Applicability of Two Universally Accepted Mixed Dentition Analysis on a Sample from Southeastern Region of Andhra Pradesh, India.

BACKGROUND: Most of the universally accepted mixed dentition analyses are based on the data derived from northwestern European descent. However, the accuracy of these methods when applied to different ethnic population is questionable. AIM: The present study is aimed to evaluate the applicability of Tanaka and Johnston (TJ) and Moyers (50(th) and 75(th) percentile) mixed dentition analysis in a sample from south-eastern region of Andhra Pradesh, India. SUBJECTS AND METHODS: Study models were prepared from a sample of 100 patients (50 males and 50 females) in the age range of 13-15 years. The mesio-distal dimension of the teeth was measured using a Digital Vernier calipers. The actual values of permanent canine and premolars on the casts were compared with the predicted values from TJ and Moyers analysis. The values derived from this study were statistically analyzed using SPSS version 17.0 (IBM, Chicago, USA). Pearson's coefficients were used to evaluate the correlations between the groups of teeth.
RESULTS: Overestimated values were noticed in males and females of both arches with TJ equation; Males showed no significant difference at Moyers 50(th) percentile (50/100), in both the arches where as females showed higher values in mandibular arch and underestimated values in maxillary arch. At Moyers 75(th) percentile, overestimated values were noticed in males for both the arches whereas in females lesser values were observed.
CONCLUSION: As the values showed significant deviation from TJ and Moyers both at 50 and 75 percentile, its applicability to the present population is limited. So, new regression equations were derived.

Introduction

Malocclusions were observed frequently during the mixed dentition stage, which spans from the 6th to 12th year of life. Most of these developing malocclusions may be reduced in severity or even eliminated entirely by timely intervention. Space evaluation is an important aspect in making decisions during orthodontic treatment, which are based on differences involving very few millimeters.

A variety of mixed dentition analysis were proposed which include Ballard and Wylie (1947); Hixon and Old Father (1958); Bull (1959); Moyers (1973, 1988); Tanaka and Johnston (1974); Staley and Hoag (1978); and Ingervall and Lennnartson (1978). However, all these methods used three main approaches – measurement of the unerupted teeth using radiographs; application of regression equations that relate the mesiodistal width of erupted teeth to those of unerupted teeth; a combination of measurements from erupted teeth and radiographs of unerupted teeth.[1]

Moyers' analysis uses the sum of the widths of the mandibular incisors to predict the sum of both the mandibular and maxillary canines and premolars at various probability levels (5–95%),[2] whereas Tanaka and Johnston's analysis uses the sum of mesiodistal width of the mandibular central and lateral incisors to develop regression equations for predicting the sizes of the unerupted canines and premolars. They established that the mesiodistal widths could be predicted by halving the width of the mandibular incisors and adding 10.5 mm for the mandibular teeth and 11.0 mm for the maxillary teeth.[3]

Despite the questionable reliability of both, Tanaka and Johnston's approach is still widely accepted because they do not require radiographs and are simple and quick to perform. However, one of the drawbacks of these methods is that they were specifically developed based on the observations on American White subjects of Northwestern European descent.[1] A review of the literature revealed that mixed dentition analyses were varied between different racial and population groups: Schirmer and Wiltshire[4] for black Africans; Lee-Chan et al.[5] for Asian-Americans; Bishara and Jakobsen[6] for population samples from Egypt, Mexico, and the USA; Flores-Mir et al.[7] for Peruvians; Nourallah et al.[8] for Syrians; Jaroontham and Godfrey[9] for Thai population; Diagne et al.[10] for Senegalese and within Indian population; and Sonahita et al.[11] and Philip et al.[12] for contemporary India. Populations of different racial origins generally had average values that were significantly different from those reported for Whites; however, in most cases, the clinical significance was questionable. In addition, there is some evidence of secular trends of changing dimensions of the teeth and jaws which may require progressive modifications of mixed dentition space analysis.[1] Studies on various populations have found sexual, racial, as well as ethnic variations in tooth size. Applicability of these analyses in studies conducted globally resulted in slight modification of the regression equations that would better suit their population.

Even though many studies were reported in the literature regarding the applicability of these mixed dentition analysis from different parts of India,[1112] the data from this region of India were sparse. Many studies on various populations have found differences in the tooth sizes between male and female subjects.[13] Hence, the present study is aimed with an objective to evaluate the applicability of two universally accepted mixed dentition analysis (Moyer and Tanaka and Johnston), to find out whether the predicting equations differ by sex, and to determine an appropriate regression equations for predicting the size of the unerupted canines and premolars on a group of sample from Southeastern region of Andhra Pradesh, India.

Subjects and Methods

In this observational, randomized, cross-sectional study, a total of 900 patients in the age ranging from 13 to 15 years without sex predilection and visited as outpatients to the Department of Pedodontics and Preventive Dentistry from October 2010 to August 2012 were screened based on the following these selection criteria – (i) The subjects should have all the first permanent molars fully erupted. (ii) Teeth that are to be measured should be free of restorations, fractures, or proximal caries. (iii) There should be no evidence of hypoplasia or anomalies of the teeth. (iv) Subjects with Angle's Class I molar and canine relationship and minor malocclusions such as rotation, crowding, or spacing were acceptable. (V) The subjects should not have undergone prior orthodontic treatment. To avoid selection bias, all the subjects were randomly selected. The appropriate sample size for this study is calculated by keeping confidence level at 95% and confidence interval at 10% for a population of one lakh. The level of accuracy is made to 50% which is estimated to be 96. The sample size for the present study is 115. After attaining the institutional ethical clearance, a thorough explanation was given to the 300/900 patients regarding the study purpose and procedure who have fulfilled the selection criteria; out of which, only 115 patients have given their willingness to participate in the study. After thorough oral prophylaxis, alginate impressions were made for both the arches with appropriate-sized rim lock trays. Measurements were obtained from each dental cast using the electronic digital caliper (Baker SDN 10, India) calibrated to the nearest 0.01 mm, according to the method described by Jensen et al.,[14] in which the caliper was held at the tooth's greatest mesiodistal diameter (anatomical contact points), parallel to the occlusal surface, and perpendicular to the long axis of the tooth [Figure 1]. The whole procedure was carried out under natural light by a single operator. To avoid interexaminer variability and determine the reliability of the measurements, twenty study models were randomly measured by a separate investigator who was unaware of the prior measurements. As the correlation coefficient was very high (r = 0.95), all the subsequent measurements were taken only once. Tanaka and Johnston and Moyer's prediction methods at 50th and 75th percentile were calculated on the present cluster of the sample.

Figure 1

Measuring mesiodistal diameter using electronic digital caliper

The values derived from this study were statistically analyzed using SPSS version 17.0 (IBM, Chicago, IL, USA). Paired t-tests were performed to examine the bilateral symmetry of the mesiodistal widths of all measured individual tooth and teeth in each arch and to test the significance of the differences between the measured and predicted values. Unpaired t-tests were carried out to compare data between male and female subjects. Pearson's coefficients were used to evaluate the correlations between the groups of teeth. Simple regression analyses were implemented to develop possible regression equations for the present sample.

Results

A high intraclass correlation coefficient = 0.95 ensured measurement reliability. Statistical significant difference was noticed between right and left sides, so an average of both the sides was taken. Further, there was statistically significant difference between the sexes, with the males having larger teeth in comparison to females [Table 1].

Table 1

Comparison of mesiodistal widths in male and female samples

In the present study, the highest correlation coefficient (r) was observed for female subjects in the maxillary arch (r = 0.49) and the mandibular arch (r = 0.38) and the least for male subjects in both the arches (r = 0.33) [Table 2].

Table 2

Regression parameters for the selected sample

The standard error of estimate (SE) indicates the error in the use of prediction equations; the lower the SEE, the better the prediction equation. The SEE in the present study ranged from 0.79 mm for males in maxillary arch and 0.99 mm for females in mandibular arch Table 2.

Regression equations are shown in Table 3, where the least square regression equations are in the form of Y = a + b (X); “Y” denotes the predicted mesiodistal size of canine and premolars (maxillary and mandibular) in one quadrant in millimeters and “X” equals the measured mesiodistal width of the four permanent mandibular incisors in millimeters. “a” and “b” are the constants to be derived (“a” is the Y-intercept and “b” the slope of the regression).

Table 3

Regression equations

Discussion

In the present study, the nonradiographic method was chosen because the results of the radiographic method depend on the quality of the X-ray film available, the technique followed and position of the crypts.[910] Calibration of the mesiodistal diameter of the teeth can be done by a pair of dividers or sliding calibrated calipers, digital calipers, MagicScan image analysis, digital method, etc. In the present study, the measurements of the teeth were done by contact method indirectly on the casts using digital calipers since it is easy, fast, accurate and also, the errors were less with this method.[15]

The combined mesiodistal diameter of the lower incisors, maxillary, mandibular canines and premolars was larger in males than females in the present study, which was statistically significant.[910]

Statistically significant differences were observed between the actual values and those predicted by Tanaka and Johnston method. Tanaka and Johnston prediction in the maxillary arch overestimated the combined mesiodistal width of permanent canine and premolars by 0.9 mm in males and 0.76 mm for the female group when compared to the actual values. These results are in agreement with the studies done by Sonahita et al.[11] However, underestimated values in females were noticed by Abu Alhaija and Qudeimat.[16]

In the mandibular arch, overestimated values were observed in both males and females by 1.2 mm and 1.13 mm, respectively. These results are in harmony with the studies by Chandna et al.,[17] Buwembo et al.,[18] and Sonahita et al.[11] Contrary to this, underestimated values were detected by Abu Alhaija and Qudeimat.[16]

Moyers' prediction at the 50th percentile in the maxillary arch showed no difference between the actual values and predicted values in males. A similar outcome was observed in the work done by Memon and Fida.[19] Underestimated values were observed in the study done by Abu Alhaija and Qudeimat[16] and Nik Tahere et al.,[20] whereas overestimated values were observed in the study by Hammad and Abdellatif.[21]

At the 50th percentile of Moyers' prediction in the maxillary arch of females, an underestimation of 1.06 mm was observed which was correlating with the study by Jaroontham and Godfrey[9] and Sonahita et al.[11] An overestimation of 0.2 mm was observed by Jaiswal et al.[22]

At the 75th percentile of Moyers' prediction in the maxillary arch of males, an overestimation of 0.33 mm was observed. Results were alike to the work done by Durgekar and Naik.[23] On the other hand, underestimated values were found by Chandna et al.[17] In females, an underestimated value of 0.37 mm was observed which is analogous to the studies done by Hammad and Abdellatif,[21] Philip et al.,[12] and Chandna et al.[17] On the contrary, Nik Tahere et al.,[20] Memon and Fida,[19] and Buwembo et al.[18] found its applicability for predicting values.

At the 75th percentile of Moyers' prediction in the mandibular arch of males and females, an overestimation of 0.92 mm and 0.46 mm was observed, respectively. These results are in consistent with the study done by Chandna et al.[17] In contrary, study by Hammad and Abdellatif[21] exhibited under prediction.

In the present study, overestimated values were noticed with Tanaka and Johnston method when compared to Moyers' 50th and 75th percentile, in the mandibular arch for both the genders.

Under and over-prediction values were observed when Tanaka and Johnston and Moyer's methods were applied to the present contemporary population, which could be due to variation in sample size, racial, ethnic, and secular trends. Thus, emphasizing the fact that one prediction method may not be applicable universally.[468]

Even though the exact etiology for variations in tooth size of different racial groups is not known, genetics along with nutrition and environment plays an important role during the tooth development.[2425]

Variable results in tooth size prediction could also be due to armamentarium and methodology followed by different investigators.[15] Sexual dimorphisms in tooth sizes have been noted in various odontometric studies.[4910] There is strong evidence that tooth size is expressed through X-linked inheritance where 2X chromosomes in females might provide a measure of control which is lacking in males.[2425] Significant sex differences in mesiodistal tooth size highlight the importance of developing mixed dentition prediction aids, separately for both the genders. Secular trends in tooth size suggest the need for frequent updating of mixed dentition prediction aids which were developed from odontometric data of previous generations thereby avoiding under-/over-estimated values for the present day children.[12] A clear secular trend in tooth 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 equation might be more accurate to calculate the tooth size in the present population. Disparity in coefficient values between the different ethnic studies illustrates tooth size variability between diverse ethnic groups.[910] The research till date, as well as the present study, supports the view that racial difference is important in tooth size prediction.

Although many studies have reported the need for specific regressions for different racial and ethnic groups, very few have addressed about the clinical significance.[8910] Authors anecdotally claimed that with a combined mesiodistal width of canines and premolars within 1 mm of the predicted value derived from Tanaka and Johnston and Moyer's techniques should be considered clinically acceptable.[6] The clinical significance of the difference between predicted and actual teeth width in the growing child, however, remains unsubstantiated by any scientific evidence. Therefore, the results of Tanaka and Johnston and Moyer's space analysis techniques when applied for growing children other than Northwestern European origins should be interpreted with caution.

The prediction equations formulated, based on the data from the present sample in Southeastern region of Andhra Pradesh, may be a guide for prediction of mesiodistal widths of unerupted canines and premolars. However, further investigation with a larger sample size is required to collect more representative odontometric data.

Conclusion

Significant sexual dimorphism in tooth size exists in the present population

The commonly used Tanaka and Johnston and Moyer's prediction methods were not accurate when applied to the current sample since it tends to over/under estimate the actual measurements

The values were more for Tanaka and Johnston than for Moyers' (50th and 75th percentile)

The new derived regression equations were more promising in predicting the mesiodistal widths of canines and premolars for males and females separately.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.