Reliability of Various Study Model Indices in an Adult Population of North Karnataka

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1 /jp-journals ORIGINAL ARTICLE JIOS Reliability of Various Study Model Indices in an Adult Population of North Karnataka 1 Renuka Lalit Pawar, 2 Vijay P Jayade ABSTRACT Objective: To check the reliability of various study model indices viz Ponts, Bolton s, Howes, Peck and Peck Index and Korkhaus Index. Materials and methods: Study models of male and female subjects between the age range of 18 and 26 years with normal Class I occlusion and an overjet or overbite < 3 mm and a crowding or spacing of < 2 mm were selected. Index values calculated were subjected to statistical comparison with earlier studies. Results: Significant differences were observed for the most of the variables with Ponts, Howes, Peck and Peck Index and Korkhaus Index. No significant differences were observed between the original Bolton study and the present study. Conclusion: It was observed that Ponts Index was least reliable while Bolton s Index proved to be a useful clinical guide. Keywords: Study model index, Ethnic differences, Sexual dimorphism. How to cite this article: Pawar RL, Jayade VP.. J Indian Orthod Soc 2013;47(4): INTRODUCTION Study models were the first diagnostic records used in orthodontic diagnosis and treatment planning. Many authors have introduced different indices to assess the relationship between the teeth and respective arch dimensions and in between the arches. 1-5 Some investigators have been impressed by the predictive values of these indices and have supported its use. 6-9 While others critically analyzed the validity of these indices Ethnic variations in the genesis of malocclusion have also been emphasized hence any index developed for a particular ethnic group cannot be applied as such, to another group without studying the relevant parameters of the latter There have been earlier attempts to establish values for some indices for the Indian population However, to our knowledge there has been no attempt to comprehensively study all the commonly employed indices. The present study is aimed to check the validity of these indices in an adult population of North Karnataka viz Pont s Index, Howes Analysis, Bolton s Index, Peck and Peck Index, Korkhaus arch length Index and Palatal height Index. 1 Professor and Head, 2 Former Professor and Head 1 Department of Orthodontics and Dentofacial Orthopedics, School of Dental Sciences, KIMSU, Karad, Maharashtra, India 2 Department of Orthodontics, SDM College of Dental Sciences Dharwad, Karnataka, India Corresponding Author: Renuka Lalit Pawar, Professor and Head Department of Orthodontics and Dentofacial Orthopedics, School of Dental Sciences KIMSU, Karad, Maharashtra, India, drrenukapawar@hotmail.com Received on: 31/5/12 Accepted after Revision: 5/12/12 AIMS AND OBJECTIVES 1. To study the validity of indices for adult population of North Karnataka 2. To correlate the various indices 3. To discuss the advantages and disadvantages of various study model indices. MATERIALS AND METHODS An original study on study models was carried out in an available adult population of North Karnataka. Study models of 47 males and 47 females subjects were obtained after a strenuous search and the readings were recorded from this population of the North Karnataka state. Inclusion Criteria 1. Subjects in the age group between 18 and 26 years with full complement of teeth 2. Dental occlusion with Class I molar and canine relation with an overjet or overbite < 3 mm 3. Cases with minimal rotations, slipped contacts, crowding or spacing in each jaw up to 2 mm were selected 4. Acceptable facial profile. Exclusion Criteria 1. Teeth with carious lesions or broken contacts 2. Poor oral hygiene 3. Subjects with previous history of orthodontic treatment. Armamentarium used 1. Masel dial caliper ( ) with a minimum reading up to 0.1 mm. Measurements were taken in four different ways (inside, outside, depth and step). The Journal of Indian Orthodontic Society, October-December 2013;47(4):

2 Renuka Lalit Pawar, Vijay P Jayade 2. Korkhaus 3D divider (Dentaurum ). 3. Metallic scale and finely pointed lead pencil. All measurements and observations were made on plaster models in accordance with the methods prescribed by the author s involved. 1-5 All the index values were calculated for the 47 males and 47 females casts and tabulated separately. All casts were measured thrice to minimize errors and only the average of the values was included in the data. RESULTS Pont s Index The mean index values obtained for the present study are as follows: The mean ratio values (index values) showed non significant differences between the two sexes (Table 2B). Nonsignificant differences were observed between the original Bolton study 2 and the present study for anterior ratio in both sexes (Table 2A). For the overall ratio significant differences were observed for the females (p < 0.05) only and the males showed no significant differences. Highly significant differences (p < 0.01) were observed in the mean values of anterior and overall ratios between the present study and the earlier Indian study 29 (Table 2C). Howes Index The index values for the present study are as follows: Premolar index SD Molar index SD Significant differences were observed for anterior arch width, posterior arch width, and sum of incisor values (Table 1A) between the two sexes. However, mean ratio values for premolar and molar indices showed no significant differences. Comparison of present study with the earlier Indian study conducted at Manipal, 27 (Table 1B) showed significant differences to sum of incisor value (p < 0.01) both for males and females and anterior arch width (p < 0.01) and posterior arch width (p < 0.05) in case of females only and no significant differences with males. Mean index values differed significantly for both males and females. Bolton s Index Bolton values for the present study are as follows: Anterior ratio SD Overall ratio SD Bicuspid ratio (Maxilla) SD Basal arch width ratio (Maxilla) SD Basal arch length ratio (Maxilla) SD Bicuspid ratio (Mandible) SD Basal arch width ratio (Mandible) SD Basal arch length ratio (Mandible) SD Comparison between males and females in the present study (Table 3C) showed statistically significant differences both in maxilla and mandible for the following variables namely, total tooth material, premolar distance, premolar basal arch width, premolar basal arch width ratio and basal arch length ratio. Significant differences between the sexes were observed for premolar distance ratio in the mandible and basal arch length in the maxilla. While no significant differences were observed for premolar distance ratio in maxilla and basal arch length in mandible. Table 1A: Comparison of Pont s index between males (n = 47) and females (n = 47) in the present study Variables Sex Mean SD Range Z-value Sum of M upper incisors F ** Anterior M arch width F * Posterior M ** arch width F Premolar M index F NS Molar M index F NS **Highly significant where p < 0.01; NS: Not significant; *Significant where p < 0.05; NS: Not significant 444

3 JIOS Table 1B: Comparison between present study with an earlier Indian study (Manipal) Variables Mean SD Z-value Sum of (n = 47) ** incisors Earlier study (n = 50) (n = 47) ** Anterior (n = 47) NS arch Earlier study (n = 50) width (n = 47) ** Posterior (n = 47) NS arch Earlier study (n = 50) width (n = 47) * **Highly significant where p < 0.01; *Significant where p < 0.05 Comparison of present study with Howes study (Tables 3A and 3B). In case of males, significant differences were observed both in maxilla and mandible for the total tooth material and basal arch width. Significant differences existed in the maxilla only for bicuspid ratio while in the mandible differences existed for basal arch width ratio, basal arch length, basal arch length ratio. Nonsignificant differences were observed both in maxilla and mandible for bicuspid distance, for bicuspid ratio only in the mandible, and for basal arch width ratio, basal arch length and basal arch length ratio in the maxilla. In case of females, significant differences were observed both in maxilla and mandible for total tooth material, bicuspid distance, bicuspid ratio, basal arch width, basal arch width ratio and basal arch length. Significant differences existed in the mandible for the basal arch length ratio. While nonsignificant differences were observed for basal arch length ratio in the maxilla between the females of present study and Howes study. 3 Comparison with the earlier Indian study 27 showed significant differences for all the variables (Table 3D). The mean values obtained for the present study were higher than the earlier Indian study. Peck and Peck Index Shape ratio obtained for the present study is as follows: Central incisor SD Lateral incisor SD In the present study, significant differences were observed for the tooth shape ratios for the well aligned central and lateral incisors between the two sexes (Table 4B). Significant differences were observed for the shape ratios between the present study and the original Peck and Peck study 4 (Table 4A). Table 2A: Comparisons of mean ratio values of males and females with earlier Bolton s study Mean SD Range Z-value Anterior (n = 47) NS ratio Bolton s study (n = 55) (n = 47) NS Overall (n = 47) NS ratio Bolton s study (n = 55) (n = 47) * *Significant at p < 0.05; NS: Not significant Table 2B: Comparison between males and females in the present study Variables Sex Mean SD Z-value Total tooth M ** material (maxilla) F Total tooth M ** material (mandible) F Anterior tooth M ** material (maxilla) F Anterior tooth M ** material (mandible) F Bolton s M NS anterior ratio F Bolton s M NS overall ratio F Table 2C: Comparison of present study with the earlier Indian study (Manipal) Variables Mean SD Z-value Anterior (n = 47) ** ratio Manipal study (n = 50) (n = 47) ** Overall (n = 47) ** ratio Manipal study (n = 50) (n = 47) ** NS: Not significant; **Highly significant at p < 0.01 The Journal of Indian Orthodontic Society, October-December 2013;47(4):

4 Renuka Lalit Pawar, Vijay P Jayade Table 3A: Comparison of Howes study with present study in maxilla Variables Mean SD Range Z-value Total tooth * material Howes study (maxilla) ** Bicuspid distance NS (maxilla) Howes study * Bicuspid ratio * (maxilla) Howes study ** Basal arch width ** (maxilla) Howes study ** Basal arch width NS ratio (maxilla) Howes study * Basal arch length NS (maxilla) Howes study * Basal arch NS length ratio Howes study (maxilla) NS NS: Not significant; *Significant at p < 0.05; **Significant at p < 0.01 Table 3B: A comparison of Howes study with present study in mandible Variables Mean SD Range Z-value Total tooth ** material mandible Howes study ** Bicuspid distance NS (mandible) Howes study * Bicuspid ratio NS (mandible) Howes study ** Basal arch ** width (mandible) Howes study ** Basal arch width ** ratio (mandible) Howes study ** Basal arch ** length (mandible) Howes study ** Basal arch length ** ratio mandible Howes study ** NS: Not significant; **Significant at p < 0.01; *Significant at p < 0.05 Korkhaus Arch Length Index Anterior arch length index SD Comparison between the two sexes (Table 5) showed nonsignificant differences for the mean values of anterior arch length and arch length index. But the sum of incisor value showed significant differences (p < 0.01) between the males and females. Large differences were observed between the original Korkhaus study 5 and the present study for the index values. Palatal Height Index Palatal height index SD Significant differences (p < 0.01) were observed between teh two sexes (Table 6) for all the variables, i.e. palatal arch width, palatal height and palatal height index. 446

5 JIOS Table 3C: Comparison of Howe s index between males (n = 47) and females (n = 47) in the present study Variables Sex Mean SD Range Z-value Total tooth M ** material maxilla F Premolar M ** distance maxilla F Premolar distance M ratio maxilla F NS Premolar basal M ** arch width maxilla F Premolar basal arch M * width ratio maxilla F Basal arch M * length maxilla F Basal arch M * length ratio maxilla F Total tooth M ** material mandible F Premolar distance M * mandible F Premolar distance M * ratio mandible F Premolar basal M ** arch width mandible F Premolar basal arch M * width ratio mandible F Basal arch M length mandible F NS Basal arch length M ** ratio mandible F *Significant difference (p < 0.05); **Highly significant difference (p < 0.01); NS: Not significant Table 3D: Comparison of present study with earlier Indian study (Manipal) Variables Mean SD Z-value Premolar distance (n = 47) ** ratio maxilla Earlier study (n = 50) (n = 47) ** Premolar basal arch (n = 47) ** width ratio maxilla Earlier study (n = 50) (n = 47) ** Basal arch length (n = 47) ** ratio maxilla Earlier study (n = 50) (n = 47) ** Premolar distance (n = 47) ** ratio mandible Earlier study (n = 50) (n = 47) ** Premolar basal arch (n = 47) ** width ratio mandible Earlier study (n = 50) (n = 47) ** Basal arch length (n = 47) * ratio mandible Earlier study (n = 50) (n = 47) ** *Significant difference at (p < 0.05); **Highly significant difference at ( p < 0.01) The Index values of the present study did not differ much with the original study. DISCUSSION Modern day diagnostic tools, however sophisticated, do have some shortcomings. It is therefore always wise to make use of all the diagnostic tools available but never forgetting to include study model analysis to arrive at an accurate diagnosis, and hence, the need to investigate the commonly used study model indices. Ethnic variations and sexual dimorphism 9 have also been emphasized, and taken into consideration previous studies have established values for some of the indices The Journal of Indian Orthodontic Society, October-December 2013;47(4):

6 Renuka Lalit Pawar, Vijay P Jayade Table 4A: Comparison of Peck and Peck index with the present study Shape ratio Mean SD Z-value Central ** incisor Peck & Peck study * Lateral ** incisor Peck & Peck study ** Table 4B: Comparison of tooth shape ratios between males and females males (n = 34) females (n = 46) Shape ratio Sex Mean SD Z-value Central * incisor Laterial * incisor *Significant at p < 0.05 *Significant at p < 0.05; **Highly significant where p < 0.01 in the Indian population but, to the best of our knowledge a comprehensive study of all the commonly employed study model indices has not been carried out. The sample was selected mainly from among the student population of North Karnataka state. Occurrence of ideal occlusion is rare and hence the criteria for sample selection included normal Class I occlusion with crowding or spacing <2 mm and overjet or overbite <3 mm and with an acceptable facial profile. Pont s Index Large differences were observed for the premolar and molar index values between the present study and the original Pont s study. The mean values for the premolar and molar indices were less both in males and females. Statistical comparison was not possible as the sample size was not specified in the original study. 1 Comparison of observed arch widths in the present study with Pont s predicted arch width showed that identical measurements to those calculated with Pont s index were very rarely seen. A majority of the cases showed values greater than Pont s predicted values while the remaining few showed values less than Pont s predicted values. This reflected the presence of large dental arches in majority of the cases. Since, the samples were either over or under Pont s prediction it is obvious that individual variation is large. Therefore use of group mean value is meaningless for the individual patients outside the sample. This provides insight into the ethnic differences between the two populations. Only moderate correlation coefficient were observed between the predicted and observed arch widths for both the males and females thus supporting the views of Joondeph et al 11 and Dalidjan et al 25 that Pont s index is unreliable in predicting dental arch width. A comparison between the two sexes showed significant differences for anterior arch width, posterior arch width, and sum of incisor values. However, mean ratio values for premolar and molar indices showed no significant differences. The values for all the variables were less in case of females. Also the female values were more variable than the males. Correlation coefficient (r) calculated for sum of incisors and arch width had moderate values indicating not particularly strong association between the variation in incisor tooth size and arch width. The r values obtained in case of males were 0.42 and 0.48 and for females 0.66 and 0.55 in the premolar and molar regions. Mean index values differed significantly for both males and females when compared with earlier Indian study. The large differences could be due to differences in the sample size between the present study and the earlier Indian study. Further it was observed that even if the arch widths could be predicted, the arch shape would still present considerable uncertainty. Bolton s Index. Bolton analyzed the ratio between maxillary and mandibular teeth sizes. Significant differences (p < 0.01) were observed for the mean values of total tooth material and anterior tooth material both in maxilla and mandible between the two sexes (Table 2B). The mean values observed for the females were lesser than those of males. In spite of these differences, the index values were maintained within the population. Although, according to Moyers, 10 the maxillary cuspids are disproportionately larger in men than in women, an ideal overbite and overjet as defined by Bolton, is less apt to be achieved in men. The present study showed a very minimal magnitude of sexual dimorphism for the two ratios (0.052 and 0.44%). It was also observed that the coefficient of variation for females was slightly higher than that of the males and hence female values were considered as more variable than those of males. Nonsignificant difference observed between the original Bolton s study and the presence study for the anterior ratio in both sexes for the overall ratio significant differences were observed for the females only (p < 0.05) male showed no significant differences. Correlation(r) between anterior and overall ratios (males 0.62; females 0.51) showed moderate values which were similar to the earlier Bolton study. 2 The closeness of the values to Bolton s original values indicates that Bolton s index is a useful clinical guide. 448

7 JIOS Howes Index Howes 3 derived his index values from a limited number of sample (n = 14). But he did not derive standard deviation for his sample except for the mean values and range. Therefore only an approximate comparison could be made. Differences were observed for most of the variables in both the maxilla and mandible for the two sexes when compared with original Howe s study (Tables 3A and B). Further, it was observed that for some cases the bicuspid widths (premolar distance) exceeded the basal arch width. This observation did not agree with Howes study. 3 Also some of the cases showed basal arch width ratios below 44% which again did not agree with Howes observations which showed that arch width ratios below 44% are considered as border line cases. Samples in the present study showed minimum values starting from 40.25% (female) and 42.9% (males) (Table 3A). This observation proves that Howes index cannot be used as a reliable guide for our population. Some indices like premolar distance ratio (maxilla) show statistically nonsignificant differences between males and females (Table 3C). But the coefficient of variation was high for the females in comparison to males and hence separate index values were proposed for both sexes. Mean values obtained for the present study were higher than earlier Indian study and showed significant differences for all the variables. Peck and Peck Index Studies by Peck and Peck 4 have shown that the crown shape is a determining factor in the presence and absence of mandibular incisor crowding. The naturally well aligned mandibular incisors possess distinctive dimensional characteristics, i.e. they are significantly smaller mesiodistally and significantly larger faciolingually. They also concluded that male-female differences in the MD/FL indices are significantly lower. In the present study, significant differences were observed for the tooth shape ratios between the two sexes. It was observed that index values were high for males than females. Sex differences for shape ratios were also observed by some authors. 32 Table 4C: Comparisons of mesiodistal widths and faciolingual widths between males (n = 34) and females (n = 46) Variables Sex Mean SD Z-value Mesiodistal width of * central incisor Faciolingual width of NS central incisor Mesiodistal * width of lateral incisor Faciolingual width of NS lateral incisor *Significant at p < 0.05; NS: Not significant This study showed significant differences for mesiodistal widths between the two sexes (Table 4C) but it is also observed that the mean faciolingual width did not show any significant difference. This proved that the main contributor for the change in shape ratios between the two sexes is the mesiodistal width. Significant differences observed for the shape ratios between the present study and the earlier Peck and Peck study. 4 This indicated that differences existed in tooth sizes between the earlier study samples and the present study samples. It was also observed that in our sample, though the tooth shape ratios were in the normal range of Peck and Peck, they had mild crowding (<2 mm). It is therefore concluded, that original Peck and Peck ratio cannot be used as an absolute guide for our population. Comparison of these findings in cases with moderate to severe crowding will be required, to conclusively prove the reliability of Peck and Peck index. Korkhaus Arch Length Index This index gives the relationship between tooth size and anterior arch length. The index values obtained in the present study were higher than the earlier study. Statistical comparison was not done because sample size was not specified in the former study. 5 Large differences were noticed from the observed and predicted arch lengths thus, pointing out that the original index could not be applied to our sample. This indicated ethnic differences between the two populations. A comparison between the two sexes (Table 5) showed no significant differences for the mean values of anterior arch length and arch length index. But sum of incisors showed significant differences between males and females. Values for all the three variables were less in case of females. Moderately positive correlation existed between arch length and sum of incisors, i.e. about 47 to 50% of variation in observed arch lengths could be explained by the variation in the observed sum of incisors. In spite of nonsignificant differences in the index values between the two sexes, coefficient of variation was more variable for the females. Also both the samples in the present study showed large standard deviations. Hence, use of such indices clinically may be misleading. Korkhaus Palatal Height Index The palatal height index proposed by Korkhaus evaluates the palatal shape. The average value for the palatal height index is 42 % according to Korkhaus. The index figure increases when palatal vault relative to the transverse arch development is high and decreases when palate is shallow. The findings in the present study did not differ much with the earlier study but here again a statistical comparison could not be done as the sample size was not mentioned in the earlier study. The Journal of Indian Orthodontic Society, October-December 2013;47(4):

8 Renuka Lalit Pawar, Vijay P Jayade Table 5: Comparisons between males (n = 47) and females (n = 47) in the present study for Korkhaus arch length index Variables Sex Mean SD Z-value Anterior arch length NS Sum of incisors ** Arch length index (%) NS **Highly significant where p < 0.01; NS: Not significant Table 6: Comparison between males (n = 47) and females (n = 47) in the present study for Palatal height index Variables Sex Mean SD Z-value Palatal ** height (mm) Posterior arch ** width (mm) Palatal height ** index (%) **Highly significant where p < 0.01 Significant differences (p < 0.01) were observed between the two sexes (Table 6) for all the variables, i.e. palatal arch width, palatal height and palatal height Index. Further a very weak correlation was observed between the posterior arch width and the palatal height. The r-values obtained for males and females were and respectively. This showed that the palatal depth was not dependent on posterior arch width. Similar observations were made by Williams. 21 This study proves that the posterior arch width is not dependent on the palatal height. The weak correlation values indicated that predicting palatal depths is not possible. Therefore use of this index as a clinical guide is questionable. Future Directions to Further Enhance the Findings of the Present Study The present study was carried out on Class I occlusion cases with mild crowding or spacing up to 2 mm and overjet and overbite up to 3 mm or less, since ideal occlusion is encountered rarely in any population. Further studies may be conducted using naturally occurring perfectly ideal samples to see how the findings compare with this study. Following factors may also be taken into consideration 1. Type of arch form: It is observed that narrow tapered arch form requires more upper tooth mass for the same amount of overjet Inclination of upper and lower incisors: Incisor steeth take up more arch length when they are tipped labially, because the contact points are further gingivally Labiolingual thickness of upper and lower incisors in the incisal region. It is observed that upper anterior teeth with greater labiolingual thickness require more overjet, thus more tooth mass is required for the same amount of overbite. 23 CONCLUSION From the present study it can be concluded that: 1. The Pont s index was the least reliable of the indices while Bolton s index proved to be a useful clinical guide. 2. Differences in the index values for Ponts, Bolton s, Howes, Peck and Peck index and Korkhaus index were observed between the present study and the original study thus indicating ethnic differences. 3. Differences in the values were observed for both sexes indicating sexual dimorphism. Thus separate index values were established for males and females for the various indices. 4. Suggestions have been made for further studies using naturally occurring perfectly ideal samples. REFERENCES 1. Worms, Speidel, Isaacson and Meskin: Pont s Index and dental arch form. JADA 1972;85: Bolton WA. The clinical application of a tooth size analysis. AJO 1962 July;48: Howes AE. Case analysis and treatment planning based upon the relationship of the tooth material to its supporting bone. AJO 1947;33: Peck H, Peck S. An index for assessing tooth shape deviations as applied to the mandibular incisors. AJO 1972;61: Rakosi T, Jonas I, Graber TM. Orthodontic diagnosis (Color Atlas of Dental Medicine) 1993 ed: p Stifter J. A study of Pont s, Howes, Rees, Neff s and Bolton s Analyses on Class I adult dentitions. Angle Orthod 1958:28(4); Crosby, Alexander. The occurrence on tooth size discrepancies among different malocclusion groups. AJODO 1989;95: Barrer HG. Protecting the integrity of the mandibular incisor position. JCO 1975;9: Boese LR. Fibrotomy and reproximation without lower retention. Nine years in retrospect Part I Angle Orthod 1980;50: Moyers RE. Handbook of orthodontics. 4th ed, Year Book, Medical Publishers Inc 1988; Joondeph, et al. Pont s index: a clinical evaluation. Angle Orthod 1970;40(2): Lew K. The effect of variation in the mandibular plane angle on the Pont s Index. Funct- Orthod 1991Mar-Apr;8(2): Shellhart WC, Lunge DW, Klumper GT, Hicks EP, Kaplan AL. Reliability of the Bolton tooth size analysis when applied to crowded dentitions. Angle Orthod 1995;65(5): Martinek E. A comparison of various surveys on the adequacy of basal bone. AJO 1956;42: Smith, et al. Incisor shape and incisor crowding. A reevaluation of the peck and peck ratio. AJO 1982;89: Kuftinec MM. Effect of edgewise treatment and retention on mandibular incisors. AJO 1975;68: Keene, Engle. The mandibular dental arch Part IV. Prediction and prevention of lower anterior relapse. Angle Orthod 1979;49: Gilmore CA, Little RM. Mandibular incisor dimensions and crowding. AJO 1984;86:

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