上颌窦底提升不同高度对种植义齿受力影响的三维有限元分析

目的:研究上颌窦底提升后种植义齿修复时,不同提升高度对种植体-骨界面应力状况的影响,为其临床应用提供生物力学参考依据。方法:采用健康志愿者的CT扫描数据,通过Mimics 11.0软件,建立上颌第一磨牙缺失、含上颌窦的上颌骨三维有限元模型,并模拟植入10 mm长标准种植体1枚。模拟上颌骨骨量不足,建立上颌窦底分别提升2、4、6 mm的种植义齿模型,并以无需窦底提升的种植义齿模型为对照。分别从垂直、颊向30°和舌向30°三个方向,对种植义齿上部结构牙冠咬合面中心点施加100 N的集中载荷,用三维有限元分析方法对不同模型的种植体-骨界面进行应力分析。结果:各模型在同一加载条件下,皮质骨的应力最大,松质骨和人工骨的应力值接近。随着窦底提升高度的增高,种植体颈部周围骨组织的应力总体呈先降后升的趋势,在提升高度为4 mm时最小。颊舌向加载时产生的应力远大于垂直载荷下产生的应力。结论:上颌骨后部骨量不足时,上颌窦底提升植骨可以大大改善种植体-骨界面内应力,植骨高度为4 mm时,种植体-骨界面应力总体最小;垂直载荷更有利于种植体-骨界面的应力分布状况,在临床设计种植义齿上部结构时应尽量减小或避免斜向载荷。     

不同螺距种植体集中载荷的有限元分析

目的:用三维有限元方法分析不同螺距种植体-骨界面应力分布状况,确定利于应力均匀分布的最佳螺纹参数设计.方法:建立包含上部结构的牙种植体、局部下颌骨块三维有限元模型,利用Cosmos/works软件分析在垂直、斜向45° 2 种集中载荷下螺距分别为0.6、 0.8、 1.0 mm的3 种种植体与骨界面的应力分布状况.结果:螺距为0.8 mm种植体周围Von-Mises应力、拉应力、压应力峰值较小,应力分布最均匀;同一螺距种植体斜向载荷下应力显著高于垂直载荷;应力集中主要出现于种植体颈部、皮质骨上缘和种植体末端最下一个螺纹处.结论:螺纹种植体螺距影响骨界面的应力分布和(牙合)力传导,为避免应力集中种植体末端螺纹应进行适当的截齿处理,种植义齿设计和修复时应尽可能减小或避免非轴向力.     

皮质骨厚度对支抗种植体-骨界面应力分布的影响

目的：研究皮质骨厚度改变对支抗种植体-骨界面应力分布的影响，供临床参考。方法：用三维有限元方法，对分别种植于皮质骨厚度为0．5mm、1．0mm、2．0mm颌骨模型中的种植体施加150g近远中方向的载荷，分析支抗种植体-骨界面应力分布情况：结果：三者种植体颈部的Von-Mises应力值分别为0．6040MPa、0．5330MPa、0．5380MPa；位移值分别为0．2110μm、0．1630μm、0．1250μm：结论：皮质骨在一定厚度内，植入体颈部皮质骨越薄，骨界面应力值就越大：但皮质骨超过一定厚度后，骨界面应力并不随其厚度的增加而做相应递减。皮质骨的厚度与界面骨的位移成反比.     

不同骨结合率对种植体骨界面应力分布的影响

目的:通过建立含牙种植体的无牙下颌骨三维有限元模型,分析不同的骨结合率对种植体骨界面应力分布的影响。为临床设计种植义齿治疗方案提供理论依据。方法:使用螺旋CT扫描、CAD技术、有限元软件等,建立含牙种植体的下颌骨三维有限元模型;分析不同的骨结合率对种植体骨界面应力分布的影响。结果:不同骨结合率都会出现种植体颈部皮质骨的应力集中;当骨结合率大于或等于60%时,颈部皮质骨处应力值明显下降。结论:随着骨结合率的增加,颈部皮质骨的应力值有下降的趋势;提示临床医生在进行种植义齿修复时,需考虑提高种植体骨结合率,避免影响骨结合的不利因素,从而提高种植的成功率。     

微型正畸支抗种植体即刻挤压植入时骨界面应力分析

目的研究微型正畸支抗种植体即刻植入时骨界面应力大小及分布,为微型支抗种植体即刻加载提供参考。方法将局部下颌骨简化成一个等腰梯形,颌骨骨块长20mm,断面高为30mm,上边宽为10mm,底边宽14mm,皮质骨厚度设定为1.6mm;微型种植体直径设定为1.2mm,长6mm。利用ANSYS9.0软件,建立局部微型种植体-骨的三维有限元模型。下颌骨材料属性设定为线性、正交各向异性,种植体-骨界面定义为完全连接。将断端处、下颌骨局部骨块面及底面的所有节点给予刚性约束。模拟种植体即刻植入时的情况,将骨界面初始位移设定为0、0.05、0.1mm,分析各指定初始位移时骨界面应力大小及分布。结果即刻加载时,0mm初始位移下,种植体骨界面无应力分布;初始位移为0.05mm时,骨界面应力集中在骨皮质内,分布较均匀,衰减幅度很小,近远中方向上的VonMises应力为1648MPa,龈向为1782MPa。初始位移为0.1mm时,近远中方向上的VonMises应力为2012MPa,龈向为2110MPa。结论微型种植体挤压植入时会产生较大的初始应力,即刻加载时,应当考虑这种初始应力。     

微型支抗种植体不同承载方向的三维有限元研究

目的 :探讨微型支抗种植体承载不同方向 2 0 0 g正畸力时的应力分布情况。 方法 :利用三维有限元软件ANSYS建立微型支抗种植体 -骨有限元分析模型 ,在与种植体长轴成 0°、3 0°、45°、60°或 90°角等加载条件下进行分析计算。结果 :承载不同方向力时 ,种植体 -骨界面的最大应力均较小 ,应力大小随着角度的增大而增大 ,5种承载方向时种植体颈部均为应力集中区。结论 :种植体可比较安全承载不同方向的 2 0 0 g正畸力 ,特别是与长轴夹角较小的力。     

眶部种植体长度对骨界面应力影响的三维有限元研究

目的 探讨不同长度的眶部种植体对骨界面应力分布的影响。方法 建立直径3.75 mm,长度分别为3、4、6、10 mm的眶部种植体-颅颌面骨三维有限元模型,分别给予沿种植体轴向和与轴向成45°的载荷,载荷大小20 N,记录两种方向载荷下种植体及骨界面的Von-Mises应力峰值和位移峰值,分析其应力分布。结果 施加沿种植体轴向载荷时,种植体周围应力集中于根部,种植体受力大于骨面;施加与轴向成45°载荷时,应力集中于种植体颈部与第一螺纹之间,种植体受力大于骨面。施加两个方向的载荷时,3 mm种植体的应力峰值明显大于其他长度种植体,而位移峰值无明显变化。在相同长度下,施加沿种植体轴向载荷时的应力峰值及位移峰值均明显低于与轴向成45°载荷时,载荷方式对界面应力分布有明显的影响。结论 临床上尽量选择4 mm以上的眶部种植体;应用3 mm种植体时,应选择骨密质较厚的区域植入。     

平台转换结构中肩台变化对种植体-骨界面应力分布的影响

目的:探究平台转换结构中肩台变化对种植体-骨界面应力分布的影响,以明确最优化的肩台形态,为指导临床应用及开发新产品提供理论依据.方法:采用三维有限元分析方法,建立不同肩台形态的种植体模型,对模型施以100N的轴向及侧向载荷,计算和分析肩台宽度及角度变化时种植体-骨界面的应力,并与传统两段式种植体进行比较.结果:轴向和侧向栽荷时,实验组与对照组的最大等效应力均位于种植体颈部周围的皮质骨中,松质骨中的应力较小;在同一模型上侧向载荷所产生的应力水平远大于轴向载荷所产生的应力;在平台转换结构中,肩台的变化将对种植体-骨界面应力产生较大的影响,相比对照组,肩台的角度越小、宽度越大,种植体-骨界面的应力分布就越好,应力峰值也越小,过大的肩台角度反而会造成比传统两段式种植体更大的骨界面应力;同时结果还表明随着种植体直径的增加,皮质骨界面的应力值有所下降.结论:在平台转换结构中,肩台的角度越小、宽度越大,种植体颈周皮质骨内的应力分布就越好,应力峰值也越小,随着种植体直径的增加,种植体-骨界面的应力值有所下降.从生物力学角度考虑,建议临床上尽量选择直径较大、肩台较宽、角度为0.的平台转换结构种植体.     

三维有限元分析过盈配合对种植体骨界面应力分布的影响

目的:分析过盈配合对种植体骨界面应力的影响。方法:分别建立不同过盈量(0.1mm、0.2mm、0.3mm)、不同种植体直径(3.3mm、4.0mm、5.0mm、6.0mm)及不同皮质骨厚度(0.5mm、1.0mm1.5mm、2.0mm、3.0mm)的有限元模型,用有限元法对过盈配合下种植体骨界面初始应力的大小和分布进行分析。结果:过盈配合下种植体骨界面初始应力随着过盈量及皮质骨厚度增大而增大,随着种植体直径的增大而减小。结论:过盈配合中过盈量、种植体直径及骨皮质厚度对种植体骨界面的初始应力影响不同,在种植设计时应综合考虑相关因素的影响。     

支抗种植体直径对骨界面应力分布的影响

目的 :研究不同直径支抗种植体对骨界面应力分布的影响 ,以供临床筛选合适的种植体。方法 :用三维有限元方法给种植体施加 1.47N(150 g)近远中方向的载荷 ,分别对直径为 3 .0、3 .75、5.0mm的支抗种植体 骨界面进行应力分析。结果 :3种直径种植体颈部的Von Mises应力值分别为 0 .80 7、0 .53 3、1.0 80 ;位移值分别为 0 .2 3 2、0 .163、0 .111μm。结论 :在选择正畸支抗种植体时 ,直径为 3 .75mm的种植体较适宜作正畸支抗体     

Mechanical anisotropy of orthodontic mini-implants

This study investigated stress distribution in the bone around orthodontic mini-implants using the finite element method and determined the difference in the stress distribution for different loading directions to identify risk factors for the loosening of mini-implants. Three-dimensional finite element models were constructed for conventional and cervical threadless mini-implants with cortical bone 1 or 3 mm thick. The authors calculated the compressive stresses on the bone elements and evaluated stress distribution according to the loading direction. Directional dependency (i.e. mechanical anisotropy) was observed with the conventional mini-implant model. The compressive stress ranged from –31 to –55 MPa depending on the loading direction. In the cervical threadless model, mechanical anisotropy disappeared and the stress was reduced. Cortical bone thickness had no influence in either model. One of the risk factors for mini-implant failure might be related to mechanical anisotropy. This report suggests ways for clinicians to avoid overload traction force when conventional mini-implants are used. The cervical threadless mini-implant can reduce mechanical anisotropy to facilitate successful placement. Inserting a conventional screw deeply beyond the threaded part might be useful in stabilizing a mini-implant.     

Effects of washer on the stress distribution of mini-implant: A finite element analysis

Objective:To investigate the biomechanical effects of ‘washer’ designed for improving mini-implant stability.Materials and Methods:Four three-dimensional finite element models of the mini-implant and surrounding bone were constructed with washers in different spike lengths (1.5 mm, 2.0 mm, and 2.5 mm). The force was applied in two directions (45° and 90°). The stress distribution on surrounding bone and the displacement of the mini-implant were analyzed. Plots of tensile stress, compression stress, and displacement were calculated, and maximum values in each category were analyzed.Results:The stress distribution was different between the models with washer and without washer. However, no remarkable differences in stress distribution were observed among the models with washer, regardless of spike length. A significantly greater displacement value was observed in the model without washer compared to the models with washer, but no notable difference in displacement value was found among the models with washer. The plots of the displacement distribution of the models with washer presented notable pattern differences as compared with that of the model without washer.Conclusion:With the use of the washer, a more homogeneous distribution of bone stress and less displacement of the mini-implant can be achieved.     

I类骨质中正畸微种植体支抗直径和长度的优化设计

目的：探讨正畸微种植体支抗长度和直径对I类骨质下颌骨的应力和微种植体稳定性的影响,为临床设计I类骨质中微种植体支抗的最佳长度和直径提供理论依据。方法：建立包含正畸微种植体支抗的颌骨骨块的三维有限元模型,设定微种植体的直径和长度为变量,直径变化范围1.0～1.8mm,长度变化范围5.0～11.0mm。设定颌骨平均主应力峰值和正畸微种植体支抗位移峰值为目标函数。观察设计变量变化对目标函数的影响。结果：随着直径的增加,皮质骨、松质骨应力峰值和种植体位移分别降低了67.98%,64.06%,78.55%;随着长度变化皮质骨、松质骨的应力峰值和种植体位移分别降低了13.94%,61.32%,0.01%。结论：种植体支抗的直径对I类骨质颌骨的应力和种植体支抗稳定性的影响更显著。长度对I类骨质颌骨的应力和种植体支抗稳定性的影响并不显著。从生物力学角度而言,直径大于1.4mm种植体支抗更加适用于I类骨质的颌骨。     

Bone stress for a mini-implant close to the roots of adjacent teeth - 3D finite element analysis

This study aimed to evaluate stress in the bone when an orthodontic mini-implant is close to the roots of adjacent teeth using finite element models (FEMs), and to investigate the causes of the high implant failure rate in the mandible. Four FEMs were used: the implant touches nothing; the implant touches the surface of the periodontal membrane; part of the screw thread is embedded in the periodontal membrane; and the implant touches the root. The effect of cortical bone thickness was evaluated using values of 1, 2 and 3 mm. Maximum stress value and stress distribution on the bone elements was determined. Maximum stress on the bone increased when the mini-implant was close to the root. When the implant touched the root, stress increased to 140 MPa or more, and bone resorption could be predicted. Stress was higher for a cortical bone thickness of 2 mm than for other thicknesses. Cortical bone 2 mm thick had a higher risk for bone resorption. A mandible with an average cortical bone thickness of 2 mm may have a higher risk for implant loosening than a maxilla with the same degree of root proximity, which may be related to the lower success rate in the mandible.     

微型种植体长度对骨界面应力分布的影响

目的 探讨微型种植体长度对骨组织内应力分布的影响.方法建立直径1.6mm,长度分别为6、8、10、12 mm的种植体-下颌骨三维有限元模型,垂直植入种植体,给以1.96 N的水平向前及前上方向的载荷,记录并分析不同情况下的应力分布.结果 种植体水平向前载荷的应力峰值范围为3.500～3.765 MPa,位移峰值范围为1...     

Effect of Compromised Cortical Bone on Implant Load Distribution

Purpose: To investigate photoelastically the difference in load distribution of dental implants with different implant neck designs in intact and compromised bone. Materials and Methods: Composite photoelastic models were fabricated using two different resins to simulate trabecular bone and a 1‐mm thick layer of cortical bone. The following parallel‐sided, threaded implants were centrally located in individual models representing intact and compromised cortical bone: Straumann (4.1‐mm diameter × 12‐mm length), AstraTech (4.0‐mm diameter × 13‐mm length), and 3i (3.75‐mm diameter × 13‐mm length). The compromised cortical bone condition was simulated by contaminating a 1‐mm neck portion with Vaseline to impair the implant–resin interface. Vertical and oblique static loads were applied on the abutments, and the resulting stresses were monitored photoelastically and recorded photograhphically. Results: For the fully intact condition, the highest stresses were observed around the crest and apical region for all implant designs under vertical and inclined loads. There were no appreciable differences in magnitude or distribution between implant types. With compromised cortical bone, for all designs and load directions, higher stresses in the supporting structures were observed. Increased stresses were noted especially at the cortical bone–trabecular bone interface. Somewhat lower stress levels were observed with the 3i implant. Conclusions: The condition of implant–cortical bone contact has considerable influence on stress distribution. A compromised cortical bone condition caused higher level stresses for all implant designs tested.     

Biomechanical effect of abutment on stability of orthodontic mini-implant. A finite element analysis

The biomechanical influences of primary factors on titanium mini-implant, which is used as an anchorage for orthodontic tooth movement, were quantified using the three-dimensional finite element method. Six types of finite element models were designed to show various thread pitches from 0.5 to 1.5 mm. Three models were designed with abutment and three other models without abutment. A traction force of 2 N was applied to the head of the mini-implant or abutment to be at 45 degrees to the bone surface. No remarkable differences were observed in the stress distribution patterns regardless of thread pitch variance. However, the stress distribution was remarkably different between models with abutment and without abutment. The maximum stress of the model with abutment and thread pitch 0.5 mm was the least as compared with the other models. Areas of high-level stress were obviously smaller than in the models without abutment. The plots of the displacement distributions of the models with abutment also presented significant pattern differences as compared with the models without abutment. The high-level area was localized to the head of the implant and the abutment in models with abutment. Therefore, the existence of the abutment is significantly useful in decreasing the stress concentration on the bone, while the effect of thread pitch was uncertain.     

An in vitro study of factors affecting the primary stability of orthodontic mini-implants

Objectives:To evaluate the effects of mini-implant features (length, design, core diameter), insertion technique (insertion angle, cortical punch), and cortical bone depth and density on mini-implant primary stability. The effect of mini-implant reinsertion was also investigated.Materials and Methods:Two hundred and sixty Infinitas mini-implants of two lengths (9 mm and 6 mm), two core diameters (0.8 mm and 0.9 mm) for an external diameter of 1.5 mm, and four designs (two tapered, external diameter 1.5 mm; two cylindrical, external diameters 1.5 mm and 2.0 mm) were inserted into synthetic bone blocks, and the maximum insertion torque (MIT) was recorded. The cortical layer of the blocks varied in density (30 and 50 lb per cubic foot) and depth (1 mm and 2 mm). Three angles of insertion (90°, 75°, and 60°) and two methods of insertion (direct and cortical punch) were tested. Forty mini-implants were also removed and reinserted.Results:A significant increase in the average MIT occurred when cortical bone density increased and when mini-implants were reinserted. The 1.5 mm diameter cylindrical design had significantly lower MIT than the 1.5 mm tapered and the 2.0 mm cylindrical designs. The other variables did not have a significant effect on MIT.Conclusions:Mini-implants achieved greater primary stability in higher-density cortical bone, and the 1.5 mm diameter tapered and 2.0 mm cylindrical designs offered greater primary stability than the 1.5 mm cylindrical design. Reinserting mini-implants resulted in significantly increased MIT, possibly because of blunting of the threads.     

The effect of cortical bone thickness on the stability of orthodontic mini-implants and on the stress distribution in surrounding bone

Cortical bone thickness (CBT) was evaluated at mini-implant placement sites in 65 orthodontic patients and was found to be directly proportional to the success rate of the mini-implant. The success rate of the mini-implant was significantly greater at sites with CBT> or =1.0mm. To examine the biomechanical effects of CBT, finite element models were made for CBT from 0.5 to 1.5mm, at 0.25-mm intervals. Cortical bone models without cancellous bone were constructed to examine the biomechanical influence on cortical bone after cancellous bone resorption. CBT influenced the stresses in the cancellous bone, but could not directly influence the stresses in the cortical bone. For CBT<1mm, the cancellous bone models exhibited von Mises stresses exceeding 6MPa, and the cortical bone models without cancellous bone showed von Mises stresses exceeding 28MPa. Greater CBT values were associated with higher mini-implant success rates. This morphometric study and mathematical simulation verify that a clinical CBT threshold of 1mm improves the success rate of mini-implants.     

种植体长度与直径对骨界面应力分布影响的三维有限元分析

目的　比较不同直径、长度的种植体对种植体-骨界面应力分布的影响。方法　按照种植体不同长度与直径,建立种植义齿的三维有限元模型。以美国3I种植体系统为参考,在Solidworks三维制图软件中绘制包含种植体、相应基台及牙冠的三维实体模型。种植体长度分别设为8、10、12、14 mm,直径分别设为3.5、4.0、4.5、5.0 mm,通过不同长度与直径交叉组合,共得到16种模型。对每个模型进行垂直向及斜向加载负荷,运用Ansys Workbench 13.0分析比较各模型受力后应力分布情况。结果　两种载荷下应力集中出现在种植体颈部皮质骨区和根尖松质骨区,随着种植体长度增加,根尖松质骨区应力集中缓慢下降;随着种植体直径的增大,根尖松质骨区应力集中明显减小。结论　在种植体长度与直径的选择中,直径与长度越大,种植体-骨界面的应力集中越小,但与长度相比,直径的影响更加显著。