The Salzmann Index and discrepancy index correlation: Determining a threshold discrepancy index score for Medicaid approval

Abstract

This study aimed to compare patients' Salzmann Index scores for those who applied for Medicaid orthodontic coverage in Pennsylvania with their corresponding American Board of Orthodontics discrepancy index (DI) scores to assess if there is a correlation between Salzmann and DI scores. In addition, a threshold DI score was calculated that would correspond to Medicaid coverage approval. The study intended to answer the following questions: is there a correlation of 0.7 or greater between a patient's Salzmann Index and their DI? If so, is there a particular DI score that can be used as the minimum score for approving Medicaid orthodontic coverage in the state of Pennsylvania? Salzmann Index scores, DI scores, and approval and disapproval results for Medicaid orthodontic coverage were obtained from 104 subjects aged between 10 and 17years. A linear regression model was generated to assess if there was a correlation between the Salzmann scores and DI scores. If a correlation coefficient of 0.7 or greater were found, a threshold Salzmann Index score would be determined for subjects who were approved for Medicaid orthodontic coverage. The threshold Salzmann score would be used in the linear regression formula to find the corresponding DI score, which would be designated as the threshold DI score for approval for Medicaid orthodontic coverage in the state of Pennsylvania. A Pearson correlation of 0.453 was calculated between the 104 Salzmann scores and DI scores, demonstrating a moderate correlation. With the correlation coefficient being lower than 0.7, binary logistic regressions were calculated to assess the predictability between a given Salzmann score and approval and disapproval for Medicaid orthodontic coverage. TheSalzmann score had an overall 68.3% success in predicting Medicaid orthodontic coverage approval/disapproval. Of the 58 subjects that were approved for Medicaid orthodontic coverage, 46.6% had Salzmann scores equal to or greater than 25. Of the 46 subjects that were disapproved for Medicaid orthodontic coverage, 78.3% had Salzmann scores equal to or less than24. With the lack of high prediction rates seen from the results of the regression models, the current system of Medicaid does not appear to show consistency for assessing the need for orthodontic treatment coverage. Multiple insurance companies that participate under Medicaid require a Salzmann score of 25 or greater for approval; however, the results show the Salzmann score is arbitrary in terms of approval and disapproval. There appear to be underlying factors apart from the Salzmann score that the Pennsylvania Medicaid system uses to justify whether a patient was approved or denied for coverage.