Extraction of maxillary first molars improves second and third molar inclinations in Class II Division 1 malocclusion.

Introduction: The aim of this study was to assess the changes in inclination of the maxillary second (M2) and third (M3) molars after orthodontic treatment of Class II Division 1 malocclusion with extraction of maxillary first molars.

Methods: Two groups of subjects were studied. The experimental group consisted of 37 subjects, 18 boys and 19 girls (mean age, 13.2 ± 1.62 years). The inclusion criteria were white origin, Class II Division 1 malocclusion, overjet ≥4 mm, no missing teeth or agenesis, and maxillary M3 present. All patients were treated with extraction of the maxillary first molars and the Begg technique. Standardized lateral cephalometric radiographs were taken at the start of active treatment (T1) and at least 3.7 years posttreatment (T2). The control group was drawn from the archives of the Nittedal Growth Material (Oslo University, Oslo, Norway) and included 54 untreated Class I and Class II subjects,18 boys and 36 girls (mean age, 13.4 ± 1.99 years) followed up for a minimum of 3.6 years. M2 and M3 inclinations relative to the palatal plane (PP) and functional occlusal plane (FOP) were measured and compared between groups and time periods.

Results: M2 to PP inclination improved significantly in both the control group (M2-PP at T1, 17.7° ± 5.81°, and at T2, 11.9° ± 4.61°) and the experimental group (M2-PP at T1, 26.7° ± 5.75°, and at T2, 6.9° ± 6.76°). There were also significant increases of the mesial inclination of M3 in the control group (M3-PP at T1, 30.1° ± 8.54°, and at T2, 19.6° ± 9.01°) and extraction group (M3-PP at T1, 32.2° ± 7.90°, and at T2, 12.8° ± 7.36°). By using the FOP as the reference system, no significant change in the inclination of M2 was observed in the control group, whereas, in the extraction group, although more distally inclined at T1, M2 ended up mesially inclined at T2 (M2-FOP at T1, 14.2° ± 4.62°, and at T2, -6.2° ± 6.10°; P <0.0001). M3 inclinations were similar between the groups at T1 (M3-FOP control, 17.3° ± 9.35°; M3-FOP experimental, 19.6° ± 7.37°), and these improved significantly in both groups. However, M3 uprighting was almost 4 times greater in the extraction group (M3-FOP from T2-T1, 5.6° vs 19.9°). The greatest distal inclination of M3 at T2 in the extraction group was 9.4°, a value attained by only 43% of the control group.

Conclusions: Extraction of the maxillary first molars in Class II Division 1 patients results in significant uprighting of M2 and M3 and facilitates the normal eruption of M3.