Skeletal and Dental Changes During Treatment of Moderate Class II Malocclusions with Fixed Class II Correctors
Creators: Fairbanks, Austin B
Publisher: name: University of Alberta Library
Year: 2024

<p>Abstract <br>
Introduction: The purpose of this this was to compare the skeletal and dental changes associated with the Herbst and Xbow fixed Class II correctors using Cone-Beam Computed Tomography (CBCT).</p>

<p>Methods: A sample of 59 Class II patients were randomly allocated into three groups. One group was treated with the Herbst appliance while another was treated with the Xbow. A control group was treated with 3M® brackets to level and align with no Class II mechanics used. All three groups had CBCT images taken before treatment and after twelve months of treatment. 3D Slicer software was used to locate skeletal and dental landmarks on the CBCT images and create 3D planes of reference to measure sagittal, anteroposterior and coronal changes of each landmark. Additionally, measurements of mandibular body length, ramus height and incisor mandibular plane angle (IMPA) were compared.</p>

<p>Results: Skeletally, there were no differences in mandibular body length or ramus height. There were no differences in skeletal landmarks in sagittal or axial directions. The Herbst group had anterior movement of mandibular landmarks gonion, B point and pogonion. Both Xbow and Herbst groups had anterior movement of the posterior nasal spine of the maxilla. The magnitude of the skeletal changes was almost exclusively less than 2mm so clinical significance is debateable. <br>
Dentally, there was differences in all three directions and lower incisor proclination. Both appliances proclined mandibular incisors almost 10° as measured by IMPA. Transversely both the Herbst and Xbow, with incorporated maxillary expanders, moved the maxillary molars and crowns laterally with crowns displacing further indicating buccal crown torque. The Xbow group had extrusion of the maxillary central incisal edge and intrusion of the mandibular central incisal edge. For dental landmarks the anteroposterior changes were the most abundant. For the Xbow group the maxillary first molar crown, maxillary central incisal edge both moved posteriorly while the mandibular central incisal edge and mandibular first molar crown and roots moved anteriorly. For the Herbst group the maxillary first molar crown moved posteriorly while the maxillary first molar root apex, mandibular central incisal edge and mandibular first molar crowns all moved anteriorly.</p>

<p>Conclusion: Neither the Xbow or the Herbst appliance caused increased mandibular dimensions. Minor skeletal changes in an anteroposterior direction occurred after use of the Herbst appliance. Overall, dental changes were similar for both appliances including: lower incisor proclination, lateral movement of molars due to incorporated expanders, distal tipping of maxillary molars. Additional retrusion and retroclination of maxillary incisors occurred in the Xbow group. In the Xbow group, the mandibular molars moved bodily anteriorly while the Herbst group had mesial crown tipping. Taken individually, the effect of each measurement’s contribution to Class II correction is negligible, but cumulatively the effects of both the Xbow and Herbst contribute to Class II correction primarily through dental correction. With the differences between the Xbow and Herbst being so small, clinical considerations will likely serve as the key factor for orthodontists in choosing which appliance to use. </p>