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JIOS ORIGINAL RESEARCH 10.5005/jp-journals-10021-1281 Mesiodistal Crown Width Digital Ratio for Kerala Population: A Cross-sectional Survey Mesiodistal Crown Width Digital Ratio for Kerala Population: A Cross-sectional Survey 1 Sashi Bhushan Ekka, 2Koshi Philip, 3Chandresh Shukla, 4Rajesh Balani, 5Kartik Swamy ABSTRACT Source of support: Nil Introduction: The orthodontic examination may be incomplete without a careful analysis of the patterns of mesiodistal crownsize relationships. No published data are available regarding tooth size—arch length discrepancy (Bolton values) for Kerala population. Conflict of interest: None Aim: To establish Bolton’s values specific to Kerala population. Thus, this was done in order to determine Bolton’s anterior and overall and posterior ratio between males and females specific to Kerala population and compare it with Bolton’s values. Secondly to determine the values outside of 1 standard deviation (SD) and 2SD. INTRODUCTION Materials and methods: The sample for the present study consisted of 160 pretreatment study casts (Group A—75 male patients and Group B—85 female patients). Digital vernier caliper (Standard Digital Caliper Series: EC16) with a 0.01 mm resolution, ±0.02 mm accuracy and 0.01 mm repeatability, manufacturer specification) was used to measure the mesiodistal width of the teeth. Result: Mean anterior, overall and posterior ratios were found to be 77.32 ± 6.67; 91.78 ± 7.43; 1.07 ± 0.06 respectively. 93.8% of the sample had anterior ratio in 1SD and 3.8% in 2SD. 94.4% were in 1SD and 2.5% in 2SD for overall ratio. Conclusion: Although the means were nearly identical with those of Bolton’s study, ranges and SDs were significantly larger. This study indicates that the Bolton’s analysis can also be used on Indian or at least Kerala population but with increased standard deviation. Keywords: Bolton’s ratio, Kerala population, Digital vernier caliper, mesiodistal crown-size. How to cite this article: Ekka SB, Philip K, Shukla C, Balani R, Swamy K. Mesiodistal Crown Width Digital Ratio for Kerala Population: A Cross-sectional Survey. J Ind Orthod Soc 2014;48(4):375-381. 1,3,4 Senior Lecturer, 2Professor and Head, 5Reader 1,3,4 Department of Orthodontics and Dentofacial Orthopedics People’s College of Dental Science and Research Centre Bhopal, Madhya Pradesh, India 2 Department of Orthodontics and Dentofacial Orthopedics Government Dental College, Kottayam, Kerala, India 5 Department of Orthodontics and Dentofacial Orthopedics Kothiwal Dental College and Research Centre, Moradabad Uttar Pradesh, India Corresponding Author: Sashi Bhushan Ekka, Senior Lecturer Department of Orthodontics and Dentofacial Orthopedics People’s College of Dental Science and Research Centre Bhopal, Madhya Pradesh, India, Phone: 07554078030, e-mail: [email protected] Received on: 2/2/14 Accepted after Revision: 24/2/14 A task of the orthodontist is the alignment of teeth to improve the masticatory efficiency as well as the appearance of the face and the dental arches. For an ideal occlusion, the mesiodistal crown diameters of the teeth in both arches should correspond. Such a task may become frustrating in the presence of crown-size discrepancies. Research in this area has been limited to the determination of ratios indicative of how large the maxillary teeth should be in relation to their lower counterpart, which is further different for each population under examination. The orthodontic examination may be incomplete without a careful analysis of the patterns of mesiodistal crown-size relationships. Mesiodistal crown-size relationships are decisive variables in the search for (1) factors associated with the development of occlusal and facial irregularities, (2) the possible effects of discrepancies upon interdigitation during and after orthodontic treatment, and (3) the isolation of discrepant teeth of minor malocclusions that may be treated in part by selective mesiodistal grinding and minor tooth movement. To accomplish this task, the clinician should be able to analyze the largest possible number of crown-size relationships; that is, the relative size differences between a single tooth or groups of teeth regardless of their location in the dental arches. Although, in recent studies, variables, such as incisor inclination (Tuverson), upper incisor thickness (Halazonetis, Rudolph et al) and arch form (Braun), have been described as important factors to be considered in achieving an optimal occlusal relationship and efforts have been made to adopt Bolton’s analysis to these variations. The Bolton’s analysis is still a robust guideline for assessing the relationship of the upper to lower dentition. REVIEW OF LITERATURE One of the first investigators to become interested in the subject of tooth size was GV Black,1 he set up tables of mean The Journal of Indian Orthodontic Society, October-December 2014;48(4):375-381 375 Sashi Bhushan Ekka et al figures which are still important references today. Gilpatric2 (1923), Ballard3 (1944), Griewe4 (1949) also investigated on mesiodistal tooth dimension. Neff5 in 1949 arrived at an ‘anterior coefficient’ by dividing the sum of six anterior mandibular sum into six anterior maxillary sum. The range was 1.17 to 1.41. Bolton’s6,7 introduction of his analysis in 1958 included comparisons of total mesiodistal widths of dental arches up to the distal surfaces of the first molars, as well as segments of the arches. Bolton evaluated 55 cases with ‘excellent’ occlusions; 44 had been treated orthodontically without extractions and 11 were untreated. The following ratios were established by Bolton: Overall ratio = Sum of mandibular ‘12’ × 100 Sum of maxillary ‘12’ Anterior ratio = Sum of mandibular ‘6’ × 100 Sum of maxillary ‘6’ The overall ratio was calculated from the greatest mesiodistal measurements of the teeth in each arch. The anterior ratio was calculated from the greatest mesiodistal measurements of the six anterior teeth in each arch. He obtained an overall ratio of 91.3% ± 1.91% and an anterior ratio of 77.2% ± 1.65%. From Bolton’s results, it can be seen that there is a relatively small range in which tooth size ratios should fall to be able to achieve optimal occlusal relationships. Although his tables for anterior and overall tooth-size ratios are still used today, the Bolton method has some limitations.8,9 First, Bolton’s estimates of variation were underestimated because his sample was derived from perfect Class I occlusions. Second, although it was speculated that overbite, overjet, tip, torque, interincisal angle, and incisor thickness influenced ideal tooth-size relationships, no definite conclusions have been drawn regarding the effect of overbite, overjet, tip, interincisal angle, and incisor thickness on the accuracy of Bolton’s analysis. Third, the population and sex composition of Bolton’s sample were not specified. Fourth, the Bolton’s analysis cannot be used in extraction treatment. Because the ratio between arches of unequal lengths would not remain constant when premolars of approximately equal size are removed from each arch, Bolton’s overall ‘12’ ratio should not be used for predicting occlusion after removing four premolars. Beside this, other investigators who also investigated Bolton’s ratio are Stifter et al.10-48 Group B—85 female patients), belonging to the patients who were reported to the Government Dental College for treatment and clinically having full complement of teeth till the second permanent molars. The sample of 160 subjects for the study was selected as per the criteria laid down as follows: (1) All the permanent teeth till second permanent molar should be present, (2) no history of any previous orthodontic treatment, (3) all the teeth which are to be measured should be fully erupted and free of interproximal restoration, distortion, fractures and caries, (4) all the teeth which are to be measured should be free of occlusal or proximal attrition, (5) there should not be any form, size or number alterations present with the teeth, (6) all the subjects which are selected for the study range from 14 to 24 years and (7) Class I occlusion with mild or no crowding. Armamentarium used in the study: (1) 160 study models, (2) Fine tip marking pen and (3) Digital vernier caliper (Standard Digital Caliper Series: EC16) with a 0.01 mm resolution, ±0.02 mm accuracy and 0.01 mm repeatability, manufacturer specification) was used to measure the mesiodistal width of the teeth. The mesiodistal width of the teeth was measured with a digital vernier caliper adjusted to the greatest mesiodistal diameter (contact points) of teeth, parallel to the occlusal surface and perpendicular to the long axis16 (Figs 1 and 2). Overall and anterior ratios were determined as per the method introduced by Bolton. The posterior mandibular arch segment was divided by the posterior maxillary arch segment to obtain ‘posterior ratio’. Only 8 to 10 pairs of models were measured each day to prevent visual fatigue.49 For method error evaluation, 20 casts were selected at random, four weeks after the original measurements. The teeth were remeasured on these casts. The first and second measurements were compared statistically. Data were analyzed using computer software, statistical package for social sciences (SPSS) version 10. Data were expressed in its frequency and percentage as well as mean and SD. To elucidate the associations and comparisons between different parameters, Chi-square (χ2) test was used as nonparametric test. Unpaired student’s t-test was used to compare mean values between two gender groups. Paired t-test was employed to compare left and right side dimensions of tooth within each gender group. For all statistical evaluations, a two-tailed probability of value, < 0.05 was considered significant. RESULTS MATERIALS AND METHODs The sample for the present study consisted of 160 pretreatment study casts (Group A—75 male patients and 376 Error analysis showed no statistically significant values (p > 0.05) in measurement of initial and after a period of 4 weeks. When tooth size measurements were compared JIOS Mesiodistal Crown Width Digital Ratio for Kerala Population: A Cross-sectional Survey Fig. 1: Digital vernier caliper Fig. 2: Measurement of mesiodistal crown width (Tables 1 and 2) as a function of gender among the whole sample, there was no significant difference in male and female. Teeth measurements were most variable in maxillary arch than in mandibular arch and more variability was found in males than females. Bolton’s ratios were compared in males and females. The results (Table 3) showed no statistically significant difference in the mean Bolton’s anterior and overall ratios between males and females. Mean anterior ratios in the present study were found to be 77.44 ± 2.84 and 77.22 ± 8.64 for male and female respectively. Since no sexual dimorphism is evident, new anterior ratio calculated was 77.32 ± 6.67. Mean overall ratios in the present study were found to be 91.83 ± 2.49 and 91.74 ± 9.95 for male and female respectively. New overall ratio calculated was 91.78 ± 7.43. Mean posterior ratios in the present study were found to be 1.08 ± 0.06 and 1.06 ± 0.05 for male and female respectively. New posterior ratio calculated was 1.07 ± 0.06. Results from Table 4 showed that overall ratio is related to both anterior and posterior ratios with correlation coefficient of 0.904 and 0.183 respectively. This suggests that overall ratio is affected mainly by anterior ratio than posterior ratio. The second part of the study was done to find the values outside 1SD and 2SD (Table 5). Most subjects in all the groups had overall, anterior and posterior ratios within 1SD interval. It was found that 93.8% of the sample had anterior ratio in 1SD and 3.8% in 2SD. For overall ratio, 94.4% were in 1SD and 2.5% in 2SD. DISCUSSION It has been widely accepted that a correct maxillary and mandibular mesiodistal tooth size relationship is important for the achievement of proper occlusal interdigitation in Table 1: Mesiodistal width of maxillary teeth comparing male and female population Parameters of maxilla Mean (mm) ±SD Variance Mean (mm) ±SD Variance Mean ±SD (mm) Variance p-value t-value (comparing sex) 8.81 0.49 0.24 8.32 0.43 0.18 8.55 0.52 0.27 6.752 < 0.001 Left 8.79 0.44 0.19 8.28 0.46 0.21 8.52 0.51 0.26 7.181 < 0.001 Right 7.08 0.46 0.22 6.87 0.51 0.26 6.97 0.50 0.25 2.666 < 0.01 Left 6.88 0.45 0.20 6.72 0.56 0.31 6.80 0.52 0.27 2.031 < 0.05 Right 7.77 0.51 0.26 7.45 0.49 0.24 7.60 0.52 0.27 4.123 < 0.001 Left 7.67 0.49 0.24 7.40 0.45 0.21 7.53 0.49 0.24 3.665 < 0.001 Right 7.06 0.40 0.16 6.84 0.46 0.22 6.94 0.45 0.20 3.081 < 0.01 Left 7.12 0.37 0.14 6.85 0.49 0.24 6.98 0.46 0.21 3.935 < 0.01 Side Central incisor Right Lateral incisor Canine First premolar Second premolar First molar Male Female Total population Right 6.67 0.39 0.15 6.54 0.44 0.19 6.60 0.42 0.18 2.069 < 0.05 Left 6.59 0.43 0.18 6.48 0.45 0.20 6.53 0.44 0.19 1.606 > 0.05 Right 10.00 0.53 0.28 9.83 0.57 0.33 9.91 0.56 0.31 1.966 < 0.05 Left 9.91 0.57 0.33 9.77 0.63 0.40 9.84 0.60 0.36 1.388 > 0.05 Unpaired Student’s t-test was used to calculate the p-value The Journal of Indian Orthodontic Society, October-December 2014;48(4):375-381 377 Sashi Bhushan Ekka et al Table 2: Mesiodistal width of mandibular teeth comparing male and female population t-value (comparing sex) p-value Variance 0.38 0.14 4.131 < 0.001 5.37 0.33 0.11 3.991 < 0.001 0.16 5.86 0.40 0.16 3.665 < 0.001 0.39 0.15 5.87 0.39 0.15 2.922 < 0.01 6.49 0.48 0.23 6.60 0.46 0.22 3.182 < 0.01 0.16 6.50 0.40 0.16 6.63 0.42 0.18 4.406 < 0.001 0.45 0.21 6.92 0.44 0.19 7.01 0.45 0.21 2.698 < 0.01 0.45 0.20 6.91 0.50 0.25 6.97 0.48 0.23 1.629 > 0.05 Right 7.08 0.51 0.26 6.89 0.51 0.26 6.98 0.52 0.27 2.329 < 0.05 Left 0.52 0.27 6.93 0.53 0.29 6.99 0.53 0.28 1.575 > 0.05 Right 10.92 0.77 0.59 10.79 0.68 0.46 10.85 0.72 0.52 1.164 > 0.05 Left 0.67 0.45 10.72 0.80 0.64 10.84 0.75 0.56 2.247 < 0.05 Parameters of mandible Side Male Central incisor Right 5.50 Left Mean (mm) ±SD Female Variance Mean (mm) 0.34 0.12 5.26 5.47 0.31 0.09 Lateral incisor Right 5.98 0.36 Left 5.96 Canine Total population Variance Mean (mm) 0.37 0.14 5.37 5.28 0.32 0.10 0.13 5.75 0.40 0.37 0.14 5.79 Right 6.72 0.42 0.18 Left 6.78 0.40 First premolar Right 7.11 Left 7.04 Second premolar First molar 7.06 10.99 ±SD ±SD Unpaired student’s t-test was used to calculate the p-value Table 3: Mean, standard deviation and coefficient of variance comparing male and female population Parameters Male Female Total population p-value Mean ±SD Variance Mean ±SD Variance Mean ±SD Variance t-value (comparing sex) Posterior ratio 1.08 0.06 0 1.06 0.05 0 1.07 0.06 0 1.901 > 0.05 Anterior ratio 77.44 2.84 8.09 77.22 8.64 74.65 77.32 6.57 43.21 0.213 > 0.05 Overall ratio 91.83 2.49 6.18 91.74 9.95 98.96 91.78 7.43 55.16 0.071 > 0.05 Unpaired student’s t-test was used to calculate the p-value Table 4: Multivariate Pearson’s correlation analysis of different parameters for total population Parameters Posterior ratio Anterior ratio Posterior ratio 1 Anterior ratio 0.117 1 Overall ratio 0.183* 0.904** Overall ratio 1 *p < 0.05; **p < 0.01 the finishing stages of orthodontic treatment. Al Tamimi and Hashim50 also found no sexual dichotomy in Bolton’s ratios in a relatively small sample of 65 Saudi subjects. In contrast, Smith et al8 found that the males had larger Bolton’s ratios than females. However, these differences were small being much less than one standard deviation from Bolton’s sample. The sample was selected according to Angle’s Class I occlusion with mild or no crowding. It is demonstrated that clinically significant measurement errors can occur when Bolton’s tooth-size analysis is performed on casts that have more than 3 mm crowding.34 All the patients were Keralites, and between the ages of 14 and 24 years old. This age group was chosen to minimize the alterations of mesiodistal tooth dimensions of attrition, restoration or caries.36 Vernier caliper was selected as a measuring tool because it was 378 proved to be the most accurate method34,43,51 for measuring mesiodistal width of tooth on models. To minimize random and systematic errors, all measurements were performed by a single examiner. The results (Tables 1 and 2) showed that males had larger teeth than females. These results are in agreement with Richardson and Malhotra,12 Merz32 who found this in their study on Black North Americans. However, the findings did not substantiate the need for sexspecific standards. Maxillary tooth material was 8.31 mm larger than mandibular tooth material, which is in agreement with Gilpatric2, who calculated that total mesiodistal tooth diameters in the maxillary arch exceeded that in mandibular arch by 8-12 mm. The sum of the six maxillary anterior teeth exceeded the sum of the mandibular teeth by 10.25 mm. The mesiodistal dimensions obtained for the present sample were less than the data available from Dominician Americans,41 North American Caucasians8 and Negro.28 Bolton’s ratios were compared in males and females. The results (Table 3) showed that there is no statistically significant difference in the mean Bolton’s anterior and overall ratio between males and females. These results are in agreement with studies of Richardson and Malhotra,12 Nie and Lin,36 Araujo and Souki,43 Al-Tamimi and Hashim,50 Basarana et al,51 Paredes JIOS Mesiodistal Crown Width Digital Ratio for Kerala Population: A Cross-sectional Survey Table 5: Percentage distribution of posterior, anterior and overall ratio outside of SD Parameters –Outside SD (%) –SD 2 (%) –SD 1 (%) Mean (%) SD 1 (%) SD 2 (%) Outside SD (%) Posterior ratio 0 15 (9.4) 69 (43.1) 16 (10.0) 40 (25.0) 15 (9.4) 5 (3.1) Anterior ratio 1 (0.6) 2 (1.3) 72 (45.0) 2 (1.3) 78 (48.8) 4 (2.5) 1 (0.6) Overall ratio 1 (0.6) 1 (0.6) 70 (43.8) 3 (1.9) 81 (50.6) 3 (1.9) 1 (0.6) et al,47 and in disagreement with studies of Arya et al,24 Keene,28 Santoro et al41. It is important to note that the possibility of gender differences in tooth size discrepancies is different from differences in absolute tooth size. Lavelle11 showed that the total and anterior ratios were both greater in males than females. However, these sex differences were small, all being less than 1%. Smith et al8 found that males had larger ratios than females. However, these differences were small being much less than 1SD from Bolton’s sample. From the results of this study, similar ratios for males and females suggested that a gender difference in Bolton’s ratio is population specific. Since there was no sexual dimorphism evident in mean anterior and overall ratios, samples of genders were pooled together to form a single group with n = 160. Mean anterior ratios in the present study were found to be 77.44 ± 2.84 and 77.22 ± 8.64 for male and female respectively. Since no sexual dimorphism was evident, new anterior ratio calculated was 77.32 ± 6.67. The mean anterior ratio closely resembles Bolton6,7 mean of 77.2 and Crosby and Alexander27 of 77.5. The anterior ratio was not in agreement with Smith8 (79.6%) in White Americans, Paredes47 (78.32%) in Spanish population, Smith et al8 (80.5%) in South Americans, Smith et al8 (79.3%) in blacks, Santoro et al41 (78.1%) in Dominician Americans, Bernabe et al44 (78.09%) in Peruvians, Uysal and Sari46 (78.26%) in Turkish population. These results suggested that mean anterior ratio was least in Southern Kerala population followed by black, white and significantly larger in Hispanics. Mean overall ratios in the present study were found to be 91.83 ± 2.49 and 91.74 ± 9.95 for male and female respectively. New overall ratio calculated was 91.78 ± 7.43. Mean overall ratio as found in various studies, Bolton6,7 (91.3%), Crosby and Alexander27 (91.4%), Smith8 (92.3%) in White Americans, Paredes 47 (91.97%) in Spanish population, Smith et al8 (93.1%) in South Americans, Smith et al8 (93.4%) in blacks, Santoro et al41 (91.3%) in Dominician Americans, Bernabe et al44 (90.79-91.33%) in Peruvians, Uysal and Sari46 (89.88%) in Turkish population. These results suggest that mean overall ratio was least in Southern Kerala population followed by white, Hispanics, and largest in black. Mean posterior ratios in the present study were found to be 1.08 ± 0.06 and 1.06 ± 0.05 for male and female respectively. New posterior ratio calculated was 1.07 ± 0.06. The posterior ratio demonstrated the greatest population differences. The mean of present study resembles with black while white and Hispanics had lesser value of 1.04 and 1.05 respectively. The second part of the study was done to find the values outside 1SD and 2SD (Table 5). Studies defined the ratios outside 2SD from the Bolton’s mean as values indicating clinically significant tooth size discrepancies.21,32,44 While some other studies defined the ratios outside 1SD from Bolton’s mean44,52 because Bolton7 suggested that a value greater than 1SD from his mean indicated a possible treatment need. In the present sample, the frequency of tooth size discrepancy outside 1 or 2SDs from Bolton’s mean values was used to determine the clinical significance of tooth size imbalance. Most subjects in all groups had overall, anterior and posterior ratios within a 1SD interval. It was found that 93.8% of the sample had anterior ratio in 1SD and 3.8% in 2SD. For overall ratio, 94.4% were in 1SD and 2.5% in 2SD. In other studies, percentage values of 9.553, 1141, 13.434, and 15.346 for overall ratio and of 21.346, 22.927, 23.753, 2841 and 30.634 for anterior ratio have been reported in different patient population. Crosby and Alexander27 and Freeman et al34 defined a significant discrepancy as a value of more than 2SDs from Bolton’s mean. On the contrary, Othman and Harradine54 stated that Bolton’s SDs were not a good guide to the prevalence of a clinically significant tooth size discrepancy. For both overall and anterior ratios in the present study, means were nearly identical with those of Bolton’s study, although the ranges and SDs were significantly larger. This finding was consistent with the results of Crosby and Alexander,27 Freeman et al34 and Santoro et al41 and Arauzo and Souki43 used the ratios outside one standard deviation from Bolton’s mean as tooth size discrepancy. Crosby and Alexander27 used the ratios outside two standard deviations. Nie and Lin,36 Smith et al8 and Al-Omari et al53 means and SDs in their studies were larger than in Bolton’s study. The probable reason for these findings may be the types of population that constituted the samples. CONCLUSION In general, male crown measurements were slightly larger and showed a higher variability than the female measurements. The Journal of Indian Orthodontic Society, October-December 2014;48(4):375-381 379 Sashi Bhushan Ekka et al A higher variability was found in the maxillary teeth as compared to the mandibular teeth. Significant sexual dimorphism for anterior, overall and posterior ratios did not exist when they were compared among the whole sample. Mean anterior, overall and posterior ratios were found to be 77.32 ± 6.67; 91.78 ± 7.43 and 1.07 ± 0.06 respectively. 93.8% of the sample had anterior ratio in 1SD and 3.8% in 2SD whereas 94.4% were in 1SD and 2.5% in 2SD for overall ratio. Although the means were nearly identical with those of Bolton’s study, ranges and SDs were significantly larger. This study indicates that the Bolton’s analysis can also be used on Indian or at least Kerala Population but with increased SD. In clinical practice, attention should be paid to tooth size discrepancies between the maxillary and mandibular teeth and that Bolton’s analysis is important for orthodontic diagnosis and treatment planning that would improve achieving optimal occlusion, overbite and overjet. It should also be borne in mind that Bolton tooth size analysis might be of assistance in the finishing phase of orthodontic treatment, especially in increasing the stability of the treatment result. Although such an analysis in some instances may appear to be time-consuming, the benefits would seem to be significant. REFERENCES 1. Black GV. Descriptive Anatomy of Human Teeth. 4th ed. SS White, Philadelphia; 1902. 2. Gilpatric WH. Arch predetermination, is it practical? J Am Dental Asso 1923;10:553-572. 3. Ballard WL. Asymmetry in tooth size. A factor in the etiology, diagnosis and treatment of malocclusion. Angle Orthod 1944;14(3):67-71. 4. Griewe PW. Tooth size and asymmetry in the human dentition. 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