A5 Malocclusion

Topic

Malocclusion is any deviation from the normal pattern of occlusal contact and the skeletal relationship between the jaws. When the skeletal relationship between the jaws is normal, the upper and lower molars fit together in a balanced molar relationship; when this skeletal relationship deviates, the mandible may be retruded relative to the maxilla—resulting in a molar relationship where the lower teeth are positioned behind the upper teeth—or it may be protruded relative to the maxilla—resulting in the opposite relationship, with the lower teeth positioned ahead of the upper teeth.

In addition to this skeletal deviation, malocclusion can manifest as premature contacts: points where a tooth touches its antagonist before the other teeth do, causing occlusal force to concentrate on that single point of contact rather than being distributed across multiple contacts, as occurs in normal occlusion. The more concentrated the occlusal force is at a premature contact, the greater the local overload borne by the affected tooth, its periodontal ligament, and the surrounding alveolar bone.

Orthodontic treatment leverages the principle that sustained force applied to a tooth affects the periodontal ligament and alveolar bone; however, instead of the uncontrolled, concentrated force of a premature contact, it applies a controlled force—ranging from fifty to three hundred grams—directed toward the desired direction of tooth movement. This controlled force triggers alveolar bone remodeling in opposite ways on either side of the tooth: on the side toward which movement is directed—where the periodontal ligament is compressed—alveolar bone is resorbed to make way for the tooth, while on the opposite side—where the periodontal ligament is under tension—new alveolar bone is deposited to fill the space the tooth leaves behind.

Within this process of alveolar bone remodeling, tooth movement does not occur all at once but rather in three successive phases. In the first phase, the tooth shifts immediately within the elastic space afforded by the periodontal ligament, before any changes occur in the alveolar bone. In the second phase, this initial movement ceases, and the tooth advances further only as the alveolar bone on the compressed side undergoes progressive resorption, gradually clearing the way. If the controlled force is removed before bone deposition on the opposite side is complete, a third phase—relapse—ensues, during which the tooth tends to return to its original position.

When the skeletal jaw discrepancy described earlier is mild, the tooth movement achieved through this alveolar bone remodeling suffices to compensate for the maxillomandibular discrepancy without altering the jawbones themselves. However, when the maxillomandibular discrepancy is too severe to be resolved by tooth movement alone, the malocclusion cannot be corrected through dental compensation alone and requires orthognathic surgery to directly reposition the jaws.

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