Skeletal effects in class II treatment with the functional mandibular advancer (FMA)?

The aim of this clinical study was to reveal skeletal effects during the treatment of Class II malocclusions in adolescents and young adults using a protrusive-acting fixed, rigid functional orthodontic appliance, and to quantify them in comparison with an untreated control group. We aimed to determine whether, and if so, to what extent skeletal effects diminish with increasing age, and whether inter-individual differences can be observed.

To correct their intermaxillary jaw relationship, the functional mandibular advancer (FMA) was inserted in 16 adolescents and young adults (eight males, eight females, aged from 12 years, 3 months to 18 years, 7 months) presenting with a skeletal Class II malocclusion. The course of treatment was documented cephalometrically.

In all patients, the FMA treatment led to neutroclusion or overcorrected neutroclusion and a marked reduction in overjet. The occlusion's improvement in the sagittal dimension (overjet reduction by 4.43 +/- 2.10 mm, molar relationship improvement by 3.88 +/- 1.12 mm) was achieved by a combination of dental effects (distalization of upper teeth, mesialization of lower teeth) and skeletal effects (mandibular growth stimulation). Excepting the position and morphology of the maxillary base and the condyle's dorsal position in the fossa, all sagittal skeletal and dental changes induced by the FMA treatment were statistically significant. There was a mean increase of 1.71 +/- 1.11 mm in sagittal length of the mandible, in the sagittal-diagonal dimension of 1.42 +/- 1.51 mm and 1.53 +/- 2.15 mm, as well as a slight, significant increase in the gonial angle area. Whereas the condylar position remained stable, a forward positioning of the chin and thus significant increase in distance length was recorded from the posterior condylar margin to the anterior mandibular margin.

Treatment with a fixed functional appliance in Class II patients effected significant changes in mandibular growth and correction of the distal intermaxillary relationship even after the pubertal growth spurt in adolescents and young adults. While the proportion of the orthopedically-induced skeletal share is subject to substantial inter-individual variability in adolescents, the overall conclusion can be drawn that skeletal effects (= stimulation of mandibular growth) in general clearly lessen with increasing patient age. In young adult patients, the correction of a distal intermaxillary jaw relationship is manifested primarily as a dento-alveolar compensation for the skeletal malocclusion.