The mandibular dental arch: Part I, lower incisor position.

The position of the lower incisor with respect to hard tissue references has been evaluated. Two samples were used for this purpose: one containing 78 patients with posttreatment records having a postretention period of at least 4 years, and the other composed of 82 normal occlusions. The results indicated: 1) There was no significant difference in relapse of lower incisor crowding between cases where the lower incisor had been moved lingually, labially, or held in the same relative position during treatment. 2) The position of the maxilla should be considered when placing the lower incisor. The APo plane adequately serves as a guide to this purpose, whereas other reference lines such as mandibular plane or facial plane do not. 3) The positions of the incisors with respect to popular cephalometric reference lines such as APo, NB, or mandibular plane were not correlated with the relapse of mandibular crowding. Therefore, other clinical guides might be more successful for determining stability.