Mechanism of Class II Correction With Fixed Lingual Mandibular Growth Modificator (FLMGM)

The current study was prospective, controlled, parallel groups, clinical trial conducted at the department of Orthodontics between May 2009 and June 2011. The protocol of study was approved by the council of scientific research and postgraduate studies, on the 5/April/2009.

Of the 43 patients initially enrolled, 38 completed this trial and comprised the final sample, and 5 (4 treated, 1 untreated) were excluded.

The final sample comprised 38 subjects who completed this trial. All patients and parents gave prior informed consent to their inclusion in the investigation.

Patients of both groups were followed on a parallel basis during a period of 8 months and the trial included all patients regardless of achievement of a Class I incisor relationship. All patient of treatment group (n=21) were treated using FLMGM without extractions or any other form of orthodontic treatment, though the treatment was continued beyond this time point if the Class II malocclusion was not fully corrected and clinical objectives were not achieved. On the other hand, no orthodontic treatment was performed during that duration for the subjects of control group (n=17), and most of control subjects were offered suitable treatment at a later date.

For each patient, a direct digital lateral cephalogram was taken pre- and post- treatment/observation using PAX 400 (VATECH CO., Korea) with the same settings. All cephalograms were digitized on screen by a cursor-driven mouse and analyzed in a blind manner by the same orthodontist using a commercial cephalometric software (Viewbox, version 3.1.1.13, dHAL Software, Kifissia , Hellas, Greece). All measurements were reduced to life size (radiographic enlargement of 7.54 % in the median plane).

At the end of the treatment/observation period, sagittal occlusal (SO) analysis, according to the method of Pancherz modified by Franchi et al, was applied to assess sagittal occlusal changes and identify the mechanism of Class II correction. Moreover, the total mandibular length (Condyle-Gnathion) was measured.

The sample was used as a whole and not differentiated by sex. Pretreatment equivalence and comparison of changes observed in the FLMGM and control groups were tested for significance with independent-sample t-test using SPSS, version 16.0. Changes occurring during the examination period in each group were tested with paired-sample t-test. P values of less than 0.05 were considered statistically significant.

To assess the method error, twenty cephalograms were picked at random from the treatment and control groups and redigitized and analyzed by the same orthodontist after an interval of 1 month, and the combined error of cephalometric method was calculated by Dahlberg's formula.

Inclusion criteria

• Cl II/1 malocclusion with an overjet greater than 4 mm.
• Mild to moderate Class II Skeletal pattern (A-N-B > 4°) with retrognathic mandible (S-N-B < 76°).
• Growth potential. Fishman skeletal maturation indicator (SMI) method was used to assess the hand-wrist radiographs, and only patients in the peak of the pubertal growth spurt, which occurs on average between SMIs 4 to 7, at the beginning of the treatment/observation period were invited.

Exclusion criteria

• craniofacial syndromes
• clinically obvious facial asymmetry
• extreme vertical disproportion
• prior orthodontic therapy
• permanent tooth extractions
• significant medical history