[Comparison of two different methods of rapid expansion combined with maxillary protraction in the treatment of skeletal class Ⅲ malocclusion].

To compare the effect of bone-anchored versus tooth-borne rapid palatal expansion (RPE) combined with maxillary protraction in the treatment of skeletal class Ⅲ patients with maxillary hypoplasia. Twenty-six skeletal class Ⅲ patients with maxillary hypoplasia in the late mixed or early permanent dentition were selected. All the patients underwent RPE combined with maxillary protraction in the Department of Orthodontics, Nanjing Stomatological Hospital, Medical School of Nanjing University from August 2020 to June 2022. The patients were divided into 2 groups. Thirteen patients were enrolled in the bone-anchored RPE group [4 males and 9 females, aged (10.2±1.7) years] and the others were in the tooth-borne RPE group [5 males and 8 females, aged (10.1±1.0) years]. Ten sagittal linear indices [Y-Is distance (the distance from the incisor edge of the maxillary incisor to the vertical reference axis), Y-Ms distance (the distance from the mesial contact point of the maxillary first molar to the vertical reference axis), the relative distance between the maxillary and mandibular molars, overjet, etc.], 6 vertical linear indices [PP-Ms distance (the distance changes from Ms to the palatal plane), etc.] and 8 angle indices [SN-MP angle (the upper external angle of the intersection of the sella-nasion plane and the mandibular plane), U1-SN angle (the lower internal angle of the intersection of the long axis of the maxillary central incisor and the sella-nasion plane), etc.] were measured on the cephalometric radiographs before and after the treatment. Six coronal indicators (the inclination of the left and right first maxillary molar, etc.) were measured on cone-beam CT images before and after the treatment. The proportion of skeletal and dental factors in the changes of overjet were calculated. The differences of the index changes between groups were compared. After the treatment, the anterior crossbite were corrected in both groups, and classⅠor classⅡ molar relationship were attained. In bone-anchored group, the changes of Y-Is distance, Y-Ms distance and maxillary and mandibular molar relative distance were (3.23±0.70), (1.25±0.34) and (2.54±0.59) mm, respectively, significantly less than those in the tooth-borned group in which the corresponding changes were (4.96±0.97) mm (-5.92, 0.001), (3.12±0.83) mm (-7.53, 0.001) and (4.92±1.35) mm (-5.85, 0.05), respectively. The change of overjet in the bone-anchored group was (4.45±1.25) mm, significantly less than that in the tooth-borned group (6.14±1.29) mm (-3.38, 0.05). Skeletal and dental factors accounted for 80% and 20% of the overjet changes in the bone-anchored group, respectively. While in the tooth-borned group, skeletal and dental factors accounted for 62% and 38% of the overjet changes, respectively. The PP-Ms distance change in the bone-anchored group [(-1.62±0.25) mm] was significantly less than that in the tooth-borned group [(2.13±0.86) mm] (-15.15, 0.001). The changes of SN-MP and U1-SN in the bone-anchored group were -0.95°±0.55° and 1.28°±1.30°, respectively, significantly less than those corresponding indices in the tooth-borned group (1.92°±0.95°, -9.43, 0.001; 7.78°±1.94°, -10.04, 0.001). In the bone-anchored group, the inclination changes of maxillary bilateral first molars in the left and right sides were 1.50°±0.17° and 1.54°±0.19°, significantly less than the corresponding indices in the tooth-borned group (2.26°±0.37°, 6.47, 0.001; 2.25°±0.35°, 6.81, 0.001). The bone-anchored RPE with maxillary protraction could reduce the adverse tooth compensation effect, including the protrusion of maxillary anterior incisors, the increase of overjet and mandibular plane angle, and the mesial movement, extrusion and buccal inclination of maxillary molars.