Evaluation Of The Asymmetry Of Miniscrew-assisted Rapid Palatal Expansion By CBCT Registration

ObjectiveThis study aims to evaluate the asymmetry of anterior and posterior nasal spine in transverse,sagittal and coronal directions and the transverse changes of bone landmarks of zygomatic maxillary complex after miniscrew-assisted rapid palatal expansion(MARPE),and to analyze the correlation between the transverse asymmetry of anterior nasal spine and the transverse asymmetry of bone landmarks of zygomatic maxillary complex.To understand the mode of MARPE,so as to provide basis for palatal expansion and treatment of patients.Research objects and methodsThe subjects of this study were 29 patients(9 males and 20 females,aged 18.83±4.86 years)who were treated with MARPE in the Department of Orthodontics,Stomatology Hospital of Shandong University from September 2016 to May 2021.Cone beam computed tomography(CBCT)were taken at the initial diagnosis(T0)and after MARPE(T1).Importing the data into Mimics 21.0 software,locating the landmarks in T0,establishing sagittal,transverse and coronal measurement planes,and registering the measurement planes of T0 into T1 through anterior skull base registration.The distances from bilateral anterior and posterior nasal spine to the three measurement planes were measured on T1.They were divided into larger groups and smaller groups to evaluate the asymmetry of bilateral anterior and posterior nasal spine in transverse,sagittal and coronal directions.According to the distance between the anterior nasal spine and the sagittal measurement plane,the face where the large side of the distance was located was defined as the dominant side and the small side was the non-dominant side.The distances from the bone landmarks of bilateral zygomatic maxillary complex to the sagittal measurement plane were measured in T0 and T1 respectively.Using SPSS25.0 software for data analysis.Independent sample t-test or Mann Whitney U-test were used for comparison between groups.Paired sample t-test or Wilcoxon signed rank sum test were used for comparison between larger group and smaller group,dominant side and non-dominant side before and after MARPE.Spearman correlation analysis was used to evaluate the correlation between the difference of anterior nasal spine width and the difference of bone landmark width of zygomatic maxillary complex between dominant side and non-dominant side.P<0.05,with statistical significance.Results1.In this study,the opening amount of expander was 5.39±1.06 mm,the total transverse opening amount of anterior nasal spine was 2.93(2.25,3.77)mm,and the total transverse opening amount of posterior nasal spine was 2.09(1.55,3.33)mm.The difference was statistically significant(P<0.05).The average sagittal parallelism was 78%.2.After MARPE,there was significant differences between the larger groups and the smaller groups at anterior and posterior nasal spine in sagittal,transverse and coronal directions(P<0.05).The degree of asymmetry within 0.50 mm accounted for the most,followed by 0.50 mm-1.00 mm,and more than 1.00 mm was the least.There was no significant difference in the degree of asymmetry between the anterior and posterior nasal spine.3.After MARPE,the width of zygomatic process,the width of piriform foramen,the distance under zygomatic bone,the width of zygomaticofacial foramen and the distance behind zygomatic bone increased,and the difference was statistically significant(P<0.05).4.After MARPE,the increase of posterior nasal spine width,zygomatic process width,piriform foramen width,subzygomatic distance,zygomaticofacial foramen width and posterior zygomatic distance on the dominant side were greater than that on the non-dominant side(P<0.05).The difference of anterior nasal spine width was positively and moderately correlated with the difference of zygomatic process width,piriform foramen width,subzygomatic distance and zygomaticofacial foramen width(rs=0.449,rs=0.552,rs=0.510,rs=0.573,P<0.05).Conclusions1.After MARPE,bilateral anterior and posterior nasal spine were asymmetric in transverse,sagittal and coronal directions;2.After MARPE,the width of zygomatic maxillary complex increased;3.After MARPE,there was transverse asymmetric expansion of zygomatic maxillary complex.