ORIGINAL RESEARCH Year : 2021  Volume : 32  Issue : 2  Page : 162166 Applicability of moyer's probability tables in north indian population of 1618 years old Manu Sharma^{1}, Sanjay Chachra^{1}, Abhishek Dhindsa^{1}, Samriti Bansal^{1}, Taranjot Kaur^{1}, Alpna Sharma^{2}, Gurpreet Kour^{1}, ^{1} Department of Paedodontics and Preventive Dentistry, Swami Devi Dyal Hospital and Dental College, District Panchkula, Haryana, India ^{2} Department of Paedodontics and Preventive Dentistry, Institute of Dental Sciences, Jammu, Jammu & Kashmir, India Correspondence Address: Aims: To determine the applicability of Moyer's probability tables in North Indian population of 16–18 year olds and to formulate a new regression equation for the same group of population. Setting and Design: Evaluative Study. Methods and Material: 1000 children aged 16–18 years were selected as sample for the measurement of mesiodistal widths of permanent mandibular incisors, maxillary and mandibular canines and premolars using study models. The recorded values were then subjected to statistical analysis. Statistical Analysis Used: Software Package for Social Sciences (SPSS) software version 22.0. Results: The actual widths of the canine and premolars showed highly significant differences in maxilla and in mandible (P < 0.001), compared to widths predicted by Moyer's probability table at 75^{th} percentile. Conclusion: Moyer's mixed dentition analysis was not an accurate method for prediction in North Indian population as it showed overestimation of tooth sizes. Hence, new regression equation has been formulated for the same.
Introduction The development and guidance of eruption of the deciduous and permanent dentitions is an essential component to help in the proper growth and development of the orofacial structure. This aids to maintain a harmony between function and aesthetics.[1] During the mixed dentition phase, both the primary and permanent teeth are present in the dental arch simultaneously and malocclusion if surfacing is usually seen during this time.[2] At this stage the role of dentist is crucial as he is able to give an accurate diagnosis and treatment of any developing malocclusions which can be achieved with a proper space analysis during mixed dentition period.[3] One commonly encountered condition is the discrepancy between space available and the space required which helps in the proper eruption pattern of the permanent canines and premolars. So, for a proper space management, it becomes necessary to predict the discrepancies between tooth size and arch length which can be achieved with a mixed dentition analysis.[4] For this prediction most commonly used and accepted methods are: radiographic and nonradiographic methods. Radiographic methods require measurements of erupted teeth on study casts and unerupted and erupted teeth on radiographic images. Disadvantage of radiographic method is exposure of child to radiation that is why non radiographic methods are preferred more. Among the nonradiographic methods, Moyers' analysis is often preferred which uses a probability chart and with the help of this chart we are able to anticipate the mesiodistal diameter of the unerupted permanent canines and premolars in both arches. The chart uses the sum of mesiodistal diameters of the mandibular incisors, and for each sum obtained, there is a standard predicted value for unerupted canines and premolars for each arch. The accuracy of this method has been shown to be dubious when used for specific population other than white, because it is already well known that there is considerable variation in tooth sizes between racial groups. Succeeding generations showing a secular trend towards increased tooth sizes is noted too. This entails that values used from probability charts developed keeping the specific population in mind, might underestimate or overestimate the tooth sizes of population belonging to various ethnic, secular trends, etc. Therefore, the purpose of the study was to formulate a new regression equation for North Indian population after verifying the applicability of Moyers probability tables in the same population. Methods The study was conducted to establish a new regression equation for the North Indian Population in the age group 1618 years after verifying the applicability of Moyers probability tables in the same population. From a total of 12 districts in Himachal Pradesh, schools from 6 random districts were selected out of which sample was derived. After ethical clearance from institution vide letter number SDDETH/15/01, permission was taken from the school authorities/Principal and children's parents/guardians. Dental study models were made of 1000 subjects in the age group 16–18 years, which fulfilled the inclusion criteria which were selected by simple random sampling and were designated as sample. The inclusion criteria selecting the sample was as follows: Subjects in which mandibular and maxillary permanent canines and premolars and mandibular permanent incisors, were fully erupted.Subjects with no or minimal crowding and without any previous orthodontic treatment.Subjects without any previous surgical dental history (fractures, bone plating or wiring etc). Subjects who showed noticeable loss of tooth material were excluded from the study. The mesiodistal width of specified teeth was obtained by measuring greatest width between contact points on the proximal surfaces. A sliding digital Vernier caliper accurate to within 0.01 mm was used to carry out all measurements [Figure 1]. The teeth measured were the maxillary and mandibular permanent canines, first and second premolars and mandibular permanent incisors. Values obtained for the right and left caninepremolars segments were averaged so that there was one value for the maxilla and one value for the mandible for each value of the sum of mandibular incisors. To better adjust for interdental spaces, the beaks of the caliper were held at the greatest mesio distal diameter of the tooth i.e., contact points which was held parallel to the occlusal surface of the tooth and perpendicular to the long axis of the tooth.{Figure 1} Statistical analysis The data was subjected to statistical analysis using Statistical Software Package for Social Sciences (SPSS) software version 22.0. Descriptive analysis, Pearson correlation, Wilcoxon signedrank test were used. Level of significance was set at P < 0.05. Results For the sum of four mandibular incisors, sum of the lower canine and premolars, and the sum of the maxillary canine and premolars for boys and girls combined means, standard deviations and standard error of the means were tabulated. Comparisons of actual tooth sizes between right and left sides Results showed that in maxilla correlation between right and left sides was 0.937 with a P value of 0.000 [Table 1].{Table 1} Results showed a correlation of 0.909 between right and left sides of mandible with a P value of 0.000 [Table 2].{Table 2} Boys and girls comparison Preliminary results indicated that differences predicted between the sexes were not statistically significant. So no separate prediction equations were formulated for boys and girls. Differences between the actual and predicted tooth size Comparison between the predicted results and the measured results for maxilla showed a correlation of 0.391 which was statistically significant with the 'P value of 0.000'. For mandible the correlation was calculated to be 0.557, which was also statistically significant [Table 3].{Table 3} This showed that the Moyer's probability tables at 75th percentile did not accurately predict the mesio distal width of unerupted canines and premolars and exhibited overestimation when the predicted values were compared with the actual sum of permanent canine and premolars. [Table 2] and [Table 3] show comparison of maxillary and mandibular, right and left sides for bilateral symmetry, respectively. Formulation of correlation coefficient (r) and Regression equation For the present study, the correlation 'r' between the mesiodistal widths of the mandibular permanent incisors and maxillary canine and premolars was calculated as 0.416 while correlation between the mesiodistal widths of mandibular incisors and the mandibular canine and premolars was calculated as 0.551, using Pearson correlation. 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 For maxilla: Y = 16.585 + 0.274(x) For mandible: Y = 14.496 + 0.366(x) Discussion Black (1897) was the first person to realize the significance of diagnosing the tooth size to arch size discrepancy during the mixed dentition phase. Unfortunately, the results of the attempts made by him were not validated as there was too much variability between the dimensions of teeth amongst individuals. To overcome the shortcomings several researchers like Hixon (1958), Moyers (1973, 1988), Tanaka (1974), Staley (1984) developed various methods for predicting the size of unerupted teeth.[5] Environmental and genetic factors mainly affect the tooth size and morphology. Other factors such as race, heredity, secular changes and bilateral asymmetry contribute to variations in permanent teeth.[6] Moyer's prediction tables were formulated at the University of Michigan. The prediction tables were based on North American Caucasian children. The mesiodistal dimensions can be easily predicted using Moyer's charts, which makes it popular and clinically attractive. Worldwide studies have been performed on Arabian,[7] Brazilian,[8] Chinese,[9] German,[6] Nepalese,[10] Peruvian,[11] Senegalese,[12] Italian,[1] Iranian,[13] Pakistani,[14] Jordanian,[15] Thai,[16] Turkish,[17] Ugandan[18] and Malaysian[19] populations to test the applicability of Moyers' analysis. These studies showed wide variability in the applicability of Moyers' at various percentiles. Thus, the study was aimed at verifying the applicability of Moyers mixed dentition analysis in the North Indian population of the age group 1618 years. Moorrees and Reed method has been used to measure the width of crowns i.e., by measuring the greatest mesiodistal crown width of each tooth measured between its contact points, with the sliding caliper placed parallel to the occlusal and vestibular surfaces. The purpose of this study was to check the applicability of Moyer's probability tables in the North Indian population of 16–18 year olds. The Moyer's probability tables at 75th percentile did not accurately predict the mesiodistal width of unerupted canines and premolars and exhibited overestimation when the predicted values were compared with the actual sum of permanent canines and premolars. Similar results showing overestimation of results were seen in studies conducted by Dasgupta B (2012)[20] in Bengali population, Durgekar and Naik (2009)[21] in Belgaum and Goyal R K (2014)[22] in Lucknow, whereas, underestimation of results was seen in studies conducted by Thimmgowda U (2012)[23] in Bangalore, Singh V et al. (2013)[24] in Sundernagar, Himachal Pradesh, Priya and Munshi (1994)[25] in South Indian population and Philip et al. (2010)[4] in Punjabi population. An average of the sum of right and left canine premolar segments were taken in both the maxillary and mandibular segments. The paired t test was used to compare the right and left individual difference in mesio distal diameter for the whole sample (N = 1000). Significant bilateral difference (P = 0.000) was seen for all the teeth in both maxilla and mandible. A number of researchers have studied the correlative relationships between groups of teeth in permanent dentition. Very high correlations exist between left and right groups of teeth in the same arch. The degree of association between the antimeres was very high in a study by Moorrees and Reed (1964), which differed with the present study. In another study by Otuyemi and Noar (1996) no left right side differences were observed. From the present study, it was concluded that Moyer's mixed dentition analysis did not accurately predict the values of unerupted canine and premolars in North Indian population and hence a new regression equation was formed. However, more regional studies with larger sample size are required in a country like India where ethnic and racial diversity is high. Conclusion The predicted values of the unerupted canine and premolars were larger as compared with measured values from the study casts. So it was concluded that Moyer's method over estimates the combined mesiodistal widths of canine and premolars in both maxillary and mandibular arches, when used in the North Indian population of 1618 years old.The correlation coefficient between the mandibular permanent incisors and the maxillary canine – premolar segments was 0.416 and for mandibular canine – premolar segments was 0.551 and new regression equations were formulated.The present study gave us the prediction equations which can be used for mixed dentition space analysis in North Indian population.On reviewing the literature it is can be concluded that there is a definite need for more regional studies required in a country like ours where ethnic and racial diversity is too high as India has more than two thousand different ethnic groups and is ranked 17th in the world for ethnic and cultural diversity. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest. References


