Sagittal Skeletal and Occlusal Changes of Class II, Division 1 Postadolescent Cases in the Herbst and Activator Therapy

Class II malocclusions are common orthodontic irregularities (they account for 27% of all orthodontic irregularities) and they are considered a major reason for consulting an orthodontist. The positive outcome of Class II malocclusion treatment has some significant advantages: the prevention of traumatic injuries of upper incisors associated with large overjet and hard palate injuries with lower incisors, prevention of trauma of temporomandibular joints resulting from excessive load during the performance of orofacial functions, prevention of the development of dysfunctions (breading, speech...) and psychosocial adaptation for children during the important process of personality development. In the treatment of skeletal Class II malocclusions, the objective is often to stimulate sagittal mandibular growth since the sagittal mandibular deficiency is the most common cause of this orthodontic irregularity. An appliance for affecting mandibular position and growth was first designed in 1877. It was introduced by Norman W. Kingsley and this treatment method was called “Jumping the bite” (Pancherz, 2008). This term denotes a treatment with an orthodontic appliance for the direction of bite mesially, advancement of the mandible. The appliance comprised of an upper plate furnished with an inclined plane that held the lower incisors and forced the mandible anteriorly. The principle of bite jumping has led to the development of the different removable functional appliances that we use today such as the Activator by Andersen and Häupl, bionator according to Balters, Fränkel appliance etc. (Graber et al., 1997). The effect of the activator on mandibular growth has been a subject of debate for many years (Bjork, 1951; Korkhaus, 1960; Harvold & Vargervik, 1971; Ahlgren & Laurin, 1976, Pancherz, 1979, 1984; Wieslander L & Lagerstrom, 1979; Luder, 1982; Jacobsson & Paulin, 1990). Some researchers claim that mandibular condylar growth can be stimulated by removable functional appliances treatment while others state that the changes in the occlusion are a result of dentoalveolar remodeling processes. This disagreement between the scientists is mainly due to the difficulties in the evaluation of treatment results as the activator, like all other removable functional appliances, has several disadvantages: 1) the appliance is mostly used only part of the day. This implies that in certain individuals the threshold for condylar growth adaptation to forward displacement of the mandible will never be reached. 2)