Assessment of Validity of Pont ’ s Index and Establishment of Regression Equation to Predict Arch Width in Nepalese Sample

objective: To evaluate the validity of Pont’s index in Nepalese population and establish the regression equation to predict probable arch width from sum of the maxillary incisors. Materials & Method: The sample comprised of 50 female and 50 male subjects of the age ranging 17-24 years. Sum of the mesio-distal widths of the maxillary incisors were measured. Descriptive statistics, Coefficient of regression, and regression equation were calculated to predict the arch width in premolar and molar regions. Independent t-test was performed to find the difference between mean values of male and female subjects. Statistical analysis was done using SPSS version 17.0. result: Mean value of Pont’s index ratio was 0.80 and 0.63 for premolar and molar respectively for Nepalese sample. Statistical analysis showed no significant difference between male and female in Pont’s premolar and molar index. The correlation of coefficient for Sum of Incisors/Premolar width and Sum of Incisors/Molar width were 0.39 and 0.46 respectively. conclusion: Pont’s analysis can be applied in Nepalese samples. There is no significant difference in values between male and female samples.


IntroductIon
Various model analytical indices have been proposed in orthodontics to help in diagnosis and treatment planning.

Majority of malocclusion can be treated with extraction
or non-extraction approaches.Non-extraction method involves proximal stripping, distalization, labialization and arch expansion.[4] All of those indices show certain correlation between the arch length, arch width and mesiodistal width of the maxillary incisors.

MAterIAlS And Method
Total sample included in the study were 100 Nepalese subjects with 50 male and 50 female of the age between 17-24 years.The predicted arch widths of premolar is termed as calculated premolar value (CPV) and in molar as calculated molar value (CMV); which were established using the formula originally proposed by Pont.
Descriptive statistics including mean, standard deviation and range, coefficient of regression, and regression equation were calculated to predict the arch width in premolar and molar regions.Independent t-test was performed to find the difference between mean values of male and female subjects.Statistical analysis was performed using SPSS version 17.0 software package.The data collection and analysis were done during June 2013 -Jan 2014 after the consent from the subjects and approval by the Institutional Review Committee.All samples were measured by the principal author.

The present study showed no significant difference between
Pont's values in female and male Nepalese samples for both premolar and molar index (Table 3).
Coefficients of regression (r) were carried out to predict premolar and molar arch width by knowing the sum of maxillary incisor widths; which were found to be 0.39 for premolar and 0.46 for molar (Table 4).Regression equations for prediction of arch widths were derived from the formula.
Premolar arch width = 0.39(S -30.43) + 37.95 Molar arch width = 0.46(S -30.43) + 47.94 (Where 'S' is sum of maxillary incisors) With the use of regression equation, prediction table was depicted to calculate the probable arch width from the sum of mesio-distal width of maxillary incisors (Table 5).9][12][13][14][15][16][17] Some investigators supported its use as a guide in expanding the dental arch. in Indian population also agreed with Pont's values.However, their studies showed difference in arch width between the gender groups while the present study did not show significant difference between male and female samples.
Comparison of various studies on Pont's index and their results are given in Table 6.Some researchers described Pont's index as a poor clinical tool for predicting the arch width.However Pont's himself has stated that a similar study be done in other population too and verify the correctness of the index in other races. 4ncluSIon One hundred samples with 50 male and 50 female with normal occlusion were evaluated to check the reliability of Pont's index on Nepalese population.It was concluded that significant correlation exist between the sum of the maxillary incisors and maxillary interpremolar and intermolar arch widths in overall, male and female samples.
Coefficients of regression were depicted and prediction table was devised to calculate the probable arch width from the sum of mesio-distal width of maxillary incisors.

AcKnowledGeMent
We Pont in 1909 proposed a method to predict arch width, which Orthodontic Journal of Nepal, Vol. 4, No. 1, June 2014 Data were collected among the patients visiting the Department of Orthodontic and students of Kantipur Dental College & Hospital, Kathmandu.Inclusion criteria for the study were subjects with Class I molar and canine relation, straight facial profile without any previous history of orthodontic treatment.Subject with anomalies in tooth size and shape, deep bite, cross bite, rotations, large restorations were excluded from the study.Alginate impression of maxillary arch was taken and cast poured with dental stone.Cast measurement of mesio-distal widths of maxillary incisors was done using digital Vernier caliper with the accuracy of 0.01 mm.The sum of the maxillary incisor measurements was calculated.Maxillary arch widths in premolar and molar region were measured.Premolar arch width is termed as measured premolar value (MPV); which was measured from distal pit on occlusal surface of right first premolar to distal pit on occlusal surface of left first premolar.Arch width in molar area is termed as measured molar value (MMV), measured from mesial pit on occlusal surface of right first molar to left first molar.
Dhakal J, Shrestha RM, Pyakurel U: Assessment of Validity of Pont's Index and Establishment of Regression Equation to Predict Arch Width in Nepalese Sample reSult Descriptive statistics for overall sample is given in Table 1.Mean of the sum of maxillary incisors of total sample (SI) was 30.43 mm (SD 2.35).Mean measured premolar value (MPV) was 37.95 and mean measured molar value (MMV) was 47.94.Calculated premolar value (CPV) was 38.03 and calculated molar value (CMV) was 47.54.Pont's index for overall sample for premolar arch width was found to be 80.51 and molar arch width was 63.65.The Pont's premolar index was 82.37 and 78.64 for female and male respectively; and Pont's molar index was 65.38 and 62.79 for female and male respectively (Table 2).Overall measured value of premolar and molar width was 37.95 and 47.49 and calculated value was 38.03 and 47.54 respectively.In females, measured values for premolar and molar were 36.53 and 46.22 and calculated values were 37.51 and 46.89 respectively.In males, measured premolar and molar values were 39.39 and 49.26 where as calculated values were 38.56 and 48.20 respectively.

table 6 : comparison of various studies on the applicability of Pont's index
47,16orms 10 et al obtained lesser values than the calculated measurement.Similarly Nimkarn et al, Khin et al, Ordoubazary et al, Hong et al showed that Pont's indices overestimate the arch width. 11-14w andjan et alshowed underestimation in values obtained using Pont's indices.15,16Kimetalfoundbothover and underestimation in value obtained.17Thevariationobserved in different studies may possibly be attributed to genetic inheritance of the various races.The present study found significant and definite correlation between the sum of four maxillary incisors and arch widths in molar and premolar regions in agreement to Pont's values.4Inourstudy premolar and molar index were found to be 80.51 and 63.65 respectively as compared to Pont's original values of 80 and 64.Similar study by Gupta et al5 and Prasad & Valiathan 7 would like to thank Dr Sujita Shrestha, Lecturer, Dept of Community & Public Health Dentistry for her help in statistical analysis and Dr Poojan Thapaliya, intern for her help in data collection