Clinical Study On Change Ratios Between Hard And Soft Tissue Of Skeletal Class Ⅲ Malocclusion After Orthognathic Surgery

Objective:To study the change ratios between soft and hard tissue in patients with skeletal malocclusion before and after orthognathic surgery,in order to better predict facial shape.Methods: Twenty adult patients were selected for this study.All of subjects who were involved were examined by spiral CT and three-dimensional(3D)stereophotogrammetry 2 weeks before surgery and 3 months after surgery.Dolphin imaging software was used to reconstrct 3D digital model and 3D measurement coordinate system.Nineteen soft and hard tissue land marks were selected and matched into 12 pairs.Ten hard tissue land marks are N(nasion)、ANS(anterior nasal spine)、A(subspinale)、Spr(superior prosthion)、UI(upper incisor)、LI(lower incisor)、B(supramental)、Pg(pogonion)、Gn(gnathion)、Me(menton);Nine soft tissue land marks are Ns(nasion of soft tissue)、Pn(pronasale)、Sn(subnasale)、UL’(upper vermilion border)、LL’(lower vermilion border)、B’(soft tissue B point)、Pg’(pogonion of soft tissue)、Gn’(gnathion of soft tissue)、Me’(menton of soft tissue).12 pairs of land marks are Ns/N(nasion of soft tissue/ nasion)、Pn/ANS(pronasale / anterior nasal spine)、Pn/A(pronasale / subspinale)、Sn/ANS(subnasale / anterior nasal spine)、Sn/A(subnasale/subspinale)、UL’/UI((upper vermilion border / upper incisor)、UL’/Spr(upper vermilion border / superior prosthion)、LL’/LI(lower vermilion border /lower incisor)、B’/B((soft tissue B point /supramental)、Pg’/Pg(pogonion of soft tissue/pogonion)、Gn’/Gn(gnathion of soft tissue / gnathion)、Me’/Me(menton of soft tissue /menton).3D coordinate value of these landmarks were read both before and after surgery and were used for statistical analysis with SPSS22.0 software package.Results: There was a linear relationship only in Pn/A,Gn’/Gn and Me’/Me in X axis(P<0.05),in Gn’/Gn in Y axis(P<0.01)and all pairs of landmarks contain a high correlation(P<0.01)except UL’/UI and UL/SPr in Z axis(P<0.05)and the result are 221%、35%、53%、31%、142%、38%、80%、117%、75%、80%、88%、86%。Additionally,the change ratio between soft and hard tissue landmarks of mandible is bigger than the maxilla.Conclusions: After orthognathic surgery,the changes between soft and hard tissue only lie in Z axis(forward and backward),each pair of matched landmarks exhibited a linear relationship,and the change ratio on mandible is bigger than maxilla.