| dc.description.abstract | Purpose
To determine the difference in treatment outcome and long-term stability of Class II molar and Class I molar finished orthodontic cases using the American Board of Orthodontics Objective Grading System in combination with irregularity index and linear measurements of the buccal segment relationships.
Materials and Methods
The sample consisted of 48 patients who were retrospectively selected from four private practice board certified orthodontists. Group 1 included 24 patients treated with 2 maxillary first premolar extractions (3 males and 21 females) treated to a bilateral Class II molar relationship. Group 2 comprised 24 patients treated with 4 premolar extractions (4 males and 20 females) treated to a bilateral Class I molar relationship. Orthodontic study models, panoramic radiographs and lateral cephalograms were collected at three timepoints: pretreatment initial (T1), day of debond posttreatment (T2), and long-term post retention (T3). Lateral cephalograms were traced to measure Frankfort-mandibular plane angle (FMA) and ANB at pretreatment initial records. Molar and canine relationships were measured at all three timepoints parallel to the occlusal plane in half millimeter increments. The ABO Objective Grading System scores and mandibular incisor irregularity were also measured at all three occasions.
Results
There were no statistically significant between-group differences in canine relationships at any of the 3 time points. There were significant differences in molar relationship after treatment (p = <0.001) and post retention (p = <0.001). Both groups showed significant reductions in incisor irregularity during treatment. The 2 premolar extraction group experienced slightly greater increases in malalignment posttreatment, but the difference was not statistically significantly. The total OGS scores of both groups decreased significantly from T1 to T2, indicating improvements in treatment outcome, and decreased from T2 to T3, indicating some posttreatment settling. The 2 maxillary premolar extraction group had a median posttreatment (p = 0.02) and post-retention (p = <0.001) score that was significantly greater than the 4 premolar extraction group suggesting a better treatment outcome for the Group treated to a Class I molar finish. After orthodontic treatment (T2), the 4 premolar extraction group had significantly better alignment (p = <0.001) and occlusal relationships (p = <0.001) than the 2 premolar extraction group. At post-retention (T3), significant between-group differences remained for alignment (p = <0.001) and occlusal relationships (p = 0.003); however, there were also significant differences in buccolingual inclination (p = <0.001) and marginally significant differences in marginal ridges (p = 0.02).
Conclusions
Posttreatment occlusion is worse in bilateral Class II molar finished patients than in Class I molar finished patients, with Class II molar finished patients scoring 17% higher total OGS scores. The anterior components of occlusion do not contribute significantly to the posttreatment between-group differences between 2 and 4 premolar extraction patterns. Posttreatment differences in overall OGS scores between 2 and 4 premolar extraction patterns are primarily due to the posterior components of occlusion, specifically alignment (p=<0.001) and occlusal relationships (p=<0.001). Bilateral Class II molar finished patients have worse occlusion post-retention. Patients treated with 4 premolar extractions and treated to Class I molar relationships scored 44% better long-term than patients treated with 2 maxillary premolar extractions. | |
