Effects of activator treatment - evidence for the occurrence of two different types of reaction

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Abstract
A longitudinal cephalometric study was made of 12 boys and 13 girls with Class 11, Division 1 malocclusion treated with activators. The findings were compared with an untreated control group of 24 boys and 15 girls. The children were aged about 9 years at the start of the investigation and they were treated, or observed, for about two years. Possible alterations of mandibular condylar growth were investigated and the results were compared with previously published hypotheses on the mode of action of the activator. Since there were significant differences in the growth increments of control boys and control girls, the sexes were treated statistically as separate groups. Mandibular growth was found to be altered by activator therapy; in the boys growth was increased and redirected posteriorly while in the girls growth was only redirected. The maxilla and the dental arches were differently affected by the treatment. The differences in the observed results are probably explained by variation in the amount of vertical activation of the appliance but the possibility that boys and girls generally react differently could not be excluded. It is also possible that at least some of the differences were due to special growth patterns associated with certain features in the initial cephalometric pattern. There was no indication that modes of appliance action led to the different reactions. The results as a whole support the concept of the activator as an appliance which transduces elastic soft tissue forces to the skeletal and dental units.

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