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Rotations of the occlusal plane not only affect the vertical dimension of the growing face but also the anteroposterior relation between upper and lower jaw. Conventional tooth born class III orthopedics often result in upper molar extrusion and posterior rotation of the mandible, with increase of the length and convexity of the face, which sometimes is wrongly interpreted as a restraint of mandibular growth. Furthermore, a counter clockwise rotation of the palatal plane, by the line of force passing below the center of resistance of the zygomatico-maxillary complex, may also result in a downward movement of the upper molars. These maxillary rotations can be altered by changing the angulation of the orthopedic force and it’s perpendicular distance to the center of resistance, or by adding an extra moment of force. Finally the moment-to-force ratio of the resulting orthopedic force system applied to the upper jaw will determine the direction of the maxillary rotation, and the subsequent rotations of the occlusal plane and the mandible.
Learning Objectives:
Identify rotations of the occlusal plane and palatal plane by different class III orthopedics.
Evaluate biomechanics of maxillary rotations.
Analyze the effect of canting of the occlusal plane on mandibular rotations.
