[Evaluation of the changes of alveolar bone around the upper incisors after retraction with mini implant anchorage...

The aim of this clinical study was to evaluate the changes of alveolar bone morphology before and after upper incisors retraction with mini implant anchorage using cone-beam CT (CBCT).

Twenty-two young patients with dentoalveolar maxillary protrusion and extraction of 2 maxillary first premolars were evaluated with CBCT. CBCT scans were obtained before treatment and 3 months after retraction of the incisors. The movement patterns of the upper incisors were assessed with Mimics15.0. The labial and palatal alveolar plates at crest level, midroot level, and apical level for bone-thickness changes and labial and palatal vertical bone level during retraction of the maxillary anterior segments were assessed with Invivo5.0. Paired t tests were used to evaluate the changes.

The edge of the maxillary incisor and the root apex appeared lingual movement horizontally, but the moving distance was larger than the root apex. The edge of the incisors was moved downward, and the root apex was moved upward obviously. The palatal thickness and total thickness of the alveolar bone showed significant decrease at the crest level and midroot level after retraction while the apical level showed significant increase(P＜0.05). The palatal vertical bone level also showed great loss (P＜0.05).

After extensive retraction of the maxillary incisors, tilt movements are controlled with high traction hooks and microscrew implants. The decreases in palatal bone thickness are much more significant compared with the increases in labial bone thickness. Alveolar bone remodeling doesn't follow the movement of tooth, suggesting that the limitation of anterior teeth retraction should be taken into consideration.