指定位移时牙种植体周围颌骨组织应力的三维有限元分析

目的：研究指定位移约束对颌骨的应力分布影响。方法：建立一个实用局部模型，采用三维有限元分析法（FEM），计算此模型在不同指定位移情况下的各节点的应力和位移。结果：种植体周围骨组织的应力沿种植体轴线对称分布，在皮质骨层应力值很大，在孔底部分松质骨层应力值较小；应力值大小与指定位移大小呈正比的线性关系。结论：在研究和预估测种植体周围颌骨组织内应力分布时，指定位移是一个不可忽略的因素。     

颌骨牙列体层技术诊断埋伏阻生牙的实验研究

目的 评价颌骨牙列体层摄片在埋伏阻生牙定位中的价值. 材料与方法使用离体牙在干颅模拟临床常见埋伏阻生牙类型,进行全景片及颌骨牙体断层摄片,观测离体牙在不同位置与其体层片影像的关系. 结果 颌骨牙列体层摄片能提供直观的埋伏阻生牙在颌骨内位置的二维影像,包括阻生牙的形态,唇侧或腭侧位置,萌出方向及与邻牙的关系. 结论 对于埋伏阻生牙的放射影像学定位,可选择颌骨牙列体层摄片,临床可以作为骨内埋伏阻生牙外科处理和正畸治疗前的检查手段.     

基于CAD技术的个体化下颌骨正交各向异性有限元模型的建立

目的 建立个体化下颌骨正交各向异性三维有限元模型.方法 利用CT薄层扫描下颌骨获取的断层图像数据,在自主开发的USIS软件的基础上,自动分辨骨皮质和骨松质轮廓边界,并对下颌骨采用"非种子区域分割"、非平行"最佳切割曲面"及"B样条曲线拟合法"一系列新型CAD方法进行人机对话自动重建精确的几何表面模型.定义结构材料参数后划分网格,并导入有限元计算软件ANSYS9.0中完成三维有限元建模.结果 建立了结构精确的个体化下颌骨正交各向异性的三维有限元模型.结论 基于CT数据和USIS软件的新型CAD方法实现了个体化下颌骨正交各向异性三维有限元模型的建立.     

人颞下颌关节CT三维重建及其有限元实体建模

目的：由活体直接获得人颞下颌关节（包括下颌骨、关节盘及关节结节）的三维影像,以建立其三维有限元模型。材料与方法：利用ＡｕｔｏＣＡＤ软件及螺旋ＣＴ扫描技术与三维有限元分析方法相结合,将ＣＴ扫描图像转换为可用于有限元实体建模的数字图像。结果：三维有限元实体模型与螺旋ＣＴ三维重建影像比较,几何相似性与还原性良好,材料构造合理,并由此建立了理想的人颞下颌关节三维有限元模型。结论：在临床实践中,借助于螺旋ＣＴ扫描及Ａｕｔｏ－ＣＡＤ软件在活体建立人颞下颌关节三维有限元模型是切实可行的,结果是满意的。     

转化生长因子β1诱导兔颌骨成骨中微血管的发生

外伤、肿瘤、牙缺失等均可造成颌骨牙槽突骨质缺损、吸收,严重影响种植义齿的修复和成功率。为修复种植体周围骨缺损,学者们进行了大量的基础与临床研究。虽然自体骨是理想的材料,但因来源有限且增加手术创口,使其临床应用受限。目前国内外资料显示,利用     

适用于临床的小腿残端有限元网格自动快速划分方法

目的：为在假肢设计CAD／CAM系统中发展小腿残端三维有限元应力分析功能建立专门的有限元网格自动划分算法。方法：针对小腿残端的特点，标准骨替代真实骨,使用校准点映射法进行骨定位和配准。采用子域分解法自动形成网格。结果：提出并实现了一种小腿残端有限元网格快速自动划分方法，实现了骨的自动定位和配准，保证了骨几何形状的完整性，能适宜不同个体的差异；网格密度可控制，可以满足不同计算量要求的有限元分析，所生成的单元都是精度较高的5、6面体单元。结论：所建立的小腿残端三维有限元网格自动划分算法可满足临床的需要，避免了CT、MRI等方法对患者的放射性损伤以及图像处理方面的难点，该方法将促进有限元分析方法在假肢设计中的临床应用，也为矫形师进行参数分析提供了一个快速便捷的网格划分工具。     

颌骨曲面及直线断层摄影在种植牙体中的临床应用

目的:探讨颌骨曲面及直线断层摄影在种植牙体中的临床应用价值。方法:对38例种植牙患者术前进行颌骨曲面及直线断层摄影,根据所得图像测出颌骨受植区的深度、宽度及厚度等相关数值,以指导临床选择合适型号的种植体制定种牙计划;种植牙体后立即重复摄影,对种植效果进行评价,及时纠正种植体植入中存在的角度和深度等问题。结果:本组病例种植牙76颗,其中61颗种植体植入效果满意,14颗种植体角度轻度偏离,但未超出正常偏离值范围,1例种植体角度偏离并穿破颌骨皮质,重新植入后效果满意。术后半年随访所有种植牙体形态位置均无异常改变。结论:颌骨曲面及直线断层摄影相结合能清晰显示受植区三维骨质结构和种植体的植入情况,对种植牙手术计划的制定与实施,提高种植牙体的成功率具有重要的临床应用价值。     

人体躯干骨骼-肌肉-韧带结构三维有限元模型的建立和验证

目的:建立正常人体躯干骨-肌肉-韧带三维有限元模型,为脊柱部生物力学研究提供数字平台。方法:获取正常青壮年男性的躯干螺旋CT扫描图像,应用逆向工程原理,通过Mimics、Geomagic软件建立躯干骨结构的三维几何模型;利用ANSYS10.0对其进行有限元网格划分,椎间盘、韧带和肌肉根据解剖学和文献数据模拟,并参照以往文献报道对模型的可靠性进行验证。结果:建立了包括374618个实体单元,110102个壳单元,427个Link单元,22个质点单元,共65998个节点的关节、椎骨、椎间盘和韧带的躯干部三维有限元模型,根据CT灰度值和杨氏模量关系式对松质骨、皮质骨和后部结构进行单独材料赋值,采用等效法构建椎间盘的纤维环。结论:运用逆向工程原理可有效构建人体躯干的三维几何模型,在此基础上基于解剖和离体标本实验结果构建其生物力学有限元模型,可用于人体脊柱生物力学变化规律的可视化分析。     

立体式分体人工牙种植体的设计

口腔骨内种植体目前被广泛应用于单个牙、部分牙列及全部牙列缺失的修复 ,目前应用于临床上的种植体主要有Branemark系统、Core -vent系统、ITI系统、IMZ系统、Astra -Tech系统 ,形状有螺旋型种植体、柱状种植体、叶状种植体、锚状种植体、穿下颌种植体、下颌支支架种植体 ,临床上常用的是螺旋型种植体、柱状种植体 ,这些骨内种植体由于其结构及其与之相适应的植入区条件及骨结合面的限制 ,存在着适应证范围小 ;承受颌力小 ;应用于低平牙槽嵴患者时手术复杂 ;单个种植体易出现各种方向上的动度及旋转。　　鉴于上述骨内种植体存在的不…     

下颌第一磨牙种植体三维有限元模型的建立

目的详细展现三维有限元建模过程,特别是种植体模型的建立,为三维有限元分析提供数学模型,为更多关注这一领域的研究者提供参考。方法论述Pro／Engineer软件建立种植体三维模型的详细步骤;mimics软件读取cT数据,通过去噪、平滑、减点建立下颌骨模型,magcis进行网格优化。结果成功建立下颌骨及种植体模型。结论该法建立下颌骨及种植体模型简便且易操作,为以后进行三维有限元分析提供了精确的模型。     

Influence of anisotropy on peri-implant stress and strain in complete mandible model from CT.

This paper reveals the influence of elastic anisotropy for the peri-implant stress and strain in personalized mandible. First, from CT data, the individual geometry of the complete range of mandible was well reproduced, also the separation between cortical and cancellous bone. Then, by an ad hoc automatic mesh generator integrated with anisotropic material assignment function, high quality anisotropic finite element model of the complete mandible was created, with two standard threaded implants embedded in posterior zone. The values of principal stress and strain in surrounding bone were evaluated under buccolingual oblique loading, and compared to that of the same FE model with equivalent isotropic material. Results of the analyses demonstrated that the percentage increase of stress and strain in anisotropic case reached up to 70%. It is concluded that anisotropy has significant effects on peri-implant stress and strain and careful consideration should be given to its use in biomechanical FE studies.     

Automated identification of anatomical landmarks on 3D bone models reconstructed from CT scan images

Identification of anatomical landmarks on skeletal tissue reconstructed from CT/MR images is indispensable in patient-specific preoperative planning (tumour referencing, deformity evaluation, resection planning, and implant alignment and anchoring) as well as intra-operative navigation (bone registration and instruments referencing). Interactive localisation of landmarks on patient-specific anatomical models is time-consuming and may lack in repeatability and accuracy. We present a computer graphics-based method for automatic localisation and identification (labelling) of anatomical landmarks on a 3D model of bone reconstructed from CT images of a patient. The model surface is segmented into different landmark regions (peak, ridge, pit and ravine) based on surface curvature. These regions are labelled automatically by an iterative process using a spatial adjacency relationship matrix between the landmarks. The methodology has been implemented in a software program and its results (automatically identified landmarks) are compared with those manually palpated by three experienced orthopaedic surgeons, on three 3D reconstructed bone models. The variability in location of landmarks was found to be in the range of 2.15–5.98 mm by manual method (inter surgeon) and 1.92–4.88 mm by our program. Both methods performed well in identifying sharp features. Overall, the performance of the automated methodology was better or similar to the manual method and its results were reproducible. It is expected to have a variety of applications in surgery planning and intra-operative navigation.     

Radionuclide imaging in oral implantations. Personal experience in maxillary sinus elevation

PURPOSE: Presently nuclear medicine techniques are not very popular in oral implantology, but they can play an interesting role in this surgical field too. In particular bone scan with 99mTc-MDP allows to evaluate the function of oral implants and the survival of bone grafts. We report our experience with skull bone scan in maxillary sinus lifting. MATERIAL AND METHODS: We performed a three-year follow-up on 13 patients treated with inlay-one stage uni- or bilateral sinus lifting with a mixture composed of 90% bovine bone powder and of 10% small bone splinters and autogenous fibrin glue. We performed imaging studies and quantitated implant MDP uptake from the mean values at the surgical site to the 5th neck vertebral ratio (M/V index). The M/V index was also statistically compared with the one measured in 13 patients with severe resorption of distal upper dental arches (bone height less than 0.5 cm) and in 63 patients with normal dental status. Scintigraphic data were interpreted in the light of clinical, radiological and histologic findings. RESULTS: All oral implants appeared to be fixed and radiographs showed good positioning and bone adhesion; bone height exceeded 1 cm. Peri implant biopsy material was formed by normal mature bone tissue without bovine bone granules, necrotic areas and inflammatory cells. The highest bone activity (M/V index: 1.54-2.57) was observed 1-4 months after sinus lifting. Then MDP uptake decreases and 18 months after surgery radionuclide uptake in maxillary arches is homogeneous, with M/V values of 0.81-0.88. The average M/V value in the 18 surgical sites was clearly higher than in the resorbed (1.44 vs 0.64; Kruskall-Wallis ANOVA test; Dunn's method; p < 0.05) and normal (1.44 vs 0.73; p < 0.05) maxillary arches. DISCUSSION AND CONCLUSIONS: 99mTc-MDP can show the transformation of newformed into mature bone and then allows in vivo visualization of implant osteointegration. The importance of our work lies in the use of radionuclide imaging to assess both the function of oral implants inserted by a complex surgical technique and the expected bioactive properties of the filling mixture. Nevertheless the strong active autogenous compounds do not permit to detect the real agent of local bone induction. An interesting finding is that implant stability is biologically gained 18 months after intervention and that the uptake index facilitates comparison of sequential scans and confirmation of local bone growth. Therefore high MDP uptake by the implant 2-3 years after surgery can suggest mechanical or septic bone injury which can lead to implant failure if not treated promptly. In conclusion we believe that quantitative bone scan is a valid diagnostic tool in the follow-up of oral implants inserted with sinus lifting, though our experience needs confirmation on larger series and new research is warranted to understand the real mechanisms of assisted bone regeneration.     

Dental CT and orthodontic implants: imaging technique and assessment of available bone volume in the hard palate

PURPOSE: Palatal implants (PI) have been introduced for orthodontic treatment of dental and skeletal dysgnathia. Due to the restricted amount of bone in this region, precise preoperative anatomic information is necessary. The aim of this study was to determine whether dental CT could serve as a tool to locate the optimal size and position for orthodontic implant placement. MATERIALS AND METHODS: In 32 patients, where palatal implant placement was planned, axial CT scans of the maxillary bone were acquired. Using a standard dental software package (Easy Vision dental software package 2.1, Philips; Best, The Netherlands), paracoronal views were reconstructed and measurements of palatal bone height in 3 mm increments, dorsally from the incisive canal, were performed in the median and both paramedian regions. RESULTS: The overall mean bone height was 5.01 mm (S.D. 2.60), ranging from 0 to 16.9 mm. The maximum palatal bone height was 6.17 mm (S.D. 2.81) at 6 mm dorsally from the incisive canal. Due to the lack of adequate bone (less than 4 mm), implant placement was not performed in 3 cases (7%). In the remaining 39 cases (93.0%), primary implant stability was achieved and complications, such as perforation of the palate, could be avoided. CONCLUSION: The results demonstrate that dental CT promises to be a valuable tool in evaluating the potential and optimal size and site for orthodontic implant placement.     

羟基磷灰石涂层多晶氧化铝陶瓷牙种植体复合骨形成蛋白的实验研究

选用螺旋形多晶硅氧化铝表面烧结羟基磷灰石（ＨＡ）涂层牙科种植体与牛骨骨形成蛋白（ｂＢＭＰ）的复合物，植入狗的下颌骨制备的牙槽窝内。结果示：①ＨＡ是具有生物活性的种植材料，种植后能形成种植体－宿主骨组织之间的骨性结合；②ＨＡ徐层的多晶氧化铝陶瓷种植体与骨诱导物体ＢＭＰ复合，能有效地加速种植体－宿主骨界面骨愈合速度；③采用螺旋形种植体形状，提高种植初期固位的稳定性。     

Diagnostic imaging of trabecular bone microstructure for oral implants: a literature review

Several dental implant studies have reported that radiographic evaluation of bone quality can aid in reducing implant failure. Bone quality is assessed in terms of its quantity, density, trabecular characteristics and cells. Current imaging modalities vary widely in their efficiency in assessing trabecular structures, especially in a clinical setting. Most are very costly, require an extensive scanning procedure coupled with a high radiation dose and are only partially suitable for patient use. This review examines the current literature regarding diagnostic imaging assessment of trabecular microstructure prior to oral implant placement and suggests cone beam CT as a method of choice for evaluating trabecular bone microstructure.     

Initial clinical assessment of “center-specific” automated treatment plans for low-dose-rate prostate brachytherapy

PurposeTo report results of an initial pilot study assessing iodine-125 prostate implant treatment plans created automatically by a new seed-placement method.Methods and MaterialsA novel mixed-integer linear programming method incorporating spatial constraints on seed locations in addition to standard dose–volume constraints was used to place seeds. The approach, described in detail elsewhere, was used to create treatment plans fully automatically on a retrospective basis for 20 patients having a wide range of prostate sizes and shapes. Corresponding manual plans used for patient treatment at a single institution were combined with the automated plans, and all 40 plans were anonymized, randomized, and independently evaluated by five clinicians using a common scoring tool. Numerical and clinical features of the plans were extracted for comparison purposes.ResultsA full 51% of the automated plans were deemed clinically acceptable without any modification by the five practitioners collectively versus 90% of the manual plans. Automated plan seed distributions were for the most part not substantially different from those for the manual plans. Two observed shortcomings of the automated plans were seed strands not intersecting the prostate and strands extending into the bladder. Both are amenable to remediation by adjusting existing spatial constraints.ConclusionsAfter spatial and dose–volume constraints are set, the mixed-integer linear programming method is capable of creating prostate implant treatment plans fully automatically, with clinical acceptability sufficient to warrant further investigation. These plans, intended to be reviewed and refined as necessary by an expert planner, have the potential to both save planner time and enhance treatment plan consistency.     

An image analysis approach for automatically re-orienteering CT images for dental implants.

In the last decade, computerized tomography (CT) has become the most frequently used imaging modality to obtain a correct pre-operative implant planning. In this work, we present an image analysis and computer vision approach able to identify, from the reconstructed 3D data set, the optimal cutting plane specific to each implant to be planned, in order to obtain the best view of the implant site and to have correct measures. If the patient requires more implants, different cutting planes are automatically identified, and the axial and cross-sectional images can be re-oriented accordingly to each of them. In the paper, we describe the defined algorithms in order to recognize 3D markers (each one aligned with a missed tooth for which an implant has to be planned) in the 3D reconstructed space, and the results in processing real exams, in terms of effectiveness and precision and reproducibility of the measure.