Overjet correction and space closure mechanisms for Class II treatment by extracting the maxillary first molars

Objective. To analyze the mechanism of overjet correction and space closure when treating Class II Division 1 patients by extracting the maxillary first molars. Patients and methods. A total of 100 prospective, consecutively treated Class II Division 1 patients (45 female, 55 male; 10.5-17.2 years old). Standardized lateral cephalograms prior to and after treatment were evaluated via a modified sagittal occlusion analysis (SO analysis). Results. The mean degree of overjet correction was 5.2 mm (95% CI = 4.8-5.6 mm) and was on average achieved by means of 1.7 mm skeletal and 3.5 mm dental changes. The relationship between the premolars improved by 4.8 mm toward a Class I relationship, facilitated by 1.7 mm skeletal and 3.1 mm dental changes. The 11.3 mm space closure in the maxillary first-molar extraction area resulted from distalization of the second premolars (1.4 mm) and a mesialization of the second molars (9.9 mm). Conclusions. Overjet correction was essentially achieved by a retrusion of the upper incisors, as well as by ventral growth of the lower jaw and protrusion of the lower incisors. Space closure was only partly achieved by distalization of the premolars.