At the 1995 ABO clinical examination, 100 cases were evaluated. A series of 15 criteria were measured on each of the final dental casts and panoramic radiographs. The data showed that 85% of the inadequacies in the final results occurred in seven of the 15 criteria (alignment, marginal ridges, buccolingual inclination, overjet, occlusal relationships, occlusal contacts, root angulation).

Therefore, at the 1996 clinical examination, a second field-test was initiated to verify the results of the previous test and to determine if multiple examiners could score the records reliably and consistently. In this field test, a subcommittee of four Directors evaluated 300 sets of post-treatment dental casts and panoramic radiographs. Again, the majority of the inadequacies in the final results occurred in the same seven categories, but the committee had difficulty establishing adequate inter-examiner reliability. The subcommittee recommended that a measuring instrument be developed to make the measuring process more reliable.

In 1997, a third field test was performed using the modified scoring system with the addition of an instrument to measure the various criteria more accurately. All of the Directors participated in this field test, and a total of 832 dental casts and panoramic radiographs were measured. The same seven criteria were evaluated. A calibration session preceded the examination to establish more accurate use of the measuring instrument and improve the reliability of the Directors. The results again showed that the overwhelming majority of the inadequacies in the finished results occurred in the aforementioned categories. However, the Directors decided to add interproximal contacts to the scoring system to raise the total number of criteria to eight. In addition, modifications were made in the measuring instrument to improve measuring accuracy among Directors.

In 1998, the fourth and final field test was initiated. Again all Directors participated in the evaluation process. The new and improved measuring instrument was used. An extensive training and calibration session was performed prior to the actual examination. The major objectives of this final field test were to refine the measuring and calibration process, and to gather enough data on general performance to establish the validity or cut-off for passing this portion of the clinical examination. This field test was extremely successful. Not only did it reaffirm the benefits of using an objective system for grading the dental casts and panoramic radiographs, but also it helped to establish standards for successful completion of this portion of the clinical examination.

Based upon the collective and cumulative results of these extensive field tests, the Board decided to officially initiate the use of this Model Grading System for examinees at the February 1999, ABO clinical examination in St. Louis. In order to assist the examinee in selecting cases that will successfully pass the examination process, the Board is providing the examinee with the same system used by the Directors. The Board encourages examinees to score their own dental casts and panoramic radiographs during their preparation for the clinical examination in order to select cases that will successfully pass the ABO Model Grading System.

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