An evaluation of maxillary and mandibular rotational responses with the Clark twin block appliance

To evaluate the dentofacial changes and growth rotational responses of Angle Class II division 1 patients treated with the Clark twin block functional appliance.

This retrospective study comprised 13 boys (8.77 +/- 0.86 years) and 13 girls (8.75 +/- 0.70 years) treated by one orthodontist with the Clark twin block appliance. Selection was not biased by outcome and sample size power estimates exceeded 90 per cent. Tracings made on the pretreatment (T1), post-treatment (T2) and observation (T3) radiographs were superimposed on anatomically stable landmarks and the dentofacial changes and growth rotational responses compared. The data were tested for normal distribution and sexual dimorphism. Pearson correlation analyses of the treatment and observation phases were performed.

In light of the few sex differences and lack of any consistent trends, the data for the boys and girls were combined. Treatment reduced the overbite, overjet and achieved Class II correction through combinations of maxillary incisor uprighting (U1-SN: -5.3 +/- 5.30), lower incisor proclination (L1-MP: 6.6 +/- 6.80), facial height increase (AFH: 5.1 +/- 4.6 mm), ramal lengthening (Co-Go: 3.3 +/- 2.4 mm) and mandibular length increase (Co-Pog: 5.9 +/- 4.6 mm). During the observation period, similar growth changes were recorded, but the overbite (2.9 +/- 1.9 mm) and overjet (3.6 +/- 2.0 mm) increased due to some reversal of the treatment-induced incisor angulation changes. Over the treatment period (T1 to T2), the angles between the cranial base and maxillary (maxillary rotation) and mandibular stable structures (mandibular internal rotation) reduced by -0.1 +/- 1.2 degrees and -0.3 +/- 2.5 degrees, respectively. The angles between mandibular stable structures and Go-Me (mandibular external rotation) and SN-GoMe (mandibular total rotation) increased by 0.6 +/- 1.7 degrees and 0.9 +/- 2.1 degrees, respectively. Between T2 and T3, maxillary rotation, mandibular internal rotation and total mandibular rotation reduced -1.4 +/- 2.0 degrees, -2.4 +/- 2.5 degrees and -0.7 +/- 1.7 degrees, respectively. Mandibular external rotation increased -1.8 +/- 2.0 degrees. Mandibular total and internal rotation angles were significantly (p < 0.5) reduced at T2, but there were no significant associations between the rotations and dentofacial parameters during or following treatment.

On average, the maxillary and mandibular internal rotations were near zero during treatment, but the small and individually variable changes were not clearly associated with the Class II correction.