Fig. 8.9 Posterior crowding has been discussed as a factor in the development of some Class III malocclusions and anterior open bite malocclusions. Posterior 'squeezing out effect' can be relieved by extraction of second permanent molars in selected cases, which is helpful to treatment mechanics.
Inter-maxillary Class 111 elastics (Fig. 8.10) are most helpful in orthodontic (non-surgical) correction of Class III cases. They tend to produce lower incisor retroclination, upper incisor proclination, and A/P correction of the molar relationship (Fig. 8.11). All components of the Class III elastic force can therefore be helpful in reaching treatment goals in average or low angle cases. With Class II elastics (Fig. 8.12) the vertical components may be perceived as disadvantageous in higher angle cases.
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