ORIGINAL RESEARCH Year : 2009  Volume : 20  Issue : 1  Page : 2630 Evaluation of Moyers mixed dentition analysis in school children Sujala Ganapati Durgekar, Vijay Naik Department of Orthodontics and Dentofacial Orthopedics, K.L.E's Vishwanath Katti Institute of Dental Sciences, KLE University, J.N.M.C. Campus, Nehru Nagar, Belgaum, Karnataka, India Correspondence Address: Background and Objective: The purpose of this study is to test the reliability of Moyers mixed dentition analysis in school children. Materials and Methods: A study was conducted on a sample of 150 school children within the age group of 13 to 16 years old who had all permanent teeth that were fully erupted. Dental impressions were taken with alginate impression material and immediately poured with dental stone. Mesiodistal dimensions of permanent mandibular incisors, maxillary and mandibular canines, and premolars were measured using a digital caliper with a resolution of 0.01 mm. Statistical Analysis: The coefficient of correlation (r) was calculated to find the correlation between the sums of the canine, premolars in both arches, and mandibular incisors. A Student«SQ»s unpaired t test was calculated to compare the tooth dimension between male and female subjects. The actual measurements were compared with the predicted values obtained with the Moyers prediction tables at the 35^{ th} , 50^{ th} , and 75^{ th} percentile confidence levels. A Student«SQ»s t test was calculated to compare the actual and predicted values. Using this data, linear regression equations were formulated for tooth size prediction. The coefficient of determination [r2] was calculated to find the accuracy of the formulated prediction equations. The standard error of estimate (SEE) was calculated to determine the validity of the proposed equations. Results: Moyers prediction tables are not an accurate method to estimate tooth dimension in our samples. The mesiodistal crown dimension in the buccal segment of the mandibular arch was larger in males (p=0.04) than in females. Conclusion: The differences noted between predicted values from the Moyers tables and that of the present investigation is the result of racial and ethnic diversity. The accuracy of the prediction equation should be tested in a larger sample.
Materials and Methods Four public schools with a total population of 800 adolescent children (aged 1316 years old) from the city of Belgaum were selected for this study. The Lingayat community has a rich cultural heritage and racial mixing is limited in this population due to strong family bonds. Students belonging to the Lingayat community were taken from their respective classrooms to a specially equipped room where oral examinations were conducted. A total of 325 subjects fulfilled the selection criteria. Criteria for the selection of the subjects were as follows: All permanent teeth (with the exception of second and third molars) should be present and fully erupted in both the maxillary and the mandibular arches.No congenital craniofacial anomalies or previous history of orthodontic treatment.Intact dentition with no proximal caries, restorations, or agerelated attrition.Parents of the subject should belong to the Lingayat community. To facilitate accurate measurements, only subjects with an arch length discrepancy of ±2 mm were included. From these 325 subjects, 150 subjects (75 males and 75 females) were selected. After achieving ethical clearance, informed consent was obtained from each selected subject. Dental impressions were taken with irreversible hydrocolloid alginate impression material (Tropicalgin) and immediately poured with dental stone (Goldstone Class III) to avoid any dimensional changes. The mesiodistal dimensions of the mandibular permanent central and lateral incisors, the maxillary and mandibular permanent canines, and the first and second premolars were measured using a digimatic caliper [Figure 1] (Mitutoyo) with a resolution of 0.01 mm. [5] Values obtained from the right and left posterior segments were averaged so that there would be one value for the maxillary canine and premolars and one value for the mandibular canine and premolars. For measurement reliability, teeth were measured manually and independently by two investigators. The two measurements obtained were compared and if they varied by 0.2 mm or less, the values were averaged. [3],[4],[6] In instances where the measurements varied by more than 0.2 mm, the teeth were remeasured and the nearest 3 measurements were averaged. Statistical Analysis Descriptive statistics, including the mean, standard deviation, and minimum and maximum values were calculated [Table 1]. The coefficient of correlation (r) was calculated to find the correlation between the sums of canine and premolars in both arches with that of the sum of mandibular incisors [Table 2]. A Student's unpaired t test was calculated to compare tooth dimensions between male and female subjects. The actual measurements were compared with the predicted values obtained with the Moyers probability tables at the 35 th , 50 th , and 75 th percentile confidence levels [Table 3],[Table 4],[Table 5],[Table 6]. A Student's t test was calculated to compare the actual and predicted values at the 35 th , 50 th , and 75 th percentile confidence levels [Table 7]. These data were then used to develop regression equations. y = a + bx a and b are regression coefficients y = summed width of mandibular incisors x = summed width of canine and premolars The coefficient of determination (r 2 ) was calculated to determine the accuracy of the formulated regression equations. The standard error of estimate (SEE) was calculated to determine the validity of the proposed equations and compared with reports of various investigators [Table 8]. Results Moyers prediction tables are not an accurate method to estimate tooth dimension in our samples. There is a variation in the mesiodistal tooth dimensions among males and females. Mesiodistal crown dimension in the buccal segment of the mandibular arch is larger ( p0 =0.04) in males than in females. With the help of the data obtained, new regression equations were derived separately for male and female subjects to be used to predict tooth dimension. Male: Maxilla  Y = 10.52 + 0.48x Mandible  Y = 9.46 + 0.50x Female: Maxilla  Y = 11.73 + 0.41x Mandible  Y = 11.67 + 0.39x Discussion The size of the teeth is related to genetics (e.g., gender and ethnicity) and environment. Racial and genderspecific mixed dentition space analyses requires revision or validation once every generation (approximately 30 years) because of changing trends in malocclusion and tooth size. [7],[8],[9],[10],[11],[12] The accurate width of an unerupted tooth is important for correct diagnosis of a case. Neither overestimation nor underestimation of width should be done for accurate treatment plan. This study reveals that the Moyers charts at the 75 th percentile confidence level overestimates tooth dimension; whereas, the 35 th percentile confidence level underestimates [Table 3],[Table 4],[Table 5],[Table 6] the size of the buccal segment in this population. When actual values were compared with Moyers chart at the 50 th percentile, it showed varied results. In males, the 50 th percentile overestimated tooth dimension in the mandibular arch [Table 3] but underestimated tooth dimension in the maxillary arch [Table 4] when the sum of the incisors was less than 24 mm. In females, the 50 th percentile underestimated tooth dimension in the mandibular arch [Table 5] when the sum of the incisors was less than 23.5 mm. Definite racial and ethnic differences are evident with regard to tooth size. This is clearly reflected by the differences seen in the data obtained in this study and that of Moyers probability tables. [Table 7] shows that there is a statistically significant difference in tooth dimension between the actual and predicted values at the 75 th (P=0.014) and 35 th (P=0.003) percentile for males and females, respectively in the mandibular arch. Accurate treatment planning in management of mixed dentition cases is of great importance. But if predicted values of the width of the canines and premolars itself is wrong, the whole treatment may be a failure. A difference of ±2 mm per arch between the predicted width and the actual width is clinically significant as it effects extraction decisions in patients with moderate crowding (47 mm) in the mixed dentition. Permanent teeth may be either inappropriately retained or extracted on the basis of such an inaccurate tooth width prediction and the whole treatment plan may be a failure. To utilize the Moyers probability tables, the sum of mesiodistal width of the lower incisors is measured and the number is used to predict the size of both the lower and upper combined width of the canines and premolars. [2] The mandibular incisors have been chosen for measuring, since they are erupted first in the mouth early in the mixed dentition, are easily measured accurately, and are directly in the midst of most space management problems. [2] The maxillary incisors are not used in any of the predictive procedures since they show too much variability in size, and the correlations with other groups of teeth are of lower predictive value. Therefore, the lower incisors are measured to predict the size of the upper as well as lower posterior teeth. The moderately high degree of linear correlation between the sum of the mandibular incisors and maxillary and the mandibular buccal segments for male subjects (r = 0.74, 0.62 in maxillary and mandibular arches, respectively) and female subjects (r = 0.50, 0.61 in maxillary and mandibular arches, respectively) makes it possible to predict the width of unerupted teeth. The use of digital calipers with a standard error of ±0.03 mm have been shown to be more accurate methods of measuring mesiodistal tooth dimension on dental study models; hence, they were chosen for this study. [13] The excellent measurement accuracy reduced the possibility of introducing systemic and random errors in measurements. [Table 1] shows that male subjects have statistically larger mesiodistal tooth dimension in the mandibular arch ( p0 =0.04) than female subjects. The difference in mesiodistal tooth dimension of the canines and premolars between both genders in the maxillary arch was not statistically significant ( p0 =0.125). Many authors [14] found similar results although many others do not differentiate the genders when predicting mesiodistal diameters of these teeth. [1],[2],[3],[15],[16],[17],[18],[19] As shown in [Table 2], males show the highest r 2 (0.56) value for the maxillary buccal segment. This shows that the prediction equation of the maxillary arch for male subjects is more precise. Female subjects have the lowest r 2 (0.25) value for the maxillary arch, which implies that the prediction equation is least precise for the maxillary arch in female subjects. In a similar study, Godfrey, et al. [20] obtained lower r 2 values (0.29 for maxillary teeth and 0.34 for mandibular teeth in males; 0.39 for maxillary teeth and 0.42 for the mandibular arch in females). In another similar study conducted on subjects in Southern Thailand, r 2 values were 0.46 and 0.47 for maxillary and mandibular teeth, respectively. The differences in the sets of r 2 of these studies might be attributable to the effects of different sample sizes and ethnic mixes. [21] An investigation was conducted in the Department of Orthodontics, College of Dental Surgery, Manipal to evaluate the applicability of Moyers mixed dentition space analysis for the south Indian population. The samples were taken from 50 male and 50 female subjects. Teeth were measured using a fine gauge calibrated to 0.1 mm. Results showed that 35% is more accurate than 75% level of probability as suggested by Moyers. [22] Measuring the radiographic width of unerupted teeth is one of the methods used to predict the width of unerupted teeth, but it is not possible to obtain due to the rotation of teeth or poor intraoral films. High quality films and a meticulous radiographic technique are essential for minimal error. The use of regression equations is a simple and relatively accurate method for predicting the mesiodistal width of teeth. Due to the possible influence of racial and ethnic differences, this proposed method must be tested in other samples to confirm its applicability and consistency. Conclusions Moyers prediction tables were not accurate when applied to our sample. The differences noted between predicted values of the Moyers tables and those of the present investigation are the result of racial and ethnic diversity.Tooth dimension shows sexual dimorphism. Mesiodistal crown dimension in the buccal segment of the mandibular arch is larger in males than in females.The simplified equations proposed are easy, practical, and precise non radiographic methods for predicting the mesiodistal width of unerupted teeth. References


