The aim of this study was to compare the orthodontic clinical outcomes of 2 maxillary premolar extraction, 4 premolar extraction, and nonextraction treatment protocols.
The sample for this retrospective study was selected randomly from the archives of postgraduate orthodontic clinics in various cities in Turkey. Posttreatment records including dental casts and panoramic radiographs of 1098 patients were divided into 3 groups: group 1 comprised 269 patients treated with 2 maxillary first premolar extraction, group 2 comprised 267 patients treated with 4 premolar extraction, and group 3 comprised 562 patients treated with a nonextraction protocol. Only 1 researcher evaluated all subjects using the American Board of Orthodontics objective grading system.
There were no statistically significant differences among the 2 maxillary premolar extraction, 4 premolar extraction, and nonextraction treatment groups for alignment, marginal ridge height, buccolingual inclination, overjet, and interproximal contact measurements. Statistically significant differences were found in occlusal contacts, occlusal relationships, and root angulation measurements between the 4 premolar extraction and the nonextraction groups.
The nonextraction patients had more teeth in occlusion than did the 4 premolar extraction patients. The nonextraction patients finished with more satisfactory sagittal dental relationships. The 4 premolar extraction group had the least satisfactory sagittal dental relationships. The nonextraction patients finished with better root angulations.
Occlusal indexes are helpful to clinicians in diagnosis, research design, decision-making, evaluating orthodontic treatment need, and clinical outcomes. The peer assessment rating (PAR) index was developed to record the measurements of a malocclusion. Holman et al evaluated extraction vs nonextraction orthodontic treatment using the PAR index. They found that dento-occlusal relationships produced in extraction treatments are as good as those in nonextraction patients. Even though it has been established to be useful for quantifying the amount of change during malocclusion correction, the PAR index cannot be used to exactly quantify tooth positions. A commission of the American Board of Orthodontics (ABO) directors was formed in 1994 to develop a system that could be used to quantify tooth positions more exactly. After 4 years of clinical trials at each yearly ABO clinical examination, in 1997 the ABO completed its objective grading system (OGS) for scoring posttreatment case records. This system includes 8 criteria that are evaluated with a numeric measure: alignment, marginal ridge height, buccolingual inclination, occlusal relationship, occlusal contact, overjet, interproximal contact, and root angulation. This system mainly has a specific gauge to standardize the measurements by the examiners. With an ABO measuring gauge, this system was used in the evaluation of the final casts and panoramic radiographs of each subject.
The validity and reliability of the ABO OGS were confirmed, and it was subsequently used in the evaluation of orthodontic records. The ABO OGS provides a method for an objective assessment of the outcome and achievement of orthodontic treatment. Onyeaso and Begole found that the ABO OGS involves more rigorous standards than the PAR or the index of complexity, outcome, and need for assessing the outcome of orthodontic treatment.
To our knowledge, no study in the literature has compared the orthodontic treatment outcomes of 2 maxillary premolar extraction, 4 premolar extraction, and nonextraction treatment protocols as we have with a large sample size using the ABO OGS. In the literature, extraction protocols have been assessed only with cephalometric evaluations or alternative occlusal indexes.
The aim of this study was to examine dental casts and radiographs to evaluate orthodontic treatment outcomes in 2 maxillary premolar extraction, 4 premolar extraction, and nonextraction protocols with the ABO OGS. The null hypothesis to be tested was that there is no difference in orthodontic treatment outcomes in 2 maxillary premolar extraction, 4 premolar extraction, and nonextraction protocols.
Material and methods
The sample for this retrospective study was selected randomly from the archives of 9 postgraduate university orthodontic clinics in various cities in Turkey. There is an important issue that the duration and quality of treatment are parallel to the practitioner’s level of orthodontic experience; thus, in this study, we used subjects who were treated only by experienced residents in orthodontics. The orthodontic competence of the residents was generally similar (third or fourth year of postgraduate education in orthodontics). All subjects were treated with traditional Roth prescription 0.018-in brackets in all orthodontic clinics.
The total sample included 1098 patients (657 girls, 441 boys) with an average age of 16.3 years at the start of treatment. Posttreatment records including dental casts and panoramic radiographs were collected. The total of 1098 patients was divided into 3 groups. Group 1 comprised 269 patients treated with fixed orthodontic protocol by 2 maxillary first premolar extraction. Group 2 comprised 267 patients treated with 4 premolar extraction and fixed orthodontic appliances. Group 3 comprised 562 patients treated with a nonextraction fixed orthodontic protocol.
The following inclusion and exclusion criteria were used during the selection of the subjects. The inclusion criteria were patients with regular appointments, who started and completed treatment in the same clinic, whose treatment was started and finished by the same orthodontist, and whose records included posttreatment dental casts and panoramic radiographs. Patients were excluded if they began treatment before 2005, they were treated by orthodontic teaching staff, the treatment was finished for personal reasons (poor oral hygiene, moving to another city, leaving treatment), their records included only digital dental casts, their dental plaster casts were broken, their records were incomplete or missing, or there were negative chart entries because of lack of cooperation or poor oral hygiene.
The principal researcher (H.A.C.) was initially trained in the ABO OGS using the ABO calibration kit from March 2011 and a tutorial for the ABO gauge. Only 1 investigator (H.A.C.) evaluated all subjects.
The ABO OGS for scoring dental casts and panoramic radiographs included 8 measurements: alignment, marginal ridges, buccolingual inclination, occlusal relationships, occlusal contacts, overjet, interproximal contacts, and root angulation. The ABO measuring gauge was used to score the casts ( Fig 1 ). A score of 0 indicates ideal alignment and occlusion; scores of 1 and 2 show deviations from the normal. The score for each patient indicates the relative deviations from the ideal score.
Furthermore, all patients were divided into subgroups according to the 3 grades of treatment quality (passing, undetermined, and failing) based on their OGS scores of the posttreatment records. These groupings were based on the ABO’s experience that cases with scores less than 20 commonly pass (passing), and cases with scores of more than 30 are generally unsuccessful (failing). Scores between 20 and 30 show undetermined outcomes.
A power analysis was established so that in a 1-way analysis of variance (ANOVA) study, sample sizes of 100, 100, and 200 are obtained from the 3 groups whose means were to be compared using a planned comparison (contrast). The total sample of 400 subjects achieves 100% power to detect a nonzero contrast of the means vs the alternative where the contrast is zero using an F test with a 0.05000 significance level.
To assess the intraexaminer reliability, we randomly selected a subsample of 20 patients from the main sample. The measurements were repeated 8 weeks after the first measurements were taken. A paired-samples t test was applied to the first and second measurements, and the differences between measurements were evaluated. The paired-samples t test results for the intraexaminer repeatability indicated that the first and second measurements, and the differences between measurements, were insignificant.
For testing independence, chi-square tests were implemented between the variables such as treatment type and treatment quality, whereas the groups’ treatment durations were compared with 1-way ANOVA, followed by pair-wise comparisons when the omnibus test was statistically significant. Paired-samples t tests were used to compare the OGS components; statistical significance was determined based on the Bonferroni-adjusted alpha level. For comparison of independent categories, first the Hotelling T square tests were performed, and then individual independent-samples t tests were used as follow-up tests to determine statistically significant differences among the categories. Statistical software (version 20; IBM SPSS, Armonk, NY) was used for the analyses.
When the P value was less than 0.05, the statistical test was determined to be significant.
The mean treatment times for the 3 groups are given in Table I . Four premolar extraction patients received the longest treatment durations (mean, 30.73 ± 10.7 months).
|Group||n||Mean (mo)||SD||SE||95% CI for mean||Minimum||Maximum|
|Lower bound||Upper bound|
|2 maxillary premolar extraction||269||27.70||11.54||0.70||26.31||29.08||8.00||64.00|
|4 premolar extraction||267||30.73||10.78||0.66||29.43||32.03||10.00||65.00|
Descriptive statistics for each component are given in Table II . Alignment was not significantly different among the groups ( Table II ). This finding indicates that the extraction (2 maxillary premolar vs 4 premolar) patients had mean tooth alignments equal to those of the nonextraction patients. The mean OGS scores are shown in Figure 2 .
|n||Mean||SD||Minimum||Maximum||F value||Significance||2 Maxillary premolar extraction||4 Premolar extraction||Nonextraction|
|2 maxillary premolar extraction||268||2.51||1.79||0.00||9.00||0.080||0.923||1.000||1.000|
|4 premolar extraction||267||2.50||1.72||0.00||10.00||1.000||1.000|
|Marginal ridge height|
|2 maxillary premolar extraction||268||3.32||2.34||0.00||11.00||1.493||0.225||0.257||0.781|
|4 premolar extraction||267||3.67||2.35||0.00||12.00||0.257||1.000|
|2 maxillary premolar extraction||268||1.88||1.77||0.00||12.00||0.246||0.782||1.000||1.000|
|4 premolar extraction||267||1.82||1.80||0.00||12.00||1.000||1.000|
|2 maxillary premolar extraction||268||4.87||3.94||0.00||16.00||2.394||0.092||1.000||0.643|
|4 premolar extraction||267||5.10||3.79||0.00||19.00||1.000||0.106|
|2 maxillary premolar extraction||268||3.36||3.44||0.00||17.00||3.759||0.024 ∗||1.000||0.244|
|4 premolar extraction||267||3.57||3.39||0.00||18.00||1.000||0.031 ∗|
|2 maxillary premolar extraction||268||1.89||2.72||0.00||13.00||11.543||0.000 ‡||0.008 †||0.594|
|4 premolar extraction||267||2.58||2.86||0.00||12.00||0.008 †||0.000 ‡|
|2 maxillary premolar extraction||246||0.37||0.86||0.00||4.00||3.442||0.532||1.000||0.091|
|4 premolar extraction||241||0.37||1.21||0.00||13.00||1.000||0.111|
|2 maxillary premolar extraction||246||0.19||0.52||0.00||2.00||4.765||0.009 †||1.000||0.112|
|4 premolar extraction||240||0.22||0.60||0.00||3.00||1.000||0.015 ∗|