[Study of the root position of palatally malposed maxillary lateral incisor based on cone-beam CT images]

The goal of this investigation was to measure and analyze the root position of palatally malposed maxillary lateral incisor based on cone-beam CT(CBCT)images, in order to provide references for orthodontists to move this kind of teeth scientifically.

CBCT data from 200 patients meeting the selection criteria with palatally malposed maxillary lateral incisor were investigated in this study. The root was divided into eight equal parts by length, then T1 to T8 were orderly pointed from root apex to alveolar ridge crest. The labial and palatal bone thickness at each point was measured; meanwhile, the angle between the long axis of the tooth and that of the alveolar bone was measured.The data was analyzed using SPSS 19.0 software package.

The mean labial bone thicknesses at all researched points were less than 1.00 mm, except for point T1,T7 and T8. The mean labial bone thicknesses at point T3, T4 and T5 were the thinnest, which were all less than 0.5 mm(P<0.05). The mean thicknesses of labial bone gradually increased from T4 to T8(P<0.05). The mean palatal bone thicknesses were all more than 1.00 mm at the eight points,the mean thicknesses of palatal bone gradually increased from T8 to T1(P<0.05). All the angulations between the long axes of teeth and those of the alveolar bone were negative, indicating the root was close to the labial alveolar wall. The average angulation was minus 31.06 degrees.

Results suggest that the root of palatally malposed maxillary lateral incisor is close to the labial wall of the alveolar bone, its labial alveolar bone is frequently quite thin or even deficient, especially in the zone between 1/4 root length to the root apex and the mid-root. If we move the palatally malposed maxillary lateral incisor labially, it is better to choose tipping movement, instead of bodily movement, in order to avoid serious bone fenestration and dehiscence or root absorption.