From Volume 15, Issue 1, January 2022 | Pages 7-10
In part one of this series we described situations where extracting a lower incisor could provide a useful alternative to premolar extractions, in addition to solutions for treatment planning certain types of cases. In part two, we look at some of the problems caused by opting to extract a lower incisor and how they may be overcome.
Extraction of a lower incisor results in loss of 5–7 mm of tooth tissue from the lower arch. This reduces the intercanine width and, therefore, affects the radial fit of the upper teeth around the remaining lower teeth. With normally proportioned upper anterior teeth, this will lead to an increased overbite and overjet,1 unless steps are taken to reduce the upper labial segment width, or increase that of the lower incisors. Alternatively, a compromise in vertical and horizontal overlap can be accepted by the clinician and patient.
In Class II cases, particularly where there is already a deep bite, any residual space after relieving crowding may result in the lower incisors retroclining further, with a concomitant increase in both overbite and overjet. The commonly used MBT prescription has a -6° torque in the lower incisors, which will result in lingual crown torque of the lower incisors and can compound a Class II incisor relationship.
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