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Applicability of the Moyers mixed dentition probability tables and new prediction aids for a contemporary population in India
ORIGINAL ARTICLE
Applicability of the Moyers mixed dentition probability tables and new prediction aids for a contemporary population in India Nebu Ivan Philip,a Manisha Prabhakar,b Deepak Arora,c and Saroj Choprad Pondicherry, Muktsar, and Ludhiana, India Introduction: The Moyers mixed dentition space analysis method is among the most commonly used in clinical practice for detecting tooth size-arch length discrepancies. In view of reported secular trends, racial, and sex differences in tooth sizes, the purposes of this study were to evaluate the applicability of Moyers probability tables in a contemporary orthodontic population of India and to formulate more accurate mixed dentition prediction aids. Methods: Odontometric data were collected from 300 male and 300 female subjects of Indian descent, who had fully erupted mandibular permanent incisors and maxillary and mandibular canines and premolars. We measured the mesiodistal crown widths with vernier scale dial calipers. The odontometric values obtained were then subjected to statistical and linear regression analysis. Results: All tooth groups showed significant differences (P \0.001) between mesiodistal widths of male and female subjects. Regression equations for the maxillary arch (males, Y 5 7.15 1 0.67X; females, Y 5 7.44 1 0.65X) and the mandibular arch (males, Y 5 5.55 1 0.71X; females, Y 5 6.15 1 0.67X) were used to develop new probability tables on the Moyers pattern. Significant differences (P \0.05) were found between our predicted widths and the Moyers tables at almost all percentile levels, including the recommended 75% and 50% levels. Conclusions: We believe that these new prediction aids could be considered for a more precise mixed dentition space analysis in Indian children. (Am J Orthod Dentofacial Orthop 2010;138:339-45)
E
very dentist who provides care for children and adolescents should be able to properly assess and manage their developing occlusions.1 Many malocclusions, especially crowding problems, originate in the mixed dentition period.2 During this critical period, the orthodontist or pediatric dentist is often asked to provide an accurate diagnosis of any developing malocclusions and an opinion on its effects, if any, on the ultimate occlusal status of the permanent dentition. One condition requiring early diagnosis and treatment is when there is a disparity between the space available in the dental arch and the space needed for the a
Assistant professor, Department of Pediatric and Preventive Dentistry, Indira Gandhi Institute of Dental Sciences, Pondicherry, India. b Professor and head, Department of Pediatric and Preventive Dentistry, Desh Bhagat Dental College, Muktsar, India. c Professor and head, Department of Orthodontics and Dentofacial Orthopedics, Christian Dental College, Ludhiana, India. d Professor and head, Department of Pediatric and Preventive Dentistry, Christian Dental College, Ludhiana, India. The authors report no commercial, proprietary, or financial interest in the products or companies described in this article. Reprint requests to: Nebu Ivan Philip, Department of Pediatric & Preventive Dentistry, Indira Gandhi Institute of Dental Sciences, Mahatma Gandhi Medical College & Hospital Campus, Pondicherry, India 607402; e-mail, drnebu@ yahoo.com. Submitted, July 2008; revised and accepted, September 2008. 0889-5406/$36.00 Copyright Ó 2010 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2008.09.035
proper alignment of the unerupted permanent canines and premolars. In planning the management of these patients, the deficit of arch space must be predicted early, and the indicated preventive or interceptive procedures instituted. The mixed dentition space analysis (MDSA) is a fundamental part of an early orthodontic assessment and helps in determining any tooth size-arch length discrepancy. If a discrepancy is present, MDSA will be a useful diagnostic aid in evaluating whether the treatment plan will involve serial extractions, guidance of eruption, space regaining, proximal stripping, space maintenance, or just periodic observation of the patient. To perform an accurate MDSA, it is vital to correctly predict the mesiodistal crown widths of the unerupted permanent canines and premolars. Two broad approaches have been used for this prediction: radiographic3-9 and nonradiographic methods.10-13 Radiographic methods require measurements of undistorted long-cone radiographic images of erupted and unerupted teeth, and also of erupted teeth on study casts. The mesiodistal widths of the unerupted canines and premolars are then estimated from multiple regression equations or graphs. Such complex methods might discourage their routine use by clinicians. Moyers11 proposed a simpler nonradiographic MDSA method in which the mesiodistal crown widths of the unerupted permanent canines and premolars of both arches can be predicted from the combined 339
340 Philip et al
mesiodistal crown widths of the 4 mandibular permanent incisors by using probability tables. The Moyers probability tables were developed at the University of Michigan based on odontometric data of American white subjects of Northwestern European descent.11 The accuracy of these probability tables is questionable when applied to population groups other than white people, because it has been well established in the literature that tooth sizes vary considerably between racial groups.14-21 Table I shows mesiodistal crown widths obtained from odontometric studies of various population groups. In addition, a few investigators noted a secular trend toward increased tooth sizes with succeeding generations.22-24 This implies that values used in probability tables or prediction equations developed from odontometric data of earlier generations might underestimate the tooth sizes of present-day children. Accordingly, the objectives of this study were to formulate new prediction aids (probability tables and prediction equations) that can enable a more accurate MDSA in Indian children, and to evaluate the applicability of Moyers probability tables in a contemporary Indian population. MATERIAL AND METHODS
Dental study casts of 300 male and 300 female subjects were selected for this study from a contemporary population of India. The casts were made from dental impressions of children in various schools of Punjab state in India, after approval was obtained from their parents and teachers. The criteria for sample selection were the following. 1.
2.
3. 4. 5.
The mandibular permanent incisors, the mandibular and maxillary permanent canines, and the mandibular and maxillary premolars were fully erupted. There was no obvious loss of tooth material mesiodistally as a result of caries, fractures, congenital defects, or interproximal attrition. The dental impressions and study casts were high quality and free of distortions. The subjects had no previous history of orthodontic treatment. All subjects had a similar ethnic background (Punjabi).
The teeth measured were the mandibular central and lateral permanent incisors, the mandibular and maxillary permanent canines, and the first and second premolars of both arches. The values obtained for the right and left canine-premolar segments in each arch were averaged, so that there would be 1 value for the mandibular canine-premolar segment and 1 value for the maxillary
American Journal of Orthodontics and Dentofacial Orthopedics September 2010
Table I. Mesiodistal crown widths from various studies of different racial groups Sample size (n)
Study
Sex
Asian populations Jaroontham and Godfrey16 (Thai)
M
215
F
215
M
200
F
300
M, F
201
M
300
F
300
M
100
F
100
M
25
F
25
Priya and Munshi17 (South India)
Lee-Chan et al18 (Asian Americans) This study (Punjab, India)
African populations Schrimer and Wiltshire19 (South African blacks)
Diagne et al20 (Senegalese)
Ferguson et al21 (African Americans) White populations Tanaka and Johnston12 (North Americans)
M, F
105
M, F
506
Arch
Mean (mm)
SD (mm)
LI UCPM LCPM LI UCPM LCPM LI UCPM LCPM LI UCPM LCPM LI UCPM LCPM LI UCPM LCPM LI UCPM LCPM
23.89 23.16 22.23 22.23 22.64 21.77 24.88 23.32 21.91 24.20 22.71 21.41 23.40 22.93 22.03 24.03 23.23 22.50 23.48 22.75 21.99
1.37 1.03 1.04 1.26 1.00 1.02 0.36 0.39 0.45 0.34 0.38 0.43 1.19 1.17 1.12 1.05 1.07 1.09 0.93 0.94 0.95
LI UCPM LCPM LI UCPM LCPM LI UCPM LCPM LI UCPM LCPM LI UCPM LCPM
23.92 23.22 23.45 23.66 22.28 22.20 23.71 22.28 22.20 22.86 22.70 22.20 23.52 22.40 22.24
1.90 1.11 1.37 1.59 1.28 1.24 1.25 1.28 1.24 1.25 1.01 1.22 1.79 1.27 1.31
LI UCPM LCPM
23.43 22.27 21.76
1.35 1.09 1.12
LI, Lower incisors; UCPM, upper canines and premolars; LCPM, lower canines and premolars; M, male; F, female.
canine-premolar segment for each value of the combined mandibular incisors. Measurements of the mesiodistal crown widths of the mandibular and maxillary teeth were made by using a dial caliper with a vernier scale, calibrated to the nearest 0.05 mm (Matsui Dial Caliper, Mitutoyo, Kawasaki, Japan). The tips of the calipers were precision engineered to ensure the greatest accuracy while measuring the various tooth groups.
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American Journal of Orthodontics and Dentofacial Orthopedics Volume 138, Number 3
Table II. Descriptive statistics for the combined mesiodistal widths of the 3 tooth groups Tooth group
Table III. Regression parameters for prediction of mesiodistal widths of canine-premolar segments
Sex Range (mm) Mean 6 SD (mm) t value
Mandibular incisors M F Maxillary M canine-premolar F segment Mandibular M canine- premolar F segment
341
Constants
20.65-27.50 20.40-26.15 20.15-26.85 20.05-26.25
24.03 6 1.05 23.48 6 0.93 23.23 6 1.07 22.75 6 0.94
6.92*
Sex
5.84*
Male
19.40-26.40 19.50-25.70
22.50 6 1.09 21.99 6 0.95
6.11*
Female
Canine-premolar segment
r
a
b
r2
SEE (mm)
Maxillary Mandibular Maxillary Mandibular
0.66 0.68 0.65 0.67
7.145 5.548 7.444 6.154
0.669 0.706 0.652 0.674
0.43 0.46 0.43 0.44
0.81 0.80 0.72 0.71
r, Correlation; a and b, regression constants; r2, coefficient of determination; SEE, standard error of estimate.
M, Male; F, female. *P \0.001.
A standardized method proposed by Moorrees and Reed25 was used to measure the mesiodistal crown widths. The greatest mesiodistal crown width of each tooth was measured between its contact points, with the sliding caliper placed parallel to the occlusal and vestibular surfaces. This method was reported to be highly repeatable and accurate for measuring mesiodistal crown widths by Doris et al.26 Measurement reliability was checked according to a method suggested by Lundstr} om,27where the same investigator measures all casts and then remeasures certain randomly selected casts. The coefficient of test-test reliability on 120 such randomly selected casts was calculated and found to be r .0.95, confirming the reliability of the measurements. RESULTS
Descriptive statistics for the 3 tooth groups measured in the study (mandibular permanent incisors, mandibular canine-premolar segment, and maxillary canine-premolar segment) are presented in Table II for the sexes separately. Student t tests comparing the mesiodistal crown widths of male and female subjects showed highly significant differences (P \0.001) in all 3 tooth groups, with males having larger teeth. Coefficients of correlation were calculated and standard linear regression equations of the form Y5 a 1 b(X) derived, to evaluate the relationship between the combined mesiodistal widths of the mandibular permanent incisors (X) and the mesiodistal widths of the canine-premolar segments (Y) of each arch. Table III records the various regression parameters: correlation coefficient, regression constants (a is the y-intercept, and b is the slope of the regression line), coefficient of determination, and standard errors of estimate (SEE). This regression analysis was used to formulate new prediction equations that can be used clinically to predict the mesiodistal crown widths of the unerupted canine premolar segments (Y) when the combined
Table IV. Prediction equations from various studies at the 50th percentile Study
Sex
This study (Punjab, India)
M
Arch
Maxillary Mandibular F Maxillary Mandibular Moyers11 M Maxillary (North American whites)* Mandibular F Maxillary Mandibular Moyers34 M, F Maxillary (North American whites)* Mandibular Tanaka and Johnston12 M, F Maxillary (North American whites) Mandibular Diagne et al20 M Maxillary (Senegalese) Mandibular F Maxillary Mandibular Lee-Chan et al18 M, F Maxillary (Asian Americans) Mandibular Jaroontham and Godfrey16 M Maxillary (Thai) Mandibular F Maxillary Mandibular
Prediction equations Y 5 7.15 1 0.67(X) 5.55 1 0.71(X) 7.44 1 0.65(X) 6.15 1 0.67(X) 9.73 1 0.51(X) 10.79 1 0.45(X) 14.17 1 0.28(X) 8.85 1 0.52(X) 9.23 1 0.55(X) 7.82 1 0.59(X) 10.41 1 0.51(X) 9.18 1 0.52(X) 9.60 1 0.55(X) 5.54 1 0.72(X) 13.77 1 0.35(X) 8.74 1 0.56(X) 8.19 1 0.63(X) 7.46 1 0.62(X) 13.36 1 0.41(X) 11.92 1 0.43(X) 11.16 1 0.49(X) 9.49 1 0.53(X)
Y, Mesiodistal width of canine-premolar segment; X, mesiodistal width of the 4 mandibular incisors. *Regression equations derived from Moyers tables at the 50th percentile.
mesiodistal crown widths of the 4 mandibular permanent incisors are known (X). These new prediction equations (after approximation) are shown in Table IV, along with prediction equations from some other studies. The regression equations derived in this study were used to prepare new probability tables on the Moyers pattern and are presented in Tables V and VI. To evaluate the applicability of the Moyers probability tables in our sample, the odontometric values we obtained were statistically compared with predicted values from Moyers tables at the 5% to the 95% confidence levels by using the Wilcoxon signed rank sum
342 Philip et al
Table V. Percentile Males 95% 85% 75% 65% 50% 35% 25% 15% 5% Females 95% 85% 75% 65% 50% 35% 25% 15% 5%
American Journal of Orthodontics and Dentofacial Orthopedics September 2010
Probability tables for predicting the mesiodistal widths of unerupted maxillary canines and premolars 19.5
20
20.5
21
21.5
22
22.5
23
23.5
24
24.5
25
25.5
20.77 20.75 20.44 20.39 20.22 20.14 20.06 19.87 19.80
21.10 21.09 20.77 20.70 20.55 20.41 20.32 20.21 20.13
21.44 21.42 21.11 20.96 20.89 20.77 20.64 20.49 20.46
21.77 21.76 21.44 21.29 21.22 21.12 20.95 20.82 20.80
22.11 22.09 21.78 21.63 21.56 21.35 21.29 21.18 21.13
22.44 22.43 22.11 21.96 21.89 21.68 21.58 21.48 21.44
22.78 22.76 22.44 22.30 22.23 22.04 21.91 21.84 21.80
23.11 23.10 22.78 22.63 22.56 22.35 22.27 22.17 22.14
23.44 23.43 23.11 22.96 22.90 22.65 22.59 22.49 22.47
23.78 23.76 23.45 23.30 23.23 22.96 22.89 22.83 22.81
24.11 24.10 23.78 23.63 23.57 23.25 23.19 23.16 23.14
24.45 24.43 24.12 23.97 23.90 23.60 23.51 23.54 23.48
24.78 24.77 24.45 24.30 24.24 23.92 23.88 23.85 23.81
20.61 20.58 20.39 20.30 20.12 20.07 19.99 19.72 19.63
20.94 20.96 20.72 20.62 20.44 20.34 20.26 20.05 19.96
21.27 21.29 21.05 20.89 20.76 20.69 20.51 20.38 20.29
21.59 21.47 21.37 21.15 21.09 20.98 20.83 20.70 20.61
21.94 21.92 21.70 21.56 21.42 21.33 21.06 21.03 20.94
22.27 22.24 22.02 21.83 21.74 21.60 21.46 21.35 21.26
22.59 22.57 22.35 22.15 22.07 21.91 21.84 21.68 21.59
22.92 22.89 22.68 22.56 22.39 22.25 22.09 22.01 21.92
23.24 23.22 23.00 22.90 22.72 22.58 22.42 22.33 22.24
23.57 23.55 23.33 23.23 23.04 22.91 22.73 22.66 22.57
23.90 23.87 23.65 23.56 23.37 23.17 23.04 22.98 22.89
24.22 24.20 23.98 23.88 23.69 23.48 23.36 23.31 23.22
24.55 24.52 24.31 24.21 24.01 23.81 23.66 23.63 23.54
test. Significant differences (P \0.05) were found at all percentile confidence levels, except at 95% and 85% for males in both arches; there were significant differences for females (P \0.05) at all percentile levels, except at 95% and 85% in the mandibular arch and at 95% in the maxillary arch (Table VII). DISCUSSION
The most important factors in the reliability of a study based on odontometric data are the characteristics of the sample chosen. The sample representation of this study was considered acceptable because of the large sample size (300 subjects of each sex) and the uniform ethnicity (Punjabi). Definite racial and ethnic differences in tooth sizes have been highlighted in several population studies14-21 (Table I). Nanda and Chawla28 found a significant disparity between the leeway space of North Indian children and the leeway space that was reported by Nance29 for American children. In another odontometric study with North Indian samples, Singh and Nanda30 derived a mixed dentition prediction scale that they found to be different from prediction tables developed by Ballard and Wylie10 for American white people and suggested that this could be due to racial tooth-size differences. The reasons for the tooth-size variations in different racial groups have not been clearly elucidated, but, obviously, genetic factors play a major role, and nutrition and environmental exposure during tooth development might have secondary roles.31 Whatever the reasons
for the racial tooth-size differences, orthodontists’ diagnostic armamentarium needs to be strengthened by developing tooth-size prediction aids from odontometric data specific to each racial group. In addition to the racial differences in tooth sizes, the descriptive statistics in Table II show that the mesiodistal crown widths of all tooth groups measured in this study were significantly larger in males than in females (P \0.001). Similar sex dimorphisms in tooth sizes have been noted in other odontometric studies.9,16-20 There is strong evidence that tooth size is expressed through X-linked inheritance, with Garn et al32,33 hypothesizing that the 2 X chromosomes in females might provide a measure of control lacking in males. The significant sex differences in mesiodistal tooth sizes emphasize the importance of developing mixed dentition prediction aids separately for male and female patients, so that a more accurate tooth size prediction can be made during the MDSA. This sex difference in tooth sizes was also considered by Moyers11,34 while modifying his original probability tables that were based on pooled odontometric data. The secular trend in stature and body size is a welldocumented phenomenon.35,36 A similar secular trend in tooth sizes has also been shown in several odontometric studies.22-24 The secular increase in tooth sizes suggests the need to progressively update mixed dentition prediction aids developed from odontometric data of previous generations, to avoid underestimating the mesiodistal tooth widths of present-day children.12 A clear secular trend in tooth
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American Journal of Orthodontics and Dentofacial Orthopedics Volume 138, Number 3
Table VI. Percentile Males 95% 85% 75% 65% 50% 35% 25% 15% 5% Females 95% 85% 75% 65% 50% 35% 25% 15% 5%
343
Probability tables for predicting the mesiodistal widths of unerupted mandibular canines and premolars 19.5
20
20.5
21
21.5
22
22.5
23
23.5
24
24.5
25
25.5
20.00 19.86 19.72 19.49 19.40 19.15 19.11 19.04 18.86
20.35 20.21 20.04 19.83 19.75 19.50 19.48 19.40 19.24
20.70 20.57 20.31 20.14 20.11 19.85 19.83 19.75 19.56
21.06 20.92 20.63 20.49 20.46 20.20 20.12 20.10 19.86
21.41 21.27 20.96 20.85 20.82 20.56 20.49 20.45 20.23
21.76 21.62 21.32 21.24 21.17 20.91 20.88 20.81 20.52
22.12 21.98 21.67 21.58 21.53 21.36 21.34 21.16 20.86
22.47 22.33 22.02 21.95 21.88 21.62 21.70 21.51 21.23
22.82 22.68 22.37 22.25 22.24 21.97 21.90 21.87 21.58
23.17 23.04 22.73 22.69 22.59 22.32 22.26 22.22 21.96
23.53 23.39 23.08 22.95 22.95 22.67 22.61 22.57 22.29
23.88 23.74 23.43 23.37 23.30 22.99 22.81 22.70 22.64
24.23 24.09 23.78 23.69 23.65 23.38 23.31 23.28 22.99
19.79 19.78 19.59 19.36 19.22 19.09 19.05 18.91 18.79
20.13 20.12 19.93 19.70 19.55 19.42 19.39 19.24 19.13
20.46 20.45 20.22 20.07 19.89 19.76 19.73 19.58 19.42
20.80 20.78 20.51 20.36 20.22 20.10 20.07 19.92 19.78
21.14 21.11 20.84 20.67 20.56 20.44 20.40 20.26 20.05
21.47 21.45 21.21 21.09 20.89 20.77 20.74 20.59 20.31
21.81 21.80 21.62 21.52 21.23 21.11 21.08 20.93 20.79
22.15 22.11 21.96 21.88 21.56 21.45 21.42 21.27 21.08
22.49 22.46 22.29 22.17 21.90 21.78 21.75 21.61 21.47
22.82 22.79 22.63 22.56 22.23 22.12 22.09 21.94 21.79
23.16 23.14 22.97 22.85 22.57 22.46 22.43 22.28 22.14
23.50 23.48 23.30 23.23 22.90 22.80 22.77 22.62 22.47
23.82 23.81 23.64 23.57 23.23 23.13 23.10 22.96 22.79
sizes could not be established in this study because of the lack of odontometric data from previous generations of this ethnic group. However, the proposed new prediction aids of this study might be more accurate for toothsize prediction in Indian children because they were derived from contemporary odontometric data. The correlation coefficients obtained in this study (Table III) approximately parallel those of several other studies: Hixon and Oldfather3 (0.69), Tanaka and Johnston12 (0.65), Ballard and Wylie10 (0.64), and Lee-Chan et al18 (0.66). It was suggested that these relatively consistent correlations (0.60-0.70), between the combined mesiodistal widths of the mandibular permanent incisors and the mesiodistal widths of the caninepremolar segments, might mean that 60% to 70% of the polygenes that determine tooth size are shared between the mandibular incisors and the canines and the premolars.12 This common genetic code gives theoretical justification for the estimation of unerupted canine and premolar widths based on the widths of already erupted mandibular incisors, even though these teeth belong to different morphologic classes. Multiple regression analysis has also indicated that the combined mesiodistal widths of the mandibular permanent incisors is the best nonradiographic predictor variable for estimating the mesiodistal widths of the unerupted canines and premolars of both arches.37 Using the mandibular permanent incisors as a predictor variable has several advantages: they erupt early in the mixed dentition, can be easily measured, show little variability in size, and are directly in the midst of most space-management problems.11
Coefficients of determination, which indicate the predictive accuracy of the regression equations, were between 0.43 and 0.46 for the different caninepremolar segments (Table III). This means that 43% to 46% of the total variances in canine-premolar widths are accounted for by knowing the combined mandibular incisor widths. The error involved in the use of the regression equations is indicated by the SEE; the lower the SEE, the better the prediction equation. The SEE values in our study were between 0.71 and 0.81 mm (Table III) and are approximately similar to the SEE values reported by Jaroontham and Godfrey16 and Ferguson et al,21 while they were slightly lower than the SEE values for the methods of Moyers11 and Tanaka and Johnston.12 The new mixed dentition prediction aids (regression equations and probability tables) developed in this study are presented in Tables IV, V, and VI. The use of these prediction aids for estimation of unerupted caninepremolar widths could result in a more accurate MDSA in Indian children. Significant differences (P \0.05) were found between the predicted mesiodistal tooth widths of our study and that of the Moyers probability tables at almost all percentile confidence levels (Table VII). It can be generally stated that the Moyers tables tend to underestimate the mesiodistal canine-premolar widths of this population group, including at the recommended 75% and 50% levels. Probability tables on the Moyers pattern have also been derived by Priya and Munshi17 (South Indians) and Schirmer and Wiltshire19 (black South
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American Journal of Orthodontics and Dentofacial Orthopedics September 2010
Table VII. Differences between the regression values of this study and those in the Moyers probability tables at various percentile levels Difference Y1-Y2 (mm) Difference Y1-Y2 (mm) Maxillary canine-premolar Mandibular canine-premolar segments segments Percentile 5 15 25 35 50 65 75 85 95
Males †
2.01 1.62* 1.32* 1.24* 1.09* 0.77* 0.67* 0.66 0.16
Females †
2.85 2.28† 2.16† 1.95† 1.53† 1.37* 1.15* 1.03* 0.35
Males †
1.98 1.55* 1.29* 0.86* 0.78* 0.71* 0.65* 0.11 0.72
Females
States with its high immigrant population, might be treating children of various racial and ethnic mixes, and will benefit by using mixed dentition prediction aids developed for specific population groups, such as those proposed in this study for Indian children. CONCLUSIONS
†
2.66 1.89† 1.61* 1.29* 0.93* 0.81* 0.74* 0.29 0.45
1.
2.
Y1, Predicted mesiodistal width of canine-premolar segments in this study; Y2, predicted mesiodistal width of canine-premolar segments in the Moyers study. *P \0.05; †P \0.001 (statistical tool: Wilcoxon signed rank sum test).
3.
Africans). Priya and Munshi also concluded that the Moyers probability tables underestimated the tooth sizes of South Indian children.17 Schirmer and Wiltshire tested the applicability of the Moyers tables in black South Africans and found highly significant differences (P \0.001) at all percentile confidence levels, in the arches of both male and female subjects, except at the 75%, 85%, and 95% levels in the maxillary arch of females.19 Al-Khadra38 found that the recommended 75% confidence level of the Moyers probability tables overestimated the sizes of canines and premolars of a Saudi Arab population. On the other hand, Tanaka and Johnston12 stated that the probability tables they developed were practically identical to those of Moyers11 at all percentile confidence levels, probably because of the similar white samples used in both studies. The importance of accurate prediction of the mesiodistal crown widths of unerupted canines and premolars during MDSA should be apparent, since often the decision to treat (or not to treat), as well as the type of treatment, is based on the results of the MDSA. The space management protocol will be adversely affected if it is based on a wrong estimation of unerupted tooth sizes, ultimately resulting in poor treatment results. Fields39 stated that the accuracy of the Moyers MDSA method is fairly good when applied exclusively to white patients. Our results confirm that the Moyers probability tables underestimate tooth sizes of Indian children. Developing new probability tables on the Moyers pattern, specifically for different population groups, can aid in achieving more accurate estimation of unerupted tooth sizes. Orthodontists, especially those in the United
4.
There is statistically significant sexual dimorphism in tooth sizes in Indian children, highlighting the importance of developing separate mixed dentition prediction aids for male and female patients. Based on odontometric data from a contemporary population in India, new probability tables on the Moyers pattern and easy-to-use prediction equations have been proposed in this study. The Moyers probability tables were found to significantly underestimate canine and premolar mesiodistal widths of Indian children, at almost all percentile levels, including the commonly used 75% and 50% levels. We recommend that the new probability tables and prediction equations proposed in this study should be used for MDSA in Indian children. However, the accuracy of the proposed prediction aids should be further tested in other ethnic groups of India.
REFERENCES 1. McDonald RE, Avery DR, Dean JA. Management of the developing occlusion. Dentistry for the child and the adolescent. 8th ed. St Louis: Mosby; 2004:p. 627. 2. Graber TM. Incidence and recognition of malocclusion. In: Graber TM, editor. Orthodontics: principles and practice. 3rd ed. Philadelphia: W.B. Saunders; 2001:p. 204-5. 3. Hixon EH, Oldfather RE. Estimation of the sizes of unerupted cuspids and bicuspids. Angle Orthod 1958;28:236-40. 4. Cohen MI. Recognition of the developing malocclusion. Dent Clin North Am 1959;6:299-311. 5. Staley RN, Hoag JF. Prediction of the mesiodistal widths of maxillary permanent canines and premolars. Am J Orthod 1978;73: 169-77. 6. Staley RN, Shelly TH, Martin JF. Prediction of the lower canine and premolar widths in the mixed dentition. Am J Orthod 1979;76:300-9. 7. Staley RN, Kerber PE. A revision of the Hixon and Oldfather prediction method. Am J Orthod 1980;78:296-302. 8. Staley RN, Gorman TW, Hoag JF, Shelly TH. Prediction of the widths of unerupted canines and premolars. J Am Dent Assoc 1984;108:185-90. 9. de Paula S, Almeida MA, Lee PC. Prediction of mesiodistal diameter of unerupted lower canines and premolars using 45 degrees cephalometric radiography. Am J Orthod Dentofacial Orthop 1995;107:309-14. 10. Ballard ML, Wylie WL. Mixed dentition case analysis: estimating sizes of unerupted permanent teeth. Am J Orthod 1947;33:754-9. 11. Moyers RE. Analysis of dentition and occlusion. In: Moyers RE, editor. Handbook of orthodontics. 4th ed. Chicago: Year Book Medical Publishers; 1988:p. 235-40.
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12. Tanaka MM, Johnston LE. The prediction of the sizes of unerupted canines and premolars in a contemporary orthodontic population. J Am Dent Assoc 1974;88:798-801. 13. Motokawa W, Masao O, Yoshio S, Yutaka Y. A method of mixed dentition analysis in the mandible. J Dent Child 1987;54:114-8. 14. Lavelle CLB. Maxillary and mandibular tooth size in different racial groups and in different occlusal categories. Am J Orthod 1972;61:29-37. 15. Bishara SE, Jakobsen JR, Abdallah EM, Fernandez Garcia A. Comparisons of mesiodistal and buccolingual crown dimensions of the permanent teeth in three populations from Egypt, Mexico, and the United States. Am J Orthod Dentofacial Orthop 1989;96:416-22. 16. Jaroontham J, Godfrey K. Mixed dentition space analysis in a Thai population. Eur J Orthod 2000;22:127-34. 17. Priya S, Munshi AK. Formulation of a prediction chart for mixed dentition analysis. J Indian Soc Pedod Prev Dent 1994;12:7-11. 18. Lee-Chan S, Jacobson BN, Chwa KH, Jacobson RS. Mixed dentition analysis for Asian-Americans. Am J Orthod Dentofacial Orthop 1998;113:293-9. 19. Schirmer UR, Wiltshire WA. Orthodontic probability tables for black patients of African descent: mixed dentition analysis. Am J Orthod Dentofacial Orthop 1997;112:545-51. 20. Diagne F, Diop-Ba K, Ngom PI, Mbow K. Mixed dentition analysis in a Senegalese population: elaboration of prediction tables. Am J Orthod Dentofacial Orthop 2003;124:178-83. 21. Ferguson FS, Macko DJ, Sonneberg EM, Shakun ML. The use of regression constants in estimating tooth size in a Negro population. Am J Orthod 1978;73:68-72. 22. Garn SM, Lewis AB, Walenga AJ. Evidence for a secular trend in tooth size over two generations. J Dent Res 1968;47:503. 23. Lavelle CLB. Secular trends in different racial groups. Angle Orthod 1972;42:19-25. 24. Harper C. A comparison of medieval and modern dentitions. Eur J Orthod 1994;16:163-73. 25. Moorrees CFA, Reed RB. Correlations among crown diameters of human teeth. Arch Oral Biol 1964;9:685-97.
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26. Doris JM, Bernard BW, Kuftinec MM, Stom D. A biometric study of tooth size and dental crowding. Am J Orthod 1981;79:326-35. 27. Lundstr}om A. Tooth morphology as a basis for distinguishing between monozygotic and dizygotic twins. Am J Hum Genet 1963; 15:34-43. 28. Nanda RS, Chawla JM. Variability of leeway space. J Indian Dent Assoc 1973;45:99-108. 29. Nance HV. Limitations of orthodontic treatment. Mixed dentition diagnosis and treatment. Am J Orthod Oral Surg 1947;33:177-223. 30. Singh M, Nanda RS. Prediction of tooth size and its clinical application. J Indian Dent Assoc 1972;44:5-8. 31. Garn SM. Genetics of dental development. The biology of occlusal development. Monograph 7, Craniofacial Growth Series. Ann Arbor: Center for Human Growth and Development; University of Michigan; 1977. 32. Garn SM, Lewis AB, Kerewsky RS. X-linked inheritance of dental tooth size. J Dent Res 1965;44:439-41. 33. Garn SM, Lewis AB, Swindler DR, Kerewsky RS. Genetic control of sexual dimorphism in tooth size. J Dent Res 1967;46(Suppl): 963-72. 34. Moyers RE. Analysis of dentition and occlusion. In: Moyers RE, editor. Handbook of orthodontics. 3rd ed. Chicago: Year Book Medical Publishers; 1973. 35. Freedman DS, Khan LK, Serdula MK, Srinivasan SR, Berenson GS. Secular trends in height among children during 2 decades. Arch Pediatr Adolesc Med 2000;154:155-61. 36. Roche AF. Secular trends in human growth, maturation, and development. Monogr Soc Res Child Dev 1979;44:1-120. 37. Huckaba GW. Arch size analysis and tooth size prediction. Dent Clin North Am 1964;43:431-40. 38. Al-Khadra BH. Prediction of the sizes of unerupted canines and premolars in a Saudi Arab population. Am J Orthod Dentofacial Orthop 1993;104:369-72. 39. Fields HW. Treatment of moderate nonskeletal problems in preadolescent children. In: Proffit WR, Fields HW, editors. Contemporary orthodontics. 3rd ed. St Louis: C.V. Mosby; 2000. p. 417-22.
Applicability of the Moyers mixed dentition probability tables and new prediction aids for a contemporary population in India Nebu Ivan Philip,a Manisha Prabhakar,b Deepak Arora,c and Saroj Choprad Pondicherry, Muktsar, and Ludhiana, India Introduction: The Moyers mixed dentition space analysis method is among the most commonly used in clinical practice for detecting tooth size-arch length discrepancies. In view of reported secular trends, racial, and sex differences in tooth sizes, the purposes of this study were to evaluate the applicability of Moyers probability tables in a contemporary orthodontic population of India and to formulate more accurate mixed dentition prediction aids. Methods: Odontometric data were collected from 300 male and 300 female subjects of Indian descent, who had fully erupted mandibular permanent incisors and maxillary and mandibular canines and premolars. We measured the mesiodistal crown widths with vernier scale dial calipers. The odontometric values obtained were then subjected to statistical and linear regression analysis. Results: All tooth groups showed significant differences (P \0.001) between mesiodistal widths of male and female subjects. Regression equations for the maxillary arch (males, Y 5 7.15 1 0.67X; females, Y 5 7.44 1 0.65X) and the mandibular arch (males, Y 5 5.55 1 0.71X; females, Y 5 6.15 1 0.67X) were used to develop new probability tables on the Moyers pattern. Significant differences (P \0.05) were found between our predicted widths and the Moyers tables at almost all percentile levels, including the recommended 75% and 50% levels. Conclusions: We believe that these new prediction aids could be considered for a more precise mixed dentition space analysis in Indian children. (Am J Orthod Dentofacial Orthop 2010;138:339-45)
E
very dentist who provides care for children and adolescents should be able to properly assess and manage their developing occlusions.1 Many malocclusions, especially crowding problems, originate in the mixed dentition period.2 During this critical period, the orthodontist or pediatric dentist is often asked to provide an accurate diagnosis of any developing malocclusions and an opinion on its effects, if any, on the ultimate occlusal status of the permanent dentition. One condition requiring early diagnosis and treatment is when there is a disparity between the space available in the dental arch and the space needed for the a
Assistant professor, Department of Pediatric and Preventive Dentistry, Indira Gandhi Institute of Dental Sciences, Pondicherry, India. b Professor and head, Department of Pediatric and Preventive Dentistry, Desh Bhagat Dental College, Muktsar, India. c Professor and head, Department of Orthodontics and Dentofacial Orthopedics, Christian Dental College, Ludhiana, India. d Professor and head, Department of Pediatric and Preventive Dentistry, Christian Dental College, Ludhiana, India. The authors report no commercial, proprietary, or financial interest in the products or companies described in this article. Reprint requests to: Nebu Ivan Philip, Department of Pediatric & Preventive Dentistry, Indira Gandhi Institute of Dental Sciences, Mahatma Gandhi Medical College & Hospital Campus, Pondicherry, India 607402; e-mail, drnebu@ yahoo.com. Submitted, July 2008; revised and accepted, September 2008. 0889-5406/$36.00 Copyright Ó 2010 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2008.09.035
proper alignment of the unerupted permanent canines and premolars. In planning the management of these patients, the deficit of arch space must be predicted early, and the indicated preventive or interceptive procedures instituted. The mixed dentition space analysis (MDSA) is a fundamental part of an early orthodontic assessment and helps in determining any tooth size-arch length discrepancy. If a discrepancy is present, MDSA will be a useful diagnostic aid in evaluating whether the treatment plan will involve serial extractions, guidance of eruption, space regaining, proximal stripping, space maintenance, or just periodic observation of the patient. To perform an accurate MDSA, it is vital to correctly predict the mesiodistal crown widths of the unerupted permanent canines and premolars. Two broad approaches have been used for this prediction: radiographic3-9 and nonradiographic methods.10-13 Radiographic methods require measurements of undistorted long-cone radiographic images of erupted and unerupted teeth, and also of erupted teeth on study casts. The mesiodistal widths of the unerupted canines and premolars are then estimated from multiple regression equations or graphs. Such complex methods might discourage their routine use by clinicians. Moyers11 proposed a simpler nonradiographic MDSA method in which the mesiodistal crown widths of the unerupted permanent canines and premolars of both arches can be predicted from the combined 339
340 Philip et al
mesiodistal crown widths of the 4 mandibular permanent incisors by using probability tables. The Moyers probability tables were developed at the University of Michigan based on odontometric data of American white subjects of Northwestern European descent.11 The accuracy of these probability tables is questionable when applied to population groups other than white people, because it has been well established in the literature that tooth sizes vary considerably between racial groups.14-21 Table I shows mesiodistal crown widths obtained from odontometric studies of various population groups. In addition, a few investigators noted a secular trend toward increased tooth sizes with succeeding generations.22-24 This implies that values used in probability tables or prediction equations developed from odontometric data of earlier generations might underestimate the tooth sizes of present-day children. Accordingly, the objectives of this study were to formulate new prediction aids (probability tables and prediction equations) that can enable a more accurate MDSA in Indian children, and to evaluate the applicability of Moyers probability tables in a contemporary Indian population. MATERIAL AND METHODS
Dental study casts of 300 male and 300 female subjects were selected for this study from a contemporary population of India. The casts were made from dental impressions of children in various schools of Punjab state in India, after approval was obtained from their parents and teachers. The criteria for sample selection were the following. 1.
2.
3. 4. 5.
The mandibular permanent incisors, the mandibular and maxillary permanent canines, and the mandibular and maxillary premolars were fully erupted. There was no obvious loss of tooth material mesiodistally as a result of caries, fractures, congenital defects, or interproximal attrition. The dental impressions and study casts were high quality and free of distortions. The subjects had no previous history of orthodontic treatment. All subjects had a similar ethnic background (Punjabi).
The teeth measured were the mandibular central and lateral permanent incisors, the mandibular and maxillary permanent canines, and the first and second premolars of both arches. The values obtained for the right and left canine-premolar segments in each arch were averaged, so that there would be 1 value for the mandibular canine-premolar segment and 1 value for the maxillary
American Journal of Orthodontics and Dentofacial Orthopedics September 2010
Table I. Mesiodistal crown widths from various studies of different racial groups Sample size (n)
Study
Sex
Asian populations Jaroontham and Godfrey16 (Thai)
M
215
F
215
M
200
F
300
M, F
201
M
300
F
300
M
100
F
100
M
25
F
25
Priya and Munshi17 (South India)
Lee-Chan et al18 (Asian Americans) This study (Punjab, India)
African populations Schrimer and Wiltshire19 (South African blacks)
Diagne et al20 (Senegalese)
Ferguson et al21 (African Americans) White populations Tanaka and Johnston12 (North Americans)
M, F
105
M, F
506
Arch
Mean (mm)
SD (mm)
LI UCPM LCPM LI UCPM LCPM LI UCPM LCPM LI UCPM LCPM LI UCPM LCPM LI UCPM LCPM LI UCPM LCPM
23.89 23.16 22.23 22.23 22.64 21.77 24.88 23.32 21.91 24.20 22.71 21.41 23.40 22.93 22.03 24.03 23.23 22.50 23.48 22.75 21.99
1.37 1.03 1.04 1.26 1.00 1.02 0.36 0.39 0.45 0.34 0.38 0.43 1.19 1.17 1.12 1.05 1.07 1.09 0.93 0.94 0.95
LI UCPM LCPM LI UCPM LCPM LI UCPM LCPM LI UCPM LCPM LI UCPM LCPM
23.92 23.22 23.45 23.66 22.28 22.20 23.71 22.28 22.20 22.86 22.70 22.20 23.52 22.40 22.24
1.90 1.11 1.37 1.59 1.28 1.24 1.25 1.28 1.24 1.25 1.01 1.22 1.79 1.27 1.31
LI UCPM LCPM
23.43 22.27 21.76
1.35 1.09 1.12
LI, Lower incisors; UCPM, upper canines and premolars; LCPM, lower canines and premolars; M, male; F, female.
canine-premolar segment for each value of the combined mandibular incisors. Measurements of the mesiodistal crown widths of the mandibular and maxillary teeth were made by using a dial caliper with a vernier scale, calibrated to the nearest 0.05 mm (Matsui Dial Caliper, Mitutoyo, Kawasaki, Japan). The tips of the calipers were precision engineered to ensure the greatest accuracy while measuring the various tooth groups.
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Table II. Descriptive statistics for the combined mesiodistal widths of the 3 tooth groups Tooth group
Table III. Regression parameters for prediction of mesiodistal widths of canine-premolar segments
Sex Range (mm) Mean 6 SD (mm) t value
Mandibular incisors M F Maxillary M canine-premolar F segment Mandibular M canine- premolar F segment
341
Constants
20.65-27.50 20.40-26.15 20.15-26.85 20.05-26.25
24.03 6 1.05 23.48 6 0.93 23.23 6 1.07 22.75 6 0.94
6.92*
Sex
5.84*
Male
19.40-26.40 19.50-25.70
22.50 6 1.09 21.99 6 0.95
6.11*
Female
Canine-premolar segment
r
a
b
r2
SEE (mm)
Maxillary Mandibular Maxillary Mandibular
0.66 0.68 0.65 0.67
7.145 5.548 7.444 6.154
0.669 0.706 0.652 0.674
0.43 0.46 0.43 0.44
0.81 0.80 0.72 0.71
r, Correlation; a and b, regression constants; r2, coefficient of determination; SEE, standard error of estimate.
M, Male; F, female. *P \0.001.
A standardized method proposed by Moorrees and Reed25 was used to measure the mesiodistal crown widths. The greatest mesiodistal crown width of each tooth was measured between its contact points, with the sliding caliper placed parallel to the occlusal and vestibular surfaces. This method was reported to be highly repeatable and accurate for measuring mesiodistal crown widths by Doris et al.26 Measurement reliability was checked according to a method suggested by Lundstr} om,27where the same investigator measures all casts and then remeasures certain randomly selected casts. The coefficient of test-test reliability on 120 such randomly selected casts was calculated and found to be r .0.95, confirming the reliability of the measurements. RESULTS
Descriptive statistics for the 3 tooth groups measured in the study (mandibular permanent incisors, mandibular canine-premolar segment, and maxillary canine-premolar segment) are presented in Table II for the sexes separately. Student t tests comparing the mesiodistal crown widths of male and female subjects showed highly significant differences (P \0.001) in all 3 tooth groups, with males having larger teeth. Coefficients of correlation were calculated and standard linear regression equations of the form Y5 a 1 b(X) derived, to evaluate the relationship between the combined mesiodistal widths of the mandibular permanent incisors (X) and the mesiodistal widths of the canine-premolar segments (Y) of each arch. Table III records the various regression parameters: correlation coefficient, regression constants (a is the y-intercept, and b is the slope of the regression line), coefficient of determination, and standard errors of estimate (SEE). This regression analysis was used to formulate new prediction equations that can be used clinically to predict the mesiodistal crown widths of the unerupted canine premolar segments (Y) when the combined
Table IV. Prediction equations from various studies at the 50th percentile Study
Sex
This study (Punjab, India)
M
Arch
Maxillary Mandibular F Maxillary Mandibular Moyers11 M Maxillary (North American whites)* Mandibular F Maxillary Mandibular Moyers34 M, F Maxillary (North American whites)* Mandibular Tanaka and Johnston12 M, F Maxillary (North American whites) Mandibular Diagne et al20 M Maxillary (Senegalese) Mandibular F Maxillary Mandibular Lee-Chan et al18 M, F Maxillary (Asian Americans) Mandibular Jaroontham and Godfrey16 M Maxillary (Thai) Mandibular F Maxillary Mandibular
Prediction equations Y 5 7.15 1 0.67(X) 5.55 1 0.71(X) 7.44 1 0.65(X) 6.15 1 0.67(X) 9.73 1 0.51(X) 10.79 1 0.45(X) 14.17 1 0.28(X) 8.85 1 0.52(X) 9.23 1 0.55(X) 7.82 1 0.59(X) 10.41 1 0.51(X) 9.18 1 0.52(X) 9.60 1 0.55(X) 5.54 1 0.72(X) 13.77 1 0.35(X) 8.74 1 0.56(X) 8.19 1 0.63(X) 7.46 1 0.62(X) 13.36 1 0.41(X) 11.92 1 0.43(X) 11.16 1 0.49(X) 9.49 1 0.53(X)
Y, Mesiodistal width of canine-premolar segment; X, mesiodistal width of the 4 mandibular incisors. *Regression equations derived from Moyers tables at the 50th percentile.
mesiodistal crown widths of the 4 mandibular permanent incisors are known (X). These new prediction equations (after approximation) are shown in Table IV, along with prediction equations from some other studies. The regression equations derived in this study were used to prepare new probability tables on the Moyers pattern and are presented in Tables V and VI. To evaluate the applicability of the Moyers probability tables in our sample, the odontometric values we obtained were statistically compared with predicted values from Moyers tables at the 5% to the 95% confidence levels by using the Wilcoxon signed rank sum
342 Philip et al
Table V. Percentile Males 95% 85% 75% 65% 50% 35% 25% 15% 5% Females 95% 85% 75% 65% 50% 35% 25% 15% 5%
American Journal of Orthodontics and Dentofacial Orthopedics September 2010
Probability tables for predicting the mesiodistal widths of unerupted maxillary canines and premolars 19.5
20
20.5
21
21.5
22
22.5
23
23.5
24
24.5
25
25.5
20.77 20.75 20.44 20.39 20.22 20.14 20.06 19.87 19.80
21.10 21.09 20.77 20.70 20.55 20.41 20.32 20.21 20.13
21.44 21.42 21.11 20.96 20.89 20.77 20.64 20.49 20.46
21.77 21.76 21.44 21.29 21.22 21.12 20.95 20.82 20.80
22.11 22.09 21.78 21.63 21.56 21.35 21.29 21.18 21.13
22.44 22.43 22.11 21.96 21.89 21.68 21.58 21.48 21.44
22.78 22.76 22.44 22.30 22.23 22.04 21.91 21.84 21.80
23.11 23.10 22.78 22.63 22.56 22.35 22.27 22.17 22.14
23.44 23.43 23.11 22.96 22.90 22.65 22.59 22.49 22.47
23.78 23.76 23.45 23.30 23.23 22.96 22.89 22.83 22.81
24.11 24.10 23.78 23.63 23.57 23.25 23.19 23.16 23.14
24.45 24.43 24.12 23.97 23.90 23.60 23.51 23.54 23.48
24.78 24.77 24.45 24.30 24.24 23.92 23.88 23.85 23.81
20.61 20.58 20.39 20.30 20.12 20.07 19.99 19.72 19.63
20.94 20.96 20.72 20.62 20.44 20.34 20.26 20.05 19.96
21.27 21.29 21.05 20.89 20.76 20.69 20.51 20.38 20.29
21.59 21.47 21.37 21.15 21.09 20.98 20.83 20.70 20.61
21.94 21.92 21.70 21.56 21.42 21.33 21.06 21.03 20.94
22.27 22.24 22.02 21.83 21.74 21.60 21.46 21.35 21.26
22.59 22.57 22.35 22.15 22.07 21.91 21.84 21.68 21.59
22.92 22.89 22.68 22.56 22.39 22.25 22.09 22.01 21.92
23.24 23.22 23.00 22.90 22.72 22.58 22.42 22.33 22.24
23.57 23.55 23.33 23.23 23.04 22.91 22.73 22.66 22.57
23.90 23.87 23.65 23.56 23.37 23.17 23.04 22.98 22.89
24.22 24.20 23.98 23.88 23.69 23.48 23.36 23.31 23.22
24.55 24.52 24.31 24.21 24.01 23.81 23.66 23.63 23.54
test. Significant differences (P \0.05) were found at all percentile confidence levels, except at 95% and 85% for males in both arches; there were significant differences for females (P \0.05) at all percentile levels, except at 95% and 85% in the mandibular arch and at 95% in the maxillary arch (Table VII). DISCUSSION
The most important factors in the reliability of a study based on odontometric data are the characteristics of the sample chosen. The sample representation of this study was considered acceptable because of the large sample size (300 subjects of each sex) and the uniform ethnicity (Punjabi). Definite racial and ethnic differences in tooth sizes have been highlighted in several population studies14-21 (Table I). Nanda and Chawla28 found a significant disparity between the leeway space of North Indian children and the leeway space that was reported by Nance29 for American children. In another odontometric study with North Indian samples, Singh and Nanda30 derived a mixed dentition prediction scale that they found to be different from prediction tables developed by Ballard and Wylie10 for American white people and suggested that this could be due to racial tooth-size differences. The reasons for the tooth-size variations in different racial groups have not been clearly elucidated, but, obviously, genetic factors play a major role, and nutrition and environmental exposure during tooth development might have secondary roles.31 Whatever the reasons
for the racial tooth-size differences, orthodontists’ diagnostic armamentarium needs to be strengthened by developing tooth-size prediction aids from odontometric data specific to each racial group. In addition to the racial differences in tooth sizes, the descriptive statistics in Table II show that the mesiodistal crown widths of all tooth groups measured in this study were significantly larger in males than in females (P \0.001). Similar sex dimorphisms in tooth sizes have been noted in other odontometric studies.9,16-20 There is strong evidence that tooth size is expressed through X-linked inheritance, with Garn et al32,33 hypothesizing that the 2 X chromosomes in females might provide a measure of control lacking in males. The significant sex differences in mesiodistal tooth sizes emphasize the importance of developing mixed dentition prediction aids separately for male and female patients, so that a more accurate tooth size prediction can be made during the MDSA. This sex difference in tooth sizes was also considered by Moyers11,34 while modifying his original probability tables that were based on pooled odontometric data. The secular trend in stature and body size is a welldocumented phenomenon.35,36 A similar secular trend in tooth sizes has also been shown in several odontometric studies.22-24 The secular increase in tooth sizes suggests the need to progressively update mixed dentition prediction aids developed from odontometric data of previous generations, to avoid underestimating the mesiodistal tooth widths of present-day children.12 A clear secular trend in tooth
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American Journal of Orthodontics and Dentofacial Orthopedics Volume 138, Number 3
Table VI. Percentile Males 95% 85% 75% 65% 50% 35% 25% 15% 5% Females 95% 85% 75% 65% 50% 35% 25% 15% 5%
343
Probability tables for predicting the mesiodistal widths of unerupted mandibular canines and premolars 19.5
20
20.5
21
21.5
22
22.5
23
23.5
24
24.5
25
25.5
20.00 19.86 19.72 19.49 19.40 19.15 19.11 19.04 18.86
20.35 20.21 20.04 19.83 19.75 19.50 19.48 19.40 19.24
20.70 20.57 20.31 20.14 20.11 19.85 19.83 19.75 19.56
21.06 20.92 20.63 20.49 20.46 20.20 20.12 20.10 19.86
21.41 21.27 20.96 20.85 20.82 20.56 20.49 20.45 20.23
21.76 21.62 21.32 21.24 21.17 20.91 20.88 20.81 20.52
22.12 21.98 21.67 21.58 21.53 21.36 21.34 21.16 20.86
22.47 22.33 22.02 21.95 21.88 21.62 21.70 21.51 21.23
22.82 22.68 22.37 22.25 22.24 21.97 21.90 21.87 21.58
23.17 23.04 22.73 22.69 22.59 22.32 22.26 22.22 21.96
23.53 23.39 23.08 22.95 22.95 22.67 22.61 22.57 22.29
23.88 23.74 23.43 23.37 23.30 22.99 22.81 22.70 22.64
24.23 24.09 23.78 23.69 23.65 23.38 23.31 23.28 22.99
19.79 19.78 19.59 19.36 19.22 19.09 19.05 18.91 18.79
20.13 20.12 19.93 19.70 19.55 19.42 19.39 19.24 19.13
20.46 20.45 20.22 20.07 19.89 19.76 19.73 19.58 19.42
20.80 20.78 20.51 20.36 20.22 20.10 20.07 19.92 19.78
21.14 21.11 20.84 20.67 20.56 20.44 20.40 20.26 20.05
21.47 21.45 21.21 21.09 20.89 20.77 20.74 20.59 20.31
21.81 21.80 21.62 21.52 21.23 21.11 21.08 20.93 20.79
22.15 22.11 21.96 21.88 21.56 21.45 21.42 21.27 21.08
22.49 22.46 22.29 22.17 21.90 21.78 21.75 21.61 21.47
22.82 22.79 22.63 22.56 22.23 22.12 22.09 21.94 21.79
23.16 23.14 22.97 22.85 22.57 22.46 22.43 22.28 22.14
23.50 23.48 23.30 23.23 22.90 22.80 22.77 22.62 22.47
23.82 23.81 23.64 23.57 23.23 23.13 23.10 22.96 22.79
sizes could not be established in this study because of the lack of odontometric data from previous generations of this ethnic group. However, the proposed new prediction aids of this study might be more accurate for toothsize prediction in Indian children because they were derived from contemporary odontometric data. The correlation coefficients obtained in this study (Table III) approximately parallel those of several other studies: Hixon and Oldfather3 (0.69), Tanaka and Johnston12 (0.65), Ballard and Wylie10 (0.64), and Lee-Chan et al18 (0.66). It was suggested that these relatively consistent correlations (0.60-0.70), between the combined mesiodistal widths of the mandibular permanent incisors and the mesiodistal widths of the caninepremolar segments, might mean that 60% to 70% of the polygenes that determine tooth size are shared between the mandibular incisors and the canines and the premolars.12 This common genetic code gives theoretical justification for the estimation of unerupted canine and premolar widths based on the widths of already erupted mandibular incisors, even though these teeth belong to different morphologic classes. Multiple regression analysis has also indicated that the combined mesiodistal widths of the mandibular permanent incisors is the best nonradiographic predictor variable for estimating the mesiodistal widths of the unerupted canines and premolars of both arches.37 Using the mandibular permanent incisors as a predictor variable has several advantages: they erupt early in the mixed dentition, can be easily measured, show little variability in size, and are directly in the midst of most space-management problems.11
Coefficients of determination, which indicate the predictive accuracy of the regression equations, were between 0.43 and 0.46 for the different caninepremolar segments (Table III). This means that 43% to 46% of the total variances in canine-premolar widths are accounted for by knowing the combined mandibular incisor widths. The error involved in the use of the regression equations is indicated by the SEE; the lower the SEE, the better the prediction equation. The SEE values in our study were between 0.71 and 0.81 mm (Table III) and are approximately similar to the SEE values reported by Jaroontham and Godfrey16 and Ferguson et al,21 while they were slightly lower than the SEE values for the methods of Moyers11 and Tanaka and Johnston.12 The new mixed dentition prediction aids (regression equations and probability tables) developed in this study are presented in Tables IV, V, and VI. The use of these prediction aids for estimation of unerupted caninepremolar widths could result in a more accurate MDSA in Indian children. Significant differences (P \0.05) were found between the predicted mesiodistal tooth widths of our study and that of the Moyers probability tables at almost all percentile confidence levels (Table VII). It can be generally stated that the Moyers tables tend to underestimate the mesiodistal canine-premolar widths of this population group, including at the recommended 75% and 50% levels. Probability tables on the Moyers pattern have also been derived by Priya and Munshi17 (South Indians) and Schirmer and Wiltshire19 (black South
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American Journal of Orthodontics and Dentofacial Orthopedics September 2010
Table VII. Differences between the regression values of this study and those in the Moyers probability tables at various percentile levels Difference Y1-Y2 (mm) Difference Y1-Y2 (mm) Maxillary canine-premolar Mandibular canine-premolar segments segments Percentile 5 15 25 35 50 65 75 85 95
Males †
2.01 1.62* 1.32* 1.24* 1.09* 0.77* 0.67* 0.66 0.16
Females †
2.85 2.28† 2.16† 1.95† 1.53† 1.37* 1.15* 1.03* 0.35
Males †
1.98 1.55* 1.29* 0.86* 0.78* 0.71* 0.65* 0.11 0.72
Females
States with its high immigrant population, might be treating children of various racial and ethnic mixes, and will benefit by using mixed dentition prediction aids developed for specific population groups, such as those proposed in this study for Indian children. CONCLUSIONS
†
2.66 1.89† 1.61* 1.29* 0.93* 0.81* 0.74* 0.29 0.45
1.
2.
Y1, Predicted mesiodistal width of canine-premolar segments in this study; Y2, predicted mesiodistal width of canine-premolar segments in the Moyers study. *P \0.05; †P \0.001 (statistical tool: Wilcoxon signed rank sum test).
3.
Africans). Priya and Munshi also concluded that the Moyers probability tables underestimated the tooth sizes of South Indian children.17 Schirmer and Wiltshire tested the applicability of the Moyers tables in black South Africans and found highly significant differences (P \0.001) at all percentile confidence levels, in the arches of both male and female subjects, except at the 75%, 85%, and 95% levels in the maxillary arch of females.19 Al-Khadra38 found that the recommended 75% confidence level of the Moyers probability tables overestimated the sizes of canines and premolars of a Saudi Arab population. On the other hand, Tanaka and Johnston12 stated that the probability tables they developed were practically identical to those of Moyers11 at all percentile confidence levels, probably because of the similar white samples used in both studies. The importance of accurate prediction of the mesiodistal crown widths of unerupted canines and premolars during MDSA should be apparent, since often the decision to treat (or not to treat), as well as the type of treatment, is based on the results of the MDSA. The space management protocol will be adversely affected if it is based on a wrong estimation of unerupted tooth sizes, ultimately resulting in poor treatment results. Fields39 stated that the accuracy of the Moyers MDSA method is fairly good when applied exclusively to white patients. Our results confirm that the Moyers probability tables underestimate tooth sizes of Indian children. Developing new probability tables on the Moyers pattern, specifically for different population groups, can aid in achieving more accurate estimation of unerupted tooth sizes. Orthodontists, especially those in the United
4.
There is statistically significant sexual dimorphism in tooth sizes in Indian children, highlighting the importance of developing separate mixed dentition prediction aids for male and female patients. Based on odontometric data from a contemporary population in India, new probability tables on the Moyers pattern and easy-to-use prediction equations have been proposed in this study. The Moyers probability tables were found to significantly underestimate canine and premolar mesiodistal widths of Indian children, at almost all percentile levels, including the commonly used 75% and 50% levels. We recommend that the new probability tables and prediction equations proposed in this study should be used for MDSA in Indian children. However, the accuracy of the proposed prediction aids should be further tested in other ethnic groups of India.
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