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Holographic determination of centers of rotation resulting from known linguolabial loads in vivo
Votume85 Number
Reviews and abstracts
189
2
treatment for preadolescent and adolescent mandibular prognathism patients.
Holographic Determination of Centers of Rotation Resulting From Known Linguolabial Loads In Vivo Robin Alan Weeks University of Connecticui, Farmington, Corm., 1983
Centers of rotation resulting from the application of known forces perpendicular to the long axis of a maxillary central incisor were calculated in vivo. Double-exposure laser holography was used to measure primary tooth displacement in three dimensions. The subject tooth was the maxillary right central incisor of a 34-year-old white woman of normal periodontal health, as determined by gingival index and periodontal probing. Radiographs and study models were used to determine the geometry of the tooth and supporting bone. A rigid loading arm with hooks was attached to an orthodontic band which was cemented to the tooth. The loading arm was parallel to the long axis of the tooth and allowed known loads to be applied at various incisal-apical positions. Tooth displacement was recorded on double-exposure holograms using a pulsed ruby laser as a source of monochromatic and coherent light. On the basis of visually observed fringe shifts using computer programs for interpretation of holograms, translations and rotations were determined in three dimensions. From the translational and rotational data, centers of rotation were calculated. For a 200-gm load applied 33 mm apical to the bracket, the center of rotation was determined to be at approximately the level of the theoretical three-dimensional center of resistance. The theoretical three-dimensional center of resistance for a tooth with this root geometry is 0.33% of the root length measured apical to the alveolar crest.
The results obtained are consistent with the results of previous in vitro tooth model studies for similar loading conditions.
A Study of Force Systems TMA ‘7” Loop Springs
Produced
by
Rohit Chaman Lal Sachdeva University of Connecticut School of Dental Medicine, Farmington, Conn , I983
This investigation was performed to study the angulations that should be placed in a TMA “T” Loop (017 x 025 inch) space-closure spring for a given force system with varying interbracket distances. Angulations in the horizontal arms of the attraction, retraction and protraction springs were varied over interbracket distances of 19 mm, 22 mm, 2.5 mm, and 28 mm. A uniplanar force and moment measuring device was used to measure the force output of the spring. The study showed that a single spring geometry was ineffective in producing a desired moment and force level over different interbracket spans. Templates based on the data for spring fabrication were a good guide to produce reasonably accurate force systems for clinical use. The load-deflection rate of the spring decreased with the placement of the preactivation bends. This factor was not affected at the clinical level by the interbracket distance or position of the “T” loop with respect to its attachments. The moments produced by the spring when activated were influenced by the “T” loop’s position between its attachments. The greater activation moment was felt at the bracket where the “T” loop was closest. In conclusion, no one spring can be used as an efficient retraction mechanism over a range of interbracket distances. During retraction of teeth attention should be paid to the position of the loop between the attachments to achieve the desired force system output.
Reviews and abstracts
189
2
treatment for preadolescent and adolescent mandibular prognathism patients.
Holographic Determination of Centers of Rotation Resulting From Known Linguolabial Loads In Vivo Robin Alan Weeks University of Connecticui, Farmington, Corm., 1983
Centers of rotation resulting from the application of known forces perpendicular to the long axis of a maxillary central incisor were calculated in vivo. Double-exposure laser holography was used to measure primary tooth displacement in three dimensions. The subject tooth was the maxillary right central incisor of a 34-year-old white woman of normal periodontal health, as determined by gingival index and periodontal probing. Radiographs and study models were used to determine the geometry of the tooth and supporting bone. A rigid loading arm with hooks was attached to an orthodontic band which was cemented to the tooth. The loading arm was parallel to the long axis of the tooth and allowed known loads to be applied at various incisal-apical positions. Tooth displacement was recorded on double-exposure holograms using a pulsed ruby laser as a source of monochromatic and coherent light. On the basis of visually observed fringe shifts using computer programs for interpretation of holograms, translations and rotations were determined in three dimensions. From the translational and rotational data, centers of rotation were calculated. For a 200-gm load applied 33 mm apical to the bracket, the center of rotation was determined to be at approximately the level of the theoretical three-dimensional center of resistance. The theoretical three-dimensional center of resistance for a tooth with this root geometry is 0.33% of the root length measured apical to the alveolar crest.
The results obtained are consistent with the results of previous in vitro tooth model studies for similar loading conditions.
A Study of Force Systems TMA ‘7” Loop Springs
Produced
by
Rohit Chaman Lal Sachdeva University of Connecticut School of Dental Medicine, Farmington, Conn , I983
This investigation was performed to study the angulations that should be placed in a TMA “T” Loop (017 x 025 inch) space-closure spring for a given force system with varying interbracket distances. Angulations in the horizontal arms of the attraction, retraction and protraction springs were varied over interbracket distances of 19 mm, 22 mm, 2.5 mm, and 28 mm. A uniplanar force and moment measuring device was used to measure the force output of the spring. The study showed that a single spring geometry was ineffective in producing a desired moment and force level over different interbracket spans. Templates based on the data for spring fabrication were a good guide to produce reasonably accurate force systems for clinical use. The load-deflection rate of the spring decreased with the placement of the preactivation bends. This factor was not affected at the clinical level by the interbracket distance or position of the “T” loop with respect to its attachments. The moments produced by the spring when activated were influenced by the “T” loop’s position between its attachments. The greater activation moment was felt at the bracket where the “T” loop was closest. In conclusion, no one spring can be used as an efficient retraction mechanism over a range of interbracket distances. During retraction of teeth attention should be paid to the position of the loop between the attachments to achieve the desired force system output.