The eruption of posterior teeth is a normal vertical molar change in a growing individual. It is a stable process that accompanies vertical facial development.
The normal eruption of posterior teeth is a contributing factor in achieving bite opening in deep-bite patients (Fig 6.5). The increase in vertical facial height in growing patients also accommodates the extrusion of posterior teeth that can occur during orthodontic treatment, when leveling of the curve of Spee and using inter-maxillary elastics (Class II, Class III, and vertical).
I Iowever, the extrusion of posterior teeth in adults with average to low mandibular plane angles is not a stable process. The musculature generally resists this extrusion and by the end of treatment, or shortly after, the molars return to their original vertical position and the mandibular plane returns to its original position. This may become a source of post-orthodontic relapse and return of the deep overbite. In high-angle adult patients with weaker musculature, orthodontic extrusion of posterior teeth may remain stable at the end of treatment, with permanent opening of the mandibular plane. This is undesirable in most high-angle cases.
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