Assessment of clinical cases using ABO discrepancy index

Introduction: The American Board of Orthodontics objectively quantifies the complexity of malocclusion before orthodontic treatment. This study aims to assess the complexity of cases as measured by ABO discrepancy index (DI) in the patients under treatment by the orthodontics residents of Kantipur Dental College (KDC). Additional objectives were to 1) Ascertain DI relative to sex, age and race/ethnicity, and 2) Differential analysis of the components of the DI. Materials & Method: DI was determined for 220 consecutive cases started by orthodontic residents of KDC in a three-year graduate orthodontics program from 2014-2018. The DI was scored and compared with the patient’s sex and age. Result: The DI is not statistically significant to age, sex and race/ ethnicity. The mean DI score (± SD) was 18.65 (±10.521). Differential analysis of the components of the DI showed that the highest scores were for cephalometric measures, followed by overjet, crowding, occlusion, and the lowest scores were for lingual posterior crossbite. Conclusion: The DI was a relatively reliable index for measuring malocclusion severity. It is independent of patient’s age and race/ethnicity but is dependent on sex. Area of possible future improvements includes malocclusion sub-categories (Class II div. 1 and 2), and scores for bony and soft tissue impactions.


INTRODUCTION
The success of the case depends upon the precise case history, diagnosis and treatment planning. Assessment of the complexity of the case is the gold standard for the optimized results. Case difficulty should be assessed which can often be subjective; however, it is related to case complexity, which can be quantifiable. Discrepancy Index (DI) has been designed by American Board of Orthodontics (ABO) to provide an objective evaluation of the complexity of a malocclusion. This might lead to a better understanding of difficulty before starting the orthodontic treatment, which improves the compliance of the patient.
The DI is an objective method which is based on the observations and measurements taken from standard pretreatment orthodontic records i.e. study model, lateral cephalogram and panoramic radiographs. 1 2 The greater the number of these conditions in a patient, the greater severity of the malocclusion and the greater the clinical effort required to achieve optimal treatment. 1,3 To the researcher's knowledge, no studies in Nepal have quantified the overall DI score of the patients who were treated or are being treated by the orthodontic residents. The purpose of this study was to assess the complexity of cases as measured by ABO discrepancy index (DI) in the patients under treatment by the orthodontic residents of Kantipur Dental College (KDC). Additional objectives were to 1) Ascertain DI relative to sex, age and race/ethnicity, and 2) Differential analysis of the components of the DI.

MATERIALS AND METHOD
Institutional review committee approval was obtained from IRC-Kantipur Dental College. This is a retrospective study conducted in Kantipur Dental College from 2014-2018. 220 consecutive cases were taken as a sample from the patient records that were started by orthodontic residents of KDC in a three-year graduate orthodontics program. Data were collected and analyzed between October and November 2018.
The criteria for inclusion were: i.
Orthodontic patients treated by the residents in the Department of Orthodontics, KDC.
ii. Natural born ethnic Nepalese. The two ethnic groups (Aryans and Mongoloids) in this study were defined as per the study of Sharma et al. 4 Cases were excluded if the records were incomplete, casts were broken/damaged or the radiographs were unclear. A total of 158 cases were analyzed. Sample size of 156 was calculated using data from the study of Schafer et al 3  score. Scores were recorded as per the guidelines of ABO Discrepancy Index scoring system and worksheet. 5,6 Pre-treatment age, sex and race/ethnicity were also recorded from the case records of the orthodontic residents. 30 cases were scored twice, 2 weeks apart to determine the inter-examiner repeatability (k = 0.89).

Statistical analysis
A Spearman correlation coefficient was calculated to evaluate the association between the patient's pretreatment age with the DI scores. Mann-Whitney tests were used to evaluate the associations of the patient's sex and race/ethnicity with the DI scores. Kruskal-Wallis Test was used to evaluate the relation between malocclusion classes and DI scores.

RESULT
An outlier, a score of 117 (next highest score, 57) was identified in the DI scores. No investigator recalled any other patient having a DI exceeding 100, so the outlier was excluded from further analysis or presentation in this report. The mean DI score (± SD) was 18.65 (±10.521).

Differential analysis of the components of the DI
showed that the highest scores were for cephalometric measures, followed by overjet, crowding, occlusion, and the lowest scores were for lingual posterior crossbite. All variables are listed in Table I

DISCUSSION
We assessed the relationship of the DI to the patient's age, sex and race/ethnicity at the beginning of treatment. Statistically, there was no effect of age and race/ethnicity on the overall DI when the patients were scores were determined to be higher in the age group of 18-year-olds. Further, the ICON weighs heavily on esthetics, which is highly subjective rather than objective. 10 Koochek et al 11

CONCLUSION
DI was found to be independent of age and Nepalese race/ethnicity but was dependent on sex. Males were found to have mean DI scores significantly higher than females.
DI was found to be relatively reliable index compared to previous indices to access the severity of malocclusion.
But the areas of possible future improvement in the current ABO DI could be the addition of malocclusion sub-categories (e.g. Class II Division 1 and Division 2), bony and soft tissue impactions scores modification.
Pyakurel U, Thapaliya KB, Gupta S, Gupta A, Dhakal J : Assessment of clinical cases using ABO discrepancy index OJN