Numerical investigation of bone remodelling around immediately loaded dental implants using sika deer (Cervus nippon) antlers as implant bed

This study combines finite element method and animal studies, aiming to investigate tissue remodelling processes around dental implants inserted into sika deer antler and to develop an alternative animal consuming model for studying bone remodelling around implants. Implants were inserted in the antlers and loaded immediately via a self-developed loading device. After 3, 4, 5 and 6 weeks, implants and surrounding tissue were taken out. Specimens were scanned by μCT scanner and finite element models were generated. Immediate loading and osseointegration conditions were simulated at the implant-tissue interface. A vertical force of 10 N was applied on the implant. During the healing time, density and Young’s modulus of antler tissue around the implant increased significantly. For each time point, the values of displacement, stresses and strains in the osseointegration model were lower than those of the immediate loading model. As the healing time increased, the displacement of implants was reduced. The 3-week immediate loading model (9878 ± 1965 μstrain) illustrated the highest strains in the antler tissue. Antler tissue showed similar biomechanical properties as human bone in investigating the bone remodelling around implants, therefore the use of sika deer antler model is a promising alternative in implant biomechanical studies.     

A histological and biomechanical study of bone stress and bone remodeling around immediately loaded implants

Immediate loading(IL)increases the risk of marginal bone loss.The present study investigated the biomechanical response of peri-implant bone in rabbits after IL,aiming at optimizing load management.Ninety-six implants were installed bilaterally into femurs of 48 rabbits.Test implants on the left side created the maximal initial stress of 6.9 and 13.4 MPa in peri-implant bone and unloaded implants on the contralateral side were controls.Bone morphology and bone-implant interface strength were measured with histological examination and push-out testing during a 12-week observation period.Additionally,the animal data were incorporated into finite element(FE)models to calculate the bone stress distribution at different levels of osseointegration.Results showed that the stress was concentrated in the bone margin and the bone stress gradually decreased as osseointegration proceeded.A stress of about 2.0 MPa in peri-implant bone had a positive effect on new bone formation,osseointegration and bone-implant interface strength.Bone loss was observed in some specimens with stress exceeding 4.0 MPa.Data indicate that IL significantly increases bone stress during the early postoperative period,but the load-bearing capacity of peri-implant bone increases rapidly with an increase of bone-implant contact.Favorable bone responses may be continually promoted when the stress in peri-implant bone is maintained at a definite level.Accordingly,the progressive loading mode is recommended for IL implants.     

A repeated sampling bone chamber methodology for the evaluation of tissue differentiation and bone adaptation around titanium implants under controlled mechanical conditions

A repeated sampling bone chamber methodology was developed for the study of the influence of the mechanical environment on skeletal tissue differentiation and bone adaptation around titanium implants. Via perforations, bone grows into the implanted outer bone chamber, containing an inner bone chamber with a central test implant. An actuator—easily mounted on the outer bone chamber—allows a controlled mechanical stimulation of the test implant. After each experiment, the inner bone chamber—with its content—can be harvested and analysed. A new inner bone chamber with a central implant can be inserted consecutively in the outer bone chamber and a new experiment can start. Pilot studies led to a reliable surgical protocol and showed the applicability of the methodology, offering the possibility to study skeletal tissue differentiation and adaptation around implants under well-controlled mechanical conditions, and this protected from external loading. Repeated sampling of the bone chamber allows conducting several experiments within the same animal at the same site, thereby excluding subject- and site-dependent variability and reducing the amount of experimental animals.     

Finite element analysis of peri-implant bone volume affected by stresses around Morse taper implants: effects of implant positioning to the bone crest

Abstract

Objectives: The purpose of the present study was to evaluate the distribution and magnitude of stresses through the bone tissue surrounding Morse taper dental implants at different positioning relative to the bone crest. Materials and Methods: A mandibular bone model was obtained from a computed tomography scan. A three-dimensional (3D) model of Morse taper implant-abutment systems placed at the bone crest (equicrestal) and 2?mm bellow the bone crest (subcrestal) were assessed by finite element analysis (FEA). FEA was carried out on axial and oblique (45°) loading at 150 N relatively to the central axis of the implant. The von Mises stresses were analysed considering magnitude and volume of affected peri-implant bone. Results: On vertical loading, maximum von Mises stresses were recorded at 6-7?MPa for trabecular bone while values ranging from 73 up to 118?MPa were recorded for cortical bone. On oblique loading at the equiquestral or subcrestal positioning, the maximum von Mises stresses ranged from 15 to 21?MPa for trabecular bone while values at 150?MPa were recorded for the cortical bone. On vertical loading, >99.9vol.% cortical bone volume was subjected to a maximum of 2?MPa while von Mises stress values at 15?MPa were recorded for trabecular bone. On oblique loading, >99.9vol.% trabecular bone volume was subjected to maximum stress values at 5?MPa, while von Mises stress values at 35?MPa were recorded for >99.4vol.% cortical bone. Conclusions: Bone volume-based stress analysis revealed that most of the bone volume (>99% by vol) was subjected to significantly lower stress values around Morse taper implants placed at equicrestal or subcrestal positioning. Such analysis is commentary to the ordinary biomechanical assessment of dental implants concerning the stress distribution through peri-implant sites.     

Evaluation of bone remodeling around single dental implants of different lengths: a mechanobiological numerical simulation and validation using clinical data

Algorithmic models have been proposed to explain adaptive behavior of bone to loading; however, these models have not been applied to explain the biomechanics of short dental implants. Purpose of present study was to simulate bone remodeling around single implants of different lengths using mechanoregulatory tissue differentiation model derived from the Stanford theory, using finite elements analysis (FEA) and to validate the theoretical prediction with the clinical findings of crestal bone loss. Loading cycles were applied on 7-, 10-, or 13-mm-long dental implants to simulate daily mastication and bone remodeling was assessed by changes in the strain energy density of bone after a 3, 6, and 12 months of function. Moreover, clinical findings of marginal bone loss in 45 patients rehabilitated with same implant designs used in the simulation (n = 15) were computed to validate the theoretical results. FEA analysis showed that although the bone density values reduced over time in the cortical bone for all groups, bone remodeling was independent of implant length. Clinical data showed a similar pattern of bone resorption compared with the data generated from mathematical analyses, independent of implant length. The results of this study showed that the mechanoregulatory tissue model could be employed in monitoring the morphological changes in bone that is subjected to biomechanical loads. In addition, the implant length did not influence the bone remodeling around single dental implants during the first year of loading.     

Design of a custom angled abutment for dental implants using computer-aided design and nonlinear finite element analysis

Computer-aided design/computer-aided manufacturing (CAD/CAM) custom abutments have been attracting more and more attention due to their advantages of accuracy fit and esthetic emergence profile. However, the CAD key technology for custom abutments has been seldom studied as well as their biomechanical behavior. This paper explored a novel method to design a CAD/CAM custom angled abutment, evaluated the biomechanical performance of the whole system and compared the difference between the custom and the conventional abutment through 3D nonlinear finite element analysis (FEA). Firstly, the digital data of the dental casts at the healing abutment level was acquired by optical scanner. Thus the position of the healing abutment and the implant can be determined by CAD technology. The custom angled abutment was then designed according to the need of restoration and esthetics with CAD software. The described system can eliminate wax and cast, create an esthetic anatomical emergence profile and provide a satisfactory angle correction. Simulation results indicate that there was no distinct difference in the stress distribution and magnitude of implant-bone interface and screw using the custom or the conventional angled abutment.     

A paradigm for the development and evaluation of novel implant topologies for bone fixation: Implant design and fabrication

The future development of bio-integrated devices will improve the functionality of robotic prosthetic limbs. A critical step in the advancement of bio-integrated prostheses will be establishing long-term, secure fixation to the remnant bone. To overcome limitations associated with contemporary bone-anchored prosthetic limbs, we established a paradigm for developing and fabricating novel orthopedic implants undergoing specified loading. A topology optimization scheme was utilized to generate optimal implant macrostructures that minimize deformations near the bone-implant interface. Variations in implant characteristics and interfacial connectivity were investigated to examine how these variables influence the layout of the optimized implant. For enhanced tissue integration, the optimally designed macroscopic geometry of a titanium (Ti)-alloy implant was further modified by introducing optimized microstructures. The complex geometries of selected implants were successfully fabricated using selective laser sintering (SLS) technology. Fabrication accuracy was assessed by comparing volumes and cross-sectional areas of fabricated implants to CAD data. The error of fabricated volume to CAD design volume was less than 8% and differences in cross sectional areas between SEM images of fabricated implants and corresponding cross sections from CAD design were on average less than 9%. We have demonstrated that this computational design method, combined with solid freeform fabrication techniques, provides a versatile way to develop novel orthopedic implants.     

Effect of electromagnetic field on bone regeneration around dental implants after immediate placement in the dog mandible: a pilot study

doi: 10.1111/j.1741‐2358.2011.00525.x Effect of electromagnetic field on bone regeneration around dental implants after immediate placement in the dog mandible: a pilot study Background: Accelerating bone healing around dental implants can reduce the long‐term period between the insertion of implants and functional rehabilitation. Objective: This in vivo study evaluated the effect of a constant electromagnetic field (CEF) on bone healing around dental implants in dogs. Materials and methods: Eight dental implants were placed immediately after extraction of the first pre‐molar and molar teeth on the mandible of two male dogs and divided into experimental (CEF) and control groups. A CEF at magnetic intensity of 0.8 mT with a pulse width of 25 μs and frequency of 1.5 MHz was applied on the implants for 20 min per day for 2 weeks. Result and conclusion: After qualitative histological analysis, a small quantity of newly formed bone was observed in the gap between the implant surface and alveolar bone in both groups.     

Human demineralised bone matrix as a bone substitute for reconstruction of cystic defects of the lower jaw

Ina retrospective study validated by a standardized clinical and radiologicalexamination, the bone regeneration in 90 patients with cystic mandibulardefectswas examined. In 50 patients bony defect reconstructions with humandemineralised bone matrix (HDBM) were carried out, while in a comparable groupof 40 patients the hollow pockets were left to regenerate bone spontaneously.The bone regeneration after the implantation of human demineralised bone matrix(HDBM) was subjected to a comparative validation. Osteoinductive proteinspresent in HDBM (bone morphogenetic proteins) can diffuse into the implant seatand induce new bone formation (osteoinduction). A markedly faster and morethorough bone regeneration was demonstrated after the surgical therapy ofcysticmandibular lesions with HDBM than without. HDBM also proved to be exceptionallybiocompatible.     

Development and adaptation of a multiprobe biosensor for the use in a semi-automated device for the detection of toxic algae

Worldwide monitoring programs have been launched for the observation of phytoplankton composition and especially for harmful and toxic microalgae. Several molecular methods are currently used for the identification of phytoplankton but usually require transportation of samples to specialised laboratories. For the purpose of the monitoring of toxic algae, a multiprobe chip and a semi-automated rRNA biosensor for the in-situ detection of toxic algae were developed. Different materials for the electrodes and the carrier material were tested using single-electrode sensors and sandwich hybridisation that is based on species-specific rRNA probes. Phytoplankton communities consist of different species and therefore a biosensor consisting of a multiprobe chip with an array of 16 gold electrodes for the simultaneous detection of up to 14 target species was developed. The detection of the toxic algae is based on a sandwich hybridisation and an electrochemical detection method.     

A novel model for the investigation of orthotopically growing primary and secondary bone tumours using intravital microscopy

Here is reported the development of an experimental model using intravital microscopy as a tool to orthotopically investigate malignant bone tumours. Although up to 85% of the most frequently occurring malignant solid tumours, such as lung and prostate carcinomas, metastasize into the bone, and despite the knowledge that a tumour's course may be altered by its surrounding tissue, there is no adequate experimental model available enabling the investigation of orthotopically grown bone tumours in vivo. Intravital microscopy is an internationally accepted experimental method, used in various acute and chronic animal models, that enables qualitative and quantitative analysis of the angiogenesis, microcirculation, growth behaviour, etc. of various benign and malignant tissues. Non-invasive investigations of up to several weeks are possible. Additionally, tissue samples can be taken after termination of the in vivo experiments for further ex vivo investigation (histology, immunohistochemistry, molecular biology, etc.), elucidating the mechanisms that underlie the in vivo observations. Severe combined immunodeficient mice were fitted with a cranial window preparation where the calvaria served as the site for orthotopic implantation of the solid human tumours Saos-2 osteosarcoma (primary) and A 549 lung carcinoma and PC-3 prostate carcinoma (secondary). In all preparations, the take rate was 100%. Histological assessment confirmed the data obtained in vivo, showing typical tumour growth with infiltration of the surrounding osseous and soft tissues. This novel model serves as a valuable tool in understanding the biology of primary and secondary bone tumours in physiological and pathophysiological situations, with implications for the most areas of tumour therapy such as chemotherapy, radiation and antiangiogenesis.     

The earliest evidence for the use of human bone as a tool

We report on the analysis of three human cranial fragments from a Mousterian context at the site of La Quina (France), which show anthropogenic surface modifications. Macroscopic and microscopic analyses, including SEM observation, demonstrate that the modifications visible on one of these fragments are similar to those produced on bone fragments used experimentally to retouch flakes. The microscopic analysis also identified ancient scraping marks, possibly resulting from the cleaning of the skull prior to its breakage and utilisation of a resulting fragment as a tool. The traces of utilisation and the dimensions of this object are compared to those on a sample of 67 bone retouchers found in the same excavation area and layer. Results show that the tool size, as well as the dimensions and location of the utilised area, fall well within the range of variation observed on faunal shaft fragments from La Quina that were used as retouchers. This skull fragment represents the earliest known use of human bone as a raw material and the first reported use of human bone for this purpose by hominins other than modern humans. The two other skull fragments, which probably come from the same individual, also bear anthropogenic surface modifications in the form of percussion, cut, and scraping marks. The deliberate versus unintentional hypotheses for the unusual choice of the bone are presented in light of contextual information, modifications identified on the two skull fragments not used as tools, and data on bone retouchers from the same layer, the same site, and other Mousterian sites.     

Zinc supplements and bone health: The role of the RANKL-RANK axis as a therapeutic target

BackgroundTo this day, empirical data suggests that zinc has important roles in matrix synthesis, bone turnover, and mineralization and its beneficial effects on bone could be mediated through different mechanisms. The influence of zinc on bone turnover could be facilitated via regulating RANKL/RANK/OPG pathway in bone tissue. Therefore, the aim of the study was to conduct a review to investigate the possible effect of the zinc mediated bone remodeling via RANKL/RANK/OPG pathway.MethodsA comprehensive systematic search was performed in MEDLINE/PubMed, Cochrane Library, SCOPUS, and Google Scholar to explore the studies investigating the effect of zinc as a bone remodeling factor via RANKL/RANK/OPG pathway regulation. Subsequently, the details of the pathway and the impact of zinc supplements on RANKL/RANK/OPG pathway regulation were discussed.ResultsThe pathway could play an important role in bone remodeling and any imbalance between RANKL/RANK/OPG components could lead to extreme bone resorption. Although the outcomes of some studies are equivocal, it is evident that zinc possesses protective properties against bone loss by regulating the RANKL/RANK/OPG pathway. There are several experiments where zinc supplementation resulted in upregulation of OPG expression or decreases RANKL level. However, the results of some studies oppose this.ConclusionIt is likely that sufficient zinc intake will elicit positive effects on bone health by RANKL/RANK/OPG regulation. Although the outcomes of a few studies are equivocal, it seems that zinc can exert the protective properties against bone loss by suppressing osteoclastogenesis via downregulation of RANKL/RANK. Additionally, there are several experiments where zinc supplementation resulted in upregulation of OPG expression. However, the results of limited studies oppose this. Therefore, aside from the positive role zinc possesses in preserving bone mass, further effects of zinc in RANKL/RANK/OPG system requires further animal/human studies.     

Development of a novel method for the strengthening and toughening of irradiation-sterilized bone allografts

Reconstruction of large skeletal defects is a significant and challenging issue. Bone allografts are often used for such reconstructions. However, sterilizing bone allografts by using γ-irradiation, damages collagen and causes the bone to become weak, brittle and less fatigue resistant. In a previous study, we successfully protected the mechanical properties of human cortical bone by conducting a pre-treatment with ribose, a natural and biocompatible agent. This study focuses on examining possible mechanisms by which ribose might protect the bone. We examined the mechanical properties, crosslinking, connectivity and free radical scavenging potentials of the ribose treatment. Human cortical bone beams were treated with varying concentration of ribose (0.06–1.2 M) and γ-irradiation before testing them in 3-point bending. The connectivity and amounts of crosslinking were determined with Hydrothermal-Isometric-Tension testing and High-Performance-Liquid-Chromatography, respectively. The free radical content was measured using Electron Paramagnetic Resonance. Ribose pre-treatment improved the mechanical properties of irradiation sterilized human bone in a pre-treatment concentration-dependent manner. The 1.2 M pre-treatment provided >100% of ultimate strength of normal controls and protected 76% of the work-to-fracture (toughness) lost in the irradiated controls. Similarly, the ribose pre-treatment improved the thermo-mechanical properties of irradiation-sterilized human bone collagen in a concentration-dependent manner. Greater free radical content and pentosidine content were modified in the ribose treated bone. This study shows that the mechanical properties of irradiation-sterilized cortical bone allografts can be protected by incubating the bone in a ribose solution prior to irradiation.     

A novel method for the on-line analysis of fermentation broth using a sampling device,microcentrifuge and HPLC

Summary This paper describes a novel system for on-line sampling and analysis of whole broth from a fermenter. The system comprises a steam sterilisable sampling device, high speed microcentrifuge and HPLC. We present results characterising the separation efficiency of the microcentrifuge under different conditions, and illustrate the system with glucose and acetate data from an Escherichia coli fermentation using the system. The on-line measurements have been confirmed by off-line analysis.     

Utility of human placental alkaline phosphatase as a genetic marker for cell tracking in bone and cartilage

It was the aim of the current study to evaluate the utility of human placental alkaline phosphatase (hPLAP) as a genetic marker for cell tracking in bone and cartilage, using transgenic Fischer 344 rats expressing hPLAP under the control of the ubiquitous R26 promoter [F344-Tg(R26-hPLAP)]. hPLAP enzyme activity was retained during paraffin and methylmethacrylate (MMA) embedding, and was best preserved using 40% ethanol as fixative. Endogenous alkaline phosphatase activity could be completely blocked by heat inactivation in paraffin and MMA sections, allowing histochemical detection of hPLAP in the complete absence of background staining. In addition, sensitive detection of hPLAP was also possible using immunohistochemistry. F344-Tg(R26-hPLAP) rats demonstrated ubiquitous expression of hPLAP in hematopoietic bone marrow cells and stromal cells such as osteoblasts, osteocytes, and chondrocytes. Osteoclasts only weakly expressed hPLAP. In conclusion, hPLAP provides superb detection quality in paraffin and plastic sections, and constitutes an excellent genetic marker for cell tracking in hard and soft tissues.     

Multiparametric comparison of mesenchymal stromal cells obtained from trabecular bone by using a novel isolation method with those obtained by iliac crest aspiration from the same subjects

Trabecular bone fragments from femoral heads are sometimes used as bone grafts and have been described as a source of mesenchymal progenitor cells. Nevertheless, mesenchymal stromal cells (MSC) from trabecular bone have not been directly compared with MSC obtained under standard conditions from iliac crest aspiration of the same patients. This is the ideal control to avoid inter-individual variation. We have obtained MSC by a novel method (grinding bone fragments with a bone mill without enzymatic digestion) from the femoral heads of 11 patients undergoing hip replacement surgery and compared them with MSC obtained by standard iliac crest aspiration of bone marrow from the same patients. We have shown that trabecular bone MSC obtained by mechanically fragmented femoral heads fulfil the immunophenotypic and multilineage (adipogenic, osteogenic and chondrogenic) differentiation criteria used to define MSC. We have also differentially compared cellular yields, growth kinetics, cell cycle assessment, and colony-forming unit-fibroblast content of MSC from both sources and conclude that these parameters do not significantly differ. Nevertheless, the finding of slight differences, such as a higher expression of the immature marker CD90, a lower expansion time through the different passages, and a higher percentage of cycling cells in the trabecular bone MSC, warrants further studies with the isolation method proposed here in order to gain further knowledge of the status of MSC in this setting. The present study was partially supported by grant HUS01B07 from the Consejería de Educación and by grant SAN196/SA13/07 from the Consejería de Sanidad, Junta de Castilla y León, Spain.     

Development and evaluation of a new methodology for the fast generation of patient-specific Finite Element models of the buttock for sitting-acquired deep tissue injury prevention

The occurrence and management of Pressure Ulcers remain a major issue for patients with reduced mobility and neurosensory loss despite significant improvement in the prevention methods. These injuries are caused by biological cascades leading from a given mechanical loading state in tissues to irreversible tissue damage. Estimating the internal mechanical conditions within loaded soft tissues has the potential of improving the management and prevention of PU. Several Finite Element models of the buttock have therefore been proposed based on either MRI or CT-Scan data. However, because of the limited availability of MRI or CT-Scan systems and of the long segmentation time, all studies in the literature include the data of only one individual. Yet the inter-individual variability can’t be overlooked when dealing with patient specific estimation of internal tissue loading. As an alternative, this contribution focuses on the combined use of low-dose biplanar X-ray images, B-mode ultrasound images and optical scanner acquisitions in a non-weight-bearing sitting posture for the fast generation of patient-specific FE models of the buttock. Model calibration was performed based on Ischial Tuberosity sagging. Model evaluation was performed by comparing the simulated contact pressure with experimental observations on a population of 6 healthy subjects. Analysis of the models confirmed the high inter-individual variability of soft tissue response (maximum Green Lagrange shear strains of 213 ± 101% in the muscle). This methodology opens the way for investigating inter-individual factors influencing the soft tissue response during sitting and for providing tools to assess PU risk.     

Validation of the ‘Marburg bone bank system’ for thermodisinfection of allogenic femoral head transplants using selected bacteria, fungi, and spores

The Marburg Bone Bank System 'Lobator sd-2' is widely used to process human femoral heads removed during aseptic surgery by thermal disinfection. The inactivating capacity of the thermodisinfection system was validated in compliance with current standards using a newly developed femoral head model. The following micro-organisms, bacteria and fungi, taken from the American Type Culture Collection were investigated: Staphylococcus aureus, Staphyloccus epidermidis, Enterococcus faecium, Pseudomonas aeruginosa, Bacillus subtilis including spores, Clostridium sporogenes, Mycobacterium terrae, Candida albicans and Aspergillus niger spores. Highly enriched suspensions of these micro-organisms were applied to the centre of the femoral heads. The reduction in the number of micro-organisms was determined by counting the colony-forming units (cfu) before and after processing the spiked test device in the 'Lobator sd-2' system.Vegetative bacteria, fungi and fungal spores were completely inactivated (reduction factor >/=6 log(10)). The numbers of B. subtilis and C. sporogenes spores, both known to be heat-resistant, were reduced by one to two orders of magnitude. These bacteria serve as a model for spore forming pathogens which are not relevant in femoral heads from living donors. By processing human femoral heads from living donors by thermal disinfection using the Marburg Bone Banking system, a high level of safety is achieved regarding clinically relevant pathogens. To further increase the safety of the thermally treated femoral heads, we recommend that the medical history and present state of the donor, as well as the necessary serological tests should be taken into account.