INTRODUCTION: This study was designed to determine the optimum vertical height of the retraction force on the power arm that is required for efficient anterior tooth retraction during space closure with sliding mechanics. METHODS: Three adults (1 man, 2 women) with Angle Class II Division 1 malocclusions were selected for this study. In each subject, the maxillary right central incisor was the target tooth. Initial tooth displacements of that tooth with sliding mechanics with various heights of retraction forces were measured in vivo by a 2-point 3-dimensional displacement magnetic sensor device. The tooth's motion trajectories on the midsagittal plane were studied. RESULTS: The location of the center of rotation of the target tooth varied according to the different heights of the retraction forces. Controlled anterior tooth movement (ie, lingual-crown tipping, lingual-root movement) can be predicted, simulated, or even manipulated by different heights of retraction forces on the power arm in the sliding mechanics force system. A power arm length of 3 to 5 mm is estimated to produce controlled lingual-crown tipping (with the apex as the center of rotation) for efficient anterior tooth retraction during sliding space closure in adults with Angle Class II Division 1 malocclusion. CONCLUSIONS: Knowing and applying the correct height of retraction force on the power arm is the key to efficient anterior tooth retraction.
INTRODUCTION: This study was designed to determine the optimum vertical height of the retraction force on the power arm that is required for efficient anterior tooth retraction during space closure with sliding mechanics. METHODS: Three adults (1 man, 2 women) with Angle Class II Division 1 malocclusions were selected for this study. In each subject, the maxillary right central incisor was the target tooth. Initial tooth displacements of that tooth with sliding mechanics with various heights of retraction forces were measured in vivo by a 2-point 3-dimensional displacement magnetic sensor device. The tooth's motion trajectories on the midsagittal plane were studied. RESULTS: The location of the center of rotation of the target tooth varied according to the different heights of the retraction forces. Controlled anterior tooth movement (ie, lingual-crown tipping, lingual-root movement) can be predicted, simulated, or even manipulated by different heights of retraction forces on the power arm in the sliding mechanics force system. A power arm length of 3 to 5 mm is estimated to produce controlled lingual-crown tipping (with the apex as the center of rotation) for efficient anterior tooth retraction during sliding space closure in adults with Angle Class II Division 1 malocclusion. CONCLUSIONS: Knowing and applying the correct height of retraction force on the power arm is the key to efficient anterior tooth retraction.