Three-Dimensional Displacement of Partial Craniofacial Bones Following Rapid Maxillary Expansion in Young Patients with Angle Class III Malocclusions

Objective: The aim of this study was to analyze the displacement in 3D direction of some craniofacial bones with the rapid maxillary expansion in Angle class III malocclusion. Method: Thirteen Angle class III patients (mean age: 12.4 +/- 1.7 years; 7 males, 6 females) using rapid maxillary expansion as part of their orthodontic treatment were selected and computed tomography scans were taken before and after expansion. The 3D models were reconstructed using the Mimics software and the maxillary, zygomata, nasal bones were separated. With 3D models correction and registration, the displacements in the 3D directions of partial craniofacial bones were measured. Quantitative variables were analyzed by using SPSS19.0 and a t value less than 0.05 was considered statistically significant. Results: Measurement results showed that rapid maxillary expansion produced significant displacement in both sides of the maxillary, zygomata, and nasal bones. In the width of the midline palatine suture, the anterior nasal spine point was expanded a mean 4.18 mm (range 2.42 mm-5.68 mm, P-left = 0.007, P-right = 0.014) and the posterior nasal spine point was expanded a mean 2.14 mm (range 1.96 mm-2.43 mm, P-left < 0.001, P-right = 0.002). In the width of the maxillary in coronal plane, the Spr point was expanded a mean 4.86 mm (range 3.34 mm-6.22 mm, P-left = 0.004, P-right = 0.008) followed by the A point expanded a mean 4.47 mm (range 2.87 mm-5.97 mm, P-left = 0.005, P-right = 0.010). The bilateral maxillary moved to both sides and the points of the front maxillary anterior nasal spine and A moved forwards and downwards. In the width of the zygomata, the Zm point was expanded 2.18 mm (range 1.87 mm-2.41 mm, P-left = 0.001, P-right = 0.002) on average and moved backwards, the retral and upper points of the zygomata Za and Mz also moved backwards. The points Zm, Za, and O all moved upwards. The external lateral side of the nasal bone expanded to both sides, the Ipa point was expanded a mean 2.04 mm (range 1.11 mm-2.46 mm, P-left = 0.008, P-right = 0.019) and the centre of the nasal bone moved backwards and downwards. Conclusion: With rapid maxillary expansion, the increasement of width in the maxillary affected the position of the zygomata and nasal bones in the 3D directions, caused changes in facial appearance.