INTRODUCTION

In the clinical dental field, arch size and shape are of particular interest to orthodontists and prosthodontists. In the anthropologic field, studies on dental arches have been conducted directly or indirectly. Direct methods involved measurements.1

Various landmarks have been described and discussed by different investigators, but universal agreement on how dental arch width should be determined has not been reached. Most studies used the dimension of the arch across the permanent canines, premolars, and first molars, at the cusp tips, central fossae, or contact points, or the greatest distance between buccal surfaces.1–11

Dental arch widths between contralateral teeth have been measured in many ways: between the most labial points1 or the most palatal or lingual points,11–20 or as a calculated mean between the most labial and palatal measurements.21 Thus, the different landmarks used in these studies have made comparisons between various studies difficult, let alone comparisons between populations. In view of this, it is necessary to investigate the dental arch width while establishing definitions that can become a standard for comparisons among different studies.

The aim of the present study was to investigate the dental arch width of the Southern Chinese across the buccal cusps, central fossae, or lingual cusps, and to compare these values with those attained in various studies from different populations.

“Southern Chinese” are defined as those Chinese whose ancestors originated from provinces south of the Yangtze River, and who speak dialects different from those of Northerners. The hypothesis was that no differences are present in dental arch widths between males and female members of a Southern Chinese population.

MATERIALS AND METHODS

Dental study casts (n = 358; 210 boys and 148 girls) were obtained as part of a multidisciplinary survey in a cross-sectional, randomly selected sample of 1247 12-year-old Chinese children from the Oral Health Project in Hong Kong.2223 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 measurement data questionable, also were omitted. Only study casts with permanent dentitions were included in the study. The various malocclusions demonstrated in the study casts followed the prevalence of malocclusion of the population, with around one-fifth showing a Class II malocclusion.

Sliding dial calipers (Mitutoyo Manufacturing Co. Ltd, Kawasaki, Japan), accurate to within ±0.02 mm, were used to carry out all manual measurements. The beaks of the calipers were machine-sharpened to a fine taper. Dental arch widths were recorded manually to the nearest 0.01 mm, after initial calibration had been provided by another orthodontist. All measurements were made and recorded by the author. The reference points and landmarks are shown in Tables 1 and 2 and Figures 1 to 3.

Table 1.  Landmarks and Reference Points for Measurements of Dental Arch Dimension: Maxillary Arch

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Table 2.  Landmarks and Reference Points for Measurements of Dental Arch Dimension: Mandibular Arch

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The method error, which represents the uncertainty of the individual observation of a variable, was determined by means of duplicate measurements of all variables. The study casts of participants from the first school were used in the pilot study. Eighteen randomly selected study casts taken from the study were measured and analyzed on two different occasions at an interval of at least 3 months. The error for the method was calculated for all parameters through the double determination method.24 The method error for manual measurements of arch dimensions was within 0.1 mm. The magnitude of this error was similar to those of previous studies.2526 Paired t-tests were also performed to compare intraobserver measurements. The two-tailed P value was greater than .05 and was considered not significant. It was considered unnecessary to take an extra alginate impression for dental study cast to account for the variance due to dimensional changes in the impression material and the dental stone. This variance was considered to be very small compared with that caused by the error of measurement.25

RESULTS

The results of dental arch widths with different definitions are presented in Tables 3 to 7. All male maxillary and mandibular arch widths were significantly larger than female arch widths (t-tests; P < .05), except in the incisor regions (Table 3).

Table 3.  Interincisor and Intercanine Widths, mm

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DISCUSSION

This young group of Southern Chinese was chosen for measurement to minimize the alteration of dental arch dimensions because of attrition, restoration, or caries. Efforts were made to ensure randomization and adequate sample size to ensure validity and adequate clinical significance of the prediction equations.

The diet of the Southern Chinese population is similar to that of persons in Southeast Asia, with the staple component of refined rice. This is different from the Northern Chinese population, for whom the major carbohydrate intake is wheat. Further study is needed to investigate the association between diet and dental arch width within different populations.

Comparisons of data on dental arch dimensions from different studies are hampered by the fact that it is not easy to tabulate all data on different landmarks. Moreover, different authors chose different sample groups for measurement. It has also been shown that individual dental arch dimensions change with age.1691927–34 This study uses definitions for dental widths that allow different studies to be compared.

Comparisons of dental arch width at the canines between Southern Chinese and various other populations (Tables 8 and 9) show that the Southern Chinese occupy the highest position when ranked in order against the quoted literature. It is interesting to note that Chinese dental arches appear to be very wide compared with those of white populations, with an intercanine width difference of about 3 mm in the maxilla and 2 mm in the mandible.

Table 8.  Comparison of Intercanine Widths (Cusp to Cusp) in Various Populations

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Table 9.  Comparison of Intercanine Widths (Deepest Point Internally) in Various Populations

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Table 10 shows that the interpremolar width of the Southern Chinese was wider than that of the Chinese who were living in Liverpool.3839 Both the Chinese from the present study and those from Liverpool were significantly wider than a white population by about 2 to 3 mm at the interpremolar width.39 When compared with Taiwan Chinese at the interpremolar width at the buccal cusp tips, the Southern Chinese were marginally larger (Table 11).40

Table 10.  Comparison of Interpremolar Widths (Fissure) in Various Populations

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Table 11.  Comparison of Interpremolar Widths (Buccal Cusp Tips) Between 12-Year-Old Southern Chinese and Taiwan Chinese

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The maxillary intermolar widths at the distobuccal cusps of the first molars of the Southern Chinese were wider than those of Caucasians635 in both sexes. The Australian Aboriginals were widest in the mandibular intermolar width at the distobuccal cusps of the first molars (Table 12). Taiwan Chinese42 were wider than Southern Chinese at the mandibular intermolar width at the distobuccal cusps of the mandibular first molars by about 1.3 mm in both sexes (Table 12). Table 13 demonstrated that Taiwan Chinese intermolar widths were wider than those of Southern Chinese by 1.1 mm and 1.8 mm for males and females, respectively.42

Table 12.  Comparison of Inter–First Molar Widths (Distal Buccal Cusp) in Various Populations

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Table 13.  Comparison of Inter–First Molar Widths (Mesial Fossa) Between 12-Year-Old Southern Chinese and Taiwan Chinese

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Both the Southern Chinese and the Taiwan Chinese had much wider intersecond molar widths at the distobuccal cusp in both sexes when compared with the Swedes (Table 14).142 The Taiwan Chinese intersecond molar widths were wider than were those of the Southern Chinese.

Table 14.  Comparison of Inter–Second Molar Widths (Central Fossae of M2–M2 and Distobuccal Cusps of M2–M2) in Various Populations

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It is important to note that the comparisons of dental arch width measurements among different populations discussed earlier in this article show very large standard deviations of around 2 to 3 mm. Statistical testing of the data between studies is needed to determine whether differences are significant.

In addition to population study data on dental arch width, this study provides a database by which various related studies involving arch widths can be compared. For example, Poosti and Jalali43 related tooth size and arch dimension using the definitions of lingual and buccal intercanine widths. This can be related to our data by applying the results from the lingual areas and buccal cusps as landmarks. Studies from Isik et al44 and Huth et al45 compared the arch widths between Class II division I and division 2 malocclusions. They used the buccal cusps as landmarks for intercanine and intermolar widths. These can be compared with our data, in which the buccal cusps are used as landmarks.

It is of interest to relate dental arch width to the prevalence of respiratory disease. Epidemiologic surveys have shown that the prevalence of asthma in Asian populations is relatively low. Within the Chinese population, schoolchildren from Hong Kong were found to have the highest incidence of asthma.

Wong et al46 studied the prevalence of respiratory and atopic disorders and the role of atopy in the development of asthma in Chinese schoolchildren from Hong Kong, Beijing, and Guangzhou. Using a standardized written questionnaire (n = 10,902), along with a skin prick test (n = 3479) and a skin examination (n = 3479), they found that the prevalence of current wheeze, speech limiting wheeze, rhinoconjunctivitis, and flexural dermatitis was significantly greater in Hong Kong than in Beijing or Guangzhou. The atopy rate was also higher in Hong Kong (41.2%) than in Beijing (23.9%) or Guangzhou46 (30.8%). Further study is needed to investigate the association between the prevalence of respiratory disease and arch widths in this population.

CONCLUSIONS

• This study yielded a database about dental arch widths with different definitions by which different studies can be compared.

• The Southern Chinese may have been characterized by a wider dental arch width when compared with whites, but variations were extensive.

• All male maxillary and mandibular arch widths in the Southern Chinese were significantly larger than female arch widths, except in the incisor regions. The hypothesis “There were no differences in dental arch widths between males and females in Southern China” was rejected.