Effect of the Andresen activator on the electromyographic activity of masticatory muscles: a literature review

Aim: to present an international literature review on neuromuscular changes caused by the Andresen functional appliance in patients with skeletal Class II and deep-bite, and to compare the different hypotheses. Functional appliances are orthodontic devices that use muscle tone to develop forces on the teeth or jaws. These forces achieve a change in the shape and growth of the facial bones. Materials and methods: A systematic review of the literature on the correlation between the use of the Andresen functional appliance and neuromuscular changes was conducted in the Medline database. Keywords chosen were: “EMG and functional appliance”, “EMG and Andresen activator”, “class II malocclusions”. Among articles, those published between 2000 and 2025 were considered. Results and conclusions: The international literature presents a variety of studies dealing with the neuromuscular effects caused by functional appliances. There may conflict hypotheses; the exact theory is not clear. Based on the scientific evidence presented in the literature, it is possible to conclude that, whatever functional appliance is used, there is always a neuromuscular adaptation. It is certain, however, that functional appliances activate the periosteal matrix, forcing the skeleton to according to the principles of remodeling and condylar morphogenesis linked to the function. The system abandons a state of compensatory neuromuscular equilibrium to achieve a new orthological equilibrium.