RESUMEN
OBJECTIVE@#The aim of this finite element study was to clarify the mechanics of tooth movement in palatal en-masse retraction of segmented maxillary anterior teeth by using anchor screws and lever arms.@*METHODS@#A three-dimensional finite element method was used to simulate overall orthodontic tooth movements. The line of action of the force was varied by changing both the lever arm height and anchor screw position.@*RESULTS@#When the line of action of the force passed through the center of resistance (CR), the anterior teeth showed translation. However, when the line of action was not perpendicular to the long axis of the anterior teeth, the anterior teeth moved bodily with an unexpected intrusion even though the force was transmitted horizontally. To move the anterior teeth bodily without intrusion and extrusion, a downward force passing through the CR was necessary. When the line of action of the force passed apical to the CR, the anterior teeth tipped counterclockwise during retraction, and when the line of action of the force passed coronal to the CR, the anterior teeth tipped clockwise during retraction.@*CONCLUSIONS@#The movement pattern of the anterior teeth changed depending on the combination of lever arm height and anchor screw position. However, this pattern may be unpredictable in clinical settings because the movement direction is not always equal to the force direction.
RESUMEN
OBJECTIVE@#The purpose of this study was to predict the optimal bending angles of a running loop for bodily protraction of the mandibular first molars and to clarify the mechanics of molar tipping and rotation.@*METHODS@#A three-dimensional finite element model was developed for predicting tooth movement, and a mechanical model based on the beam theory was constructed for clarifying force systems.@*RESULTS@#When a running loop without bends was used, the molar tipped mesially by 9.6° and rotated counterclockwise by 5.4°. These angles were almost similar to those predicted by the beam theory. When the amount of tip-back and toe-in angles were 11.5° and 9.9°, respectively, bodily movement of the molar was achieved. When the bend angles were increased to 14.2° and 18.7°, the molar tipped distally by 4.9° and rotated clockwise by 1.5°.@*CONCLUSIONS@#Bodily movement of a mandibular first molar was achieved during protraction by controlling the tip-back and toe-in angles with the use of a running loop. The beam theory was effective for understanding the mechanics of molar tipping and rotation, as well as for predicting the optimal bending angles.