Anterior dental crossbite: relationship between incisor crown length and incisor irregularity before and after orthodontic treatment.

The purpose of this study involving a sample of children with single central incisor crossbite was to determine the relationship between clinical crown lengths of the crossbite and noncrossbite mandibular incisors, incisor irregularity, and orthodontic correction of the crossbite. In addition, for comparison, the normal maturational change in position of the labial gingival margin of mandibular incisors not undergoing orthodontic correction was examined. Twenty-one children treated for single central incisor crossbite were matched individually by gender and age to a comparison group. Pre- and post-treatment mandibular central incisor crown lengths and incisor irregularity were measured. In 10 of the 21 anterior crossbite cases, the crown length of the crossbite incisor was more than 1.5 mm greater than that of the noncrossbite incisor. This difference improved with orthodontic treatment by a combination of apical movement of the gingival margin of the noncrossbite incisor (0.9 +/- 0.8 mm) and coronal movement (0.2 +/- 0.6 mm) of the gingival margin of the crossbite incisor. In contrast, for the remaining 11 anterior crossbites without such a crown length difference, and for the comparison cases, the gingival margins of both mandibular central incisors moved equally from pre- to post-treatment by 0.5 +/- 0.5 mm in an apical direction. Pretreatment crown length difference between crossbite and noncrossbite incisor was associated strongly to incisor irregularity (P < or = 0.005, r = 0.65). Orthodontic correction of the crossbite produced an improvement in irregularity index (IR) that was greatest in those anterior crossbite cases with a pretreatment crown length difference.(ABSTRACT TRUNCATED AT 250 WORDS)