不同角度后倾曲对下颌第二磨牙作用力的三维有限元分析

目的：探讨0.018〞澳丝弯制的不同角度后倾曲对下颌第二磨牙作用力的情况。方法：应用CT扫描技术、Auto CAD及ANSYS相结合的建模程序,以中国人正常下颌骨为建模的实体参照,建立下颌第二磨牙及其牙周组织的三维有限元模型,同时建立用0.018〞澳丝弯制附5°、10°、15°、20°、25°、30°六个不同角度磨牙后倾曲唇弓的三维有限元模型,利用弯曲梁应变原理,计算出不同角度后倾曲作用下,下颌第二磨牙颊面管近中端及远中端力的大小及方向。结果：第二磨牙近中受到向伸长力,远中受到龈向压低力,其大小随着角度的增大而增大,近中力值大于远中力值。结论：后倾曲对第二磨牙产生远中倾斜力矩;随着后倾曲角度增大,磨牙呈现远中直立的趋势,同时牙冠舌向倾斜趋势加大。     

Tip-Edge力系后倾曲对上颌磨牙初始位移影响的三维有限元分析

目的 研究Tip-Edge力系中上颌第一磨牙在后倾曲作用下的初始位移情况,探讨后倾曲曲度和位置对上颌第一磨牙初始位移的影响。方法 采用牙列完整的干颅,用CT扫描建立Tip-Edge差动直丝弓三维有限元模型,模拟5种后倾曲曲度（20°、30°、40°、50°、60°）以及4种后倾曲位置（2、4、6、8 mm）对模型进行加载,计算上述情况下磨牙的初始位移情况。结果 在后倾曲作用下,上颌第一磨牙出现远中方向移动以及伸长移动。当后倾曲曲度增加时,磨牙的远中初始位移以及伸长位移增加;当后倾曲距离增加时,磨牙的远中初始位移以及伸长位移减少。结论通过改变后倾曲的曲度和位置,可以有效地控制Tip-Edge力系下上颌磨牙的初始位移方式以及移动量。     

差动直丝弓矫治技术打开咬合过程中不同磨牙后倾弯曲度对下颌前牙及牙周膜应力分布的影响

目的：研究在差动直丝弓矫治技术打开咬合过程中,不同下颌磨牙后倾弯角度对下颌前牙应力分布及位移趋势的影响。方法利用志愿者锥体束CT,建立下颌牙列和差动直丝弓矫治器的三维有限元模型,模拟下颌30°、35°、40°和45°四种后倾弯,对模型加载进行有限元分析。结果下颌前牙牙根和牙周膜所受应力均随后倾弯度数增大而增大,当后倾弯角度大于40°时应力出现减小,其应力分布符合非控制性倾斜移动的特点。下颌前牙的初始位移趋势随后倾弯的增大而增大,当大于40°时初始位移趋势开始减小。下颌尖牙在颊舌向上表现为冠颊倾,下颌切牙冠唇倾,在垂直向上表现为先尖牙再切牙的顺序压低,在近远中向均表现为冠近中移动趋势。结论在差动直丝弓打开咬合阶段,通过调整磨牙后倾曲的角度可获得下颌前牙段适宜的压入以及匹配的上下颌牙弓宽度。     

尖牙近、远中小圈簧在Begg系统打开咬合的应用

笔者在Ｂｅｇｇ技术的实际应用中 ,设计尖牙近中或远中垂直小圈曲簧 ,结合磨牙前小角度后倾曲打开咬合 ,经临床应用 ,前牙压低效果明显 ,前磨牙适当升高 ,整平牙弓快 ,运用国产仿澳丝也能快速打开咬合。方　法1.改进后Ｂｅｇｇ唇弓的弯制 :根据尖牙高低位及是否需压低在尖牙远中或近中龈向打垂直小圈曲并后倾 30°,在第一恒磨牙近中打 15°后倾曲。2 .改进后Ｂｅｇｇ唇弓的应用 :①尖牙高位需压低采用15°后倾曲 30°尖牙远中小圈曲 Ⅱ类颌间牵引。②尖牙低位需升高采用 15°后倾曲 30°尖牙近中小圈曲 Ⅱ类颌间牵引。③尖牙无需升高或…     

多曲方丝弓与镍钛方丝在各牙位间的局部载荷挠曲率的对比研究

目的测量并比较多曲方丝弓与镍钛方丝分别在各牙位间的局部载荷挠曲率，分析多曲方丝弓的力学特性。方法用0．016×0．022英寸的不锈钢方丝按Kim标准弯制MEAW弓丝中独立的“L”形曲。用Instron 2343型电子万能材料力学试验机及Series Ⅸ软件在室温下对“L”形曲及0．016×0．022英寸NiTi平直方丝分别在上下颌各牙位间进行加载和卸载实验，测得各自的局部载荷挠曲率SPSS11．0软件包进行统计分析。结果“L”形曲与NiTi方丝在各牙位间加载和卸载时，在牙位1—2和2—3，各“L”形曲的局部载荷挠曲率比NiTi方丝的大，而在后牙区各牙位间的各“L”形曲的局部载荷挠曲率比NiTi方丝的小，其差异有显著性（P〈0．01）。结论MEAW的局部载荷挠曲率较之NiTi方丝，在前牙区更大，在后牙区更小，在牙位3—4和4—5下降得更多。     

利用压低辅弓增加后牙支抗的生物力学研究

目的确定远中移动尖牙时,使用压低辅弓增加后牙支抗的最适后倾弯角度。方法按照Burstone方法弯制0．017×0．025英寸（1英寸-2．54cm）伊钛丝（TMA）的压低辅弓,主弓丝采用0．016×0．016英寸不锈钢丝,拉尖牙远中移动的拉簧为150g力。设计后倾弯分别为20°、30°、40°,采用口外正畸模拟生物力学检测系统（OrthodonticMeasurementandSimulationSystem,（）Mss）模拟临床加力,分别测量三维状态下切牙段、尖牙段和后牙段受力和力矩情况。结果尖牙远移过程中,无压低辅弓时,尖牙远中移动并倾斜,磨牙近中倾斜10°;压低辅弓的后倾弯为20°时,尖牙远中移动并倾斜,磨牙近中倾斜5°;后倾弯为30°时,尖牙远中移动基本保持直立,磨牙远中倾斜5°;后倾弯为10。时,尖牙远中移动有压低倾向,磨牙远中倾斜超过10°。结论尖牙远中移动时,弯制有30。后倾弯的乐低辅弓既能够增加后牙专精．又不影响前牙的覆[牙合]覆盖。     

上颌第一磨牙控制的生物力学研究

目的    利用三维有限元方法模拟在上颌第一磨牙加载不同角度及位置的后倾曲和末端内收曲时,其受力分布规律和位移趋势,并阐明其生物力学机制。方法    建立上颌全牙弓三维有限元模型。（1）使用0.018英寸×0.025英寸（0.48 mm × 0.64 mm）不锈钢方丝在不同部位建立弯折15°、30°及45°后倾曲弓丝模型。观测不同工况下上颌第一磨牙在Z向的位移;（2）在不同部位建立弯折15°、30°以及45° Toe-in曲弓丝模型,观测不同工况下上颌第一磨牙在X和Y向的位移情况。结果    （1）后倾曲弯折的角度增加,第一磨牙受到净力随之增加;弯折点越靠近第一磨牙近中,其压入力量越大;弯折点靠近第二前磨牙时,磨牙呈整体伸长趋势。（2）Toe-in曲弯折角度增加,第一磨牙的旋转位移角度随之增加;Toe-in曲弯折点靠近第一磨牙颊面管近中时,第一磨牙呈整体舌向位移;弯折点靠近第二前磨牙时,呈顺时针旋转趋势。结论    后倾曲对第一磨牙垂直位移影响较大,其弯折点靠近第二前磨牙时有利于支抗控制及咬合打开;Toe-in曲的弯折则有利于平衡第一磨牙旋转的副作用。     

后倾曲作用下上颌支抗磨牙运动趋势的三维有限元法研究

目的分析Ｂｅｇｇ技术第一期后倾曲作用下上颌支抗磨牙的运动趋势。方法三维有限元法,模型采用中国人上颌第一磨牙平均几何尺寸,包括５１６个单元,１１２８个节点。结果牙体瞬间转动中心是一个范围,位于根分叉处偏近中颊根及舌侧根区域的牙槽骨中。牙体呈现出“螺旋式”不平衡近中舌向旋转伸长趋势,伸长的量从多到少顺序：近中颊尖、近中舌尖、远中颇尖、远中舌尖。结论支抗磨牙的各部分运动趋势不平衡。     

潜在性开(殆)的矫治及稳定性初探

目的探讨后倾曲在潜在性开矫治中的作用及肌功能训练对正畸稳定性的影响。方法潜在性开伴双颌前突女性患者1例,年龄11岁6个月,治疗时间为2.3年,内收上下前牙后,下磨牙近中弯制15°后倾曲,同时辅以前牙垂直牵引,建立前牙区正常覆覆盖及后牙区良好咬合关系,全程进行肌功能训练,对矫治前后及保持1年后头颅侧位X线片进行对比分析。结果治疗结束后上下前牙均内收,下磨牙远中直立,L6-PP增大6.2°,下切牙伸高,L1-PP减小1.9 mm,这是平面变平的主要原因,保持1年后咬合稳定,软组织侧貌更为美观和谐。结论后倾曲加前牙垂直牵引是一种简单有效的治疗潜在性开的方法,提倡辅以肌功能训练以获得正畸疗效的长期稳定性和更为美观和谐的侧貌面型。     

多曲方丝弓在不同牙位间的局部载荷挠曲率的实验研究

目的:测量并比较多曲方丝弓(MEAW)在不同牙位间的局部载荷挠曲率,分析多曲方丝弓的力学特性.方法:用0.41 mm ×0.56 mm的不锈钢方丝按Kim标准弯制MEAW弓丝中独立的"L形"曲.用Instron 2343型电子万能材料力学试验机及Series IX软件在窒温下对"L"形曲分别在上下颌不同牙位间进行加载和卸载实验.实验中横梁速度为1.0 mm/min.最大形变量为1.0 mm.各牙位间的待测弓丝分别取5个样本重复实验,测得各自的局部载荷挠曲率.数据用SPSS11.0软件包进行统计处理,分析其差异.结果:"L"形曲在各牙位间加载和卸载时.其局部载荷挠曲率除在尖牙、第一前磨牙间与第一、二前磨牙间相等外,在其余各牙位间均小同,前牙区大,后牙区小,差异有显著性(P＜0.05).结论:MEAW在不同牙位间的局部载荷挠曲率符不相同,由前向后递减.     

多曲方丝弓技术矫治骨性Ⅲ类错前后变化的观察

目的对比多曲方丝弓(MEAW)技术矫治骨性Ⅲ类错畸形前后患者X线片变化,探讨MEAW技术矫治骨性Ⅲ类错畸形的机制。方法选用骨性Ⅲ类错畸形患者15例采用0.56mm×0.64mm的直丝弓托槽系统治疗。测量矫治前、后患者的定位X线头颅侧位片并进行比较。结果由于下后牙的远中直立,L6/MP,L7/MP平均增加了7.2°和7.6°,OP-FH平均减少4.23°,OP-MP平均增加5.64°。结论MEAW技术矫治骨性Ⅲ类错畸形主要通过下后牙的远中竖直,以及平面的改变来完成,而矫治前后骨组织及软组织的变化有限。     

垂直矫治曲结构与力学性能的有限元分析

目的:研究垂直曲的结构与力学性能之间的关系,为临床上更好地应用垂直曲提供参考依据。方法:根据垂直曲在应用过程中的作用方式,建立垂直曲的几何模型,应用有限元分析软件ANSYS对曲的力学性能进行模拟计算,最后对其规律进行总结。结果:增加垂直曲的臂长、高度或弯曲半径,曲变形时产生的力和力矩值下降。增加臂长时力和力矩的比值减小,而增加高度和弯曲半径时却增大。加大垂直臂间隙时,产生的力和力矩值增大,而力和力矩的比值变化不大。结论:实际应用中,可适当改变垂直曲的结构,调整曲的力、力矩及力和力矩的比值,以满足治疗中不同个体的需要。     

垂直曲的力学行为的研究

目的 研究比较不同材质矫治垂直曲及不同形状的矫治曲的力学特性。方法 利用大型有限元软件 ANSYS进行模拟计算。结果 钛镍丝材料的矫治曲的作用力较符合临床正畸应用;双垂直曲的作用力比垂直曲的柔和的多。结论 掌握各种垂直曲的力学行为的变化规律,可更好地指导临床。     

上颌“T”形曲内收弓丝矫治上颌前牙的三维有限元分析

为了全面研究“Ｔ”形曲连续内收弓丝对前牙所产生的矫治力作用,以３根弹簧模拟牙周组织－牙齿－托槽对矫治弓丝的弹性支持作用,用三维有限元方法对“Ｔ”形曲内收弓丝对上前牙产生的矫治力系统进行了分析。得出以下结论：①“Ｔ”形曲连续内收弓丝末端回抽加力时,除水平力外,还产生使牙齿伸高的垂直力与根舌向力矩。②用“Ｔ”形曲内收前牙时,需同时弯制合适的根舌向转矩和“人”字形曲,方可有效地控制牙齿移动。③使用“Ｔ”形曲内收弓丝,加力不宜过大。④适当选用较细的弓丝,可使矫治力更柔和、持久。本研究对临床应用方丝弓技术内收前牙弓、关闭拔牙间隙有明确的指导意义。     

台阶式垂直闭合曲内收上颌切牙的三维有限元分析

目的 研究台阶式垂直闭合曲在三维空间内对上颌切牙位置的控制作用.方法 选择一名正常 志愿者,对其上颌牙列和牙槽骨进行三维螺旋CT扫描,只对上颌右侧中、侧切牙及牙槽骨进行建模和数据计算,利用Ansys软件生成右侧弓丝-托槽-上颌切牙段及牙周支持组织的三维有限元模型,最后根据镜像对称原理建立弓丝-托槽-上颌切牙段及牙周支持组织的三维有限元模型.模拟台阶式垂直闭合曲在临床上的使用情况加力,分析上颌切牙的位移趋势以及牙周支持组织中的应力分布规律.结果 台阶式垂直闭合曲作用下,上颌中切牙舌向、唇向最大位移分别为5.29×10-2和0.71×10-2 mm;龈向、向最大位移分别为10.47×10-3和10.20×10-3 mm;近中、远中最大位移分别为10.26×10-3和1.63×10-3 mm;侧切牙舌向、唇向最大位移分别为3.31×10-2和0.41×10-2 mm;龈向、向最大位移分别为10.52×10-3 和5.10×10-3 mm;近中、远中最大位移分别为6.29×10-3 和4.64×10-3 mm;二者均表现为舌向、龈向的近似整体移动趋势.中切牙牙齿、牙周膜、牙槽骨的最大应力值分别为31.35、2.52、4.64 MPa;侧切牙牙齿、牙周膜、牙槽骨的最大应力值分别为19.59、1.28、4.12 MPa;二者的应力分布规律相似,牙周膜对应力起缓冲作用.结论 台阶式垂直闭合曲在上颌切牙内收阶段可控制其在三维方向上的位置,对抗"钟摆效应",对临床实践具有一定参考意义.

Abstract：

Objective To investigate the displacement and stress distribution of upper incisors in three-dimensional(3D) space controlled by step-shaped vertical closing loop. Methods The maxillary teeth and alveolar bone of a volunteer with normal occlusion were scanned with 3D spiral CT. Modeling and calculation were only carried out on right upper central incisor, lateral incisor and their alveolar bone in order to simplify the procedures. A 3D finite element model of archwire-brackets-upper incisors and periodontal tissues was developed using Ansys finite element package. Finally, a 3D finite element model of archwire-brackets-upper incisors and periodontal tissues was established based on mirror symmetry principle. The displacement of maxillary incisors and stress distribution in periodontal tissues were analyzed. ResultsWhen step-shaped vertical closing loop was simply drew back 1 mm, the maximum displacement of upper central incisor in labial and lingual direction were 5.29×10-2 and 0.71×10-2 mm; 10.47×10-3 and 10.20×10-3 mm in gingival and occlusal direction, 10.26×10-3 and 1.63×10-3 mm in medial and distal direction; the maximum displacement of upper lateral incisor in labial and lingual direction were 3.31×10-2 and 0.41×10-2 mm, 10.52×10-3 and 5.10×10-3 mm in gingival and occlusal direction, 6.29×10-3 and 4.64×10-3 mm in medial and distal direction, the displacement trend of them were moving lingually and gingivally similar to bodily movement. The stress peach of upper central incisor, periodontal ligament and alveolar bone were 31.35, 2.52 and 4.64 MPa, the stress peach of upper lateral incisor, periodontal ligament and alveolar bone were 19.59, 1.28 and 4.12 Mpa, the stress distribution of them were similar and the periodontal ligament buffered the stress imposed on the tooth. Conclusions The position of upper incisors in 3D space could be controlled by step-shaped vertical closing loop and the pendulum effect could be confronted.     

The influence of medial implant location in three-unit posterior cantilever fixed partial dentures on stress distribution in surrounding mandibular bone

This study examined the influence of medial implant location in three-unit posterior cantilever fixed partial dentures (FPDs) on stress distribution in mandibular bone surrounding two implants. A three-dimensional finite element model that included three-unit FPD and two cylindrical-type implants (4 mm in diameter and 10 mm in length) osseointegrated in the posterior mandible, was digitized. Five different models were created according to the medial implant location between the missing second premolar and the first molar location. The distal implant was fixed at the missing second molar location. Oblique bite force of 100 N at 30 degrees buccal to the vertical direction was directed on each of three artificial teeth, respectively and simultaneously, while the lower surface of the mandible was fixed. The maximum equivalent stress in the cortical and the trabecular bone generally increased as the medial implant shifted to a distal position. Under the simultaneous bite force, relatively low maximum stresses within the cortical bone: between 55 MPa and 57 MPa, were shown in the models with the medial implant placed within the range of one implant diameter from the most medial position, while higher maximum stresses: between 64 MPa and 73 MPa, were demonstrated with more distally placed medial implants. The results suggest that reasonably low mechanical stress in the surrounding bone may be assured when the medial implant is placed in the range between the missing second premolar position and one implant diameter distal from that location.     

Comparison of five different fixation techniques of sagittal split ramus osteotomy using three-dimensional finite elements analysis

The aim of this study was to compare the mechanical stress over hemimandible substrate and hardware after sagittal split ramus osteotomy (SSRO) fixed with five different techniques using three-dimensional (3D) finite element analysis. A 3D finite element model of a hemimandible was created and a 5mm advancement SSRO was simulated on a computer model. The model was fixed with five different techniques: 3 linear 60° screw arrangement; 3 linear 90° screw arrangement; 3 inverted L screw arrangement; 1 conventional miniplate; and 1 locking miniplate with four monocortical screws. Load was applied until 3mm displacement was reached and the results were compared with previous mechanical and photoelastic tests, thus analysing the mechanical stresses developed in the proximity of miniplates and screws and within the fixation system itself. The maximum principal stress values demonstrate a lower mechanical stress rate in bone and in the fixation system with the inverted L arrangement, followed by the linear 90° and linear 60° arrangements. The locking miniplate/screw system presented lower maximum principal stress and better stress distribution compared with the conventional system. Under the conditions tested, the reversed L arrangement provided the most favourable stress dissipation behaviour.     

An unusual "sebaceous cyst"

A 41-year-old man was referred by his general practitioner to the general surgeons with an "infected sebaceous cyst" above the right medial canthus. "Cyst" was excised by the general surgeons. But this was followed by its recurrence after a number of weeks. A lateral skull radiograph showed the presence of a radio-opaque foreign body within the right orbit.     

Influence of occlusal forces on stress distribution in preloaded dental implant screws

STATEMENT OF PROBLEM: Abutment and prosthetic loosening of single and multiple screw-retained, implant-supported fixed partial dentures is a concern. PURPOSE: The purpose of this study was to investigate stress distribution of preloaded dental implant screws in 3 implant-to-abutment joint systems under simulated occlusal forces. MATERIAL AND METHODS: Three abutment-to-implant joint systems were simulated by using the 3-dimensional finite element analysis method: (1) Branemark external hexagonal screw-retained abutment, (2) ITI 8-degree Morse tapered cemented abutment, and (3) ITI 8-degree Morse tapered plus internal octagonal screw-retained abutment. A thermal load and contact analysis method were used to simulate the preload resulting from the manufacturers' recommended torques in implant screw joint assemblies. The simulated preloaded implants were then loaded with 3 simulated static occlusal loads (10 N; horizontal, 35 N; vertical, 70 N; oblique) on the crown position onto the implant complex. RESULTS: Numeric and graphical results demonstrated that the stresses increased in both the abutment and prosthetic screws in the finite element models after simulated horizontal loading. However, when vertical and oblique static loads were applied, stresses decreased in the external hexagonal and internal octagonal plus 8-degree Morse tapered abutment and prosthetic screws with the exception of the prosthetic screw of ITI abutment after 70-N oblique loading. Stresses increased in the ITI 8-degree Morse tapered cemented abutment after both vertical and oblique loads. CONCLUSION: Although an increase or decrease was demonstrated for the maximum calculated stress values in preloaded screws after occlusal loads, these maximum stress values were well below the yield stress of both abutment and prosthetic screws of 2 implant systems tested. The results imply that the 3 implant-to-abutment joint systems tested may not fail under the simulated occlusal forces.     

Use of medial upper arm free flap in oral cavity reconstruction: a preliminary study

The medial upper arm has previously been proposed as a potential free flap donor site, but the clinical application of such flaps in head and neck reconstruction has not been popular. The preliminary results of the clinical application of medial upper arm free flaps in oral cavity reconstruction are reported here. Five patients with oral cancer underwent surgical resection and neck dissection, with simultaneous reconstruction using a medial upper arm free flap. Functional outcomes were investigated using the University of Washington Quality of Life Questionnaire. Sensory-motor functions of the upper arm donor site were recorded before and after surgery. Four flaps were successfully transferred. One flap was abandoned during surgery because of a lack of perforators, and a forearm flap was used instead. All patients survived without loco-regional recurrence or distant metastasis. Functional outcomes, especially swallowing and speech, were satisfactory. The donor site scar was well hidden, with no functional impairment. This initial experience shows that the medial upper arm free flap represents an alternative perforator flap for oral cavity microsurgical reconstruction. The well-hidden scar and better texture match compared with other flaps make it suitable for oral cavity reconstruction.