Hemisection: one large step toward management of congenitally missing lower second premolars.

When the primary molar cannot be retained in cases of agenesis of the lower second premolar (CML5), there is the possibility of alveolar atrophy, and space closure might have a negative impact on facial fullness. Bearing these in mind, the removal of the distal half of the second primary molar might allow closure in stages. Subsequent removal of the mesial half can be followed by space closure. Using this hemisection approach, space closure can be continued with ease improving treatment results. In order to test the amount of anchorage loss resulting from this approach, the pitchfork analysis was used to compare a group of 23 consecutively treated patients, each treated by hemisection, with two groups of 30 patients, each of whom was treated with the extraction of four premolars. One group had four first premolars removed and the second group had second premolars removed. In order to obtain an untreated "control," these were further compared with the difference between the Bolton templates at ages nine and twelve. The CML5 group was divided into those which had upper teeth extracted in order to facilitate the correction and those who were treated without extraction in the upper. The hemisection groups showed statistically significant diminished distal movement of the upper incisor as well as the upper and lower lip. Lower molar protraction and molar relation was significantly increased. The process facilitates the keeping of upper premolars, which further enhances the facial fullness.