Technology and Health Care - Volume 14, issue 4-5

Authors: Lenich, A. | Fierlbeck, J. | Al-Munajjed, A. | Dendorfer, S. | Mai, R. | Füchtmeier, B. | Mayr, E. | Hammer, J.

Article Type: Research Article

Abstract: Conventional osteosynthesis of proximal femur fractures is still affected by serious complication rates between 4–18%, even though advanced implant modifications and surgical techniques are common practice. In terms of increasing age and co-morbidity of patients this complication ratio is expected to increase even further in the immediate future. One major reason for implant failure is the decreasing stability potential of the implant due to a loss in mechanical properties of cancellous bone. Therefore, efforts in new intramedulary techniques specifically focus on the load bearing characteristics of the implant by developing new geometries to improve the implant-tissue interface. This …investigation discusses first clinical results of the trochanteric fixation nail TFN (145 patients) and a biomechanical analysis of the blade/femur head interaction under different static loading conditions. The TFN shows promising performance in first clinical results. In the clinical study the overall complication rate was significantly lower compared to other similar osteosynthesis. For the investigation of the biomechanical stability of the helical TFN blade the following experiments were performed: Analysis of the axial load required for insertion of the blade by free rotation; measurement of the corresponding rotation angle for total insertion (32 mm) (n=8); pull-out forces with suppressed rotation (n=4); loads for rotational overwinding of the implant in the fully inserted condition (n=4). All investigations were performed on human femoral heads. The bone mineral densities of the specimens were detected by QCT-scans. Prior to cadaveric testing the experimental set-up was validated (n=8) by the use of synthetic foam blocks (Sawbone® ). Show more

Keywords: Proximal femur, intramedullary osteosynthesis, TFN

DOI: 10.3233/THC-2006-144-521

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 403-409, 2006

Authors: Helwig, P. | Faust, G. | Hindenlang, U. | Kröplin, B. | Eingartner, C.

Article Type: Research Article

Abstract: Static analysis with finite element of a realistic femur nail bone-implant system in a typical proximal femoral fracture under physiological load bearing situations provides results for stress, displacement and strain. The question to be answered is, if simulation with the finite element analysis is able to explain biomechanically clinical observed patterns of failure. Surface-Reconstruction with CT database of a proximal femur and reconstruction with CT based density data was done. Next steps were to unite the bone structure with the Proximal Femoral Nail and to model two relevant fractures (31-A2.2 and A2.3 according AO). After modelling of geometry, …isotropic material behaviour and load application numeric calculation of the femur-nail system with FE-software was performed. FE simulation mainly shows an axial dislocation of the femoral head screw with nearly no dislocation of the antirotation screw. This so-called z-effect therefore means: (1) Tilting of the proximal main fragment around the sagittal axis between the screws and (2) relative movement of both screws in the frontal plane. Relative movement of the two screws against each other could be the reason for implant failure, the so called cut out. Furthermore simulation shows different gliding of the screws explaining the so called z-telescoping. The analyzed stress patterns have to be relativized, because isotropic material behaviour of cancellous bone was assumed. Further examinations for this issue are necessary. Show more

DOI: 10.3233/THC-2006-144-522

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 411-419, 2006

Authors: Cruz, Mauro | Lourenço, Adelino Francisco | Toledo, Elson Magalhães | da Silva Barra, Luis Paulo | de Castro Lemonge, Afonso Celso | Wassall, Thomaz

Article Type: Research Article

Abstract: Statement of problem: Different implant geometries present different biomechanical behaviors and in this context, one arising question is how cuneiform implant geometry compares to clinical successful cylindrical threaded implant geometry. Purpose: The purpose of this work was to study stress distribution around cuneiform and cylindrical threaded implant geometries using three-dimensional finite element stress analysis taking the latter as a reference. Material and methods: A model was generated from a computerized tomography of a human edentulous mandible with implants placed in the left first premolar region. The model was supported by the mastication muscles and by temporomandibular …joint. A vertical load of 100N was applied at the top of each implant in the direction of their long axes. The mandibular boundary conditions were modeled considering the actual muscle supporting system. Taking muscle forces intensities and directions, balance moment equations were employed to assess the system equilibrium. Cortical and medullary bones were assumed to be homogeneous, isotropic and linearly elastic. Results: The analysis provided results for maximum (S1) and minimum (S2) principal stress and Von Mises (SEQV) stress field. For both geometries, the results showed concentration on one side of the neck, smooth stress distribution along the body and no considerable concentration at the apical area. Conclusion: Results showed similar stress distribution pattern for cuneiform and cylindrical threaded geometries. The stresses profiles along the implants length reproduced their morphology. In both occurred stress concentration at one side of the neck and no body or apical stress concentration. Show more

Keywords: Biomechanics, dental implants, dental stress analysis, finite element analysis

DOI: 10.3233/THC-2006-144-523

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 421-438, 2006

Authors: Asbia, S. | Ibbetson, R. | Reuben, R.L.

Article Type: Research Article

Abstract: This work is concerned with the performance, under dynamic compression, of the adhesives used to simulate cementation of gold crowns onto nickel chromium dies. A measurement system, based on the mounting of strain gauges onto the outer surface of the crowns, has been developed, which allows a semi-quantitative estimate of the state of adhesion. A preliminary study was carried out where miniature gauges were bonded onto the buccal, lingual, mesial and distal surfaces of gold crowns cast to fit onto a chromium-cobalt die, as a precursor to the final design of the instrumented crown. The crowns were then loaded in …compression periodically measuring the strain at all four gauges. The results showed the load-strain relationship in fully, partially and uncemented crowns, along with repeated load-unload behaviour to close to the ultimate strength of the bond. The load-strain relationship is linear and repeatable and the slope varies over a factor of about 30 between the un-cemented and fully cemented crown, demonstrating that there is significant sensitivity to bond integrity. These results were used to determine the parameters for a systematic study of S-N relationships in restorative dentistry crowns. Show more

Keywords: Restorative dentistry, adhesives, mechanical testing

DOI: 10.3233/THC-2006-144-524

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 439-448, 2006

Authors: Karoglan, M. | Schütz, K. | Schieferstein, H. | Horch, H.-H. | Neff, A.

Article Type: Research Article

Abstract: The development of new methods and materials for osteosynthesis requires in vitro testing prior to clinical use to exclude major problems or difficulties. In the field of oral and maxillofacial surgery no standardized testing procedures have so far been established. From a biomechanical point of view the lower jaw can be described as a lever that during the chewing cycle various forces at various points of the bone act upon. Standardized solid foam polyurethane mandibles (Sawbones®, Malmö, Sweden) were used for the testing of various types of screws and different types of fractures. Via linkages that were connected to hydraulic …cylinders defined forces were exerted on the polyurethane mandibles and the deformation was registered depending on the force. Monitoring was carried out contactless and therefore without back coupling by the use of a video system that recorded well-defined points on both sides of the fracture line. The photographs were then evaluated by special software (SIMI MOTION CAPTURE®). The control of the cylinders was performed through a processor that besides static forces also allowed dynamic testing (e.g. sinusoid oscillation with defined amplitude and number of cycles). For the standardized and realistic three-dimensional static or dynamic testing of new methods and materials for osteosynthesis of the lower jaw this test stand has proved to be optimally suitable. Independent on the type of fracture and the material used the field of application for our test stand is the complete lower jaw. Therefore an ethically correct and economically reasonable testing of industrial products and clinical methods of osteosynthesis can be performed with this simulator. Show more

DOI: 10.3233/THC-2006-144-525

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 449-455, 2006

Authors: Carvalho, L. | Moreira, R.A.S. | Simões, J.A.

Article Type: Research Article

Abstract: The performance of a tooth replacement by using a dental implant relies on the mechanical and biological capability of the anatomical substitute to restore lost physiological functions. The design of an implant device able to properly replace the physiological tooth requires the study of the load transfer mechanism at the implant-bone interface and the understanding of the relevance of the periodontal ligament (PDL) in this mechanism. The PDL is a connective soft tissue that provides the fixation of the tooth in its bone-socket and the attenuation of occlusal loads. It also provides the ground cells that are involved in the …remodelling process, induced by a change in the stress-strain pattern of the alveolar bone and also in the cementum of the tooth root. The purpose of this study was to determine the PDL effects on the dynamic load transfer mechanism, from the tooth to the alveolar bone, evaluating the equivalent dynamic stiffness of the ligament structure. A porcine fresh mandible with a tooth was used within the study, applying an experimental procedure to identify the dynamic transmissibility of the entire system. The transmissibility function provided information about the stiffness and damping of the PDL, information that can assist the design of an improved dental implant system. Show more

DOI: 10.3233/THC-2006-144-526

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 457-465, 2006