12 industry clinical This muscular hyper-contractibility produces higher blood flow in the muscles protruding the mandible, and thus the excess of lactic acid accumulated during the period the trainer was in the mouth is removed from the muscles. This increase in blood flow brings to OrthO tribunE | OctObEr 2009 the muscles more undifferentiated cells, which have the ability of differentiating into myoblasts that can produce new muscular fibers in those muscles. One of the muscles playing an important role in stimulating mandibular growth and development when these kind of functional appliances are used is the lateral pterigoid muscle. This muscle inserts on the mandibular condyle and is in charge of moving the mandibular condyle forward, together with the articular capsule and the interarticular disc at the temporo-mandibular joint, when the mandible protrudes or performs lateral excursions. As previously explained, there are small movements of the condyle within the glenoid fossa at the temporo-mandibular joint that are interpreted by the patient as discomfort in the morning. It is noth- f OT page 11 cannot maintain the teeth in maximum contact (maximum intercuspation) and cannot maintain the mandible in a relaxed position. The muscles protruding the mandible are still performing contractions. ADS Fig. 3: Patient is 8 years old. After treatment with a TRAINER Appliance (T4K) for more than 16 months (two bottom photos), the mandible is positioned forward and the inclination of the maxillary incisor teeth improved. ing more than the movement of the mandibular condyle, produced by the hyper-contractibility of the lateral pterigoid muscle raising after the appliance is removed from the mouth. These forward and backward movements of the mandibular condyle within the glenoid fossa stretch the retro-discal pad (also known as Zenckel’s zone) where the blood vessels release nutrients and growth factors that reach the mandibular condyle, stimulating mandibular growth and development through endochondral ossification. This was reported by Prof. Alexandre Petrovic, who showed through his studies (Petrovic et al., 1991; Stutzmann and Petrovic 1990) how these FMO appliances maintain the mandible over a certain period of time in an edge-to-edge position and how mandibular growth is stimulated by this action. (It is