Aim: To investigate the number of molar cusps of the Southern Chinese and compare these with studies in different populations.

Materials and Methods: The number of molar cusps of study casts of an unselected sample from a 12 year old Hong Kong Oral Health Survey of 12 year old children (n=459; 295 boys and 164 girls) were studied.

Results: For upper first molars, 5-cusp molars were the most prevalent in males (39%) while 4-cusp molars were the most prevalent in females (39%). For lower first molars, 5-cusp molars were the most prevalent in both sexes (63%-72%). For lower second molars, 5-cusp molars were the most prevalent in both sexes (43%-53%).

Conclusion: Different from traditionally described, the Southern Chinese has more 5-cusp lower second molars than the 4- cusp ones.published_or_final_versio

Ling, JYK

Wong, RWK

The Open Anthropology Journal

HKU Scholars Hub

Title Molar cusps in Southern ChineseAuthor(s) Ling, JYK; Wong, RWKCitation The Open Anthropology Journal, 2010, v. 3, p. 16-19Issued Date 2010URL http://hdl.handle.net/10722/66577Rights Creative Commons: Attribution 3.0 Hong Kong License16 The Open Anthropology Journal, 2010, 3, 16-19  1874-9127/10 2010 Bentham OpenOpen Access Molar Cusps in Southern Chinese John Y.K. Ling and Ricky W.K. Wong* Orthodontics, University of Hong Kong, Hong Kong Abstract: Aim: To investigate the number of molar cusps of the Southern Chinese and compare these with studies in dif-ferent populations.  Materials and Methods: The number of molar cusps of study casts of an unselected sample from a 12 year old Hong Kong Oral Health Survey of 12 year old children (n=459; 295 boys and 164 girls) were studied.  Results: For upper first molars, 5-cusp molars were the most prevalent in males (39%) while 4-cusp molars were the most prevalent in females (39%). For lower first molars, 5-cusp molars were the most prevalent in both sexes (63%-72%). For lower second molars, 5-cusp molars were the most prevalent in both sexes (43%-53%). Conclusion: Different from traditionally described, the Southern Chinese has more 5-cusp lower second molars than the 4-cusp ones. Keywords: Molar cusp, Southern Chinese. INTRODUCTION  It is generally believed that the numerous morphologic characteristics of the teeth are genetically determined [1, 2]. Detailed description and study of these traits could provide valuable information regarding phylogeny of man and dis-tinctions between races and subraces [1, 3-12]. Features of morphology which closely reflect genetic structure should be examined in determining the evolutionary (phylogenetic) relationships of populations and in establishing taxonomies that reflect these relationships [12]. Although tooth mor-phology may be an indicator of genetic distances between populations, it should be viewed with caution [11]. The study of the number of cusps are not only important in an-thropology, it is also important in the study of dental occlu-sion, orthodontics, restorative dentistry and prosthetic den-tistry.  In modern man, the number of cusps of the upper molars is frequently reduced from four to three. The formula for the number of cusps of the upper molar series is changing from 4-4-4 to 4-4-3 and 4-3-3. The trend is more marked in fe-males than in males of all populations that have been stud-ied. In most studies, males generally showed a lesser ten-dency than females to reduction in the number of cusps of the upper molars. The process of reduction occurs through the elimination of the hypocone or distolingual cusp, with a subsequent decrease in the mesiodistal crown diameter and in the occlusal area.  Moorrees [1] reported that living Aleut females pos-sessed fewer five-cusped second molars than males, the dif-ference being significant (N.B. small sample size of 36). In  *Address correspondence to this author at the 2/F, Orthodontics, Prince Philip Dental Hospital, 34 Hospital Road, Sai Ying Pun, Hong Kong;  Tel: 852 28590554; Fax: 852 25593803; E-mail: fyoung@hkucc.hku.hk the Aleuts, the frequency of 4 cusps is 100 % for the first molars, 69 % for the 2nd molars and 31 % for the 3rd mo-lars.  There are normally five main cusps on a lower molar. The fifth or disto-buccal cusp is the most variable, which may be absent. If the fifth cusp is present it is often placed lingually, out of line with the other two buccal cusps. The fifth cusp may be divided into two parts by a fissure which runs antero-posteriorly, thus the tooth may have three lingual and three buccal cusps [8]. A total of ten cusps can be theo-retically present on a lower molar tooth. There is a large amount of publications on molar morphology, numbers of molar cusps, origins, and evolution of both cusps and teeth [13]. There are no standards yet available to determine whether a cusp should be recorded as one because of its in-adequate size.  Suzuki & Sakai [14] found no significant differences in first and second molar cusp numbers of 392 male and female Japanese.  The frequency of cusp 6 on first and second molars [65 and 63 % respectively] from Indian crania was found to be about three times that of Aleuts (21 and 18 %) and Eskimos (22 and 18 %). All three groups (Indian, Aleuts and Eski-mos) showed five or six cusped first lower molars. No four-cusped molars were found. Four-cusped second lower molars occurred most often in the Aleuts [9 %], less in Indians [3 %] and least in the Eskimos [1 %] [15].  Europeans and American Whites have the highest and unique frequency of four-cusped lower first molars (10 %) while the rest of the world's populations that have been sam-pled, which included African and American Negroes, Aus-tralians, Melanesians, Chinese, Japanese, Aini and native Americans, possessed on the average less than 3 % four cus-ped first lower molars [16-18]. Molar Cusps The Open Anthropology Journal, 2010, Volume 3    17 Moorrees [1] stated that bilateral symmetry was perfect for lower molars, permitting him to report his observations on an individual basis. Cusp 6 was infrequently present on the lower second molar when it was not expressed on the first molar in Southwest Indians [19]. This accounted for the moderate association for cusp 6 between these teeth. This pattern was in line with the concept of field effect. Dahlberg [20] concluded that the field for cusp 6 had reversed polarity, that is the field is reversed for size but not for total inci-dence.  Dental traits generally showed a positive correlation with tooth size, which probably explains why the inter-trait corre-lations are mostly positive [21]. Dahlberg [22] presented evidence for a relationship between cusp number and tooth size.  Sexual dimorphism in cusp number was evident in that females tend to have more cusps for the same crown diame-ter. Larger teeth of the same class had a greater number of cusps [23].  ‘Southern Chinese’ are defined as those Chinese whose ancestors originated from provinces south of the Yangtze River and they speak different dialects from the northerners. There is no study about the prevalent of various dental mor-phologies in this population.  The aim of our study is to investigate the cusp numbers of the upper first permanent molars and lower first and sec-ond permanent molars of the Southern Chinese and compare these with studies in different populations.  MATERIALS AND METHODS  Dental study casts (n=459; 295 boys and 164 girls) were obtained as part of a multi-disciplinary survey of cross-sectional, randomly selected sample of 1247 12-year-old Chinese children from the Oral Health Project in Hong Kong [24, 25]. The participants needed to complete a questionnaire to ask about the country and province in origin of both father and mother. Teeth found to be carious, missing, restored at the measurement landmark, hypoplastic, worn or malformed or orthodontically moved were excluded from the present investigation. Damaged casts which made the assessment data questionable were also omitted. Only study casts with permanent dentition were included in the study. The number of cusps of the upper first permanent molars and lower first and second permanent molars were recorded. Any elevation of enamel that was tuberculate in form occurring at an ex-pected cusp location with a free apex was considered to be a cusp regardless of its size. RESULTS  Table 1 shows the frequency distribution of number of cusps of the permanent molars in both arches. For upper first molars, 5-cusp molars were the most prevalent in males (39%) while 4-cusp molars were the most prevalent in fe-males (39%). For lower first molars, 5-cusp molars were the most prevalent in both sexes (63%-72%). For lower second molars, 5-cusp molars were the most prevalent in both sexes (43%-53%). Very few 4 cusped lower first permanent molars were noted (1%), unlike the lower second permanent molars which have 34% and 41% four cusps for males and females respectively. DISCUSSION  This young age group of Southern Chinese was chosen for measurement to minimize the alteration of the dental arch dimensions because of attrition, restoration or caries. Efforts were made to ensure randomization and adequate sample size to ensure validity.  With the above results, the number of molar cusps in Southern Chinese is compared with other population as be-low:  For upper first molars:  From Table 1, while most upper first molars were de-scribed as having 4 cusps (29%-39%), there existed 1% male in this sample that had only 3 cusps.   Equally as abundance as 4 cusps were the 5-cusps upper first molars (30%-39%). As described by Scott and Turner [26], cusp 5 in upper first molars was termed distal accessory tubercle, metaconule and this trait took the form of an occlu-sal tubercle on the distal marginal ridge of the upper molars. It was positioned between the metacone and the hypocone although it was more closely associated with the metacone. For an accessory tubercle, this trait showed a relatively wide range.  From Scott and Turner [27] the geographic variation in cusp 5 of the upper first molar could be summarized in the following manner: (1) Low frequency groups (10-25%): Western Eurasia, Sino-Americas. (2) Intermediate (30-40%): Sunda-Pacific, Sub-Saharan Africa? (3) High frequency groups (45-60%): Sahul-Pacific, Sub-Saharan Africa?  Therefore, the data from the Southern Chinese fitted the intermediate frequency groups.  In addition, there existed 6-cusps upper first molar, which were quite common (21%-24%), around two-thirds of 5-cusps upper first molars; and some 7-cusps upper first mo-lars (5%-7%); and 8-cusps upper first molars (2%-4%).  For lower first molars:   From Table 1, while most lower first molars were de-scribed as having 5 cusps (63%-72%), there existed some cases (0.5%, 36, male) in this sample that had only 3 cusps and some cases (1%) in this sample that had only 4 cusps.  From Scott and Turner [28] geographic variation in lower molar cusp number shows the following pattern: Lower first molar (4-cusped forms) (1) Low frequency groups (0-3%); Sub-Saharan Africa, Sino-Americas, Sunda-Pacific, Australia. (2) Intermediate (5-10%): New Guinea, Melanesia, pre-historic Europe. (3) High frequency groups (10-20%): Western Eurasia.  Therefore, the data from the Southern Chinese fitted the low frequency groups. 18    The Open Anthropology Journal, 2010, Volume 3 Ling and Wong  In addition, there existed 6-cusps lower first molar, which were quite common (22%-32%), around one half of 5-cusps lower first molars;   From Scott and Turner [29] cusp 6 lower first molar on a world scale was summarized as follows: (1) Low frequency groups (0-10%): Western Eurasia. (2) Low intermediate (10-20%): Sub-Saharan Africa, South Siberia, Altaic-speakers, New Guinea. (3) High intermediate (30-50%): North and East Asia, Americas, Melanesia. (4) High frequency groups (>50%): Polynesia, Australia.  Therefore, the data from the Southern Chinese fitted the intermediate frequency groups.  Furthermore, there existed some 7-cusps lower first mo-lars (3%-5%). Scott and Turner [30] summarized world val-ues for more than 270 samples, confirmed this succinct char-acterization of cusp 7 variation. They suggested this was a trait common in Africa and rare, or at least uncommon, in all other human groups and it was difficult to even trichotomize variation as there was no distinct pattern evident among the low frequency groups: (1) Low frequency groups (0-10%): Western Eurasia, Sino-Americas, Sunda-Pacific, Sahul-Pacific. (2) High frequency groups (25-40%): Sub-Saharan Af-rica.  Therefore, the data from the Southern Chinese fitted the low frequency groups.  For lower second molars:   From Table 1, while many lower second molars were described as having 4 cusps (31%-43%), most lower second molars were identified as having 5 cusps (43%-53%), and some cases (13-18%) in this sample that had 6 cusps and some even have 7 cusps (1%-2%). Scott and Turner [30] summarized world values for lower second molar (4-cusped forms): (1) Low frequency groups (10-30%): San, Americas. (2) Low intermediate (30-60%): South Africa, East Asia, North Asia, Altaic (Mongolian/Tungusic), Sunda-Pacific, Australia. (3) High intermediate (60-80%): New Guinea, Melane-sia; East Africa, Altaic (Turkic). (4) High frequency groups (>80%): Western Eurasia. Table 1. Prevalence (%) of Number of Cusps of Upper First Molars and the Lower First and Second Molars in 12 Year Old  Southern Chinese Males (n = 270) and Females (n = 149) Upper Arch  Males Females  (n = 270) (n = 149) Number of Cusps 16 26 16 26 3 cusps 1 1 0 0 4 cusps 30 29 39 39 5 cusps 39 39 30 30 6 cusps 22 24 21 21 7 cusps 6 5 7 6 8 or more cusps 3 2 3 4 Lower Arch  Males Females Males Females  (n = 262) (n = 145) (n = 118) (n = 81) Number of Cusps 36 46 36 46 37 47 37 47 3 cusps 0.5 0 0 0 0 0 0 0 4 cusps 1 1 1 1 31 36 39 43 5 cusps 64 63 72 70 53 45 45 43 6 cusps 31 32 22 23 14 18 14 13 7 cusps 3 3 5 5 2 1 2 1 8 or more cusps 0 0 0 0 0 0 0 0 Molar Cusps The Open Anthropology Journal, 2010, Volume 3    19 Therefore, the data from the Southern Chinese fitted the low intermediate frequency groups.   The lower second molars are usually described as having 4 essential cusps [31]. The finding that the Southern Chinese has more 5-cusp lower second molars than the 4-cusp ones is an exception to this rule. CONCLUSION  Different from traditionally described, the Southern Chi-nese has more 5-cusp lower second molars than the 4-cusp ones. REFERENCES [1] Moorrees CFA. The Aleut dentition. Cambridge: Harvard Univer-sity Press 1957. [2] Lundstrom A. Tooth morphology as a basis for distinguishing monozygotic and dizygotic twins. Swed Med Res Counc 1962;  34-43. [3] Hrdlicka A. Shovel-shaped teeth. Am J Phys Anthropol 1920; 3: 429-66. [4] Hrdlicka A. Further studies of tooth morphology. Am J Phys An-thropol 1921; 4: 141-76. [5] Dahlberg AA. The dentition of the American Indian. In: Laughlin WS, Ed. Dental anthropology. Papers on the physical anthropology of the American Indian. Fourth Viking Fund summer seminar. The Viking Fund, Inc., New York, 1951; pp. 138-76. [6] Lasker GW. Observations on the teeth of Chinese born and reared in China and America. 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The anthropol-ogy of modern human teeth. Cambridge Univ Press: Cambridge, 1997; p. 204. [28] Scott GR, Turner II CG. Geographic variation in tooth crown and root morphology. In: Scott GR, Turner II CG, Eds. The anthropol-ogy of modern human teeth. Cambridge Univ Press, Cambridge, 1997; p. 211. [29] Scott GR, Turner II CG. Geographic variation in tooth crown and root morphology. In: Scott GR, Turner II CG, Eds. The anthropol-ogy of modern human teeth. Cambridge Univ Press: Cambridge 1997; pp. 216-17. [30] Scott GR, Turner II CG. Geographic variation in tooth crown and root morphology. In Scott and Turner ed. The anthropology of modern human teeth. Cambridge Univ Press, Cambridge, 1997; 217. [31] Carlsen O, The Permanent Lower Molars. In Dental Morphology.Munksgaard, Copenhagen, 1987; 144-146. Received: March 14, 2008 Revised: May 26, 2009 Accepted: May 26, 2009 © Ling and Wong; Licensee Bentham Open.This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited. 

Molar cusps in Southern Chinese

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Molar cusps in Southern Chinese

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