Objective: The aim of the study was to evaluate the masticatory muscle adaptability level, the dimensional variability, the mandibular propulsion and the dental-alveolar effects induced by functional Class II appliance, activated in two steps, in growing rats.
Method: 10 rats (Wistar type) were selected at pubertal growth spurt. A fixed propulsion appliance was applied in 5 rats, then reactivated after 14 days. The remaining 5 rats were the control group. The study lasted 28 days. At the end of the experiment, muscular analysis and morphometric mandibular investigations was conducted. The fibers cross section area (C.S.A) and the weight of single muscle was calculated in order to evaluated the level of adaptability induced by the appliance. Cephalometric analysis was conducted in order to reveal the level of mandibular propulsion, dimensional variation and dental effects.
Results: In the testing group a decreasing of temporal muscle’s weight, a reduction of pterygoid C.S.A and increasing of digastric C.S.A. were registered. No difference in mandibular length and height was observed between the testing and the control group. The mandibular propulsion in treated rats was higher but the difference was no statistically significant. Moreover, in the study group an important proinclination of lower incisors was found.
Conclusions: The mandibular propulsion appliance activated step by step induced alterations in masticatory loading and masticatory muscles adaptations. The appliance didn’t produce a significant mandibular propulsion, nor an increasing in mandibular growth, but primarily dental effects on lower incisors.