不同长度种植体对骨界面应力影响的三维有限元分析

作者应用牙ＣＴ扫描图像建立三维有限元种植模型，研究不同长度种植体在垂直，斜向，水平三种受载条件下周围界面的应力，结果显示：种植体长度增加两倍左右，而种植体骨界面最大应力区域的最大应力值只下降１０％左右，从而提示，种植体长短对骨界面最大应力值影响不大，临床上进行口腔种植手术设计时无须过分强调种植体的长度选择。     

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。     

种植体穿通下颌骨对骨界面应力分布的影响

目的：为了探讨下颌种植牙穿通下颌骨后对骨界面应力分布的影响。方法：采用三维有限元方法,通过单个穿下颌螺旋型种植体的种植,了解穿下颌种植后对骨界面应力分布的影响。结果：穿下颌种植减小了颈周密质骨内的应力,加大了根端侧穿下颌骨下缘处的应力,减小了骨界面的位移。结论：穿下颌种植,改变了骨界面的最大应力分布部位,使最大应力位于根端侧下颌骨下缘处。     

Peri-implant bone loss around posterior mandible dental implants placed after distraction osteogenesis: preliminary findings

BACKGROUND: The present study evaluates implant survival and peri-implant bone loss around posterior mandible dental implants placed at sites of distraction osteogenesis. METHODS: On removal of the distraction devices, 34 dental implants were inserted into 14 posterior mandible sites in 10 healthy, non-smoking female patients. Prosthetic treatment was performed 4 months after implant placement using fixed implant prostheses. After 6 to 16.5 months, periapical radiographs were taken and evaluated for peri-implant bone loss and radiolucency. The distance between the implant margin and the first visible bone-implant contact was measured on the mesial and distal aspects of the implants using imaging software. Radiographic dimensional distortion was corrected as a function of the known true dimension of the implant. RESULTS: Of the 34 implants placed, two (5.9%) failed to integrate at reentry surgery. Both were replaced and restored during the course of the study so that a total of 34 implants was followed for 12.1 +/- 3.8 months post-restoration and 16.1 +/- 3.8 months post-insertion. Mean loss of marginal bone height was 2.6 +/- 1.0 mm. During the follow-up period, radiolucent lines along the implant surface were absent. CONCLUSIONS: The mean peri-implant bone loss in areas of alveolar bone distraction was 1.9 mm/year. A high implant survival rate was observed.     

下颌4枚与6枚种植体全口固定义齿的有限元分析

目的：采用有限元分析法,比较4枚和6枚种植体支持下颌固定全口义齿的骨及种植体应力分布特点,为临床种植修复提供生物力学参考依据。方法：建立4枚种植体6mm悬臂和6枚种植体6mm悬臂的2组下颌种植支持式固定全口义齿的三维有限元模型,在悬臂末端垂直加载100N,应用Ansys软件进行分析处理,得到2组设计的种植体,测定最大压应力和最大拉应力。结果：2组设计的骨应力都集中在离受载区最近的2枚种植体颈部骨皮质区。6个种植体组骨应力较小,种植体应力集中在末端和中间种植体的颈部,修复支架应力集中在与远中末端种植体相连接处。2组的种植体应力和种植上部结构应力相近。结论：末端种植体骨应力集中,易发生松动失败;种植体颈部应力集中,易发生植入体与基桩连接失败。2组设计都符合生物力学分布原理。但4种植体设计骨应力较高,适用于前牙区骨质量较好的病例。     

Oral squamous cell carcinoma around dental implants.

It is well documented that oral squamous cell carcinoma (OSCC) is related to risk factors such as smoking and alcohol consumption as well as premalignant lesions and conditions such as leukoplakia, oral lichen planus (OLP), and previous malignancy of the upper respiratory system and gastrointestinal tract. Osseointegrated dental implants are rarely reported in association with OSCC. This article presents 2 cases of OSCC adjacent to dental implants in patients at risk for oral cancer--1 was a heavy smoker with OLP; the other had a history of previous oral and colon cancer. Six additional cases of malignancy adjacent to dental implants were retrieved from the literature; the majority of cases had at least 1 recognized risk factor for oral cancer. Although such cases are rarely reported, patients at risk for oral cancer, especially those with multiple existing risk factors, that present with failing dental implants should be thoroughly evaluated to rule out the presence of malignancy disguised as peri-implant disease.     

Pathogenesis of bony pocket formation around dental implants.

This study was undertaken to explain differences in the pathogenesis of periodontitis and peri-implantitis. Histological observations were made on experimental and human material obtained at autopsy. The sections were prepared without decalcification and without removal of the implants by the cutting and grinding technique. In some cases the implant was exposed but the mucosa surrounding it showed no inflammation. In other cases granulation tissue had formed around the implants resulting in a polypoid mass and the adjacent mucosa was inflamed. A discussion and comparison of the pathogenesis of periodontitis and peri-implantitis is given.     

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 analysis of porous rooted dental implants.

A model based on a continuously bonded interface predicts high punching stresses at the apex of the implant and low stresses in the cortical plates. A model based on a continuously bonded interface predicts high stiffness and a resultant low implant displacement-load ratio. A model based on a tissue ingrowth-bonded interface predicts uniform distribution of stresses around the implant through the cortical plates. A model based on a tissue ingrowth-bonded interface predicts an implant displacement-load ratio close to the ratio measured with actual implant specimens.     

Current periodontal plastic procedures around teeth and dental implants.

Periodontal plastic procedures are performed to prevent or correct anatomical, developmental, traumatic or plaque-induced defects of the gingiva, alveolar mucosa or bone. The majority of these procedures are performed in combination with restorative and/or orthodontic therapy, with the primary goal of enhancing esthetics. In this review, some of the more prominent techniques currently available to address mucogingival deficiencies, including pedicle grafts, free soft tissue grafts and combination grafts, are illustrated. In addition, potential complications associated with periodontal plastic procedures will be discussed.     

Standardized radiographs of the alveolar crest around implants in the mandible.

The techniques currently used for standardized longitudinal radiographic evaluation of the supporting bone around dental implants are not suitable for general application. An aiming device is described for intraoral radiography used to evaluate the crestal bone height around dental implants used as retention for overdentures. This aiming device has been tested on four different implant systems by four dentists. Error analysis of serial radiographs indicates small deviations in reproducibility. It is concluded that this method is suitable for routine evaluation of dental implants.     

The influence of a flexible coating on the bone stress around dental implants

summary The influence of a three-layered flexible coating of Polyactive® on bone stress distribution was investigated by three-dimensional finite element models of mandibular bone, in which a titanium implant (coated or uncoated) was located. Poly-active® is a system of poly(ethylene oxide) poly(butylene terephthalate) segmented co-polymers with bone-bonding capacity. In the case of sagittal and transversal loading, the use of a Polyactive® coating reduced both the minimum principal stress in the bone and the compressive radial stress at the bone-implant interface. However, it raised the maximum principal and the tensile radial stress. In the case of vertical loading, the application of a flexible coating reduced the compressive radial stress at the bone-implant interface around the neck of the implant by a factor of 6.6 and the tensile radial stress by a factor of 3.6. Variations in composition and thickness of the coating did not affect the results significantly.     

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.     

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

STATEMENT OF PROBLEM: It is unclear which implant inclination and position are most favorable in relation to the supporting anatomy and loading direction in the maxilla. PURPOSE: This study was designed to examine stress distribution around implants in a 2-dimensional photoelastic anatomic model. MATERIAL AND METHODS: Two 2-dimensional photoelastic models were prepared with opposing 8-degree cylinder metal implant and molar teeth analogues. A frontal anatomic sectional plate model based on a CT section at the first molar was symmetrically loaded through its long axis. A midfacial rectangular model based on the same section was loaded in a different direction with varying supporting geometries. RESULTS: Stress distribution around the maxillary implant was highest in the buccal concavity at the apical buccal third and in the lingual concavity on intercuspal loading. No stress concentration occurred at the implant apex under the sinus for axial and nonaxial loading in both anatomic model geometries. On lateral loading, stress concentration was observed at the buccal concavity and at the implant neck. In the midfacial block model, principal stresses were concentrated at the maxillary implant neck on nonaxial loading and at the apex on axial loading. CONCLUSION: This 2-dimensional skull model showed different patterns of stress distribution among the maxillary implant, mandibular implant, and teeth. The highest principal stress concentration was seen at the buccal concavity of the maxillary implant; this may play a role in osseointegration with highly angled implants in the posterior maxilla. Differences in stress distribution between anatomic and nonanatomic models showed how the supporting geometry (for example, sinus/nasal anatomy), boundary conditions, and loading direction influence stress distribution.     

Breast metastasis around dental implants: a case report

Background Metastases to the oral cavity and to the jaws are rare; hence, the clinical manifestations of the oral metastasis lesion could frequently be simulating general pathologic entities, making the diagnosis a challenging process to the dental team. Local factors, such as trauma, have been observed to facilitate the growth of blood‐borne tumors. To this end, surgical procedures such as fixture placement might cause cancer cells to spread. Purpose Careful clinical examination is a valuable help in diagnosing oral lesions, which can improve the quality of life of patients and reduce the risks of oral complications. Materials and Methods A female patient was referred to the clinic with symptoms of irritation, swelling, and pain associated with implants in the mandible and the maxilla. Results Clinical examination, x‐ray, and histopathology revealed that the patients suffered from a metastatic lesion, primary tumor being an adenocarcinoma of the breast diagnosed at the same time. Conclusion Optimal clinical examination in conjunction with radiography and histopathology is a necessity in order to discover malignant lesions in time. Routine dental check‐ups must comprise more thorough soft‐tissue examination.     

Intraoral radiographs of dental implants in the edentulous mandible

Radiographs of dental implants in the edentulous mandible, which are suitable for evaluation studies, are difficult to obtain. This article describes the development of an aiming device for intraoral radiography of the crestal bone around the neck of dental implants. Error analysis of serial radiographs indicated only small deviations in reproducibility. Subsequently three methods of measurements of marginal bone level around the neck of dental implants are described, measurements with: 1. a computerized image analysis system, 2. a magnifying glass, and 3. a digital sliding gauge. The intra- and interobserver error analysis showed that determining the precise bone height on the image is responsible for a large standard deviation for each method. Measurements with a digital sliding gauge are preferable, since this method is easy to put into practice, whereas the accuracy matches the accuracy of the two other methods.     

Immediate loading of dental implants in the edentulous mandible

BACKGROUND: The authors review the literature regarding immediate implant loading in the anterior edentulous mandible, demonstrate the technique they currently use, review preliminary results and present an illustrative case. MATERIALS AND METHODS: The authors conducted a literature search using PUBMED and Ovid databases. They considered for review 31 articles in English from 1969 to 2003 that pertained to immediate loading of the anterior mandible. The authors developed a technique to provide a bar-supported prosthesis on the day of surgery. They treated five patients and followed them up for at least six months. The preliminary results are presented. RESULTS: This literature review demonstrated that immediate loading of anterior mandibular implants is an acceptable method, with predictable results. This case series demonstrates the potential for delivering a final bar on the day of surgery, based on the current evidence and clinical application. CONCLUSIONS AND PRACTICE IMPLICATIONS: The method described provides patients with immediate prosthetic restorations and a decreased treatment time compared with that for the traditional two-stage implant approach.     

Effect of diameter and length on stress distribution of the alveolar crest around immediate loading implants

Background: Many clinical observations have shown that immediate loading is indicated when the stabilization of the bone/implant is optimal and when the estimated loads are not excessively high. Nonetheless, more experimental studies are needed to consider the immediate loading protocol as a safe procedure. Mechanical analysis using the finite element (FE) method analysis has been employed by many authors to understand the biomechanical behavior around dental implants. Purpose: This study was to evaluate the effect of the diameter and length on the stress and strain distribution of the crestal bone around implants under immediate loading. Materials and Methods: By an ad hoc automatic mesh generator, high‐quality FE models of complete range mandible was constructed from computer tomography, with three Straumann (Straumann Institute, Waldenburg, Switzerland) implants of various sizes embedded in the anterior zone. The implant diameter ranged from 3.3 to 4.8 mm, and length ranged from 6 to 14 mm, resulting in seven designs. The implant–bone interface was simulated by nonlinear frictional contact algorithm. For each design, vertical and oblique loadings of 150 N were applied, respectively, to each implant, and stresses and strains in the surrounding cortical bone were evaluated. Results: The biomechanics analysis provided results that the oblique loading would induce significantly higher interfacial stresses and strains than the vertical loading, while the intergroup stress difference significant levels was evaluated using t‐tests method and the level of significance (.05) that was accepted for significance. Under both loadings, the maximal values were recorded in the 3.3 (diameter) × 10 (length) mm implant configuration, whose mean and peak values were both higher than that of others with significant statistical differences. The second maximal one is 4.1 × 6 mm configuration, and the minimal stresses were recorded in 4.8 × 10 mm configuration, whose strains were also near to lowest. Conclusions: Increasing the diameter and length of the implant decreased the stress and strain on the alveolar crest, and the stress and strain values notably increased under buccolingual loading as compared with vertical loading, but diameter had a more significant effect than length to relieve the crestal stress and strain concentration.