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Scientific Section |
College of Dental Surgery, UCMS, Bhairahawa, Nepal
Address for correspondence: Alok Kumar Jaiswal, College of Dental Surgery, UCMS, Bhairahawa, Nepal., Email: dralokjaiswal{at}gmail.com
Received 28 March 2008; accepted 11 July 2009
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Abstract |
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Design: Cross-sectional.
Source and setting: Dental, medical and nursing science students at the B.P. Koirala Institute of Health Sciences, Dharan, Nepal.
Subjects and methods: The sample consisted of 100 Nepalese males and 100 females aged between 17 and 23 years. Subjects without any previous orthodontic treatment, fully erupted permanent teeth and with no dental anomalies were recruited. Dental study models were taken and measurements of the mesio-distal widths of teeth were carried out using digital caliper. The measured values were compared with predicted values derived from Moyers method and Tanaka and Johnston equations. Independent t tests were used to examine differences between genders. Correlation coefficients and linear regression equations were used to compare the actual Nepalese tooth widths with predicted values
Results: Moyers method at 50% tends to underestimate the actual width of the canine and premolars in males by 0.3 mm and overestimate the width in females by 0.2 mm. The Tanaka and Johnston method tends to overestimate the actual width of the canine and premolars in both males (0.7 mm) and females 1.0 mm.
Conclusion: The newly developed regression equations are more accurate for prediction of width of unerupted permanent teeth in a Nepalese population. Further studies are required based on larger sample size, to confirm the applicability of the new regression equations proposed.
Key words: Dental, space prediction, Nepalese
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Introduction |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionConclusionsContributorsReferences |
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–3 and one aspect of a space analysis in the mixed dentition might be the prediction of future space requirements. The common methods used for space analysis and prediction are:
,5 –8 –11
Most authors suggest that a combination of methods is more accurate than one technique.12,13 Ballard and Wylie14 state that the reliability of the radiographic method depends on several factors such as technique sensitivity, accuracy of measurement and whether the teeth are rotated in their crypts. Due to concerns about radiation protection radiographic methods may be less frequently used. Also in some developing country, such as Nepal, there may be limited availability of dental radiographic machines.
At present most prediction methods depend upon data derived from white northern European and North American Caucasian populations.4,5 The most widely used Moyer’s probability tables4 and the Tanaka and Johnston’s method5 for space analysis were developed from this population and according to Profit and Fields,1 the reliability of Moyers table is good for Northern Europeans, but is not valid for other ethnic groups.
To-date, only one study has demonstrated tooth size variations in the Nepalese population compared to other racial groups.15 According to this study, the mean tooth width in the Nepalese populations was smaller than in the white northern European and North American Caucasian population, except for the maxillary lateral incisors in males.
Since there are variations in permanent tooth sizes among different ethnic groups the application of non-radiographic approaches has been questioned.16–19 Other variations can occur due to environmental factors,20 heredity21 gender differences4 and bilateral asymmetry.22,23
Several studies have been conducted to evaluate the accuracy of the Tanaka and Johnston and Moyer’s probability tables in non-white populations. The populations studied include Black South African,16 Asian-American,10 Saudi Arabian,18 Thai,24 Jewish-Israeli,25 Syrian,26 Senegalese,27 Peruvian,28 Jordanian29 and Chinese.30 All the investigators concluded that neither direct nor radiographic measurements accurately predicted tooth size when applied to non-white groups. Thus it is necessary to develop a Nepalese prediction equation in order to carry out an accurate space analysis in this population.
The objectives of this study were to:
and Tanaka and Johnston5). |
Materials and methods |
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The inclusion criteria were native Nepalese with Nepalese phenotypical characteristics such as brown skin colour, black hair and eye colour ranging from brown to black, age ranging from 17 to 23 years and all permanent teeth erupted (except third molar). The exclusion criteria were subjects with proximal or occlusal wear, interproximal caries or restorations, crowding, spacing or diastema, any cross bite, any over retained deciduous tooth, missing permanent tooth, deep carious tooth, any hypoplasia or dental anomalies and any past history of orthodontic treatment.31,32
Alginate impressions were taken at BPKIHS and immediately cast in dental plaster. Measurements were carried out directly from the study models using a Starrett digital calliper (0–150 mm, 799A-6/150, Starrett tools (Suzhou) Co. Ltd, China accuracy of ±0.01 mm). The mesio-distal dimensions of the following teeth were measured: the mandibular permanent incisors, the mandibular and maxillary permanent canines and the mandibular and maxillary first and second premolars. All measurements were made by a single investigator. A maximum number of 10 pairs of casts were measured per day to avoid fatigue. All measurements were taken perpendicular to the long axis of the tooth with the calliper beak entering the interproximal area from the buccal or occlusal side.31 The maximum mesio-distal width of each tooth was measured and recorded to 0.1 mm. Repeat measurements were performed after 2 weeks to minimize the possibility of error. Intra-examiner reliability was predetermined as 0.2 mm.17,23 If the variation in the repeat measurements was greater than 0.2 mm a third measurement was taken. Repeat measurements that varied by 0.2 mm or less were averaged.
Statistical analysis
Descriptive statistical analyses were carried out which included calculation of the mean values, standard deviation and ranges. All prediction methods used in this study were based on an average of both sides of the arch. Before combining the data a paired t test was performed and no statistically significant differences were found between the right and left sides. An independent t test was performed to compare the tooth sizes between genders. The significance level was set at P<0.05. Correlation coefficients (r) and linear regression equations were formulated to express the relationships between the sum of the mesio-distal widths of the four mandibular incisors (x) and the sum of the mandibular and maxillary arch canines and premolars (y). The constants a and b in the linear regression equation (y=a+bx), coefficient of determination (r2) and the standard error of estimate (SEE) were calculated for male, female and both sexes in combination. The data derived from the present study were used to frame prediction equations and to compare with Moyers prediction method and Tanaka and Johnston equations. All statistical analyses were performed using Stata software (version 10.0) in the Department of Biostatistics at Nanjing Medical University.
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Results |
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Table 1 shows the sum of the mesio-distal widths of the teeth measured. The differences between males and females are shown in Table 1. A statistically significant difference was found between the widths of the male and female teeth. The correlation coefficients (r) between the mesio-distal widths of the mandibular incisors and canine to premolars for male, female and a combined group and the regression values of a and b, the SEE (standard error of the estimate) and the coefficient of determination (r2) of the maxillary and mandibular regression equations are shown in Table 2.
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Discussion |
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The coefficients of determination (r2) values are indications of predictive accuracy. In the present study, Nepalese females possessed higher r2 values (0.32 for maxillary teeth and 0.36 for mandibular teeth) compared to males (0.16 and 0.15 respectively). Some authors19,27 obtained higher r2 values for males whereas others24 have reported higher r2 values for females. These differences in r2 values might be due to differences in sample sizes and ethnic diversity. The SEE denotes error involved in the use of prediction equations. The lower the SEE, the better the prediction equation. For the present study, the SEE ranged from 0.82 to 0.99 (Table 2
). The SEE was lower for the maxillary teeth (0.82) compared to the mandibular teeth (0.97).
Applying the values of coefficients a and b, listed in Table 2, four equations for the prediction of mesio-distal dimensions of the maxillary and mandibular canines and premolars were derived as follows:
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Using these regression equations, we can predict the mesio-distal width of unerupted permanent canines and premolars for Nepalese subjects. Here ‘x’ is the sum of the widths of the lower permanent incisors and ‘y’ is the predicted value of the mesio-distal width of the unerupted permanent canines and premolars. Table 5 shows the prediction equations formulated from different populations found in the literature.
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). For Nepalese females, the Moyers method at 50% tends to overestimate the actual sum of canine and premolars by 0.2 mm (SD 1.0 mm) and the Tanaka and Johnston method tends to overestimate the actual sum of the canine and premolars by 1.0 mm (SD 1.0 mm) (Table 4). The Moyers method uses percentiles to increase the accuracy of their prediction method. They suggested that the 75th percentile is the most accurate level for the prediction of crowding. In the present study, we found that when the Moyers method was applied to our Nepali sample at the 50th percentile it overestimated tooth size, therefore if it was applied at the 75th percentile the prediction error would be even greater. Tanaka and Johnston framed their equations for predicting the sum of the unerupted canine and premolar widths as regression formula without mentioning any percentage level.
Using the new regression equations, the mean difference between the predicted and actual width of the canine and premolars was calculated. The values are –0.10 (SD 0.96) for males, and 0.02 (SD 1.02) for females. These values were not statistically significant (Tables 3 and 4).
Many authors16,17,23 have reported variations in the mesio-distal widths of permanent teeth in different racial and ethnic groups. Table 5 shows comparisons between the regression equations of the present study with different ethnic groups from other studies. Nepalese males have the largest constant ‘a’ (15.52) in the maxillary arch (Tables 2 and 5).
A previous study by Shrestha15 in a Nepalese population found that the mesio-distal widths of permanent teeth in Nepalese subjects were between 0.5 and 1.2 mm smaller than those of white North Europeans. The data from our sample also suggested similar differences. Therefore, data derived from one ethnic group might not be applicable to another ethnic group for the purpose of the prediction of the size of unerupted permanent teeth.3,18,19 The prediction equations obtained, from the data based on a Nepalese population, would be more accurate and reliable to Nepalese subjects despite the ethnic diversity of Nepal. Sexual dimorphism has also been noticed by different authors;8,19,24 however, there are no raw data available to compare with the present study. Further investigations are required to test the accuracy of the newly developed prediction equations in different ethnic groups of Nepal.
There is a difference between statistical and clinical significance. Proffit1 suggests that a mean error of <1.5 mm is not clinically significant for a Bolton’s analysis. Our results found differences between predicted and actual tooth size of less than 1 mm per quadrant; however if multiplied for all four quadrants then the findings could be clinically significant. The other limitation is that the prediction correlations only account for a small percentage of the variation. This suggests that differences in tooth size between individuals may limit the accuracy of the prediction correlations and therefore they should only be used as a guide as to future space requirements.
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Conclusions |
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Contributors |
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Acknowledgments |
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References |
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