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      Does the flatting of the curve of spee affect the chewing force distribution in the mandible? (3D finite element study)

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          To search the effects of Curve of Spee (COS) flatting on the stresses and displacement on the different mandible landmarks and lower teeth during posterior teeth loading using three-dimensional (3D) finite element analysis.


          Three-dimensional hemi mandibular model was created from real selected mandible. The lower teeth was aligned originally in a curved form with 2.4 mm depth at the cusp tip of the second premolar. Another replica with flat aligned teeth was formed to confirm the analysis by up righting premolars and molars. A load was applied at mesio-buccal cusp of the lower first molar on both models, and the resultant stresses and displacements on the mandibular landmarks and the lower teeth were tested.


          Von mises over the mandible was higher in flat than in curve model. The highest stress levels were detected at the Mesio-buccal cusp tip of first molar for flat and curved simulation (5053, 3304) Mpa respectively. Mesio-distally, the teeth displacement was higher in curve model than in flat one. The maximum distal displacement, in flat model, was seen in central and lateral incisors. While, in curve model, the maximum distal displacement was grasped within first and second premolars.


          Flatting the COS magnify the stresses over whole mandible and reduce lower teeth displacement mesio-distally. We speculated that the readjustment of the COS after orthodontic treatment could reduce the stress and displacements on the lower anterior teeth and decrease the lower anterior teeth crowding relapse.

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          Most cited references 51

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          The six keys to normal occlusion.

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            Young's modulus of trabecular and cortical bone material: ultrasonic and microtensile measurements.

            An ultrasonic technique and microtensile testing were used to determine the Young's modulus of individual trabeculae and micro-specimens of cortical bone cut to similar size as individual trabeculae. The average trabecular Young's modulus measured ultrasonically and mechanically was 14.8 GPa (S.D. 1.4) and 10.4 (S.D. 3.5) and the average Young's modulus of microspecimens of cortical bone measured ultrasonically and mechanically was 20.7 GPa (S.D. 1.9) and 18.6 GPa (S.D. 3.5). With either testing technique the mean trabecular Young's modulus was found to be significantly less than that of cortical bone (p < 0.0001). However, the specimens were dried before microtensile testing so Young's modulus values may have been greater than those of trabeculae in vivo. Using Young's modulus measurements obtained from 450 cubes of cancellous bone and 256 cubes of cortical bone, Wolff's hypothesis that cortical bone is simply dense cancellous bone was tested. A multiple regression analysis that controlled for group membership showed that Young's modulus of cortical bone cannot be extrapolated from the Young's modulus vs density relationship for cancellous bone, yet the Young's modulus of trabeculae can be predicted by extrapolation from the relationship between Young's modulus vs density of the cancellous bone. These results suggest that when considered mechanically, cortical and trabecular bone are not the same material.
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              Deep overbite correction by intrusion.

              Not all patients with deep overbite should be treated with the same mechanics. Some patients require intrusion of the anterior teeth, while others require primarily extrusion. This article has discussed the principles of incisor and canine intrusion and has demonstrated the use of intrusion springs that are capable of intruding incisors with minimal side effects on the posterior teeth. Six principles must be considered in incisor or canine intrusion: (1) the use of optimal magnitudes of force and the delivery of this force constantly with low-load-deflection springs; (2) the use of a single point contact in the anterior region; (3) the careful selection of the point of force application with respect to the center of resistance of the teeth to be intruded; (4) selective intrusion based on anterior tooth geometry; (5) control over the reactive units by formation of a posterior anchorage unit; and (6) inhibition of eruption of the posterior teeth and avoidance of undesirable eruptive mechanics.

                Author and article information

                J Orthod Sci
                J Orthod Sci
                Journal of Orthodontic Science
                Wolters Kluwer - Medknow (India )
                19 February 2021
                : 10
                Collage of Dentistry, University of Mosul, Mosul, Iraq
                Author notes
                Address for correspondence: Dr. Sarmad S. Salih Al Qassar Department of Orthodontics, Prevention and Pedodontics, Collage of Dentistry, Mosul University, Mosul, Iraq. Email: sarmadsobhi@ 123456yahoo.com ; sarmadsobhi@ 123456uomosul.edu.iq
                Copyright: © 2021 Journal of Orthodontic Science

                This is an open access journal, and articles are distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as appropriate credit is given and the new creations are licensed under the identical terms.

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