Study Of Maxillofacial Morphology Characteristics And Treatment Strategy In Children With Severe Hemifacial Microsomia

ObjectivesHemifacial microsomia(HFM)is a kind of common congenital craniofacial deformity.The aberrant structures and functions of mandible and temporomandibular joint have always been the focus of attention.How the maxillary development being affected of different types is not clear.The correlations between mandibular dysplasia and maxillary deformities in HFM patients have not yet been clear.There is no such three-dimensional measurement system specifically for the HFM maxilla.Because of insufficient understanding of the etiology and jaw deformity of HFM,the function of stomatognathic system,and the interaction among these factors and treatment choices,the treatment of severe HFM children is very difficult and the therapeutic effect is not satisfied.The purpose of this study is to establish a reliable method for maxillary measurement in patients with HFM using spiral CT and digital medical software.The authors sought to comprehensively evaluate the hemifacial maxillary deficiency and to assess for Pruzansky-Kaban score correlation.We also seek to examine the association of maxillary volumetric and linear measurements with mandibular ramus height or corpus length on the affected side in children with unilateral HFM.On this basis,we sought to observe the short-term therapeutic outcomes of patients with severe unilateral HFM who underwent mandibular distraction osteogenesis(MDO)first,and study the effect of MDO on facial skeleton morphology and development in patients with severe HFM.MethodsIn this retrospective research,a total of 87 children with unilateral HFM were enrolled at our department from 2010 to 2020.The patients were grouped according to Pruzansky-Kaban classification system:9 patients type Ⅰ,26 patients Ⅱa,35 patients type Ⅱb,17 patients type Ⅲ.Chapter 1,Section 1 and 2:Demographic information of 67 patients with untreated unilateral HFM were recorded,and craniofacial computed tomographic scan were reconstructed and analyzed by segmentation,volumetric and cephalometric measurements using Mimics and ProPlan software.Chapter 1,Section 3:In addition,the preoperative craniofacial helical CT scan data of 70 HFM children were selected for three-dimensional reconstruction,and the maxillary volume,maxillary height,maxillary width,mandibular ramus height and mandibular corpus length were measured respectively.Chapter 2,Section 1:A retrospective study of 36 children with severe HFM who underwent MDO first was conducted.Perioperative and follow-up medical records,photos and imaging data were collected.Cephalometric measurements and clinical variables were analyzed to evaluate the effectiveness of MDO first strategy for severe cases and compare disparity between groups.Chapter 2,Section 2:Finally,twenty-nine children with severe HFM who had received MDO treatment were included.The craniofacial helical CT data of the patients before MDO and after the removal of MDO devices were collected.The CT data were inputted into Mimics and ProPlan software for three-dimensional reconstruction.The maxillary volumetric and cephalometric measurements,mandibular ramus height and corpus length were measured before and after treatment.Statistical analyses involved interclass correlation coefficient(ICC),Pearson correlation coefficient,t-test,Spearman correlation coefficient,univariable and multivariable linear regression.ResultsThe reliability of the novel HFM maxillary three-dimensional measurement system established in this study is good(ICC>0.75).In terms of the maxillary morphology of various HFM types,the maxillary total volume was found to be significantly decreased on the affected side in patients with type Ⅱa(p=0.0426)and Ⅱb(p=0.0004).No notable differences in maxillary sinus volume were found.No significant differences in maxillary width measurements were found between groups type Ⅰ and Ⅲ.A descending trend in maxillary bone volume ratio,an increasing trend in maxillary posterior width ratio and a decreasing trend in maxillary middle height ratio was observed from group Ⅰ to Ⅱb(pmbv*=0.020;pmpw*=0,002;pmmh*=0.004).In addition,we found mandibular ramus height(MRH)was positively associated with the maxillary bone volume(MBV)(r=0.484,p<0.001)and maxillary total volume(MTV)(r=0.520,p<0.001).Similarly,mandibular corpus length(MCL)was significantly associated with the MBV(r=0.467,p<0.001)and MTV(r=0.520,p<0.001).Multivariate regression analysis revealed that the MRH or MCL were significantly and independently associated with MBV or MTV(MRH/MBV β=0.420,p<0.001;MRH/MTV β=0.391,p<0.001;MCL/MBV β=0.403,p<0.001;MCL/MTVβ=0.307,p<0.01).In this study,all the patients with severe HFM received MDO first strategy and used a vertical vector(>60 degrees)for distraction.At the last follow-up period,MDO acquired significant improvement in mandibular height,maxillary cant and chin deviation in all patients(p<0.001).Distraction results were stable during the short-term follow-up in terms of the mandibular height ratio and maxillary cant(p>0.05).Slight recurrence can be observed in chin deviation(p<0.05).Clinical evaluation revealed that the lip commissural line tilt and clinical chin deviation were all significantly corrected(p<0.001).Three-dimensional measurements confirmed that,after MDO treatment,the average maxillary occlusal cant decreased significantly from 19.28±5.75°to 16.49 ±5.30°(p<0.001),and the mean maxillary sinus volume,maxillary total volume,maxillary width,maxillary anterior and posterior height,and mandibular corpus length increased significantly on both sides(p<0.05).In addition,MDO significantly increased the average maxillary middle height and mandibular ramus height on the affected side(p<0.001).The growth of the anterior,middle and posterior height of maxilla on the affected side was significantly faster than that on the contralateral side(p<0.01).After the treatment,the maxillary width(affected/contralateral)ratio did not change significantly(p>0.05),but the maxillary height ratio increased significantly(p<0.01).Thereinto,the maxillary anterior and posterior height ratio was close to 1.The average mandibular ramus height ratio increased significantly to 0.87(p<0.001).ConclusionsIn this study,a reliable three-dimensional measurement method for evaluating the maxillary morphology of HFM was established by using digital technology.This study comprehensively characterized the HFM maxillary deficiency.For maxillary total volume and transverse development,the type Ⅲ group presented characteristics similar to the typeⅠ group.The severity of maxillary deformity increased gradually from type Ⅰ to type Ⅱb.We concluded that the severity of maxillary deficiency is not completely consistent with the mandibular deformity classification.These results demonstrated that the MBV and MTV are independently associated with MRH or MCL on the affected side in children with unilateral HFM,suggesting a potential interaction between mandibular dysplasia and maxillary deformities.Based on these findings,we adopted the MDO first treatment strategy for children with severe HFM.Our study found that:(1)MDO first can promote the overall development of the facial skeleton and the improvement of facial symmetry.(2)In this process,the increase of maxillary volume mainly comes from the expansion of maxillary sinus,the longitudinal development of maxilla on the affected side is faster than that on the opposite side,and the growth of bilateral mandibular body is obvious.(3)MDO can achieve the downgrade of HFM deficiency severity.(4)MDO can immediately and significantly improved the facial skeleton deficiency,expands the associated soft-tissue at the same time and increase bone stock for secondary orthodontic surgery.Hence,MDO first is a proper primary method for type Ⅱb and type Ⅲ HFM cases.MDO followed by CCG can get satisfactory aesthetic and architectural consequences for type Ⅲ patients.These results enrich the study of the characteristics of HFM jaw deformity,provide a basis for the improvement of classification system,confirm the effectiveness and necessity of MDO in the treatment of growing children with severe HFM,and provide a new idea for the treatment of severe HFM in children.These results also provide a theoretical basis for the formulation and improvement of personalized sequential comprehensive treatment strategy in the future.