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| 2. |
- Halldin, Anders, et al.
(author)
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Implant Stability and Bone Remodeling after 3 and 13 Days of Implantation with an Initial Static Strain
- 2014
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In: Clinical Implant Dentistry and Related Research. - : John Wiley & Sons. - 1523-0899 .- 1708-8208. ; 16:3, s. 383-393
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Journal article (peer-reviewed)abstract
- Objective Bone is constantly exposed to dynamic and static loads, which induce both dynamic and static bone strains. Although numerous studies exist on the effect of dynamic strain on implant stability and bone remodeling, the effect of static strain needs further investigation. Therefore, the effect of two different static bone strain levels on implant stability and bone remodeling at two different implantation times was investigated in a rabbit model. Methods Two different test implants with a diametrical expansion of 0.15 mm (group A) and 0.05 mm (group B) creating initial static bone strains of 0.045 and 0.015, respectively. The implants were inserted in the proximal tibial metaphysis of 24 rabbits to observe the biological response at implant removal. Both groups were compared to control implants (group C), with no diametrical increase. The insertion torque (ITQ) was measured to represent the initial stability and the removal torque (RTQ) was measured to analyze the effect that static strain had on implant stability and bone remodeling after 3 and 13 days of implantation time. Results The ITQ and the RTQ values for test implants were significantly higher for both implantation times compared to control implants. A selection of histology samples was prepared to measure bone to implant contact (BIC). There was a tendency that the BIC values for test implants were higher compared to control implants. Conclusion These findings suggest that increased static bone strain creates higher implant stability at the time of insertion, and this increased stability is maintained throughout the observed period.
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| 3. |
- Halldin, Anders, 1971, et al.
(author)
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On a Constitutive Material Model to Capture Time Dependent Behaviour of Cortical Bone
- 2014
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In: World Journal of Mechanics. - : Scientific Research Publishing, Inc.. - 2160-049X .- 2160-0503. ; 4:11, s. 348-361
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Journal article (peer-reviewed)abstract
- It is commonly known that cortical bone exhibits viscoelastic-viscoplastic behavior which affects the biomechanical response when an implant is subjected to an external load. In addition, long term effects such as creep, relaxation and remodeling affect the success of the implant over time. Constitutive material models are commonly derived from data obtained in in vitro experiments. However during function, remodeling of bone greatly affects the bone material over time. Hence it is essential to include long term in vivo effects in a constitutive model of bone. This paper proposes a constitutive material model for cortical bone incorporating viscoelasticity, viscoplasticity, creep and remodeling to predict stress-strain at various strain rates as well as the behavior of bone over time in vivo. The rheological model and its parameters explain the behavior of bone subjected to longitudinal loading. By a proper set of model parameters, for a specific cortical bone, the present model can be used for prediction of the behavior of this bone under specific loading conditions. In addition simulation with the proposed model demonstrates excellent agreement to in vitro and in vivo experimental results in the literature.
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| 4. |
- Halldin, Anders, et al.
(author)
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The effect of static bone strain on implant stability of bone remodelling
- 2011
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In: Bone. - : Elsevier. - 8756-3282 .- 1873-2763. ; 49:4, s. 783-789
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Journal article (peer-reviewed)abstract
- Bone remodeling is a process involving both dynamic and static bone strain. Although there exist numerous studies on the effect of dynamic strain on implant stability and bone remodeling, the effect of static strain has yet to be clarified. Hence, for this purpose, the effect of static bone strain on implant stability and bone remodeling was investigated in rabbits. Based on Finite Element (FE) simulation two different test implants, with a diametrical increase of 0.15 mm (group A) and 0.05 mm (group B) creating static strains in the bone of 0.045 and 0.015 respectively, were inserted in the femur (group A) and the proximal tibia metaphysis (groups A and B respectively) of 14 rabbits to observe the biological response. Both groups were compared to control implants, with no diametrical increase (group C), which were placed in the opposite leg. At the time of surgery, the insertion torque (ITQ) was measured to represent the initial stability. The rabbits were euthanized after 24 days and the removal torque (RTQ) was measured to analyze the effect on implant stability and bone remodeling. The mean ITQ value was significantly higher for both groups A and B compared to group C regardless of the bone type. The RTQ value was significantly higher in tibia for groups A and B compared to group C while group A placed in femur presented no significant difference compared to group C. The results suggest that increased static strain in the bone not only creates higher implant stability at the time of insertion, but also generates increased implant stability throughout the observation period.
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| 5. |
- Halldin, Anders, et al.
(author)
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The effect of static strain
- 2012
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In: AstraTech World Congress, May 9-12, 2012, Göteborg, Sweden.
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Conference paper (other academic/artistic)
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| 6. |
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| 7. |
- Hansson, Lisa
(author)
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Public Procurement at the Local Government Level : Actor roles, discretion and constraints in the implementation of public transport goals
- 2011
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Doctoral thesis (other academic/artistic)abstract
- The overall purpose of this thesis is to gain further knowledge of how the Swedish local government level is affected by requirements to use public procurement through competitive tendering and, more specifically, understand the actions taken by included actors when public procurement is required in implementation of public transport goals. Through case study method, an in specific process tracing, various implementation processes have been examined. One studied process complied with the procurement regulations, while the others included elements that circumvented them. In each process, the actions taken by involved actors have been the focus. The findings are presented in four papers. An overall conclusion is that, when public procurement is required in implementation at the local government level, several actors need to interact. These actors may use procurement to expand, maintain, or restrain their discretion towards others actors. In addition, various control mechanisms, such as e.g. monitoring, are used to restrain an actor’s discretion when the actor is circumventing procurement legislation.
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| 8. |
- Hansson, Stig, et al.
(author)
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Characterisation of Titanium Dental Implants. II: Local Biomechanical Model
- 2010
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In: The Open Biomaterials Journal. - : Bentham Science Publishers Ltd.. - 1876-5025. ; 2, s. 36-52
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Journal article (peer-reviewed)abstract
- A theoretical model for estimation of the bone-to-implant interfacial shear strength induced by implant surface roughness has been developed. Two different assumptions regarding the constitutive behaviour of the interfacial bone were made. 1) The bone exhibits an ideally plastic deformation – the plastic mode. 2) The bone exhibits a linearly elastic deformation – the elastic mode. In the plastic mode it was found that the estimated interfacial shear strength was directly proportional to the 2D surface roughness parameter mean slope. For the elastic mode a new 2D surface roughness parameter was defined. With this parameter a direct proportionality between parameter value and estimated interfacial shear strength was also obtained in the elastic mode. The model was extended into 3D mode. The model was used to evaluate topographies of implant surfaces. The calculated results showed a similar trend to interfacial shear strength results reported in vivo.
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| 9. |
- Hansson, Stig, et al.
(author)
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Global biomechanical model for dental implants.
- 2011
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In: Journal of biomechanics. - : Elsevier BV. - 1873-2380 .- 0021-9290. ; 44:6, s. 1059-65
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Journal article (peer-reviewed)abstract
- The osseointegration of titanium dental implants is a complex process and there is a need for systematization of the factors influencing anchoring of implant. A common way of analyzing the strength of the fixation in bone is by measuring the torque required to remove the implants after healing. In this paper, a global biomechanical model is introduced and derived for removal torque situations. In this model, a gap is allowed to form between the bone and the implant and the size of the gap at fracture is a function of the surface roughness and can be shown to be directly related to the mean slope of the surface. The interfacial shear strength increases almost linearly with the mean slope and was also found to increase with an increase in the 2D surface roughness parameter, R(a). Besides the surface roughness, the design of the implant, the bone anatomy and the bone quality were shown to influence the interfacial shear strength. The Global biomechanical model can be used as a tool for optimizing the implant design and the surface topography to obtain high anchoring strength.
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| 10. |
- Löberg, Johanna, 1981, et al.
(author)
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Characterisation of titanium dental implants I:critical assessment of surface roughness parameters
- 2010
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In: The Open Biomaterials Journal. - : Bentham Science Publishers Ltd.. - 1876-5025. ; 2, s. 18-35
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Journal article (peer-reviewed)abstract
- Titanium is commonly used for dental implants because of its unique ability to get incorporated into living bone. There is an ongoing development to obtain better anchorage and surface properties such as roughness and chemical composition are modified to reach this. In this study titanium dental implant surfaces were characterised by recording the topographical changes induced by each individual processing step such as cleaning, blasting, and HF etching. To fully describe the different surfaces, the same point was analysed before and after each step using Atomic Force Microscopy (AFM) and 3D-Scanning Electron Microscopy (3D-SEM). A set of 3D surface parameters were calculated as a function of filter size to describe the topographic features at different levels. The chemical treatment introduces nano-sized features while blasting changes the topography at the micrometer level and by combining AFM and 3D-SEM the entire range can be assessed. The results show that the chemically induced changes in the topography can only be revealed by AFM while 3D-SEM gives a clear description of the topography of blasted surfaces. The fractal dimension for the chemically treated surface was the same as for the blasted surfaces but crossover size was much smaller. Besides the commonly used Sa parameter it is suggested that the root-mean-square of the surface slope (Sdq) and the void volume (Vvc) parameters are included in the characterisation of rough surfaces. These parameters can be used for correlation with in vivo performance.
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