The Measurement And Analysis Of The Posterior Space Of Maxillary Molars Of Class ? And Class ? Equiangular Osteofacial Type

Purpose: To compare the reliability of cephalogram(CEPH)and cone beam CT(CBCT)in measuring the posterior space of molars.CBCT was used to measure the posterior space of maxillary molars in patients with skeletal class I malocclusion and skeletal class II malocclusion,to compare the posterior space of maxillary molars in patients with class I and class II equiangular osteofacial type malocclusion.The three-dimensional morphological measurement and analysis of the posterior space of maxillary molars in patients with skeletal class II malocclusion were carried out to understand the anatomical structure of the maxilla and the relationship between the posterior space which can be used to distalization the molars,to explore the posterior movement anatomical limit of the of maxillary molars in patients with skeletal class II maxillary protrusion.So as to guide the clinical orthodontists to better use the molar distalization of the molars to treat mild and moderate skeletal class II.Methods: From December 2017 to December 2018,the data of CEPH and CBCT of malocclusion patients who needed orthodontics in the Department of Orthodontics,the first hospital of Shanxi Medical University were collected.The same imaging technician used the same equipment to conduct CBCT scanning and took cephalometric films.The length and height of the posterior space of the left and right lateral CBCT and the molars of CBCT were measured three times respectively.Spss23.0 statistical software was used to analyze the measured data.The distribution characteristics of the test data were normal distribution and the variance was even.The consistency between the three measurements was checked and the reliability of the two measurement methods was compared;Take the average value of three measurements,make paired t-test on the measured value of CBCT left and right posterior molar space to compare the consistency of left and right posterior molar space of the same test object;then take the average value of left and right measurement value and CEPH data to compare,and observe the difference between the two measurement methods.The CBCT data of 136 sides of the posterior segment of maxilla in 68 cases were measured and analyzed according to the bone type?and bone type II malocclusion as the control group and the experimental group.In three-dimensional measurement,The functional Cusp Line of the maxillary first and second molars and the median sagittal line were used as reference lines,which is on the plane of the distal buccal root of the second maxillary molars,The distance from the second molar to the edge of the cortex was measured at the level of the cemento-dental junction(CEJ),the level of the root bifurcations,the level of the distance from the root bifurcations(2,4,6 mm)and the level of the distal buccal root tip.At the level of the CEJ,root bifurcation level,2,4,6 mm distance from the root bifurcation and the level of the distal buccal root tip,Comparison of the size of the retromolar space between the maxillary molars and the skeletal class ?and skeletal class?on different measurement reference lines.Results: 1.A study on the measurement of the posterior space of maxillary molars(1)The ICC values of all items measured by left and right CBCT and CEPH are greater than 0.75,indicating that the values measured by the two kinds of data are of high reliability,while the data measured by CBCT three times are of higher consistency.(2)There is no statistically significant difference in the length and height of the CBCT left and right maxillary molars of the same test subject: (3)There was significant difference in the measurement of the length of the posterior space between the left and right sides of CBCT and the measurement of CEPH;there was no significant difference in the measurement of the height of the posterior space between the left and right sides of CBCT.2.Three-dimensional measurement of the posterior space of maxillary molars in skeletal Class I and skeletal Class II by CBCT(1)It is concluded that there is no significant difference in the measurement of the posterior molar space between different sexes in this study(P > 0.05),indicating that there was no gender difference in the measurement of the retromolar space;(2)In the posterior space of maxillary molars based on cusp line,the CEJ level,the level of root bifurcation,the level of 2,4,6 mm and the level of distal buccal root tip of maxillary second molars were higher in Skeletal Class II group than in Skeletal Class I group(p < 0.001).The measured values of molar posterior space in Class II group and Class I group were the smallest at CEJ level and the largest at root tip,as the measurement level moves up,the measured clearance value increases.(3)The maxillary molar posterior space based on the sagittal line has no significant difference between the bony class ? and skeletal class ? groups at all measurement levels.Conclusions: 1.The reliability of CBCT and CEPH is higher,but the repeatability of CBCT is higher than that of CEPH,and there are statistical differences between the two methods.2.Compared with patients with skeletal class I malocclusion,patients with skeletal class II malocclusion have larger posterior space of molars measured along the bite line in all planes.Therefore,patients with skeletal class II malocclusion have larger posterior space of upper molars to provide distal displacement or arch expansion.3.At the level of CEJ,the measurement value of posterior space of maxillary molars was the lowest in patients with skeletal class II or skeletal class I malocclusion.Therefore,more attention should be paid to the anatomical limit of the level of CEJ in the distal direction of the second maxillary molar along the occlusal line when pushing the molar backward in patients with skeletal class II or skeletal class I malocclusion.