Biomechanical effect of anteriorly directed extraoral forces on the craniofacial complex: a study using the finite element method

This study was designed to investigate the biomechanical effect of protractive maxillary orthopedic forces on the craniofacial complex by use of the three-dimensional finite element method (FEM). The three-dimensional FEM model was developed on the basis of a dry skull of a young human being. The model consisted of 2918 nodes and 1776 solid elements. Eighteen cranial and facial sutural systems were integrated in the model. An anteriorly directed 1.0-kg force was applied on the buccal surfaces of the maxillary first molars in both a horizontal parallel direction and a 30 degree obliquely downward direction to the functional occlusal plane. The nasomaxillary complex showed a forward displacement with upward and forward rotation in a horizontal protraction case, whereas a downward force produced almost translatory repositioning of the complex in an anterior direction. High stress levels were observed in the nasomaxillary complex and its surrounding structures. However, the pattern of stress distributions within the complex was different in two force systems. A downward protraction force produced relatively uniform stress distributions, indicating the importance of the force direction in determining the stress distributions from various orthopedic forces.     

Photoelastic effects of maxillary protraction on the craniofacial complex

The conventional treatment of anterior crossbites has been the application of orthopedic force to the mandible to redirect its growth. However, in the patient with an underdeveloped maxilla, this treatment alone is not sufficient. Therefore, the purpose of this investigation was to study the orthopedic effects of maxillary protraction appliances in the treatment of anterior crossbites. A three-dimensional anatomic model of a human skull was fabricated with birefringent materials for photoelastic analysis. Three maxillary protraction appliances that utilized different anchorage units were used. The protraction forces placed on these appliances were parallel to the occlusal plane, a downward vector 20 degrees to the occlusal plane, and a combination of these two vectors. The resulting stress patterns were observed. The effects of the forces produced by the three appliances were transmitted to the maxilla and distant craniofacial structures. Both a parallel traction and a 20 degrees downward pull to the occlusal plane caused a constriction of the anterior portion of the maxilla. The parallel traction caused a counterclockwise (opening) rotation of the molar tooth and palatal plane. A 20 degrees downward force to the occlusal plane decreased this effect.     

Three-dimensional finite-element analysis of maxillary protraction with and without rapid palatal expansion

The aims of this study were to determine the reaction of the craniofacial bones on the protraction force transferred to the maxillary body, and whether or not the midpalatal suture had opened during skeletal Class III treatment. A computerized tomograph was obtained from a dry skull with a normal occlusion to construct a three-dimensional finite-element model (3D.FEM) of the craniofacial bones and the maxillary teeth to simulate actual bone reactions. A protraction force of 500 g was applied at the first premolar region, directed 20 degrees inferior to the occlusal plane. The displacement and the stress distribution of the craniofacial bones and sutures were then calculated using the ANSYS 5.3 program dividing the analysis into two simulations, based on whether or not the midpalatal suture was opened. The results showed that there was less compressive stress and greater tensile stress in the circumaxillary suture areas when the midpalatal suture was opened. The amount of displacement and deformation when the midpalatal suture was opened also demonstrated a decrease in upward-forward rotation of the maxilla and zygomatic arch and greater amounts of displacement in the frontal, vertical, and lateral directions compared with no opening of the midpalatal suture. Analysis of these results showed that maxillary protraction produce similar changes to normal downward and forward growth of the maxilla and was achieved with accompanying opening of the midpalatal suture.     

前方牵引矫治器不同力值反作用力的三维有限元分析

目的：通过建立包含颞下颌关节的颅颌面三维有限元模型,模拟前方牵引矫治器反作用力的加力方式,分析其在颞下颌关节区、颌骨的应力分布情况以及对各部位节点位移的影响。方法：选择1名健康男性受试者,通过CT扫描得到颅颌面的二维图像数据,借助Mimics、Magics、MSC等专用软件,采用连续、均质、线性、各向同性的线弹性材料,建立包括颞下颌关节和上、下颌骨的颅颌面三维有限元模型。然后在此基础上,根据前方牵引装置的反作用力原理建立加力模型,即采用与平面成后上方37°的施力方向,于下颌最底部加载3~6 N的力值,采用ANSYS10.0有限元分析软件,测定颞下颌关节区、颌骨的应力分布情况以及各部分位移的变化,并对结果进行分析、归纳和整理。结果：在同一角度下,关节窝和髁突头、颈部应力随加载力的增大而增大,下颌最大应力出现在节点力加载部位颏部,上颌最大应力出现在刚性固定面。同时该模型出现微小的位移变化,颅颌面各部分位移随节点力的增大而增大,颅上颌位移由颅底部和平面向颅顶部逐渐减小,下颌骨的位移由前部到后部逐渐减小,并出现顺时针方向旋转。结论：前方牵引矫治器对颞下颌关节区及颌骨产生反作用力的影响,且随着加载力的增大,其产生的反作用力和形变随之增大。颏部可能出现变形,下颌顺时针方向旋转。     

A study of holographic interferometry on the initial reaction of maxillofacial complex during protraction

Most extraoral appliances used for protracting small or retropositioned maxilla do not allow for variations in the point of force application or in its direction. This variation may be necessary to control vertical, anteroposterior, as well as transverse effects. The purpose of this study was to investigate the initial reaction of the maxillofacial complex according to force magnitude, force direction, and point of force application. For this purpose, an antenna-type modified protraction headgear was tested with double exposure holographic interferometry on a dry human skull with well-aligned upper teeth. Fringe patterns of each protraction condition were compared and analyzed. In most cases, upward rotation of the anterior portion of the maxilla changed to translation, or to downward rotation, as force direction was changed from parallel to the occlusal plane to 20° downward to the occlusal plane. Furthermore, a 500 gm force applied 15 mm above and directed 20° below the occlusal plane produced a translation of the maxillary complex, indicated by a typical circular fringe pattern on the holographic plate, which represents the center of resistance of the maxilla. In most cases, with all force variables tested, a protraction of the maxilla with palatal expansion was more effective in producing translation of the maxilla than was protraction without palatal expansion. By varying force magnitude, force direction and point of force application with maxillary protraction, the amount of maxillary rotation and translation might be controlled. (Am J Orthod Dentofac Orthop 1997;111:623-32.)     

不同承力点前牵引颅面骨骼的三维有限元研究

目的：从生物力学的角度比较分析,不同部位承力颅面骨骼前牵引的生物力学变化特点。方法：采用三维有限元方法,建立颅面复合体三维有限元模型,在模型上分别以牙列承力前牵引和梨状孔底骨骼承力的前牵引,比较分析其生物力学变化。结果：以梨状孔底骨骼承力的前牵引,矢向位移面中上1／2前移比牙列承力的前牵引多,面中下1／2位移相对较少,垂直向及侧向位移值均小于牙列承力的前牵引,等效应力集中范围明显小于牙列承力的前牵引,鼻根区压应力减少明显。结论：与传统的牙列承力的前牵引比较,以梨状孔底骨骼承力的前牵引可整体前移上颌,减少上颌的逆向旋转,减少硬腭前部压缩现象。     

微钛板辅助上颌前方牵引支抗稳定性的三维有限元分析

目的　为临床不同方向下进行前方牵引时,不同形态微钛板的选用提供参考。方法　构建6种改良型微钛板及上颌骨的三维有限元模型。对该模型牵引位点施加大小为4.9N/侧,方向为与上颌平面夹角为0°-50°向前下的力,分析各工况下微钛板所受应力及其固位螺钉所受拉力和应力。结果 1.不同微钛板均可固定于上颌骨颧牙槽嵴处且无受力过大或应力中断现象。2.固位螺钉受力具有差异性。角度为0°时,Y3型微钛板固位螺钉受力离散程度较小为3.899,10°-40°时,L3型微钛板固位螺钉受力离散程度较小为4.544、4.170、3.820、3.547,50°时,L2型微钛板固位螺钉受力离散程度较小为2.687。结论　微钛板辅助上颌骨发育不足患者在不同方向下进行前方牵引时,应考虑选用不同形态：牵引方向与平面夹角为0°时,选用Y3型微钛板;夹角为10°-40°时,选用L3型微钛板;夹角为50°时,选用L2型微钛板。     

单侧完全性唇腭裂植骨患者上颌前牵引矫治的有限元分析

目的:探讨唇腭裂患者牙槽突裂植骨前、后上颌骨前牵引的生物力学变化特点,研究植骨前、后以及植骨区吸收时前牵引对唇腭裂颅上颌复合体的影响,为临床上应用前牵引治疗唇腭裂患者上颌发育不足提供理论依据。方法:采用三维有限元方法,在已建立的唇腭裂上颌复合体有限元模型中模拟植骨及植骨吸收,利用Ansys12.0软件,分别对各个模型在双侧上颌尖牙牙槽骨处施加与平面呈30°的牵引力,大小为每侧5N(约500g),模拟临床上的上颌前牵引,分析其生物力学变化情况。结果:相同加载条件下,植骨前患侧的水平位移显著大于健侧,且患侧与健侧骨缝的应力分布不均匀。植骨后,患侧与健侧的位移差值减小,患侧与健侧骨缝的应力分布趋于更均匀。在所观察的骨缝中,应力最大值出现在翼腭缝,其次为颧颞缝、颧颌缝和颧额缝。结论:植骨前对上颌骨进行前牵引,裂隙有扩大化趋势;植骨有利于上颌前牵引矫治力分布更均匀,健、患侧位移变化趋于接近;且植骨不吸收时,上颌前牵引效果最佳。在模拟植骨发生吸收的几种情况中,植骨区上方发生吸收的上颌前牵引效果比植骨区下方发生吸收的前牵引效果差。     

不同前方牵引力对颅上颌复合体影响的有限元分析

目的:建立并使用上颌发育不足三维有限元模型,研究不同前方牵引力值对颅上颌复合体的影响,以期为上颌前方牵引的临床应用提供理论依据。方法:选择1例9岁上颌发育不足的女性志愿者,采用螺旋CT扫描、数据传输与转录、Mimics10.0软件建立颅上颌复合体的三维有限元模型,利用ANSYS10.0软件,在上尖牙近中牙槽骨处加载与水平面呈向下30°的3～8N前方牵引力,分析颅上颌复合体的位移变化和内部应力分布。结果:不同力值下,N、A、ANS点在Y、Z向位移趋势一致,上颌骨向前上方移动;上牙弓后牙区近中向位移;随牵引力的增大,位移量及颅上颌复合体范式应力和最大主应力也增大。当牵引力大于5N/侧时,各向位移及应力更显著。结论:上颌骨的前方牵引可产生颅上颌复合体的前上方向位移以及上牙弓缩窄。慎用>5N的牵引力。     

种植体支抗前牵上颌体的三维有限元分析

目的：探讨对上颌种植体支抗施加不同大小和方向的前牵引力时颅面复合体骨缝处的应力变化。方法：用螺旋 CT扫描安氏Ⅲ类患者颅面部以获取原始二维图像 DICOM数据,建立颅面复合体的三维有限元模型,种植支抗设计在3223间。模拟前牵引力值1～10 N,1 N 递增,方向平行于眶耳平面向前下呈0°～60°,10°递增,两两组合共70种工况。分析各工况下颅面复合体各骨缝处第一主应力及 Von Miese 等效应力分布情况。结果：牵引角度相同力值不同时,各骨缝应力变化规律相同;牵引力值相同角度不同时,不同区间各骨缝应力变化不同。当牵引角度小于30°时,应力变化分析提示上颌体向前生长并向上旋转;等于30°时上颌体出现向前生长;在40°～50°时,上颌体向前生长方向与牵引方向大致相同;大于50°时,上颌体出现向前生长并向下旋转。结论：种植体支抗眶耳平面向前下30°～50°牵引加载力1～10 N 利于上颌体向前生长。     

前方牵引反作用力对颞下颌关节区受力状况影响的有限元研究

目的：建立并使用颅颌面三维有限元模型,研究前方牵引反作用力对颞下颌关节区以及整个下颌骨的应力分布和位移变化状况的影响。方法：选择1例健康成年男性志愿者,采用薄层螺旋CT扫描获取其颅颌面复合体二维图像原始DICOM数据,利用Mimics、Magics、MSC．Marc等图像处理软件建立颅颌面复合体三维有限元模型。利用AN-SYSIO．0软件,在下颌骨颏顶点处施加与耠平面成37。角,大小为5N的力并分析其受力状况。结果：①获得了精确细致的颅颌面复合体三维几何模型,其网格划分准确合理,与重建生物模型的形态相似性好,力学特性体现准确性高。②下颌骨的应力集中区域位于髁突顶部及颈部,髁突表面最大受力区域位于髁突前斜面。上颌骨表面应力集中区域位于关节窝,其中关节窝表面受力最大区域位于关节结节后斜面。③下颌骨的位移图显示位移大小从颏部至髁突逐级递减,其方向与施力方向一致。下颌骨位移变化最大处位于节点力加载部位,髁突部位位移变化量最小。结论：成功建立了包括颞下颌关节在内的颅颌面三维有限元模型,该模型具有很高的精确性,可用于前方牵引反作用力的相关研究。前方牵引反作用力会对颞下颌关节区以及下颌骨的应力分布和位移状况产生影响,但其是否会造成颞下颌关节紊乱还有待进一步研究。     

The effects of a modified protraction headgear on maxilla.

Protraction headgears are commonly used in the treatment of Class III malocclusion characterized by maxillary retrognathism. The upward and forward rotation of the maxilla during protraction is a major unwanted side effect. The aim of this study was to eliminate the upward and forward rotation of maxilla while protracting. Seventeen patients with Class III malocclusion as a result of maxillary retrognathism were treated for 3 months; their average age was 12.81 years. A full coverage acrylic cap splint-type rapid maxillary expansion appliance was cemented and activated twice a day for 5 days. After sutural separation, a maxillary modified protraction headgear was worn and 750 g of force was applied. Wilcoxon signed rank test was carried out to evaluate 42 parameters measured on cephalometric radiographs. The maxilla was displaced anteriorly by downward and backward rotation. The mandible was displaced downward and backward due to anterior elongation of the maxilla. Extrusion and lingual tipping of the upper incisors and intrusion of upper molars and downward and backward rotation of functional occlusal plane were observed. The aim of our study was achieved, which was to avoid upward and forward rotation while protracting the maxilla. In conclusion, maxillary modified protraction headgear (MMPH) can be used effectively in Class III patients with retrognathic maxilla and anterior open bite tendency.     

两类改良型微钛板种植体辅助上颌前方牵引时上颌骨位移趋势的三维有限元分析

目的　为微钛板种植体辅助上颌前方牵引的临床应用提供参考。方法　建立两类（L/Y）改良型微钛板种植体辅助上颌前方牵引的三维有限元模型,模拟牵引力大小为500g/侧,牵引方向与上颌牙合 平面呈0°～50°斜向前下,分析各工况下上颌骨的位移趋势和变化规律。结果　L、Y型微钛板种植体辅助上颌前方牵引对上颌骨位移趋势的影响基本一致;上颌前方牵引时,上颌牙列有缩窄的趋势;牵引方向斜向前下与牙合 平面呈在0°～20°之间时,上颌骨发生逆时针旋转,30°～50°时,上颌骨发生顺时针旋转。结论　1、微钛板种植体的形态对前方牵引时上颌骨位移趋势影响较小;2、上颌前方牵引时,上牙列有缩窄趋势;3、上颌骨位移趋势会随着牵引方向的改变而不同,牵引方向斜向前下与牙合 平面呈0°～20°时,对治疗反覆牙合 患者有积极意义,30°～50°时,对治疗反牙合 伴开牙合 趋势的患者有积极意义。     

上颌前牵引联合扩弓对唇腭裂植骨患者上颌骨影响的有限元分析

目的:探讨唇腭裂患者牙槽突裂植骨前、后上颌对前牵引联合扩弓的生物力学变化特点,研究植骨前、后上颌前牵引联合扩弓对唇腭裂颅上颌复合体的影响,为临床上应用前牵引治疗唇腭裂患者上颌发育不足提供理论依据。方法:采用三维有限元方法,在已建立的完全性唇腭裂上颌复合体有限元模型中模拟植骨,用Ansys12.0软件,分别对植骨前后的模型在双侧上颌尖牙牙槽骨处施加与平面成30°的力,大小为5N/侧。同时,在双侧上颌第一前磨牙和第一磨牙上各加载5mm的横向水平位移,模拟临床上上颌前牵引方式以及扩弓器的作用对其进行前牵引联合扩弓,分析其生物力学变化。结果:在相同前牵引力作用下,植骨后,上颌复合体患侧、健侧的位移分布较植骨前均匀。无论是植骨前还是植骨后,在前牵引联合扩弓的作用下,患侧健侧各标志点的位移值较不扩弓时均增大,各骨缝的应力值显著大于前牵引力单独作用下骨缝的应力值。结论:对完全性唇腭裂患者而言,上颌前牵引联合上颌扩弓治疗,有利于获得更好的前牵引效果。若配合植骨术,则可使上颌前牵引矫治力分布趋于均匀。     

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目的建立颅颌面三维有限元模型,分析前牵引角度顺时针增大时其反作用力在颞下颌关节（TMJ）和颌骨的应力及位移变化,为正畸临床更好地治疗骨性Ⅲ类错铪,避免对TMJ和颌骨的损伤提供实验依据。方法本研究于2010---2012年在山东大学机械工程学院机械制造及其自动化实验室完成。选择1名健康青年男性志愿者作为研究对象,建立完整的包含TMJ的颅颌面三维有限元模型,模拟前牵引矫治器反作用力,直接在颏部施以一定大小的力并顺时改变施力的方向,测定TMJ和颌骨应力及位移的变化情况。结果（1）应力方面：从不同角度加载节点力之后产生最大应力点出现在加栽部位颏部,关节窝、髁突头颈部等部位应力也比较集中;从不同角度施加相同载荷时,上下颌骨均产生接触应力,40°时最小。（2）位移方面：以一定力值不同角度施加节点力后,该模型产生微小的位移变化,位移最大部位产生在加栽部位;下颌发生了顺时针旋转。结论（1）前牵引矫治器在牵引上颌向前的同时,确实对TMJ及颌骨产生反作用力,临床上在保证上颌牵引效果的同时,要考虑将其不利的反作用力降到最低;（2）传统加力方式中的角度（37°）似乎并不是最佳的选择,从作用力与反作用力两方面考虑40°要优于37°。     

The experimental study of the effects of J-hook type headgear on the craniofacial complex. A study using strain gauge method

In this study, the dry skull with Multibanded appliance was employed in several tractional directions and positions for the investigation of the effects of J-hook headgear on the craniofacial complex including the palate. The traction was carried out by the tractor constructed by J-hook headgear exerting the load of 3 kg on the dry skull applied with the strain gauges. The tractor was connected to the four positions: the gingival and the incisal hooks on the archwire between the central and the lateral incisors, and onto archwire mesial to the canine and the 1 st premolar brackets. The tractional directions were five, varied from -20 degrees - (+)60 degrees to the occlusal plane at the interval of 20 degrees. The distribution of two-dimensional strain in several tractions and the effects on the craniofacial complex were investigated. The results were as follows: 1. In the right side view, the maxillary complex was not rotated when the tractional directions were set about at +40 degrees in the incisal traction, and between +40 degrees and +60 degrees in the canine and the 1 st premolar tractions. In the maxillary complex, clockwise rotation was induced by downward traction less than these angles, and the counterclockwise rotation was induced by upward traction more than these angles. 2. In the horizontal view, the degree of the curvature of the zygomatic arch tend to increase by the horizontal traction in any positions. 3. The palatine region was suggested to enlarge in the lateral direction at -20 degrees traction in any tractional positions. The enlargement gradually lessened in upward traction by the incisal traction. The palatine region between the canines was suggested to compress at +40 degrees and +60 degrees traction in the gingival hooks, and at +60 degrees traction in incisal hooks. In the canine and the 1 st premolar tractions, palatine region was suggested to enlarge in the lateral direction in any tractional directions. 4. The palatine region was suggested to compress in the backward direction in any tractional direction. The trend was not found to be different among tractional points. The maximum compression was produced in -20 degrees traction, and then gradually decreased in upward traction.     

三种快速扩弓联合前方牵引装置作用效果的三维有限元分析

目的 应用三维有限元法比较三种快速扩弓联合前方牵引装置对颌骨及牙齿的作用效果,为临床治疗提供参考.方法 建立Hyrax联合牙性前方牵引装置、骨支持式扩弓器(maxillary skeletal expander,MSE)联合牙性前方牵引装置、MSE联合骨性前方牵引装置及颅上颌复合体的三维有限元模型,对扩弓螺旋器施加0....     

侧向(牙合)力对楔状缺损充填材料应力分布的影响

目的 研究楔状缺损充填治疗后,侧向(牙合)力作用对充填材料的应力分布影响.方法 建立含楔状缺损的上颌第一前磨牙三维有限元模型,在模型的缺损部分用模拟玻璃离子材料进行充填;对模型施加不同方向的载荷,对充填体部分进行应力分析.结果 当(牙合)力方向与牙体长轴平行时,充填体受到的应力较小.当(牙合)力方向与受力牙尖斜面垂直时...     

Biomechanical and clinical changes of the craniofacial complex from orthopedic maxillary protraction

The present study was designed to investigate biomechanical and clinical changes in the craniofacial complex resulting from orthopedic maxillary protraction by means of finite element and cephalometric analyses, respectively. An analytical model developed from a young human dry skull was used for finite element analysis. Three principal stresses were determined in the complex and its sutures. For evaluating morphological changes of patients, lateral cephalograms taken before and after maxillary protraction therapy were analyzed. Tensile stresses were produced in the maxillary and zygomatic bones in an anterior direction with corresponding compressive stresses in a perpendicular direction. In the sutural systems, compressive stresses were induced by counter-clockwise rotation of the complex. Cephalometric investigation demonstrated that significant improvement of the maxillo-mandibular relationship was obtained by maxillary protraction, however, maxillary growth and repositioning were not as great when compared to mean growth in the control group.     

上颌复合体手术辅助腭扩展应力分布和位移的研究

目的 模拟手术辅助腭扩展术,分析上颌骨复合体应力分布与位移趋势.方法 在力学相似性较高的上颌骨复合体三维有限元模型上,模拟第一磨牙处颊侧骨皮质切开辅助腭扩展术,计算各标志点的应力及位移,所得结果与常规腭扩展相比较.结果 颊侧骨皮质切开术辅助腭扩展开展牙弓,可有效增加横向扩展的位移,尤其在尖牙和前磨牙区.同时鼻腔和腭盖下降,有助于降低通气阻力.结论 颊侧骨皮质切开辅助腭扩展的方法效果确切.