University clinic and private practice treatment outcomes in Class I extraction and nonextraction patients: A comparative study with the American Board of Orthodontics Objective Grading System


The aim of this study was to compare treatment outcomes in university vs private practice settings with Class I patients using the American Board of Orthodontics Objective Grading System.


A parent sample of 580 Class I patients treated with and without extractions of 4 first premolars was subjected to discriminant analysis to identify a borderline spectrum of 66 patients regarding the extraction modality. Of these patients, 34 were treated in private orthodontic practices, and 32 were treated in a university graduate orthodontic clinic. The treatment outcomes were evaluated using the 8 variables of the American Board of Orthodontics Objective Grading System.


The total scores ranged from 10 to 47 (mean, 25.44; SD, 9.8) for the university group and from 14 to 45 (mean, 25.94; SD, 7.7) for the private practice group. The university group achieved better scores for the variables of buccolingual inclination (mean difference, 2.28; 95% confidence interval [CI], 0.59, 3.98; P = 0.01) and marginal ridges (mean difference, 1.32; 95% CI, 0.28, 2.36; P = 0.01), and the private practice group achieved a better score for the variable of root angulation (mean difference, −0.65; 95% CI, −1.26, −0.03; P = 0.04). However, no statistically intergroup differences were found between the total American Board of Orthodontics Objective Grading System scores (mean difference, −0.5; 95% CI, −3.82, 4.82; P = 0.82).


Patients can receive similar quality of orthodontic treatment in a private practice and a university clinic. The orthodontists in the private practices were more successful in angulating the roots properly, whereas the orthodontic residents accomplished better torque control of the posterior segments and better marginal ridges.


  • Treatment results were compared between private practices and a university clinic.

  • The American Board of Orthodontics Objective Grading System was used to assess outcomes.

  • The probability of acceptable treatment was the same and unrelated to setting.

  • The university group had better scores for buccolingual inclination and marginal ridges.

  • The private practice group was more efficient in angulating the roots properly.

The choice of a treatment provider is an important concern when patients seek treatment. Expectations regarding curative outcomes is a main determinant in the choice of a treatment provider. Other parameters such as socioeconomic background, distance from the clinic, and quality of the clinical facilities also play important roles in a patient’s decision process. Only a few research studies have assessed the differences between orthodontic treatment outcomes in university clinics and private practices. Therefore, it is still unclear whether the clinical skills of a private orthodontist can outweigh the detailed and supervised practice of a university graduate student.

The assessment of success of an orthodontic treatment ideally involves the evaluation of a patient’s posttreatment records. However, without a valid and reliable evaluation method, it is difficult and often subjective to assess treatment outcomes. Since the 1970s, several indexes that aim to assess objectively orthodontic treatment outcomes have been introduced. The Peer Assessment Rating index, introduced by Richmond in 1992, focused mainly on a patient’s degree of improvement. Specifically, it evaluated the malocclusion improvement between the initial and final situations, but it did not measure tooth positions and occlusal results with precision. Subsequently, the Index of Complexity Outcome and Need (ICON) was introduced by Daniels and Richmond in 2000. It evaluates complexity, need for orthodontic treatment, improvement of malocclusion, and treatment outcome. Among the main advantages of the ICON are objectivity of the treatment assessments, simplicity, and lack of need for any special equipment. Its main drawback was that esthetic considerations constituted the most important part of the evaluation.

The American Board of Orthodontics (ABO) recommended a more precise way of evaluating treatment outcomes. The ABO Objective Grading System (OGS) uses a specific instrument to measure dental casts, and final panoramic radiographs are also evaluated by visual inspection ( Fig 1 ). In detail, the ABO OGS index rates the final occlusion with 8 criteria that contribute to ideal intercuspation and function. Best occlusion and alignment receive a score of 0 points. For each parameter that deviates from the ideal, 1 or 2 penalty points are added. Cases are classified as “successful” or “failed” according to their ABO OGS scores. A case with a total score of 20 points or less passes the ABO examination, and one with more than 30 points fails. Those scoring between 20 and 30 are subject to individual reassessment.

Fig 1
Use of the ABO gauge on a plaster cast.

Consequently, a high percentage of accordance can be achieved in both interexaminer and intraexaminer assessments. In recent orthodontic literature, the ABO OGS has been widely used to compare treatment outcomes of mutually exclusive treatment approaches or techniques. In addition to being an objective clinical examination tool, it has been also used to increase the reliability, validity, and precision of the assessment of treatment progress and final outcome.

The purpose of this study was to compare the results of orthodontic treatments in a private practice with those provided by graduate residents in a university orthodontic clinic. Furthermore, we investigated whether the patient’s sex or age has an impact on treatment quality.

Material and methods

An initial sample of 580 Class I patients was gathered from the graduate orthodontic clinic of the University of Athens in Athens, Greece, and 5 private orthodontic practices in Athens, Greece. Of these patients, 329 were treated in the university clinic and 251 in the private practices; 427 patients received nonextraction treatment, and 153 patients were treated with removal of the 4 first premolars. Each of the orthodontists who treated the patients in the private practices had at least 15 years of clinical experience. The inclusion criteria for the sample were white male or female patient with a Class I skeletal and dental malocclusion, a full complement of teeth excluding the third molars, no previous orthodontic treatment, and no dentofacial deformities or clefts. Furthermore, all patients were treated with preadjusted edgewise appliance in both arches without temporary anchorage devices of any form. The records used in this study were plaster dental casts and panoramic and lateral cephalometric x-rays; a complete set of diagnostic records was required for a subject to be included in the study. All lateral cephalometric x-rays were taken in natural head position and analyzed using ViewBox software (version; dHAL Software, Kifissia, Greece).

To obtain a subsample, a discriminant analysis was used, and a borderline sample that could have been treated either with or without extractions was identified. The discriminant analysis ensured that all patients in the borderline sample had the same degrees of dental and skeletal discrepancies at the start of treatment. To secure an accurate representation of all dental, skeletal, and soft tissue traits that have an impact on the orthodontist’s treatment decision, the discriminant analysis encompassed a large set of data consisting of 26 cephalometric, 6 model, and 2 demographic variables. Each patient received a discriminant score that ranged from −3.45 to 3.16, and the optimal cutoff score according to which the subjects were placed into the extraction or the nonextraction group was determined as 0. As patients’ discriminant scores draw away from 0 to negative values, patients are predicted to need extractions, and when the scores reach positive values, patients are predicted to be nonextraction patients. With regard to the extraction modality, the borderline subjects were selected around the cutoff score. Because all patients had similar discriminant scores, a matched sample was secured. Statistical analysis in this study was carried out using SPSS software (version 19.0; IBM, Armonk, NY).

Because there were no orthodontic anomalies requiring particular clinical skills, these patients sought treatment in 1 of the 2 orthodontic clinical settings (university clinic and private practices) with no particular preference for either of them. Furthermore, because many clinicians treated the patients—about 20 residents in the university clinic and 12 different orthodontists in the private practices—the elimination of selection and proficiency biases was ensured.

A power test was calculated to assess the sample size required. The power test resulted in a sample size of 60 subjects needed to detect a clinically significant difference in the total score of 5 units with a common standard deviation of 7 units, assuming a 2-sided type I error of 5% and a power of 80%.

The final sample consisted of 66 Class I patients who were considered borderline regarding the extraction modality ( Table I ). Of these patients, 34 were treated in private orthodontic practices and 32 in the university clinic; 41 (62.1%) were female and 25 (37.9%) were male. Of the university clinic patients, 19 (59.4%) were female and 13 (40.6%) were male. Of the private practice patients, 22 (64.7%) were female and 12 (35.3%) were male. Their mean ages were 14.88 years (SD, 7.36 years) and 17.06 years (SD, 7.87 years) for the university and the private practice groups, respectively. Of the university patients, 10 were treated with extractions, whereas 22 received nonextraction treatment. Of the private practice patients, 20 were treated with extractions, and 14 received nonextraction treatment. The treatment outcomes were evaluated using the 8 variables of the ABO OGS: alignment, marginal ridges, buccolingual inclination, overjet, occlusal contacts, occlusal relationships, interproximal contacts, and root angulation. Initially, the principal investigator (B.M.) completed the necessary calibration process as instructed by the ABO. Then the measurements were obtained using the special ABO gauge.

Table I
Descriptive statistics for age and sex of the subjects
Sex Age
Male Female Total n Mean (y) SD (y)
Private practice
Count (n) 12 22 34
Within treatment 35.3% 64.7% 100.0% 34 17.06 7.87
Count (n) 13 19 32
Within treatment 40.6% 59.4% 100.0% 32 14.88 6.72
Count (n) 25 41 66
Within treatment 37.9% 62.1% 100.0% 66 16 7.36

Fisher’s exact test, P = 0.8; t test, P = 0.23.

To examine the intergroup differences between the scores of the 8 ABO OGS variables as well as between the total ABO OGS scores for the university and the private practice groups, descriptive and inferential statistics were performed, and t tests for independent samples were used ( Table II ). The significance level was predetermined at 5% ( P ≤0.05). Evaluations were performed for both random and systematic errors of the method.

Table II
Descriptive and inferential statistics for the 8 ABO OGS variables and total ABO OGS scores in the 2 groups
ABO OGS variable Private practice (SD) University (SD) Mean difference 95% CI P value
Alignment 5.12 (2.20) 5.41 (3.47) −0.29 −1.73 1.16 0.69
Marginal ridges 3.85 (2.40) 2.53 (1.76) 1.32 0.28 2.36 0.01
Buccolingual inclination 5.94 (3.43) 3.66 (3.44) 2.28 0.59 3.98 0.01
Overjet 2.62 (2.17) 3.16 (2.30) −0.54 −1.64 0.56 0.33
Occlusal contacts 4.47 (3.65) 5.25 (3.78) −0.78 −2.61 1.05 0.40
Occlusal relationships 2.53 (2.78) 3.38 (3.02) −0.85 −2.27 0.58 0.24
Interproximal contacts 0.15 (0.44) 0.16 (0.45) −0.01 −0.23 0.21 0.93
Root angulation 1.26 (0.86) 1.91 (1.51) −0.65 −1.26 −0.03 0.04
Total 25.94 (7.69) 25.44 (9.81) 0.5 −3.82 4.82 0.82
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Apr 6, 2017 | Posted by in Orthodontics | Comments Off on University clinic and private practice treatment outcomes in Class I extraction and nonextraction patients: A comparative study with the American Board of Orthodontics Objective Grading System
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