The Mandibular Condyle Process In Infants With Isolated Pierre Robin Sequence:a 3D Morphometric Analysis

BackgroundPierre Robin Sequence(PRS)is a congenital malformation mainly characterized by micromandibular deformity,retrolingual fall and upper respiratory tract obstruction.The treatment options are classified into non-surgical treatment,including position improvement and nasopharyngeal ventilation tube placement.Surgical treatment mainly includes lip-lingual adhesions,Mandibular Distraction Osteogenesis(MDO),and airway amputation,etc.MDO is widely used because it plays a stabilizing role in solving the serious problems of poor ventilation.At present,the main characteristics of PRS are micromandibular deformity,and the studies on mandibular morphology mostly focus on 2D(2D).However,since the mandibular body and ascending rami of children with Piro are curved or irregular,2D is easy to lose its true shape,and these shortcomings promote the development of 3D morphological analysis.As a new method to study morphological differences,3D chromatogram was used to calibrate the mandibular images of PRS children and normal infants with the premental contour as the stable area,and the two images were automatically aligned.The chromatogram was defined as the linear distance,and the final results were displayed in the form of chromatogram,so as to facilitate the observation of regional displacement changes and compare the characteristic areas.Studies have shown that the development of condyle in children is closely related to the development of mandibular body and ascending rami.This suggests that PRS,as a disease mainly characterized by mandibular deformities,may have a close relationship between the condyle and the morphology of mandibular body,ascending rami and mandibular Angle in the pathological mandible during the development process.Currently,there are three osteotomy lines for mandibular distraction osteogenesis in children with PRS:(1)linear osteotomy line,(2)broken osteotomy line,and(3)arc-shaped osteotomy line,corresponding to the large sample cluster analysis conducted by Gao Zijun et al.in 2020 after collecting marks for PRS mandibular morphology in our research group,and the morphology of PRS mandible is mainly divided into three categories: Type Ⅰ:Mandibular body short small;Type Ⅱ: short mandibular body with small ascending rami-body curvature;Type Ⅲ: mandibular body and ascending rami are short and small.Clinically,it was found that the application of the above osteotomy methods would cause condyle rotation,and the reasons for the condyle rotation.There was no clear analysis of the relationship between the change direction of condyle rotation and the rotation Angle and the body lengthening length in children with different types of PRS.PurposeOur research group intends to compare the morphology of the condyle,body,ascending branch,and mandibular angle between different types of PRS children and normal children through three-dimensional morphological analysis,identify their characteristic regions,and further explore the mechanism of this difference.We aim to elucidate the relationship between the condyle,mandibular body,ascending branch,and mandibular angle in PRS children,and find new treatment methods to further promote the development of the mandible in PRS children.Simulate the changes in condylar angle after MDO surgery and summarize the rules of condylar angle for different types of PRS.MethodCollect PRS cases from the oral and maxillofacial surgery department of Guangzhou Women and Children’s Medical Center from September 2020 to September 2022.Based on the preoperative maxillofacial CT data of the patients,use Proplan software to perform three-dimensional reconstruction of the maxillofacial bone and extract the mandible.Import 3D data into Geomagic Studio software and automatically overlap with the mandibles of normal developing children of corresponding age and gender in 3D.The definition of a chromatogram is linear distance,and the final result is displayed in the form of a chromatogram.Use Proplan to measure mandibular morphology values in children with I-PRS and normal infants,including distance,angle,volume,surface area,and posterior curvature of the mandibular ramus.Conduct statistical analysis on the morphological characteristics of the mandibular condyle and the mandibular body,ramus,and mandibular angle,and conduct correlation analysis.Perform mandibular osteotomy in different directions for different types of PRS children,extend the mandibular body,and rotate the condyle to study the changes in condylar angle.Results1.The characteristic regions of different types of I-PRS are different.Type Ⅰ characteristic areas: condyle,ascending branch,chin,mandibular angle;Type Ⅱ characteristic areas: condyle,mandibular angle area,ascending branch;Type Ⅲ characteristic areas: condyle,mandibular angle area,ascending branch,chin.2.As the growth and development center of the ascending branch and body,the shape of the condyle has a specific impact on the mandibular angle,mandibular body,and ascending branch.Through correlation analysis,specific conclusions can be drawn:the higher the condyle,the wider the mandibular branch,the longer the mandibular body,the smaller the mandibular angle,and the thinner the mandibular body;The larger the internal and external diameter of the condyle,the wider the neck of the condyle,the wider the mandibular branch,and the thicker the mandibular body;The larger the anterior and posterior diameter of the condyle,the wider the neck of the condyle,the higher the mandibular branch,and the thicker the mandibular body;The width of the condyle neck and the thickness of the mandibular body are jointly affected by the anterior and posterior diameters of the condyle,but the height of the mandibular branch is affected by the anterior and posterior diameters of the condyle,and the width of the mandibular branch is affected by the inner and outer diameters of the condyle;The wider the neck of the condyle,the greater the angle between the transverse axis of the condyle and the horizontal plane.3.Compared with the preoperative data after the I-PRS simulation of type Ⅰ,Ⅱ and Ⅲ,the included angle between the transverse axis of the condyle and the horizontal plane,sagittal plane became larger,and the included angle between the transverse axis of the condyle and the coronal plane became smaller,among which the included angle between the transverse axis of the condyle and the horizontal plane became larger statistically.The shorter the condyle before surgery,the shorter the body,and the longer the body distance needs to be extended.The smaller the anterior and posterior diameter of the condyle before surgery,the shorter the ascending branch,and the longer the distance of the ascending branch needs to be extended.Conclusion1.The characteristic regions of different types of I-PRS are different.Type Ⅰ characteristic areas: condyle,ascending branch,chin,mandibular angle;Type Ⅱ characteristic areas: condyle,mandibular angle area,ascending branch;Type Ⅲ characteristic areas: condyle,mandibular angle area,ascending branch,chin.2.TypeⅠI-PRS has small condyle size,short body,normal ascending rami and small mandibular Angle;Type Ⅱ I-PRS had normal condylar volume,shorter body,shorter ascending rami and large mandibular Angle.Type Ⅲ I-PRS condyles are small in size,short in body,short in ascending rami,and slightly small in mandibular Angle.3.Condyle is the center of growth and development of ascending rami and body.The higher condyle is,the longer mandibular body is and the smaller mandibular Angle is.The larger the inner and outer diameter of the condyle,the wider the mandibular rami.The larger the anteroposterior diameter of the condyle,the higher the mandibular rami.4.Compared with the preoperative data of type Ⅰ,Ⅱ and Ⅲ I-PRS simulation,the Angle between the horizontal axis of condyle and the horizontal plane of condyle increased.