| Abstract|| |
Background and Aim: One of the important aspects of diagnosis and treatment planning in the mixed dentition is estimation of the size of unerupted permanent canines and premolars. One of the most commonly used the prediction methods are Tanaka and Johnston, which are based on data from a sample of Northern European descent children. The accuracy of this method when applied to a different ethnic population is questionable. The aim of this study was to determine the modified equations from Tanaka and Johnston for Iranian population.
Materials and Methods: This study was an analytic and cross-sectional investigation with the randomized cluster sampling in Ahwaz. Fifty four students of 14-18 years age (32 girls, 22 boys) were selected between 320 students and plaster models of their maxillary and mandibular arches were prepared. Subjects had fully erupted teeth, class I canine and molar relationship and presented no proximal caries or fillings, morphological anomalies, missing teeth or occlusal abrasion, and bruxism. The mesiodistal crown diameters of the permanent teeth were measured with using the sharpened boley gauge (accuracy 0.01 mm). The data were analyzed by using the regression correlation analyses and t-test.
Results: The size of permanent canines and premolars were larger in maxilla than mandible and males than females. These values in Iran were different from other countries.
Conclusion: In this study to predict the space (in mm) required for alignment of unerupted canine and premolars in Iranian children, halve the sum of mesiodistal dimension of the four mandibular incisors and add the respective constants 10.5 for upper jaw and 10 for lower jaw.
Keywords: Mixed dentition, space analysis, Tanaka and Johnston
|How to cite this article:|
Khanehmasjedi M, Bassir L. Prediction of the size of unerupted canines and premolars in an Iranian population. Indian J Dent Res 2013;24:493-7
One of the most important steps for diagnosis and treatment planning in mixed dentition is calculation and estimation of mesiodistal width of unerupted canines and first and second premolars and its comparison with the dental arch space. There are three basic approaches to doing this: (1) Measurement of the teeth on radiographs such as Nance Method. (2) Estimation from prediction tables such as Moyer's and Tanaka-Johnston's Method. (3) Combination of radiographic and prediction table methods such as Staley-Kerber Method.
|How to cite this URL:|
Khanehmasjedi M, Bassir L. Prediction of the size of unerupted canines and premolars in an Iranian population. Indian J Dent Res [serial online] 2013 [cited 2019 Jun 26];24:493-7. Available from: http://www.ijdr.in/text.asp?2013/24/4/493/118389
In Tanaka and Johnston method the mesiodistal width of lower incisors are used to predict the size of unerupted canine and premolars with two formula, y = 11 + X / 2 in maxilla and y = 10.5 + X / 2 in mandible. In this formula is the estimated width of canine and premolars in one quadrant and x is the sum of the mesiodistal width of four lower incisors. Despite a tendency to overestimate the size of unerupted teeth accuracy with this method is fairly good for the Northern European white children on whom the data is based on. No radiographs are required and it can be used for the upper or lower arch. 
In this study, the authors tried to obtain a linear equation for Iranian children, so that it can be used as easy and accurate method for estimation and space analysis in this region. The first attempt to estimate the size of the teeth was carried out by Black in 1897.  He presented the mesiodistal width of the teeth in a tabular format. In 1946, Sepiel for the first time estimated the unerupted permanent canines and premolars using erupted teeth.  In 1964, Moorrees and Reed, Invented a method for measuring the crown of primary teeth and permanent teeth; however, they finally reached to conclusion that using the radiography is the best way for determining the mesiodistal width of the teeth.  Ballard and Wylie in 1974 developed the formula x = (9.41 + 0.572) y using the calculation of dental casts in mixed dentition period for estimation of unerupted canines and premolars based on the width of lower incisors. In this formula, x is the sum of the width of canines and premolars and y is the sum of the width of the four lower permanent incisors. 
In 1982, Pitek based his calculations on the buccolingual width of the first permanent molar did not reach any conclusive result.  In 1973, Moyers presented a table for American white children based on the relationship between the size of permanent erupted incisors in the mandible and unerupted permanent canines and premolars in the maxilla and mandible. The size of the lower incisors correlates better with the size of the upper canines and premolars than does the size of the upper incisors, because upper lateral incisors are extremely variable teeth. The accuracy of this method for Northern Europe children is acceptable regardless of the fact that the sizes of the unerupted teeth have been overestimated.  In 1974, Johnston and Tanaka introduced the linear formulae y = 10.41 + 0.51 x in maxilla and y = 9.18 + 0.54 x in the mandible for prediction the size of unerupted canines and premolars based on lower permanent incisors. After rounding up and consideration of about 0.5 mm magnification the formula was y = 11 + X / 2 for the maxilla and y = 10.5 + X / 2 for the mandible.  In 1993, AL-Khadra investigated Tanaka-Johnston equation and Moyers prediction tables in Saudi Arabia. His findings were as follows: y = 7.2 + 0.63 x in the maxilla and y = 8.6 + 0.55 x in the mandible. The results of AL-Khadra's studies showed that level 35% in Moyers prediction table has the least error possibility in prediction of the required space for permanent canines and premolars in Saudi Arabia. 
In 1998, Yuen et al.  reached the formula y = 8.2 + 0.6 x for the maxilla and y = 7.5 + 0.6 x in the mandible for Chinese children residing in Hong Kong.  The present study was performed on Iranian children in order to estimate width of unerupted canines and premolars using the sum of the mesiodistal width of the four lower permanent incisors.
| Materials and Methods|| |
This study was an analytic and cross-sectional investigation with the randomized cluster sampling in Ahvaz. 54 students 14-18 years old (32 girls, 22 boys) were selected among 320 students who were Persian and from Khozestan province with parents of similar origin. Plaster models were prepared from both arches.
- Mandibular and maxillary canines and premolars should be fully erupted on both sides.
- The permanent incisors of the mandible should be fully erupted.
- Class I canine and molar relationship.
- The participants should be below 18 (14-18) to have the least proximal abrasion.
The teeth were measured using the boley gauge (Serial no. F259229) made in china with the precision of 0.01 mm and using the Seipele and Moorres method.  In this method, the largest mesiodistal width of the given teeth from mesial contact point to distal contact point measured while boley gauge is perpendicular to long axis of teeth. The beaks of the boley gauge were machine-sharpened to a fine taper to improve accessibility to the proximal surface of teeth, especially for the mesiodistal dimension. For higher precision, the mean of left and right sides were used for the statistical analysis. Data were analyzed with regression and correlation analysis and t-test (SPSS version 13). After 3 months, 10 study model randomly selected and re measured for random error with correlation analysis and there was no significant differences (r = 98.8%).
- Anomaly in size and shape of the teeth.
- Caries or amalgam filling especially on proximal surfaces.
- Orthodontic treatment history or tooth restoration.
- Missing teeth.
- Abrasion and bruxism.
| Results|| |
The mesiodistal permanent width of incisors, canines, and premolars are shown in [Table 1].
|Table 1: Range, mean, variance, interval confidence, max, min of total size in maxillary and mandibular teeth in both gender separately|
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The results indicates that the size of permanent canines and premolars are larger in the maxilla than mandible and males than females.
Estimation of unerupted canines and premolars width were determined by a regression equation of the form Y = A + B (x). In this equation, Y represent dependent variable or sum of the width of uneruped canine and premolars in each quadrant and x represent independent variable or sum of the mesiodistal width of the four mandibular incisors and A and B are constants.
The regression equations are follows:
TUCPM 1 PM 2 = Total upper canine and first and second premolars.
TLCPM 1 PM 2 = Total lower canine and first and second premolars.
FUCPM 1 PM 2 = Female upper canine and first and second premolars.
MUCPM 1 PM 2 = Male upper canine and first and second premolars.
FLCPM 1 PM 2 = Female lower canine and first and second premolars.
MLCPM 1 PM 2 = Male lower canine and first and second premolars.
TUCPM 1 PM 2 Y = 10.716 + 0.47 X
TLCPM 1 PM 2 Y = 8.615 + 0.539 X
MUCPM 1 PM 2 Y = 12.722 + 0.376 X
FUCPM 1 PM 2 Y = 10.229 + 0.497 X
MLCPM 1 PM 2 Y = 9.708 + 0.485 X
FLCPM 1 PM 2 Y = 9.555 + 0.505 X
B was suggested to be half.  In order to change the B (X) to 1/2 , in the maxilla and mandible, A was changed to 10.0395 and 9.5125 respectively. Then, 0.4605 mm was added to A in maxilla and 0.4875 in mandible in order to simplify the A and for 0.5 mm magnify the y values. Simplified equations were presented as follow:
TUC PM 1 PM 2 Y = 10.5 + X/2
TLC PM 1 PM 2 Y = 10 + X/2
The results of the standard error and correlation coefficients of the above equations are shown in [Table 2] and [Table 3].
|Table 2: Correlation coefficient and standard error for estimation of canine and premolars width in both gender and jaw separately|
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|Table 3: Standard error for A and B linear coefficient in canine and premolars in both gender and jaw separately|
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| Discussion|| |
Tanaka and Johnston method is a good way to use the width of the lower incisors to predict the size of unerupted canines and premolars. For children from a European population group, the method has good accuracy despite a small bias toward overestimating the unerupted tooth sizes. The method, however, is less accurate for another population groups and appear to have systemic errors for specific race. If the patient does not fit the population group, direct measurement from the radiographs is the best approach unless a modified equation from Tanaka-Johnston is available for that particular group or race. ,,
The results of this study showed that the size of canines, premolars, and incisors teeth are larger in males than females and maxilla than mandible, which is mainly due to larger canines in the maxilla. Results of this study are almost similar to other studies [Table 4].
|Table 4: Mean of size of canines and premolars and mandibular incisors in both jaw and comparison with different researches|
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In this study, correlation coefficients and regression in the maxilla and mandible were r = 0.68 and r = 0.691 respectively (P < 0.05), which is higher than many previous studies. Correlation coefficient lower than 0.5 is not acceptable and the obtained equations do not have the necessary precision for space estimation [Table 5]. Another factor that makes the estimation equation more precision is the standard deviation. The lower standard deviation leads to more precise equations. The standard deviation in this study was lower than previous studies [Table 6]. As shown in [Table 7], A and B are equal to previous studies. ,,,,,
|Table 5: Correlation coefficients for mandibular incisors with mandibular and maxillary canines and premolars in different researches|
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|Table 6: Standard error in different researches in both gender and jaw separately and total|
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| Conclusion|| |
In order to determine the relationship between teeth groups and using this correlations in Iranian children, the following relationships are true between the sum of mesiodistal width of lower incisors and the sum of mesiodisal width of upper and lower canines and premolars.
One-half of the mesiodistal width of the four lower incisors + 10.5 = Estimated width of maxillary 3, 4, 5 in one quadrant.
One-half of the mesiodistal width of the four lower incisors + 10 = Estimated width of mandibular 3, 4, 5 in one quadrant.
| Acknowledgments|| |
We thank research Deputy of Ahwaz Jundishapur University of Medical Sciences for approving and funding this research. We also appreciate Ali Rezaei for his corporation in this reaserch 
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Department of Pediatric Dentistry, Dental School, Ahwaz Jundishapur University of Medical Sciences, Ahwaz
Source of Support: Deputy of Ahwaz Jundishapur University of Medical Sciences, Conflict of Interest: None
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]