The Bone Thickness Of The Infrazygomatic Crest And The Height Of The Maxillary Sinus Measured With Cone-beam Computed Tomography For Skeletal Class Ⅱ Malocclusion Patients With Different Facial Types

Objective:At present,the miniscrew implant anchorage（MSIA）in the infrazygomatic crest is the most effective measure of anchorage control for skeletal Class Ⅱ malocclusion patients.But the bone thickness of infra-zygomatic crest and the height of the maxillary sinus are not very clear for skeletal Class Ⅱ malocclusion patients,and related researchs are rare.In this study,we measured the bone thickness of the infrazygomatic crest and the height of the maxillary sinus by cone beam computed tomography（CBCT）in different vertical bone surface type for skeletal Class Ⅱ malocclusion patients in teenagers,and compared the differences the characteristics of the measurement data by the statistical software.To provide the reference for the application of the MSIA in the infrazygomatic crest.Methods:In teenagers,collected the oral and maxillofacial CBCT datas of 60 skeletal Class Ⅱ malocclusion patients,including the low-angle groups（20 cases）、normal-angle groups（20 cases）、and high-angle groups（20cases）.Measured the bone thickness(L_1-13、L_1-15、L_1-17、L_2-13、L_2-15、L_2-17、L_3-13、L_3-15、L_3-17)of infrazygomatic crest at 13mm、15mm、and 17mm from the reference line（the maxillary occlu-sal plane）on the different coronary layes（The first layer:divide equally the distance between the first premolar and the first molar,the second layer:divid-e equally the distance between the first molar root bifurcate,the third laye-r:divide equally the distance between the first molar and second molar）of the infrazygomatic crest,and Measured the height of the maxillary sinus on the different coronary layes（H1,H2,H3）.Use the SPSS19.0 software pack-age to for statistical analysis,the bone thickness of infrazygomatic crest and the height of the maxillary sinus were compared in gender、left and right side、in different vertical bone surface type,to analyse the signifiicance of these differences.Results:（1）the bone thickness of infrazygomatic crest and the height of the maxillary sinus in the skeletal Class Ⅱ malocclusion patients in teenagers had no statistically significant meaning in gender、left and right side（P>0.05）.Axial plane（from bottom to top）,the bone thickness of infrazygo-matic crest all gradually thinned(L_1-13>L_1-15>L_1-17、L_2-13>L_2-15>L_2-17、L_3-13>L_3-15>L_3-17)in the low-angle groups、normal-angle groups and high-angle gro-ups,and there were statistical significance（P<0.05）in the group;Coronary slice（from front to back）,the bone thickness of infrazygomatic crest all show-ed a trend of changes in the following in 3 groups:the bone thickness was thickest at the first layer and thinnest at the third layer,the bone thickness of the second layer was between 1 and 2 layer(L_1-13>L_2-13>L_3-13、L_1-15>L_2-15>L_3-15、L_1-17>L_2-17>L_3-17).And there were no statistical significance in the group（P>0.05）.These were not significant difference（P>0.05）in the bone thick-ness of infrazygomatic crest in the different vertical facial types for the skeletal Class Ⅱ malocclusion patients in teenagers,in addition to the thick-ness of L_1-13、L_2-13、L_3-13（P<0.05）.The values of the high-angle group is the lowest,the values were measured of the low-angle group were the highest,the values of the normal-angle group was between the high-angle group,and the low-angle group;The height of the maxillary sinus had significant diff-erence（P<0.05）in the different vertical facial types for the skeletal Class Ⅱ malocclusion patients in teenagers.The values of the low-angle group is the lowest,the values were measured of the high-angle group were the highest,the values of the normal-angle group was between the high-angle group,and the low-angle group.The height of the maxillary sinus had no statistically meaning（P>0.05）,and gradually increased（H3>H2>H1）on coronary slice from front to back.Conclusion:The thickest bone of the infrazygomatic crest was at the interradicular space of the maxillary second premolar and first molar for the skeletal Class Ⅱ malocclusion patients in adolescents,which was the best micro-implant anchorage placement sites of the infrazygomatic crest in the skeletal Class Ⅱ in adolescents.The thickest bone of the infrazygomatic crest and the lowest height of the maxillary sinus were measured in the low-angle patients in the skeletal Class Ⅱ malocclusion patients in adolescents;The lowest bone of the infrazygomatic crest and the highest height of the maxillary sinus were measured in the high-angle patients in the skeletal Class Ⅱ malocclusion patients in adolescents.To provide the reference for the clinicians when they wanted to implant the MSIA in the infrazygomatic crest for the skeletal Class Ⅱ malocclusion patients in adolescents,and reduce loss rate of the MSIA and the risk of break-overing the maxillary sinus.