In orthodontics, biomechanics represents the application of mechanics to the biology of tooth displacement and is based on certain principles
Clinically, forces can be applied in three ways to determine tooth displacement:
1.Single force that results in significant crown inclination;
2.Pair of forces that allows a controlled inclination of the root in the mesio-distal sense (tipping) or in the vestibulo-lingual sense (torque);
3.Single force + force pair, a combination that allows to obtain a translation of the tooth while maintaining good control of the root inclination.
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The concept of “ideal”: The purpose of orthodontic treatment is to transform a malocclusion into an “ideal” dento-skeletal Class I occlusion. The word dento-skeletal indicates that an “ideal” occlusion consists of two components (dental and skeletal).
When the teeth are in occlusion, the mesio-vestibular cusp of the upper first molar occludes in the vestibular sulcus of the lower first molar (Angle’s Class I molar ratio), with the upper canines located between the canines and the lower first premolars (Class I canine ratio).
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A fundamental prerequisite for achieving normal occlusal relationships during orthodontic treatment is the correct positioning in the three planes of space of the maxillary bone and mandible, which must also be correctly proportioned to each other.
Under normal conditions, the right and left halves of the face are almost symmetrical and the upper arch overlaps the lower arch for its entire length. When this condition does not occur, there is a “transverse discrepancy,” which represents a “developmental abnormality in the transverse plane.” Although the diagnosis of transverse discrepancy is often straightforward, some asymmetries can sometimes be masked by dental compensations. Depending on the structures involved, these problems may have a dental, skeletal, or functional origin, or a combination of these factors may be present.
In a normal occlusion, in the transverse plane, the palatine cusps of the upper molars and premolars occlude into the pits of the lower molars and premolars while in the anteroposterior plane, the upper incisors occlude on the buccal surfaces of the lower incisors.
A crossbite represents a discrepancy in the vestibulo-lingual relationship of the upper and lower teeth. It can affect entire segments of the dental arch or individual teeth, or be mono- or bilateral. An anterior crossbite is present when the lower incisors occlude further forward than the upper incisors, resulting in a tooth relationship of complete inversion and decreased (or negative) overjet.
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