| Bimaxillary protrusion(BP) is a common malocclusion in Asian adults. Facial esthetic problems related to BP include extreme protrusion of the anterior teeth and lip, lip incompetence, strain with hypermentalis action on closure, thick-looking lips with an everted vermilion border, convex profile, and toothy appearance in cases of chin deficiency, bringing some negative effects to their psychological and social life. For adult patients with bimaxillary protrusion, orthodontic treatment alone can hardly effectively improve the esthetic facial profile. In recent years, with the development and popularization of the orthognathic surgery, more and more clinicians try to solve the problem through orthodontic and orthognathic treatment. The surgery usually consists of extraction of one premolar on each side. Vertical bone cuts are subsequently made at the extraction site. A horizontal bone cut about 5 mm beneath the tooth apices is carried out to join the vertical osteotomies on either side. Thereafter the axial inclination of the mobilized anterior segment can be altered. Once the desired vertical, anterior or posterior location of the anterior segment has been achieved, it is fixed with plates and screws. Oral cavity proper is one of the most important space in maxillofacial region, mainly consists of tongue, mouth floor tissues, some muscles and glands, and it is closely related to the hyoid bone and upper airway. However, the effects of volume change of oral cavity proper have seldom been taken into account. Previous studies on bimaxillary protrusion mainly concentrated in the pre- and post-operative soft and hard tissue profile changes, while the changes of the oral volume size are seldom reported. Considering the technical limitations, most of the previous researches are based on two dimensional lateral cephalograms, rather than volume or diameter measurements. Application of computer tomography in orthognathic surgery provids a better way to study the oral cavity proper.ObjectiveIn this study, female adult bimaxillary protrusion patients with orthodontic surgery were selected as the research objects. Patients who met the inclusion criteria received CT scans, conducted under the same condition. Rebuild 3D models of oral cavity proper with 3D-reconstruction technology to compare the differences between female adults patients with bimaxillary protrusion and individual normal occlusion in oral cavity proper volume and related lines, and compare the pre- and post-operative changes of oral cavity volume and related lines in bimaxillary protrusion patients, and provide a reference for the treatment and prognosis of orthognathic operation, and lay the foundation for further research.MethodsExperiment 1:3D model of the oral cavity proper was established. We selected 30 cases of female adults with individual normal occlusion(18 to 35 years old) from the CT database in the Department of Radiology at The Fourth Military Medical University, and selected 1 patient randomly, and transfered the CT data into Mimics software, mark the related points and planes, and then segmentation, 3D model of oral cavity proper is finally established.Experiment 2: 15 cases of female adults with bimaxillary protrusion who needed Orthognathic operations(20 to 35 years, mean age 23.6 years) from 2013 June to 2014 October in The Fourth Military Medical University Hospital of Stomatology Department were selected as the research objects, and we randomly selected 15 cases from the individual normal occlusion in experiment 1 as the control group(mean age was 22.4 years)., and reconstructed 3D models of the groups according to the method in experiment 1. Compare the oral capacity, the median sagittal plane area and lines measurements, and analyze the correlation between area and linear with the oral volume. SPSS17.0 statistical software was used, with independent samples t test and correlation analysis on the research datas.Experiment 3: 15 female adults with bimaxillary protrusion who undertook anterior subapical osteotomy received CT scans a week before surgery and six months after surgery. Compare the changes between the two groups. The paired t-test was used for comparison of preoperative and postoperative oral cavity proper changes.Results1. A method for 3D segmentation of the oral cavity proper is established, providing a viable research method for further study. 2. There were no significant differences in the mandibular capacity of the oral cavity proper between bimaxillary protrusion group and individual normal occlusion group. Bimaxillary protrusion,however, was significantly larger than the normal occlusion in the capacity of the oral cavity proper, maxillary capacity of the oral cavity proper, the midsagittal area, the midsagittal length and palatal height occlusion. Bimaxillary protrusion of the mandible width and mandibular length is less than the width of individual normal occlusion. The general indication was that width was more related to the size of the capacity of the oral cavity proper than length was. 3 The capacity of the oral cavity proper in bimaxillary protrusion patients after treatment decreased 10.13%, the mean decreased quantitative capacity was 7.08cm3,. The average reduction in sagittal plane was 6.31 mm, sagittal area average was reduced by about 2.35cm2; posterior dental arch width, volume of maxilla and mandible were reduced in the same degree, the sagittal plane height and width did not change, while the length of mandible increased after surgery.ConclusionThree dimensional measurement of the oral cavity proper is more accurate than the two-dimensional, as width size is one of the important factors that affect the capacity. The capacity of the oral cavity proper decreased after orthognathic surgery, while the sagittal changes in the same degree. In order to evaluate the effect of oral surgery, we should consider the relative size and surrounding soft tissues. |
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