Distal movement and retraction of the lower incisors within the mandibular bone

In most non-surgical Class 111 treatments, it is helpful to retract and retrodine the lower incisors (Fig. 8.23). This can compensate for mild mandibular prognathism or mild maxillary retrognathism, and hence mask the underlying skeletal discrepancy. The anatomy of the mandibular bone in the lower incisor region places limits on what should be attempted. Retraction and retrod ¡nation beyond a figure of approximately 80° to the mandibular plane (Fig. 8.24) is undesirable, because of the risk of dehiscence and lack of bone support for the over-retracted incisors. Also, dental esthetics and function will be adversely affected. The figure of 80° compares with the Michigan normal1 of approximately 95°. Although 80° is a good rule of thumb, in some cases a limit of 85° may be appropriate, and a case-by-case assessment is recommended.

The required retraction and retroclination of the lower incisors is normally achieved with the assistance of Class III elastics, and treatment mechanics are easier in cases where lower teeth have been extracted. Lower first premolar extractions are most favorable in assisting lower incisor distal movement, but loss of lower second molars can also be considered (Case KB, p. 242).

If the lower arch is managed on a non-extraction basis, Class III mechanics can be used to produce some retraction and retroclination of the lower incisors. This can produce distal tipping of the lower premolars and molars, which in turn reduces the available space for the lower third molars (Case MS, p. 241 ). F.arly removal of lower third molars can be considered in some cases.

A non-extraction approach to Class III treatment may not achieve sufficient lower incisor movement for the needs of the case. Correction of the malocclusion may be possible, but not over-correction. Thus, there is no provision in the result for any late growth changes, which occur relatively frequently in Class III cases, especially among male patients.

Hockey Stick Incision Wisdom

Fig. 8.23 Retraction and retroclination of lower incisors is helpful in most non-surgical Class Nil treatments.

Fig. 8.24 As a general rule, retraction and retroclination of lower incisors beyond 80° to the mandibular plane is undesirable.

Fig. 8.23 Retraction and retroclination of lower incisors is helpful in most non-surgical Class Nil treatments.

Fig. 8.24 As a general rule, retraction and retroclination of lower incisors beyond 80° to the mandibular plane is undesirable.

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