Three-dimensional evaluation of upper anterior alveolar bone dehiscence after incisor retraction and intrusion in adult patients with bimaxillary protrusion malocclusion

Abstract

Objective: The purpose of this study was to evaluate three-dimensional (3D) dehiscence of upper anterior alveolar bone during incisor retraction and intrusion in adult patients with maximum anchorage.

Methods: Twenty adult patients with bimaxillary dentoalveolar protrusion had the four first premolars extracted. Miniscrews were placed to provide maximum anchorage for upper incisor retraction and intrusion. A computed tomography (CT) scan was performed after placement of the miniscrews and treatment. The 3D reconstructions of pre- and post-CT data were used to assess the dehiscence of upper anterior alveolar bone.

Results: The amounts of upper incisor retraction at the edge and apex were (7.64±1.68) and (3.91±2.10) mm, respectively, and (1.34±0.74) mm of upper central incisor intrusion. Upper alveolar bone height losses at labial alveolar ridge crest (LAC) and palatal alveolar ridge crest (PAC) were 0.543 and 2.612 mm, respectively, and the percentages were (6.49±3.54)% and (27.42±9.77)%, respectively. The shape deformations of LAC-labial cortex bending point (LBP) and PAC-palatal cortex bending point (PBP) were (15.37±5.20)° and (6.43±3.27)°, respectively.

Conclusions: Thus, for adult patients with bimaxillary protrusion, mechanobiological response of anterior alveolus should be taken into account during incisor retraction and intrusion. Pursuit of maximum anchorage might lead to upper anterior alveolar bone loss.

Figures

Fig. 1

Miniscrews of pre-(a) and post-treatment (b) Miniscrews were placed in the interradicular locations between the first molar and second premolar at the attached gingival level height

Fig. 2

Effect of point-registration The teeth and maxilla were registered with the surface points that did not change after orthodontic treatment. (a) Most protruding points on the inferior margin of the zygomatic arch (black arrows); (b) Registration of pre- and post-treatment models; (c) Pre-models of the teeth; (d) Post-models of the teeth; (e) Pre- and post-models of the teeth that were matched to each other after the registration of maxillary

Fig. 3

Effect of STL registration (a) STL registration with cranial base; (b) STL model occlusal view; (c) T1 STL model occlusal view; (d) T2 STL model occlusal view

Fig. 4

Distance between T1 and T2 models (a) The landmarks identified on CT scan; (b) Bending angles of labial cortex and palatal cortex between T1 and T2 models; (c) Measurements of the retraction distance at the cusp tip of the crown and the apex of the root in sagittal plane between T1 and T2 models; (d) Vertical distance differences from UICE to LAC and PAC measured parallel to long axis between T1 and T2 models

Fig. 5

Data measured at landmark points (a) Bone height losses at labial and palatal sides; (b) Bone height loss percentages at labial and palatal sides; (c) Bending angles of labial and palatal cortex; (d) Amounts of upper incisor retraction at edge and apex. *P<0.05 (n=20)