Three-dimensional Craniomaxillofacial And Dentition Morphology Analysis Of Skeletal Class ? Mandibular Retraction

ObjectiveMeasure the Cone Beam Computed Tomography(CBCT)and model measurements of patients with skeletal class ? mandibular retraction and normal occlusion,to study the structural differences of the three-dimensional craniomaxillofacial and dentition morphology,and to investigate the mechanism of skeletal class ? mandibular retraction,which provides a valuable reference for the orthodontic doctor's clinical diagnosis,treatment plans and prognosis results.MethodsThirty patients with skeletal class ? mandibular retraction(24.94±6.59y)and 30 normal volunteers(23.50±3.63y)are treated with pre-treatment CBCT and tooth model.Then,the obtained CBCT image data is imported into Invivo dental 5.0 image processing software for 3D reconstruction,and We analyze all data to obtain measurement data such as bone,tooth,soft tissue and dental model.The subject measurement data are analyzed by independent sample t-test statistical methods between two groups to obtain the craniomaxillofacial and dentition morphology of patients with skeletal class ? mandibular retraction.Results1.Bone measurement results show that ?SNB,NP-FH,Co-Go,Go-Pg,S-Go,lower alveolar ridge thickness,APTC measurement item of skeletal class ? mandibular retraction is smaller than that of normal occlusion group,statistically different(p<0.05),while ?ANB,NA-PA,?NGoMe,SN-MP,FMA,Yaix of the skeletal class ? mandibular retraction is statistically greater than the individual normal occlusion group(p< 0.05),the other cranial and maxillofacial bone measurement items are not statistically significant(p>0.05);2.Tooth measurements,L1-NB distance of the skeletal class ? mandibular retraction was larger than that of the normal occlusion,statistically significant difference(p<0.001).and the rest are not statistically significant(p>0.05);3.Soft tissue measurements,tongue length(TGL),glossopharyngeal distance(PtPw),lower lip thickness(L1-Li),lower lip length(Stmi-Me'),no significant difference between the two groups(p>0.05);4.The measurement results of the dental model show that the 36FA-WALA,46FA-WALA,OJ,Spee curve,the skeletal class ? mandibular retraction are statistically larger than that of the normal occlusion(p<0.05).The MCA16 of skeletal class ? mandibular retraction is significantly lower than that of the normal group(p<0.05),and the rest are not statistically significant(p>0.05).Conclusions1.Compared with the normal occlusion,the cranio-maxillofacial features of the skeletal class ? mandibular retraction are as follows:the normal sagittal position of the maxilla,the mandibular sagittal position retraction,the short mandibular,insufficient anteroposterior thickness of condylar head,suggesting that the total volume of the skeletal class ? mandibular retraction mandible is too small;the vertical mandibular ascending branch is shorter,and hyperdivergent facial patiern;the horizontal maxilla and mandible width is not significantly different from the normal occlusion.In addition,the skeletal class ? mandibular retraction group also has the problem of insufficient thickness of the alveolar bone and insufficient width of the maxillary and alveolar arch.2.Compared with the normal occlusion,the dentition features of the skeletal class ? mandibular retraction are the normal upper incisor lip inclination,the more lower incisor lip inclination;and the maxillary right first molar is mesial rotation,The mandibular first molars are lingually tipping,and the mandibular spee curve is deeper,suggesting that dentition is compensated to obtain a good occlusion relationship3.There is no obvious difference between the skeletal class ? mandibular retraction and the normal occlusion on soft tissue.One reason is that the degree of mandibular retraction of the subjects selected in this study is not serious,and they are all nonsurgical patients;the other is the compensation effect of the patient's dentition and soft tissue,including the small sample size of this study.