern in M1 and M2 than women.[6]

In our study, the predominant pattern with respect to 36 and 46 was 5Y pattern and 37 and 47 showed 4+ pattern. Other patterns that were observed include 4X, 6X, and 6Y. The 6X pattern was found more in males, while the 6Y pattern was found in one female case. Majority of the cases showed bilaterally equal distribution of patterns except for 17 cases (9 males and 8 females).

There was a significant difference between the distribution of patterns with respect to the first and second molar (P < 0.001) and also between males and females with respect to the second molar (P < 0.001).

The relationship between these patterns and evolutionary trends has been extensively studied in the past. After examining the relative frequency and modification of groove pattern and cusp number on the three lower molars in a considerable number of ethnic groups, Hellman divided the changes in the Dryopithecus pattern into four successive stages.[7]

Jorgensen (1955) concluded that M1 is most primitive, M3 most modified, while M2 occupies an intermediary stage more nearly approaching M1 and M3. Between the three molars, the difference in the Y pattern is very clear, and the difference between M1 and M2 is distinctly greater than that of M2 and M3. The + pattern can be regarded as both the highest evolutionary degree of the Y pattern and also as an incipient X pattern. Furthermore, there are divergencies in the distribution of patterns on the right and left side.

The knowledge of these may be of little anthropologic value in itself, but in comparative studies between different populations, or between species and genera, shows difference and it is necessary to make clear that molars in question belong to which side.[7]

Conclusion

The results of our study indicated significant difference in the distribution of patterns in permanent first and second molar among Indians. Mandibular first molar shows a more conservative pattern of 5Y and mandibular second molar shows a more evolved pattern of 4+ and 4X. Significant difference was observed in the distribution of patterns between males and females with respect to the second molar. There was not much difference in the distribution of patterns bilaterally. This data related to Indian population may provide information related to dental morphological characteristics which can be used for further population-based anthropological research.

Acknowledgments

We wish to acknowledge Mr. Mallapur, M.Sc Statistician, J.N.M.C Medical College, Belgaum, for helping out with the statistics of this study.

References

1.  Mosharraf R, Ebadian B, Ali Z, Najme A, Niloofar S, Leila K. Occlusal morphology of mandibular second molars in Iranian adolescents. Indian J Dent Res 2010;21:16-9.

2.  Macesic M, Kaic Z. Characteristics of the occlusal surfaces of lower molars in a sample of the Croatian population. Acta Stomat Croat 2003;37:69-73.

3.  Dahlberg AA. Relationship of tooth size to cusp number and groove conformation of occlusal surface patterns of lower molar teeth. J Dent Res 1961;40:34-8.

4.  Bigham JP. An Evolving Dentition:Human Teeth from an Evolutionary Perspective. Available from:http://www.manticmoo.com/articles/jeff/scholarly/an-evolving-human-dentition.php. [Last accessed on 2017 Dec 30].

5.  McCollum M, Sharpe PY. Evolution and development of teeth. J Anat 2001;199:153-9.

6.  Hasund A, Bang G. Morphologic characteristics of the Alaskan Eskimo dentition:IV. Cusp number and groove patterns of mandibular molars. Am J Phys Anthropol 1985;67:65-9.

7.  Jorgensen KD. The dryopithecus pattern in recent Danes and Dutchmen. J Dent Res 1955;34:195.