Stress distribution around maxillary implants in anatomic photoelastic models of varying geometry. Part II

STATEMENT OF PROBLEM: Insufficient buccal bone volume can be a significant problem when loading dental implants in the maxilla. Increased potential for buccal fenestration and dehiscence can result in an exposed implant surface, mucosal irritation, decreased support, and potential implant failure. PURPOSE: The objective of this study was to model the stress distribution around maxillary implants by comparing simulated occlusal loading of maxillary implants in a 2-dimensional photoelastic anatomic model and a dry skull model. MATERIAL AND METHODS: Two model systems were used. First, a 2-dimensional photoelastic anatomic frontal skull sectional model was prepared in the first molar region. Left and right maxillary metal cylinder implant analogues inclined at 0 and 25 degrees to the sagittal plane were loaded in simulated intercuspation. Second, a dry skull lined with a photoelastic coating on the buccal aspect over an embedded cylinder implant was prepared in the first molar region. Principal stress concentration was photographed on axial and nonaxial implant loading. RESULTS: On simulated intercuspal loading, maximum stress concentration occurred at the buccal concavity in both the 2-dimensional anatomic photoelastic and skull models. There was no stress concentration at the apices of the maxillary implants in the 2-dimensional model. On lateral loading of the skull model, stress was distributed along the entire buccal aspect of bone adjacent to the implant, with a higher concentration at the buccal concavity. CONCLUSION: Preservation of buccal supporting bone volume is desirable to obtain a physiological modeling response and to enhance the facial plate. Insufficient bone volume may result in buccal fenestration or dehiscence, which can precipitate mucosal irritation, decreased support, and potential implant failure.     

平台转换种植体周围应力分布的三维有限元分析

目的:分析平台转换种植体周围的力学分布特点。方法:利用CATIA画图软件,建立种植体支持的上颌第一前磨牙三维模型,分析垂直向和斜向加载条件下平齐对接(PM)和平台转换(PS)种植体周围的应力分布差异;比较不同材料基台平台转换冠修复后种植体周围的应力分布差异。结果:①PS型种植体在垂直加载和斜向加载时种植体周围骨组织内最大von Mises应力值均较PM型小。②不同材料基台种植体周围应力分布云图相似,应力均集中在种植体颈部。结论:①PS种植体周围骨组织最大应力值较PM种植体小,但基台、中央螺丝、种植体的应力增大。②斜向加载较垂直向加载种植体周围应力值大大增加,特别是基台及种植体部位较为明显。③基台材料对种植体周围应力值无明显影响。     

Stress distribution around dental implants: influence of superstructure, length of implants, and height of mandible.

The stress distribution around dental implants was investigated by use of a two-dimensional model of the mandible with two implants. A vertical load of 100 N was imposed on abutments or the bar connection. The stress was calculated for a number of superstructures under different loading conditions with the help of the finite element method. The length of the implants and the height of the mandible were also varied. A model with solitary abutments showed a more uniform distribution of the stress when compared with a model with connected abutments. The largest compressive stress was also less in the model without the bar. Using shorter implants did not have a large influence on the stress around the implants. When the height of the mandible was reduced, a substantially larger stress was found in the bone around the implants because of a larger overall deformation of the lower jaw.     

种植体周围骨内应力分布的三维有限元分析

目的针对不同类型的牙槽骨科学地选用种植体,提高种植体临床疗效,延长使用寿命。方法采用三维有限元分析方法,将圆柱状、螺纹状和台阶状种植体分别植入4类骨质结构中,对此12种情况进行应力分析。结果在同种骨质模型中,圆柱状种植体颈部周围骨内的应力集中最小;就同种形态种植体而言,较低的骨质密度不利于种植体的应力分布。结论圆柱状是一种最有利于降低颈部骨质吸收的形态结构。螺纹状种植体周围骨内应力最大值大于圆柱状,而螺纹自身非力学优势极大的拓展了该型种植体的使用范围,但螺纹尖端处的高应力区域和螺纹之间的低应力区域是影响其长期使用效果的潜在不利因素。台阶状种植体相对较适合骨质好的情况,其根部出现局部高应力区域,若应力处于骨生理承受范围之内,将有利于减少根部骨质疏松。     

Nasal anatomy and maxillary surgery. I. Esthetic and anatomic principles

The LeFort I osteotomy is commonly performed to correct maxillary dentofacial deformities. Secondary changes in the nasolabial region that have occurred following this procedure include widening of the alar bases of the nose, upturning of the nasal tip, flattening and thinning of the upper lip, and downturning of the commissures of the mouth. Surgical techniques can modify undesirable secondary changes. Applying these surgical techniques and achieving the desired results require an understanding of the underlying anatomy. This paper will present a thorough review of the nasolabial anatomy (both external and internal) as it pertains to the patient undergoing maxillary surgery.     

辛伐他汀促进种植体骨整合的实验研究

目的：在建立大鼠上颌骨牙种植模型的基础上,探讨口服辛伐他汀对种植体周围骨整合的影响。方法：3月龄雌性SD大鼠在上颌骨第一磨牙前方植入0．8 mm×2．0 mm纯钛种植体,随机分为对照组和实验组,每日分别给予生理盐水和辛伐他汀灌胃。术后1、2、4周检测大鼠体质量、血清碱性磷酸酶（ALP）和骨钙素（BGP）表达量,HE染色、microCT检测观察术后种植区新骨形成情况,并对各组之间的成骨差异进行统计分析。结果：辛伐他汀实验组的大鼠体质量要轻于对照组,差异有统计学意义（P＜0．05）;实验组血清ALP和BGP明显高于对照组,且差异有统计学意义（P＜0．05）。 HE染色表明,2周时实验组新骨明显增加,对照组有少量新骨形成;microCT显示,4周时两组间骨小梁厚度、骨小梁数目、骨体积百分比：实验组＞对照组,骨小梁间距：实验组＜对照组,且差异都有统计意义（ P＜0．05）。结论：口服辛伐他汀对种植体周围新骨的形成有明显的促进作用。     

支抗磨牙及支持组织三维光弹应力分析

目的 分析中国人上颌第一磨牙在后倾弯作用下,牙及牙周组织的应力分布规律,牙体瞬间旋转中心位置。方法 三维光弹冻结切片法。结果 后倾弯以产生水平推力和近远中向的弯矩为主;同时也产生沿牙长轴的扭矩和冠根向的拉力;牙旋转中心位于三牙根分叉下方附近。结论 支抗磨牙的应力并不仅仅是一种力单独作用的结果,而且是由弯矩,扭矩,推力,压力,拉力共同作用形成的复杂应力。     

The quadhelix maxillary expansion appliance: Part I. Mechanics

The mechanics of the quadhelix maxillary expansion appliance have been derived using the complementary (strain) energy approach, and the results checked experimentally on enlarged models. Good agreement between theory and experiment was obtained, for both the lateral stiffness and the magnitude of the molar couple induced. The analysis shows that the spring characteristics are defined by three parameters, the lateral stiffness, and two other parameters M1 phi and M1 y which are the rate of change of the molar couple with phi and y respectively, where phi is the angle the molar arm is rotated on engagement and y the lateral displacement.     

侧方(牙合)时线性(牙合)种植覆盖全口义齿下颌种植体周围骨组织的应力分布

目的 通过比较侧方(牙合)时线性猞和解剖袷种植覆盖全口义齿下颌种植体周围骨组织的应力分布,为线性牙合种植覆盖全口义齿的临床应用提供依据.方法 选择牙槽嵴重度吸收的无牙颌志愿者1名.采用薄层CT及ANSYS 7.0软件建立志愿者颌骨、黏膜、两枚位于下颌尖牙区由杆卡附着体连接的种植体、线性(牙合)和解剖(牙合)种植覆盖全口义齿的三维有限元模型,模拟咀嚼肌肌力加载下侧方(牙合)时两种模型下颌种植体周围骨组织的应力分布.结果 侧方胎时解剖骀模型下颌种植体周围骨组织的应力主要集中于工作侧种植体的舌侧偏远中;线性(牙合)模型下颌种植体周围骨组织的应力分布于工作侧与非工作侧种植体偏远中,且两侧均有较广泛的应力分布.两种模型种植体周围骨组织的应力峰值均出现于工作侧,垂直方向上应力(σz)显示,解剖(牙合)和线性(牙合)模型的压应力分别为-6.47 MPa、-4.86 MPa,拉应力分别为6.81 MPa、3.04 MPa,最大主应力(σl)显示,解剖(牙合)和线性(牙合)模型的压应力分别为-4.20 MPa、-3.48 MPa,拉应力分别为7.20 MPa、5.33 MPa.结论 对于两枚种植体支持的、杆卡附着体固位的下颌种植覆盖全口义齿,在(牙合)力相同的情况下,侧方(牙合)时线性(牙合)种植覆盖全口义齿下颌两侧种植体负载的(牙合)力比解剖(牙合)更均匀,且种植体所受负荷小.     

Stress distributions in maxillary bone surrounding overdenture implants with different overdenture attachments

In this study, effects of different overdenture attachments on the stress distributions in the maxillary bone surrounding the overdenture implants are studied. Four different types of attachment are considered. They are rigid Dalbo Stud, movable Dalbo Stress Broken, movable Dalro, and movable O-ring attachments. Three-dimensional finite element analysis was conducted with commercial package to obtain the stress distributions in the maxillary bone. Varying the attachment types and angle of inclination of load, the stress distributions in the portions of compact bone and trabecular bone were monitored separately. The analysis was conducted by assuming two different boundary conditions at the interface between cap and overdenture abutment in order to evaluate influence of interface boundary condition on stress distribution in the maxillary bone. They were perfect bonding condition and contact with friction at the interfaces. However, it is preferable to assume perfect bond condition at the interface for rigid type attachment systems and contact with friction at the interface for movable type attachment systems. From the numerical results, it was found that the load transfer mechanism of the implant system is altered significantly by the types of the overdenture attachment and also special care must be taken to assign proper boundary conditions at the interface for the analysis. The movable type Dalro attachment generated the highest maximum effective stress in the maxillary bone among the models under the same inclined loading condition for contact with friction. The rigid type Dalbo Stud attachment generated the smallest maximum effective stress in the maxillary bone among the models under the same inclined loading condition for perfect bonding condition.     

三种桩材桩核修复上颌中切牙光弹模型的建立

目的:为分析不同弹性模量桩对根管壁应力分布的影响,建立上颌中切牙桩核修复的光弹模型.方法:以环氧树脂模拟上颌中切牙牙根部、牙槽骨;室温硫化硅橡胶模拟牙周膜;复合树脂制作核,建立桩为成品纤维桩、铸造钛合金、铸造镍铬合金的上颌中切牙桩核修复光弹模型.结果:建立了表面光洁、透明度高,几何尺寸接近实际情况,牙根、牙槽骨、牙周膜弹性模量比接近于1.37:1:0.0003的光弹模型.结论:该模型可以用于分析不同弹性模量桩对根管壁应力分布影响的光弹性实验.     

Autogenous maxillary bone grafts in conjunction with placement of I.T.I. endosseous implants. A preliminary report.

Small bone defects due to atrophic, traumatic or periodontal bone loss can be grafted with autologous bone grafts taken from the maxillary tuberosity. This study presents a 1-3 years follow-up of 22 patients who were treated according to this technique. Thirty-two implants were placed 6 months after bone grafting. All implants were functioning well at the time of investigation.     

Critical design errors in maxillary subperiosteal implants.

A maxillary full arch subperiosteal implant consists of a metallic framework that rests closely on the atrophied residual ridge beneath the mucoperiosteum and offers support for a dental prosthesis by means of posts or bars with O-ring protrusions or internal clip attachments. The maxillary subperiosteal implant is indicated for those patients presenting with advanced atrophy of the maxilla leaving the patient with three existing stable dense bony areas (the anterior nasal spine, the canine eminences, and the palatal surface of the existing crest) for its support. Over 300 cases with up to 12 years in function are presented. The importance of the basic anatomic and physiologic background required to optimize results are emphasized. The first 600+ subperiosteal implant cases that were placed prior to 1985 showed considerably lower success rates.     

Finite element analysis of the stresses around endosseous implants in various reconstructed mandibular models.

PURPOSE: To calculate the location and intensity of the maximum stresses occurring around implants in the reconstructed mandible. MATERIAL AND METHODS: Human preserved mandibles and fibulae were used to design 3-D mandibular models on a Desktop Computer. Various 3-D simulation models representing mandibles were made. Implants (fixtures) and superstructures were then embedded in each model and occlusal pressure was applied to the cantilever portion of the superstructure. Von Mises stress, the maximum and minimum principal stress on each model were calculated using finite element structural analysis software. Finally, evaluation of the stresses around each fixture hole was performed. RESULTS: It appeared that for each fixture hole, the direction and the magnitude of the stresses were influenced by complex factors such as the thickness of the cortical bone where the fixtures were embedded, the degree of vertical displacement under load, and the relationship between adjacent fixtures. CONCLUSION: Location and intensity of the stresses occurring around fixtures differs significantly between various types of mandibular reconstruction.Copyright 2002 European Association for Cranio-Maxillofacial Surgery. Published by Elsevier Science Ltd.