Evaluation of validity of Tanaka-Johnston analysis in Mumbai school children.

INTRODUCTION: Estimation of the mesiodistal dimensions of the unerupted canines and premolars in the early mixed dentition is a necessary diagnostic aid in space management. Tanaka-Johnston analysis was developed for North American children. Anthropological study reveals that tooth size varies among different ethnicities. The present study was performed to evaluate the validity of Tanaka-Johnston method of mixed dentition arch analysis in Mumbai school children. AIMS: (1) To determine the correlation between the sum of the mesiodistal widths of the permanent mandibular incisors and combined mesiodistal widths of the permanent mandibular and maxillary canines and premolar in Mumbai school children. (2) To examine the applicability of Tanaka-Johnston method of prediction.
MATERIALS AND METHODS: Dental casts of maxillary and mandibular arches of 300 children, 147 boys and 153 girls within the age group of 12-15 years, with permanent dentitions were fabricated. The mesiodistal crown dimensions of teeth were measured with a dial caliper. Tanaka-Johnston method of mixed dentition arch analysis was performed for the study population, and statistical analysis was done. STATISTICAL ANALYSIS USED: Descriptive statistics including the mean, standard deviation, range, and standard error were calculated and tabulated.
RESULTS: Tanaka-Johnston's equation when applied to the data available for Mumbai school children, it was observed that it slightly overestimates the tooth size.
CONCLUSIONS: (1) There was a positive correlation between the width of mandibular incisors and mandibular and maxillary canines and premolars. (2) The Tanaka-Johnston prediction method was not accurate for a sample of Mumbai school children.

Introduction

Mixed dentition arch analysis is an important criterion in determining whether the orthodontic treatment plan is going to involve serial extraction, guidance of eruption, space maintenance, space regaining, or just periodic observation of the patient. The determination of tooth size-arch length discrepancy in the mixed dentition requires an accurate prediction of the mesiodistal width of the unerupted permanent teeth.[1]

Space analysis in mixed dentition can be grouped into three categories: (1) Use regression equations,[23] (2) radiographs,[2456] or (3) a combination of both methods.[789] Of all the mixed-dentition analysis, the regression equations based on already erupted permanent teeth are used most widely, especially the Moyers probability charts and Tanaka-Johnston equations.[10]

A simplified analysis proposed by Tanaka and Johnston[3] comes handy for chair side evaluation. Original Tanaka-Johnston analysis was done on a population of North European descent.[11] Thus, the accuracy of these predictive methods is questionable when applied to the Indian population. The objective this study was to evaluate the validity of Tanaka-Johnston method in predicting the size of unerupted permanent canines and premolars in children of Mumbai.

The present study, therefore, was conducted in Department of Paediatric and Preventive Dentistry, Nair Hospital and Dental College with following aims and objectives :

To determine the correlation between the sum of the mesiodistal widths of the permanent mandibular incisors and combined mesiodistal widths of the permanent mandibular and maxillary canines and premolar in Mumbai school children

To examine the applicability of Tanaka-Johnston method of prediction.

Materials and Methods

The study was carried out in Department of Pedodontics and Preventive Dentistry of Nair Hospital and Dental College, Mumbai. The sample for the study consisted of 300 children (147 boys and 153 girls) each within the age group of 12–15, studying in four Municipal Secondary Schools, Mumbai. Schools selected for the study were: West Byculla Municipal School, Shanti Nagar Municipal School, Agripada Municipal School, East Byculla Municipal School.

Inclusion criteria

Children with complete eruption of permanent mandibular incisors and permanent mandibular and maxillary canines and premolars

Children with a maximum age of 15 years to preclude any discrepancies based on significant proximal wear.

Exclusion criteria

Teeth with clinical evidence of hypoplasia or hypocalcification

Teeth with proximal caries, proximal wear restoration, or fractures

The subject with history of orthodontic therapy

Presence of dental anomalies

The presence of cross bite relationship, reverse curve of spee, attrition, or other abnormality.

Cast preparation

Alginate impressions were made using standard procedures for material mixing as recommended by the manufacturer. The impressions were rinsed in running water and were disinfected with 2% glutaraldehyde. The impressions were poured on the same day with a hard dental stone using the standard procedure for mixing. The dental casts were neither soaped nor waxed.

Measurement of teeth

The teeth were measured using a dial caliper accurate to 0.05 mm (Mitutoyo Corporation, Tokyo, Japan) shown in Figure 1. The largest distance between the contact points of the four mandibular incisors and the maxillary and mandibular canines and premolars was measured with the dial caliper held parallel to the occlusal plane and perpendicular to the long axis of the tooth. Inter- and intra-examiner variability was also calculated, and it was observed that correlation for inter-examiner variation was 0.95, and for intra-examiner, the correlation was 0.98.

Figure 1

Dial caliper

Statistical analysis

Descriptive statistics including the mean, standard deviation, and minimum and maximum values, range, and standard error were calculated and tabulated.

Results

Means, standard deviations, range, and standard error of the means for the sum of four lower mandibular incisors, sum of the lower canine and premolars, and the sum of the maxillary canine and premolars for the male, female, and combined were tabulated.

Comparisons of tooth size between the right and left sides

No significant difference was found between the mesiodistal diameter of the permanent canine and first and second premolars of the right and left sides. P value ranged from P = 0.675–0.786 showing a greater amount of similarity in size of both sides [Tables 1 and 2].

Table 1

Mesiodistal width of mandibular and maxillary teeth of males (in mm)

Table 2

Mesiodistal width of mandibular and maxillary teeth of females (in mm)

Male and female comparisons

The mesiodistal width of teeth in males was significantly larger than that of female [Tables 1 and 2].

Differences between the actual and predicted tooth size

Tables 3 and 4 show statistically significant differences observed between the measured values of children from schools of Mumbai and the Tanaka-Johnston prediction values for the mandibular and maxillary arches for males and females.

Table 3

Actual sum of mesiodistal width of teeth groups

Table 4

Comparison between actual and predicted values of combined widths of canines and premolars in male and female subjects

A good correlation between the actual and predicted values was found with greater deviation from the actual values in a mandibular arch in females [Table 4]. This being caused by the fact that Tanaka-Johnston analysis over-predicts the combined tooth sizes and that the teeth are smaller in females as compared to males. The mean difference between actual and predicted combined widths of canines and premolars was found to be 0.6 mm in maxilla and 0.7 mm in mandible in males, 1.1 mm in maxilla, and 2.4 mm in mandible in females.

Graphs 1 and 2 show the scatter diagram of comparison between actual and predicted values of combined widths of canines and premolars in male and female subjects

Graph 1

Scatter diagram of comparison between actual and predicted values of combined widths of canines and premolars in male subjects

Graph 2

Scatter diagram of comparison between actual and predicted values of combined widths of canines and premolars in female subjects

Discussion

Prediction of the mesiodistal dimensions of unerupted permanent canines and premolars during the mixed dentition is of clinical importance in diagnosis and planning treatment. Accurate estimation of the size of the canines and premolars allows the dentist to better manage tooth size/arch length discrepancies. However, great care must be taken to avoid letting numbers dictate the prediction of tooth size because dental arch perimeter may change with time. In addition, it is obvious that the best predictor tooth is the erupted antimere in the same patient, and the best estimate is from radiographs.[12]

Factors that affect tooth size are extrinsic as well as intrinsic. The intrinsic factors being heredity, race, sex. The extrinsic factors being caries, attrition, measuring methods of the mesiodistal tooth size which includes method of cast preparation, material used for cast preparation, instrument used for measurement of tooth size, and method of analysis of error.

Tanaka-Johnston analysis for predicting mesiodistal diameters of canines and premolars was based on Northern European children; the present study was performed to assess the test's precision among Mumbai school children.[13] The literature review showed that of all the three methods applied in mixed dentition analysis, Tanaka-Johnston's is widely used.[14] Young age group (12–15 years) was chosen for measurement to minimize the alteration of the mesiodistal tooth dimensions because of attrition, restoration, or caries.

Deciduous teeth are not used as predictors of the breadths of unerupted premolars and permanent canines because the relation between the breath of deciduous teeth and permanent teeth is weaker than that between the breaths of permanent teeth.[7] Furthermore, one or more of the deciduous teeth is often missing because of premature extraction or exfoliation. Most of the previous studies used mandibular incisors in their mixed analysis.[231516] Multiple advantages of using mandibular incisors in the mixed dentition analysis including early eruption, ease of measurement, least prone to caries, and fewer anomalies have been reported.[1718] The maxillary incisors were not used in any predictive procedures because they show too much variability in size and their correlations with other groups of teeth are of lower predictive values. The present analysis also showed a positive correlation (0.49 for mandibular and 0.43 for maxillary) between mandibular incisors and combined widths of mandibular and maxillary canine and premolars. These positive correlations in a series of teeth should, within certain limits, fairly accurately allow the calculation and prediction of the size of unknown components, e.g., unerupted or ectopically displaced teeth. The largest distance between the contact points of mandibular and maxillary incisors as well as mandibular canines and premolars was recorded using a calliper held parallel to occlusal plane and perpendicular to the long axis of the tooth,[13] the same method was used in this study. According to Staley and Kerber,[8] Staley and Hoag,[9] a dial caliper is the measurement instrument of choice.

Studies have found that male teeth to be larger than female teeth, sex differences in the mesiodistal tooth sizes, were greater in the permanent dentition than in the primary dentition and the largest sex difference was in the canines in both dentitions.[131719] Analysis of our data collected also revealed that on average, males had larger tooth size than females.

Conclusion

The mesiodistal width of teeth in males was significantly larger than that of female

There was a positive correlation between the combined mesiodistal width of mandibular incisors and mandibular and maxillary canines and premolars

The Tanaka-Johnston prediction method was not accurate for a sample of Mumbai School children.