The cancellous structure in the calcaneus and its relation to mechanical stressing

Summary The structure of the cancellous bone in the calcaneus is comparable to a three-dimensional trajectorial system, best adapted to resisting bending stresses. This can be seen from the curve trend of the tensile fascicles. Since stressing takes place mainly in the sagittal plane, the adaptation of the structure must be examined in this plane.The photoelastic experiments prove that similar trajectorial patterns result from different types of loading (e.g., standing with and without muscular contraction, the transmission of forces before and after the fusion of the tuber apophysis); and therefore the stresses remain the same. The trajectorial patterns, already established from the experiments, correspond with those of the cancellous structure, which indicates that a state of adaptation exists. Using the definition given in Roux's maximum-minimum law, this means that the bone achieves maximum resistance with a minimum of material.The photoelastic experiments can also be successfully applied to a short, skeletal element, which has been stressed in a complex manner.Furthermore, the theory of causal histogenesis in the supporting tissues can be proved, since the position of the epiphyseal center coincides with that of a singular point (hydrostatic pressure) in the trajectorial pattern.A division of the trajectorial pattern, into lateral and medial fascicles (as described by T. von Lanz and W. Wachsmuth) cannot be seen in the bone sections and consequently cannot be regarded as being factual.

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Zusammenfassung Der Spongiosaverlauf im Calcaneus entspricht einem dreidimensionalen Trajektoriensystem und ist optimal an die Beanspruchung — in diesem Fall Biegung — angepaßt. Aus dieser Biegebeanspruchung resultiert ein gebogener Verlauf der Zugbündel.In der Sagittalebene liegt die Hauptbeanspruchung, so daß eine Anpassung der Struktur in dieser Ebene nachgeprüft werden muß.In spannungsoptischen Versuchen läßt sich nachweisen, daß bei verschiedenen Belastungen (z.B. Stand mit und ohne Muskeleinsatz, Kraftübertragung vor und nach Synostose der Tuberapophyse) gleichartige Trajektorienverläufe entstehen; damit bleibt also die Beanspruchung gleich. Die gefundenen Trajektorienbilder stimmen mit der Ausrichtung der Spongiosa überein, das heißt, es liegt ein Zustand des Angepaßtseins vor. Im Sinne des Maximum-Minimum Gesetzes von Roux bedeutet dies, daß der Knochen mit einem Minimum an Material ein Maximum an Widerstand leisten kann.Die Methode der Spannungsoptik läßt sich auch an einem kleinen Skelettelement erfolgreich anwenden, das in komplizierter Weise beansprucht wird.Die theorie der kausalen Histogenese der Stützgewebe wird durch die Übereinstimmung der Lage des Epiphysenkerns mit der Lage eines singulären Punktes (hydrostatischer Druck) in einem weiteren Fall bestätigt. Eine Aufteilung der Trajektorienverläufe in laterale und mediale Bündel-wie sie im Buch von T. v. Lanz und W. Wachsmuth vorgenommen wird — findet sich nicht in den Knochenschnitten und entspricht somit nicht der Wirklichkeit.

     

不同长度和直径桩核的三维光弹性应力分析

目的 对比不同长度和直径的桩核受力后应国分布情况。方法 根据桩的长短、粗细胞将实验分成四组,通过垂直和斜向加载,采用三维光弹性应力冻结法,经模型切片观察计算出模型各测点的最大剪应力。结果 桩的直径增加根尖区最大剪应力相应增高,桩核交界处和核与根面交界面最大剪应力的明显增高。桩的长度增加,应力分布更为均匀。结论 从抗力固位角度出发有一定和蔗的粗细合适的柱形桩核较为理想。     

口腔医疗中光合片应用的基础研究

作者对光　法用于临床口腔医学的光塑性理论──双折射光程差的双本质理论作了深入分析，并且从实验和数值计算两方面对由残余塑性应变引起的双折射光程差δ与外部咬　力Ｐ作了标定。给出了可供临床应用分析的数据参考资料。     

Photoelastic study of the internal and contact stresses on the knee joint before and after osteotomy

Introduction The treatment of knee osteoarthrosis represents a difficult task. Osteotomy is one of the treatment regimes which, in earlier times, was the only surgical procedure giving reliable mid-term results. The improvement was attributed either to the changing of the acting forces or to the so-called biological factor. The use of a photoelastic model allows the observation of the direction of the significant contact and internal stresses at every point in a single plane.Materials and methods In the present study, we investigated the stress-strain situation of the knee joints in models made from 1 cm thick Araldite plates. These models reproduce tracings from anteroposterior X-ray views of monopodal loading of human knee joints. The models represent: normal knee joints, normal varus or valgus knee joint, knee joints suffering osteoarthrosis in varus or valgus, and knee joints suffering osteoarthrosis, following corrective osteotomies. The models were first loaded along the longitudinal axis with the leg in full extension, with 70 kg (body weight) and then with 140 kg, representing double the normal body weight.Results The application of longitudinal force on a normal knee joint, in full extension, results in symmetrical arrangement of trajectories in the condyles. Loading of the leg in varus or valgus produces shifting of stresses towards the inclination side. Increased contact stresses are always greater in the tibial condyles. The concentration of strain is directed towards the cortices of the loaded area. In a knee joint with osteoarthrosis, deviation of the trajectories in the condyles towards the inclination of the leg axis is observed. Also, increased contact stresses appear in the articular surfaces, on the inclination side. Isoclinics have meeting points on the loaded cortices. Supracondylar femoral osteotomy, or high tibial osteotomy, restores the axis of the leg, redistributes internal stresses (strain) in the condyles, corrects the trajectorial lines, and redistributes contact stresses in the articular surfaces towards the normal values.Conclusion Correction of the femorotibial axis results in redistribution of the isochromatics, isoclinics, trajectorial lines and contact stresses. The values of the above parameters are corrected and remain closer to these of the normal knee, but in no case does the correction of all the above factors attain normal values. The change of direction of the main stresses following osteotomies towards those of the normal knee probably represents the biomechanical explanation of the way the osteotomy relieves pain and improves function.     

不同基牙数目附着体义齿对支持组织应力分布的影响

目的探讨铰链式冠外附着体修复末端游离缺损时,不同基牙数目对支持组织应力分布的影响。方法以铰链式附着体为固位体,修复右下第二磨牙游离缺损,分别制作以第一磨牙为基牙的单基牙附着体义齿的三维光弹模型和以第一磨牙及第二前磨牙为基牙的双基牙附着体义齿的三维光弹模型。采用光弹性应力分析法,定性分析不同基牙数目时,该附着体义齿对基牙牙周支持组织应力分布的影响。结果附着体义齿在正中咬合情况下,单基牙时,在该附着体义齿的缺牙区牙槽骨内、基牙的远中根尖和近中根尖处,可见应力集中;双基牙时,得到的结果相似。结论用该附着体修复第二磨牙末端游离缺损时,在正中咬合情况下,基牙数目对支持组织的应力分布无明显影响,提示临床可采用单基牙;在正中咬合情况下,基牙与牙槽嵴黏膜应力分布均匀,提示该附着体适用于基牙条件稍差、而牙槽嵴黏膜条件较好的患者。     

垂直载荷对哈氏棒中应力影响的光弹性分析

本文用二维光弹性方法研究了垂直载荷对哈氏棒应力分布的影响。发现在垂直载荷作用下棒的棘齿区呈现高应力集中，棘齿区应力高于光滑区，棘齿区应力值受垂直载荷影响最大，棒的前侧各点应力与垂直载荷呈线性相关。当增加水平载荷作用后，哈氏棒应力分布发生变化。     

Hierarchical modelling of in situ elastic deformation of human enamel based on photoelastic and diffraction analysis of stresses and strains

Human enamel is a typical hierarchical mineralized tissue with a two-level composite structure. To date, few studies have focused on how the mechanical behaviour of this tissue is affected by both the rod orientation at the microscale and the preferred orientation of mineral crystallites at the nanoscale. In this study, wide-angle X-ray scattering was used to determine the internal lattice strain response of human enamel samples (with differing rod directions) as a function of in situ uniaxial compressive loading. Quantitative stress distribution evaluation in the birefringent mounting epoxy was performed in parallel using photoelastic techniques. The resulting experimental data was analysed using an advanced multiscale Eshelby inclusion model that takes into account the two-level hierarchical structure of human enamel, and reflects the differing rod directions and orientation distributions of hydroxyapatite crystals. The achieved satisfactory agreement between the model and the experimental data, in terms of the values of multidirectional strain components under the action of differently orientated loads, suggests that the multiscale approach captures reasonably successfully the structure–property relationship between the hierarchical architecture of human enamel and its response to the applied forces. This novel and systematic approach can be used to improve the interpretation of the mechanical properties of enamel, as well as of the textured hierarchical biomaterials in general.     

高跟鞋足的平面光弹试验及应力分析

作者通过光弹实验，分析和计算高跟鞋足在不同跟高和坡度的情况下（０．０ｃｍ，３．８ｃｍ，７．５ｃｍ，９．０ｃｍ），足弓及跖趾部和足跟部的应力分布，为临床某些足病提供了力学依据。     

牙内骨内联合种植的三维光弹性应力分析

应用三维光弹性法研究上颌中切牙根管内分别植入光滑面柱形针、螺纹面柱形针和光滑面锥形针后,根尖附近牙槽骨及针尖附近颌骨内应力的分布;研究了下颌尖牙采用螺纹面柱形种植针植入骨内5mm、7mm、10mm时应力的分布。结果表明:螺纹面柱形种植针的固位和应力分布性能较好;种植深度在 5.8mm-8.6mm间选取较为适宜。