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3-Dimensional Finite Element Analysis in Stress Distribution of Maxillary Protraction and the Clinical Research of Maxillary Protraction on the Angle’s III Malocclusion

Author: HuZuoYing
Tutor: DongFuSheng
School: Hebei Medical University
Course: Surgery
Keywords: FEM maxillary protraction RME cranioface craniofacial sutures
CLC: R783.5
Type: PhD thesis
Year: 2012
Downloads: 132
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Abstract


Objective: It was the most effect to treat the class III malocclusion forthe maxillary protraction in all the treatment methods that approved by thescholars in this world. Preferable profile could be gained by the treatment ofthe maxillary protraction if it had been performed at prepubertal growth spart.The scholars devoted themself to improving the effect of the protraction so asto abtained the better effect of the craniofacial skeletons. The directions, theforce value and the site of the protraction could make a difference for theprotraction. Unbalance displacement of the teeth and bone could be caused byimproper force loading. And the teeth displaced discordantly and the jawrotated inappropriately. This would disadvantaged to improve midfacialskeleton hypoplasia, especially for those who had suffered collapsedobviously from sutura nasofrontalis to the base of nose. So we cried out toclarify the influence of maxillary protraction. For instance,how to influencethe craniofacial skeleton, sutures and the teeth,and what different effects hadon midfacial skeleton by loading in different ways.This article established the database of children head sample slice(DCHS)and CT data at prepubertal growth spart, which were at intervals in0.1mmand0.625mm respectively. The3-dimensional finite element model(3-D FEM)which included sutures and teeth was developed from the CT data and wasrefered to the DCHS by the Mimics and Geomagic and ANSYS softwares.With or without the maxillary expansion, stress distribution trend would beanalysed at the craniofacial skeleton, sutures and teeth after different levels offorce loaded. To analyse the effect of the different conditions of the maxillaryprotraction on the skeleton, sutures and teeth of the midface. To explore therelevance between the changes in the maxillary and the teeth and the effect of the maxillary protraction on the stress distribution under different directions,different values and RME. To provide evidence for the treatment of theangle’s III malocclusion with midfacial skeleton hypoplasiain order to gain thebest effect on the craniofacial structures, especially all the above1/2of themidface forward displace. At the same time, to overcome the teeth anchoragelose and avoid the compensation of anterior teeth in maxillary.Methods:Part1Database establishment of children head sample slices1SpecimenThe immobiled skull of an8-year-old chinese boy was selected fromHebei Medical Univercity, Department of human anatomy. The specimen hada coherent concordant face type,1.35m height,a middle growth and had nodeformity, especially in the skull. The skull was abtained by cutting alongcartilago thyroidea.2CT scanAfter24hours freezing, the skull was transported to perform CBCTscanning with a0.625mm inter-spacein in the frozen state.368sections CTimages of the skull were gained. Each image was515KB in size and the wholedatabase reached185MB. The CBCT images were saved at the format ofDICOM.3the specimen milling and the images gainning3.1the specimen millingBased on the request of the mill, a cube shape embedding utensil wasdesigned to encase milling specimen and the embedding materials. Beforeembedding, four paralleled crystalline plastic cement tube were meristicdraged at the four homs of the embedding utensil. The tube was scaled on thebasis of coordinate system.5%red gelatin solution filled up it. The specimenwas adjusted in the middle in the utensil and fixed by blue gelatin solution tokeep the milling surface correspondence with the frankfurthorizontal. Theembedding materials was3%gelatin solution colored blue with food dye.The gelatin was infunding into the embedding utensil and the filling was approximately12.5%of it at the first time. Once the gelatin was solid, theembedded workpiece was transferred to the Freezer (-75℃) for at least12hours. All of the8layers fininshed the filling. When the final layer was solid,the embedded workpiece was again transferred to the Freezer for completefreezing and storage at the tempreture-75℃for30days to gain a gelatin cubeice body.In-13℃homothermic cryogenic laboratory, the slice-cutting of thespecimen was performed at0.1mm intervals.3.2Image gainningAfter milling, Canon EOS-1DS MarkII(Canon company,Japan) was usedto photograph the transverse sliced specimens. Focal distance:0.60m; Pixelsetting:4992×3328. Original image data were saved at the format of RAWwhich was transferred to file format of PSD. and.JPG for sharing andcommumication more generally.4segmentation and extract of the images4.1segmentation and extract of the images in the skull surfaceThe gained images were draw the outline of the skull surface by manualin the photoshopCS310.0software to segmentated and extracted the skull fromthe clutter backround to change the black backround.4.2segmentation and extract of the images in the maxillary,mandible and thezygoma.The gained images in4.1were respectively draw the outline of themaxillary,mandible and the zygoma surface by manual in the photoshopCS310.0software to segmentated and extracted the maxillary,mandible andthe zygoma from all the structures of the skull and saved.Part2Establishment of the finite element model with the craniofacialSutures defined alonely in children1From DICOM files to IGES formatThe DICOM files had gained were imputed in MIMICS10.0andGeomagic9.0sofeware successively to set up3D geometrical model of IGESformat. The modal included the structures as followed:Skeleton—All the craniofacial skeleton. Craniofacial sutures—frontomaxillary suture; medianPalatine suture; zygomaticomaxillarysuture; Zygomaticotemporal suture; Zygomaticofrontalis suture. Teeth—central maxillary incisor, maxillary primary lateral incisor, mandibular firstprimary molar and maxillary first molar.2To establish the finite element models in ANSYS13.0softwareThen IGES files were imported into the finite element analysis softwareAnsys10.0on the base of the X/Y/Z coordinate system. Young’s modulus andPoisson’s ratio for various materials were set. The medianPalatine suture wasassumed two states which was opened or not.10nodes solid187element(tetrahedron) were used for meshing, whose sizing grid was set in twonorms:2.2mm(skeletons and teeth) and1.6mm(sutures). So far, the3D finiteelement models were finished. The FEM model involved ten sutures, eightteeth and all the craniofacial skeleton. It took30minutes to achieve the modelwhich was from geometrical model to the FEM.Part3The effect of stresses distribution under different modes ofmaxillary protraction on the craniofacial bone and teeth1Analysis modal: The modal gained in the second part was selected.2determinedYoung’s modulus and Poisson’s ratio for various materials3Analysis condition assumedRestraints were established at all other nodes of the cranium lying on thesymmetrical plane, and appropriate boundary conditions were imposed. Inaddition, zero-displacement and zero-rotation boundary conditions wereimposed on the nodes along the foramen magnum.4Loading2N and5N of force was directed anteriorly and0°,15°,30°,45°downward relative to the occlusal plane near the canine to simulateorthopedic maxillary protraction forces, with or without the medianPalatinesuture was opened. There were16conditions.5the stress analysisPart4The effect analysis of maxillary protraction in angle ’s Ⅲmalocclusion with midfacial hypoplasia 1Subjects selectedForty subjects(aged8-12years and mean age was10.3y) were diagnosedas skeletal Class III malocclusions with midfacial hypoplasia. The subjectshad a cephalometric index ANB<0°; with the clinical manifestations such asthe molars showed mesiocclusion, and the mandible could not recess. On thebase of Baccetti T improving cervical vertebra analysis method to evaluate thespart of growth and development of the subjects. Forty subjects were dividedinto two groups. The spart of Cvs1and Cvs2and Cvs3were select.2GroupingForty subjects were divided into two groups. Group A was at the phase ofCvs1and Cvs2(prepubertal growth spart). Group B was at the phase of Cvs3(pubertal growth spart). There were20subjects in each group. Each group wasrandomly divided into two groups respectively. A group was at the phase ofCvs1and Cvs2(prepubertal growth spart). B group was at the phase of Cvs3(pubertal growth spart). Maxillary protraction with rapid maxillary expansion(RME)were used in group a. Maxillary protraction alone were used in group b.There were10subjects in each group.The name of the group was1(young ageand RME group=Aa group),2(young age and no RME group=Ab group),3(older age and RME group=Ba group),4(older age and no RME group=Bbgroup).3Treatment.All subjects underwent the treatment of maxillary protraction With orwithout the rapid maxillary expansion Unilateral300-600g of force wasdirected anteriorly and20~40°downward relative to the occlusal plane atpalatal side5-8mm place of the canine.4Completion criteria①The protraction time was6-12months,and which could not exceed12months.②The appearance improved and cross bite removed in anterior teeth.③The molars showed class I or II occlusion.④The overject was about2mm in anterior teeth 5Testing methodCephalometric radiographs were conducted taken before treatment(T0)and after maxillary protraction(T1). All the landmarks were taken andmeasured for three times for the averaging by one person at short time byWinceph8.06software. The means differences between the before and posttreatment were gained(T0-T1=⊿T)。6Statistics analysisThe means and standard deviations (means±SD) of the changes invarious measurements were obtained by SPSS13.0software. α=0.05, P<0.05was considered as statistical significance.6.1The effects of each groups(group) on craniofacial structures wereinvestigated by means of a paired t-test. Differences were investigatedbetween the T0and T1.6.2The difference of the craniofacial structures in four groups wereinvestigated by means of a ANOVA-test. Differences(⊿T) were investigatedalong the four groups.Results:Part1Database establishment of children head sample slices1The database of children head sample slices consisted of a total of2150images with an approximate data size of20.4MB. For the convenience ofdifferent potential users of this dataset, the image data were stored at3different file formats to allow variously oriented studies, as listed below:RAW format resolution:4992*3328pixels,42.83GB in size.PSD format resolution:4992*3328pixels,104.98GB in size.JPG format resolution:4992*3328pixels,789.03MB in size.2The size of the facial boneMaxilla: A total of552photographs were from NO.392-NO.944, at the lengthof5.52cm.Mandible: A total of883photographs were from NO.33-NO.916, at thelength of8.83cm.Zygoma: A total of324photographs were from NO.616-NO.940, at the length of3.24cm.os nasale: A total of86photographs were from NO.804-NO.890, at thelength of0.86cm.Part2Establishment of the finite element model with the craniofacialSutures defined alonely in children1The FEM model consisted of775,700elements1173,588nodes.2To establish the craniofacial sutures defined which involved in fronto-maxillary suture; medianPalatine suture; zygomaticomaxillary suture;Zygomaticotemporal suture; Zygomaticofrontalis suture.3To Establish the finite element model with the craniofacial Sutures definedalonely in childrenPart3The effect of stresses distribution under different modes ofmaxillary protraction on the craniofacial bone and teeth1Analysis of the craniofacial stress in simulating maxillary protraction withdifferent directionAt different direction, and different force value, the changes of stressdistribution were similar with the medianpalatine suture was opened or not.Distribution of von Mises strains showed:It was the same for the distribution of strains at the direction anterior and0°、15°、30°downward relative to the occlusal plane. The strains distributed inthe bridge of the nose and dextro-ala nasi. But the area was decreased at thedirection of45°Distribution of the stress at the X/Y/Z coordinate system showed:The distribution showed mainly a forward stress at the sagittal plane. Thestress distribution focus on the area of the dextro-ala nasi and focus on thearea of the bridge of the nose which was up across the frontonasal-frontomaxillary suture to the area of the geisoma. Compared to the direction of30°, the area of the stress distribution reduced but the force values were higherat the direction of0°. Stress dstribution were no difference at the direction of15°and45°At the vertical plane, force values were higher with the angle downward relative to the occlusal plane was larger. The inferior stress distribution focuson the area of the dextro-ala nasi and on the area of the bridge of the nosewhich was up across the frontonasal-frontomaxillary suture to the area of thegeisoma at the direction of45°. Different parameter of the medianpalatinesuture and difference of the force values caused different stress distribution.The stress showed a upward derection at the direction of0°and15°, which wasnot seen at30°and45°.Distribution of the displacement at the X/Y/Z coordinate system showed:Craniofacial structures showed anterior and downward displacement. Thedistribution showed mainly anterior displacement at the sagittal plane. Theforward displacement included frontonasal-frontomaxillary suture,medianpalatine suture, zygomatico-maxillary suture, part of zygoma, part ofsphenoidalia, palate bone, os nasale, and maxillary teeth. The distributionincreased in the area of zygomaticofrontalis suture, all of zygoma, part offrontal bone, most of basis cranii at the derection of30°and45°.Zygomaticotemporal suture showed mostly a backward distribution of thedisplacement. At the vertical plane, the maximum displacement upward was atthe derection of0°.2Analysis of the craniofacial stress in simulating maxillary protraction with orwithout the medianpalatine suture was opened.Whether medianpalatine suture was opened or not,distribution of thestress was similar at the same protraction angle. They showed a defferencethat the force value of stress concentration became lower and other areabecame higher when the medianpalatine suture was opened or not.3Analysis of the craniofacial stress in simulating maxillary protraction withdifferent force valueDistribution of the stress were similar at the different force value. Theyshowed a defference when the stress value became higher with the force valuehigher at all the craniofacial structures.As aboved, distribution of the stress at the midface after maxillaryprotraction showed a forward, upward and outward displacement at the direction of0°. And it showed a forward, downward and outwarddisplacement at the direction of0°. The distribution of the stress showed wasbetween the both above at the direction of15°. But it showed a more obviousdownward displacement at the direction of45°.When the medianpalatine suture was opened,5N of force was directedanteriorly and30°downward relative to the occlusal plane showed a stressconcentration at the above1/2of the midface which could open thefrontonasal-frontomaxillary suture, protracted the area of the bridge of thenose and the dextro-ala nasi forward and downward. So it could improve classIII profile to gain the best effect of the midfacial forward and larger area ofstress concentration had not appeared in the maxillary teeth that avoid teethanchorage loss. Better effect of skeleton emerged in whose medianpalatinesuture was opened. Midfacial skeleton showed a counterclockwise rotationthat lead to the teeth and the alveolar bone Anterior-Superior shift,consequently much more inclining in the maxillary incisors appeared at thederection of0°, although it could achieve midfacial skeleton forward.Part4The effect analysis of maxillary protraction in angle ’s Ⅲmalocclusion with midfacial hypoplasia1Comparision of the hard parameters both the before and post treatment:After the treatment, the mark point of A,Ns,Ss,Zy and Zm representedcranioface diaplaced forward and downward at the group1and3(P>0.05).The mandible plane showed a forward and downward rotation. And B pointdisplaced forward and downward. So the combination of the forwardmaxillary and the backward mandible caused the concave profile improvedmuch more. Concave profile changed to vertical profile, even to be prominenta bit. All the midface displaced forward and downward,included the above1/2of the midface which is difficult to achieve。Compared to the group1,theeffect was less at the group2,but was better than that at the group4.2Comparision of the teeth parameters both the before and post treatment:Compared to the before treatment, U1-NA(°) and U1-SN (°)wasdecreased at the group1and2and4, but U1-NA(mm)increased after the treatment. These indicated that the teeth displaced forward and downwardwith all the craniofacial structures. The teeth had not moved inside thealveolar bone. It overcomed inclining to lip in maxillary incisors as before.But the inclining to lip in maxillary incisors increased in group3. Thatindicated that anchorage of maxillary teeth lost. The reason may be thattheforce loading was larger than500g.3Comparision of the soft tissue parameters both the before and posttreatment:After the treatment, the mark point of A’、TN、SN、Zy’ and TULrepresented cranioface soft tissue diaplaced forward and downward at thegroup1and3(P>0.05). And the SB and TC and TLL point displaced forwardand downward. So the combination of the above parameters caused theconcave profile improved much more to achieve plastic effect. As the samewith the hard parameters, compared to the group1, the effect was less at thegroup2,but was better than that at the group4.4Compared the effect after treatment in four groups4.1Compared the effect of treatment in four groups by the hard parametersThe parameters represented the maxillary or mandible alone compared inthe four groups. There was no statistics significance. But combined the bothcould show a statistics significance. At group B, RME had a beneficial effecton the A,Rhi,O,Ns,Ss,Zy and Zm points forward and B, Pg pointsbackward(P<0.05). But it had no statistics significance at the group A. Atgroup a, skeletal age had no effect on the A,Rhi,O,Ns,Ss,Zy and Zm pointsforward and B and Pg points backward(P>0.05). But it had statisticssignificance at group b(P>0.05).It had no statistics significance for the parameters which representedanterior teeth to be compared in four groups(P>0.05).RME and young skeletal age caused the mandible plane clockwiserotation after the treatment of maxillary protraction.4.2Compared the effect of treatment in four groups by the soft tissueparameters After the treatment of maxillary protraction, the soft tissue improved withthe hard tissue changed. The soft tissue parameters represented the maxillaryor mandible alone compared in four groups had no statistics significance. Butcombined the both could show a statistics significance. At group B, RME hada beneficial effect on the TN and SN points forward and SB and TC pointsbackward(P<0.05). But there was no statistics significance at the group A. Atgroup a, skeletal age had no effect on the A,Rhi,O,Ns,Ss,Zy and Zm pointsforward and B and Pg points backward(P>0.05). But it had statisticssignificance at at the group b(P>0.05).NLA,TUL-E and TLL-E had no statistics significance whether amongfour groups or inside each group.Conclusion:1. It was the first to successfully establish the serial anatomical cross-sectionalimage data of the craniofacial structure of the child prepubertal growthspart in this world. Compared to other data before, The data with atintervals0.1mm were demonstrated thinnest and more efficient anatomicalinformation to provide various related studies of the children for thecraniofacial structure.2. The craniofacial sutures were the first treated as a entity to be definedalonely in the world and consequently it is a skull of FEM with moresimilar and finer than previously presented in the world.3. It was important implications for the effect of maxillary protraction whetherthe medianpalatine suture was opened or not. compared to the groupwithout medianpalatine suture opened, the better effect of skeletonappeared in the treatment with the medianpalatine suture opened and thiswould avoid teeth anchorage lost. But the distribution tendency of thestress was not affected with or without medianpalatine suture opened4. The highest forward and upward stress caused by maxillary protractionappeared in the frontonasal-frontomaxillary suture at the anterior directionof0~15°downward relative to the occlusal plane. When the directing angleexceed15°(whitin45°), the zygomatico-maxillary suture and zygomaticofrontalis suture showed a more forward and downward stresswith the angle increased, but the zygomaticotemporal suture showed abackward stress.5. The midfacial skeleton showed a counterclockwise rotation at the anteriordirection of0°and15°downward relative to the occlusal plane, whereasshowed a clockwise rotation at the direction of30°and45°which overcomethe teeth anchorage loss.6. Combined the force value and the force direction should be takewasn intoaccount simultaneously. It could improve class Ⅲ profile to gain the besteffect, especially the above1/2of the midface which is difficult to achieve.That overcome the teeth anchorage loss to prevent the compensatory of theinclining to lip in maxillary incisors.7. Different force direction would be loaded on the base of the location wherethe deformity appeared Anterior-Inferior15~45°relative to the occlusalplane should be adopted to improve the above1/2of the midface,especially the protraction direction of30°. But if the case showed alveolarbone deformity or the maxillary incisors inclining to tongue, the anteriordirection of0~15°downward relative to the occlusal plane should beadopted to gained the satisfying effect8. Skeletal age had a negatively correlative impact on the effect of maxillaryprotraction. The eldder age, the less effect of protraction. But this could beeliminated by RME. RME had a positively correlative impact on the effectof maxillary protraction and it was not affected by skeletal age.

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