Biomedical subjects

J Vander Sloten

Publications and source records attributed to J Vander Sloten.

At least 37 records · Page 2Linked to original sources

PubMed2001

The influence of static and dynamic loading on marginal bone reactions around osseointegrated implants: an animal experimental study.

Although it is generally accepted that adverse forces can impair osseointegration, the mechanism of this complication is unknown. In this study, static and dynamic loads were applied on 10 mm long implants (Brånemark System, Nobel Biocare, Sweden) installed bicortically in rabbit tibiae to investigate the bone response. Each of 10 adult New Zealand black rabbits had one statically loaded implant (with a transverse force of 29.4 N applied on a distance of 1.5 mm from the top of the implant, resulting in a bending moment of 4.4 Ncm), one dynamically loaded implant (with a transverse force of 14.7 N applied on a distance of 50 mm from the top of the implant, resulting in a bending moment of 73.5 Ncm, 2.520 cycles in total, applied with a frequency of 1 Hz), and one unloaded control implant. The loading was performed during 14 days. A numerical model was used as a guideline for the applied dynamic load. Histomorphometrical quantifications of the bone to metal contact area and bone density lateral to the implant were performed on undecalcified and toluidine blue stained sections. The histological picture was similar for statically loaded and control implants. Dense cortical lamellar bone was present around the marginal and apical part of the latter implants with no signs of bone loss. Crater-shaped bone defects and Howship's lacunae were explicit signs of bone resorption in the marginal bone area around the dynamically loaded implants. Despite those bone defects, bone islands were present in contact with the implant surface in this marginal area. This resulted in no significantly lower bone-to-implant contact around the dynamically loaded implants in comparison with the statically loaded and the control implants. However, when comparing the amount of bone in the immediate surroundings of the marginal part of the implants, significantly (P < 0.007) less bone volume (density) was present around the dynamically loaded in comparison with the statically loaded and the control implants. This study shows that excessive dynamic loads cause crater-like bone defects lateral to osseointegrated implants.

Animals↗

PubMed2001

On the assets of CAD planning for craniosynostosis surgery.

SkullWiz is a computer-aided design program that transforms computer tomographic data of the neurocranium into a mathematical model that can be interactively manipulated to plan craniosynostosis surgery. Proper planning of this type of surgery involves reference to the underlying viscerocranium and to normal neurocranial dimensions, simulation of all basic surgical actions (closed and open osteotomy, translation, rotation, bending, removal, burring), and reference to the mechanical properties of calvarial bone at a given age. With SkullWiz, infinite trials are possible to develop a surgical plan that combines minimal action with maximum morphologic result. In contrast, physical models, e.g., foam milled or stereolitographic, provide just a single (or double, after gluing) opportunity to visualize three-dimensional morphology and simulate a treatment plan, without reference support. Validation of SkullWiz is difficult due to parameter variability. Its assets are therefore graphically exemplified in two common types of nonsyndromatic single-suture craniosynostosis-trigonocephaly and anterior plagiocephaly. SkullWiz is one of the most accurate planning tools currently available for craniosynostosis surgery. Accurate transfer of the planning by aluminium templates results in efficient and precise surgery by avoiding per-operative "chipping and fitting."

Age Factors↗

PubMed2001

Structural and radiological parameters for the nondestructive characterization of trabecular bone.

Trabecular bone is characterized by compositional and organizational factors. The former include porosity at microlevel and mineralization. The latter refer to the trabecular architecture. Both determine the mechanical properties of the trabecular bone. The aim of this study is to investigate the relationship between the mechanical properties and the local HU value, the bone mineral density, the in vitro histomorphometric properties assessed by means of microcomputed tomography, and the Young's modulus determined by ultrasound measurement. Also the correlation between local HU values based on CT data of the full bone and HU values based on CT data of excised trabecular bone cylinders is investigated. Therefore density and strength related parameters of 22 trabecular bone cylinders retrieved from a fresh cadaver femur were measured by using different techniques. The mean HU value of the excised bone samples is very highly correlated with the pQCT density (R2=0.95) and the microCT-based morphometric parameter BV/TV (R2=0.95). The mean HU values, determined from the CT images of the planned and excised bone samples, are less highly correlated (R2=0.75). The Young's modulus E(US) determined from the ultrasound measurement is highly correlated with the maximal stress sigmamax (R2 = 0.88) but not with the mechanically determined Young's modulus Emech (R2 = 0.67). The maximal stress sigmamax correlates well with the density parameters (R2 varies between 0.76 and 0.86). On the contrary the mechanically determined Young's modulus Emech does not correlate well with the density parameters (R2 varies between 0.52 and 0.56). The absorbed energy Eabs during the deformation is only highly correlated with the maximal stress sigmamax (R2 = 0.83). The inclusion of structural parameters besides a density related parameter did improve the prediction of the Young's modulus and the maximal stress. In conclusion, it seems that the HU value from clinical CT scanning is a good predictor of the local bone density and volume fraction. A combination of local density and a measure of the structural anisotropy is clearly needed to achieve good predictions of bone mechanics.

Bone and Bones↗

PubMed2001

Pre-load on oral implants after screw tightening fixed full prostheses: an in vivo study.

The fit of implant supported fixed prostheses is said to be of clinical concern because of the rigid fixation of an oral implant in its surrounding bone. The influence of the torque sequence of the set screws during fixation of implant supported fixed full prostheses on the final pre-load was investigated in vitro. No significant effect of the torque sequence of the set screws on the final pre-load was observed. The main objective of this study was to quantify and qualify the pre-load in vivo on implants supporting a fixed full prosthesis. This was performed when the prostheses were supported by all five or six implants and was repeated when the prostheses were supported by only four and three implants. A total of 13 patients with a fixed full implant supported prosthesis were selected. The existing abutments were changed for strain gauged abutments. After tightening the set screws with a torque of 10 N cm, the pre-load conditions were registered. The average (SEM) axial forces and bending moments in case of five or six, four and three supporting implants were 323 N (43 N), 346 N (59 N), 307 N (60 N) 21 N cm (3 N cm) and 21 N cm (2 N cm), 23 N cm (5 N cm), respectively. In addition, the pre-load was registered after fixation of a machined gold cylinder, as delivered by the manufacturer, on each of the supporting implants, representing the 'optimal fit' situation. The corresponding average (SEM) axial forces and bending moments in case of five or six, four and three supporting implants were 426 N (36 N), 405 N (40 N), 413 N (46 N) and 8 N cm (1 N cm), 8 N cm (1 N cm), 8 N cm (1 N cm), respectively. The induced axial forces after tightening the prostheses were significantly lower then after tightening the gold cylinder in case of five or six supporting implants (P < 0.02). The induced bending moments after tightening the prostheses were statistically significantly higher (P < 0.0001) then after tightening the gold cylinder in all test conditions (five or six, four or three supporting implants). This study underlines the static load present after screw tightening implant supported fixed full prostheses.

Adult↗

PubMed2000

Bone strains and anterior lift-off, measured with three alternative designs of tibial components of TKA.

Total knee replacement is a successful procedure with high clinical success rates. Problems are mostly initiated on the tibial side, and may be due to - amongst others - improper mechanical design of the tibial base plate. In this paper some new design concepts for the tibial component of a total knee prosthesis are presented. They are evaluated experimentally using a model for a proximal tibia, and strain gauge measurements and displacement measurements as experimental techniques. The designs are meant to yield a physiological load sharing between the trabecular and the cortical bone in the proximal tibia, and to minimize anterior lift-off of the tibial base plate. The optimal design required a metal backing of the plastic part and a thin continuous metallic rim in contact with the proximal tibial cortex. An optimal macro-composite structure within the plastic part was obtained by using thin steel wires in the transversal direction, connected to the metallic rim. With this optimal design, it was shown that the force required to close the anterior gap at simulated knee bending was smaller than 250 N, which can easily be applied clinically by an anteriorly placed clamp or bone screw.

Journal Article↗

PubMed2000

Magnitude and distribution of occlusal forces on oral implants supporting fixed prostheses: an in vivo study.

Since loading is increasingly believed to be a determining factor in the treatment outcome with oral implants, there is a need to expand the knowledge related to the biomechanics of oral implants. The aim of this study is to gain insight in the distribution and magnitude of occlusal forces on oral implants carrying fixed prostheses. This is done by in vivo quantification and qualification of these forces, which implies that not only the magnitude of the load but also its type (axial force or bending moment) will be registered. A total of 13 patients with an implant supported fixed full prosthesis were selected. Occlusal forces on the supporting implants were quantified and qualified during controlled load application of 50 N on several positions along the occlusal surface of the prostheses and during maximal biting in maximal occlusion by use of strain gauged abutments. The test was conducted when the prostheses were supported by all (5 or 6) implants and was repeated when the prostheses were supported by 4 and by 3 implants only. Despite considerable inter-individual variation, clear differences in implant loading between these test conditions were seen. Loading of the extension parts of the prostheses caused a hinging effect which induced considerable compressive forces on the implants closest to the place of load application and lower compressive or tensile forces on other implants. On average, higher forces were observed with a decreasing number of supporting implants. Bending moments were highest when 3 implants only were used.

Adult↗

PubMed2000

Three-dimensional force measurements on oral implants: a methodological study.

This paper describes a methodology that allows in vitro and in vivo quantification and qualification of forces on oral implants. Strain gauges are adapted to the outer surface of 5.5 and 7 mm standard abutments (Brånemark System, Nobel Biocare, Sweden). The readings of the strain gauges are transformed into a numerical representation of the normal force and the bending moment around the X- and Y-axis. The hardware and the software of the 3D measuring device based on the strain gauge technology is explained and its accuracy and reliability tested. The accuracy level for axial forces and bending moments is 9.72 N and 2.5 N x cm, respectively, based on the current techniques for strain gauged abutments. As an example, an in vivo force analysis was performed in a patient with a full fixed prosthesis in the mandible. Since axial loads of 450 N and bending moments of 70 N x cm were recorded, it was concluded that the accuracy of the device falls well within the scope of our needs. Nevertheless, more in vivo research is needed before well defined conclusions can be drawn and strategies developed to improve the biomechanics of oral implants.

Aged↗

PubMed2000

Influence of prosthesis material on the loading of implants that support a fixed partial prosthesis: in vivo study.

BACKGROUND: Since loading is increasingly believed to be a determining factor in the treatment outcome with oral implants, there is a need to expand the knowledge related to the biomechanics of oral implants and its influencing factors. PURPOSE: The aim of this study was to investigate the influence of prosthesis material on the distribution and magnitude of load on oral implants carrying a fixed partial prosthesis by in vivo quantification and qualification of this load. METHODS: Eight patients with in total nine three-unit fixed partial prostheses on three implants and three patients with in total four two-unit fixed partial prostheses on two implants were selected. Both metal and acrylic resin prostheses were made. Strain gauged abutments were used to measure the load on the supporting implants during controlled load application of 50 N on several positions along the occlusal surface of the prostheses and during maximal biting in maximal occlusion. Additional tests were conducted when the three-unit prostheses were supported only by two implants, thereby creating an extension pontic. RESULTS: A significantly better distribution of bending moments with the metal prostheses in comparison to the acrylic resin prostheses was observed in the case of the three-unit prostheses on two implants. No other difference in load or load distribution with the different prosthesis materials was noted. CONCLUSION: The clinical significance of the study reveals an increased risk for bending overload of the implants that are closest to the point of load application only in the case of acrylic resin long span prostheses or acrylic resin prostheses with extensions.

Acrylic Resins↗

PubMed2000

Use of microfocus computerized tomography as a new technique for characterizing bone tissue around oral implants.

Qualitative and quantitative analysis of peri-implant tissues around retrieved oral implants is typically done by means of light microscopy on thin histological sections containing the metal surface and the undecalcified bone. It remains, however, a labor-intensive and thus time-consuming job. Moreover, it is a destructive technique that allows tissue quantification in only a limited number of two-dimensional sections. As an alternative, we evaluated the bone structure around screw-shaped titanium implants by means of microfocus computerized tomography (micro-CT) because it presents a number of advantages compared to conventional sectioning techniques: micro-CT is nondestructive, fast, and allows a fully three-dimensional characterization of the bone structure around the implant. Images can be reconstructed in an arbitrary plane, and three-dimensional reconstructions are also possible. Because of its high resolution, individual trabeculae can be visualized. The accuracy of micro-CT was qualitatively evaluated by comparing histological sections with the corresponding CT slices for the same specimen. The overall trabecular structure is very similar according to both techniques. Even very close to the interface, the titanium implant does not seem to produce significant artifacts. Furthermore, because the complete digital data on the trabecular bone structure around the implant is available, it is possible to create finite-element models of the bone-implant system that model the trabeculae in detail so that mechanical stress transfer at the interface can be studied at the level of individual trabeculae. Therefore, micro-CT seems to be very promising for the in vitro assessment of the three-dimensional bone structure around oral implants. Further research will be needed to evaluate its accuracy in a more quantitative way.

Animals↗

PubMed1999

Adhesion of new bioactive glass coating.

A valuable alternative to the existing biomedical implant coatings is a bioactive glass (BAG) coating that is produced by reactive plasma spraying. A mechanical performance requirement that is of the utmost importance is the adhesion strength of the coating. Considering the application as dental implant, a new adhesion test (shear test), which was close to the service conditions, was designed. A Ti6Al4V rod (3 mm) with a sprayed BAG coating of 50 microm was glued with an epoxy glue to a hollow cylindrical counterpart and was used as such in the tensile machine. This test was evaluated by finite element analysis (FEA). Preliminary experiments showed that a conversion from shear to tensile adhesion strength is possible by using the Von Mises criterion (sigma = 3(1/2)tau), indicating that thin coatings of brittle materials can behave as a ductile material. The new coating technique was proved to produce a high quality coating with an adhesion strength of 40.1 +/- 4.8 MPa in shear and 69.4 +/- 8.4 MPa in tension. The FEA revealed that no one homogeneously distributed shear stress is present but several nonhomogeneously distributed stress components (shear and tensile) are present in the coating. This analysis indicated that real service conditions are much more complicated than standard adhesion tests.

Adhesives↗

PubMed1999

Computer-aided craniofacial surgical planning implemented in CAD software.

Accurate presurgical planning is imperative for successful cranial surgery. This article introduces a simulation program developed in a computer-aided design environment. The neurocranium is introduced as a mathematical surface, since this is the part on which the actual operation will be performed. The viscerocranium, which serves as reference, is visualized using small triangular surfaces. The development of the program commenced with a classification of the different surgical techniques mentioned in the literature into six basic actions. The use of mathematically described surfaces has the advantage that the program can simulate actions which change the shape of a surface and perform an on-line estimation of the fracture risk during bending. Three-point bending tests were carried out to provide the necessary data to perform the mathematical check, as these data are not available in the literature. A database with reference distances was introduced to guide the surgeon to obtain the best possible results. During one clinical trial, the computer was taken into the operating room so that the surgical plan developed with the simulation program could be applied to the actual operation.

Brain↗

PubMed1999

In vivo forces on oral implants supporting a mandibular overdenture: the influence of attachment system.

This study was designed to gain insight into the influence of the attachment system on the loading conditions of oral implants supporting a mandibular overdenture on two implants. Five patients were selected and were provided with two implants in the canine area of the mandible (Brånemark System). All patients received a new mandibular overdenture that could be mounted on an ovoid-shaped bar (Dolder, C&M): (a) with and (b) without bilateral extensions and (c) on ball-attachments (Nobel Biocare). Using three strain gauges attached to the outer surface of the 5.5-mm standard abutments, the axial forces and bending moments on both supporting implants could be quantified. Load registrations were made during application of 50 N on seven predetermined positions along the occlusal surface of the prosthesis and during maximal biting in maximal occlusion (clenching). The results revealed no differences in induced axial force for the various anchorage devices, unlike the differences in bending moment. Although there is a tendency for better axial load sharing with bars and better sharing of bending moments with ball attachments, these differences were not significant.

Dental Implantation, Endosseous↗

PubMed1998

Machining and accuracy studies for a tibial knee implant using a force-controlled robot.

Total knee arthroplasty requires accurate preparation of the bone surfaces to maximize bone implant contact area in cementless surgery and to obtain proper joint kinematics and ligament balancing. Robots can make the cuts with the necessary high precision. The purpose of this article is threefold: to propose an alternative method for intraoperative registration using an intramedullary rod and an alternative method for force control using the hybrid force-velocity control scheme; to demonstrate that the accuracy and the surface flatness of the cuts machined by a robot are better than in a conventional operation; and to monitor the machining process and to try to derive some information about the local bone quality from it. The results of the laboratory study are promising: the surface flatness of the tibial plateau, calculated using a least squares method, is 0.1-0.2 mm, which is significantly better than in conventional surgery; and the high angular accuracy of the robot allows the bone cuts to be located precisely. Further, an exponential relation between milling forces and local bone density was established, so measurements of the milling forces can provide the surgeon with on-line information about the local bone quality.

Animals↗

PubMed1998

Materials selection and design for orthopaedic implants with improved long-term performance.

Design and materials selection are equally important in the development of orthopaedic implants. Two case studies are presented to illustrate this: the development of a femoral component of a total hip prosthesis and the study of alternative designs of a tibial component of a total knee prosthesis. Bioactive surface coatings may be applied to enhance the stability of fixation of the implant, even in difficult clinical cases. It is argued that an improved long-term performance of an implant can only be achieved by considering the biomechanics and biomaterials aspects of joint replacement together, and at the same time guaranteeing the quality of surgery by providing the surgeon with better pre-surgical planning systems and advanced surgical tools.

Biocompatible Materials↗

PubMed1998

The influence of bone mechanical properties and implant fixation upon bone loading around oral implants.

Finite element models were created to study the stress and strain distribution around a solitary Brånemark implant. The influence of a number of clinically relevant parameters was examined: bone-implant interface (fixed bond versus frictionless free contact), bone elastic properties, unicortical versus bicortical implant fixation and the presence of a lamina dura. Bone loading patterns in the vicinity of the implant seem to be very sensitive to these parameters. Hence they should be integrated correctly in numerical models of in vivo behaviour of oral implants. This necessitates the creation of patient-dependent finite element models.

Biomechanical Phenomena↗

PubMed1998

Finite element analysis of non-axial versus axial loading of oral implants in the mandible of the dog.

The influence of axial and non-axial occlusal loads on the bone remodelling phenomena around oral implants in an animal experiment is simulated in a finite element analysis. The axial and non-axial loading conditions were introduced by inserting a bilaterally supported fixed partial prosthesis and a cantilever fixed partial prosthesis on two IMZ implants in the mandible of beagle dogs. Earlier quantitative and qualitative histological analyses revealed a statistically significant different remodelling response between both loading conditions. Two-dimensional and three-dimensional models are built to analyse and compare von Mises equivalent stress, maximum principal stress, maximum principal strain and strain energy density distributions, first around a free-standing implant and subsequently around the implants of the two prosthesis designs under the respective resultant in vivo loads. Strong correlations between the calculated stress distributions in the surrounding bone tissue and the remodelling phenomena in the comparative animal model are observed. It is concluded that the highest bone remodelling events coincide with the regions of highest equivalent stress and that the major remodelling differences between axial and non-axial loading are largely determined by the horizontal stress component of the engendered stresses.

Alveolar Process↗

PubMed1998

Applications of computer modelling for the design of orthopaedic, dental and cardiovascular biomaterials.

Biomaterials do not escape from the general trend present in all contemporary science and technology towards increasing use of computers and information technology. In this paper the use of computer modelling for the design of biomaterials is discussed. The word 'biomaterials' is interpreted in its broadest sense, i.e. referring to any foreign object brought into the body for temporary or permanent use. Computer modelling will first be discussed as a tool to model biological structures (bones, arteries) or to investigate and simulate biological interactions at implant-host interfaces. It will then be illustrated how computer modelling, using insights gained from the modelling of the biological structures themselves, is used in the design process of dental, orthopaedic and cardiovascular prostheses. The area of computer modelling for biomaterials applications has become so vast that an exhaustive overview is impossible in the framework of one paper. Rather, some illustrative case studies will be discussed which are, in the opinion of the authors, representative of general trends in this challenging domain of science on the boundary between engineering and medicine.

Cardiovascular Diseases↗

PubMed1997

High labial incisions for genioplasty.

Clinical experience in genioplasty has shown that high labial incisions heal with fewer scar bands than conventional deep labial incisions. In a prospective randomized trial, we compared 18 high labial curvilinear incisions with 27 high labial W-shaped ('royal') incisions for access and visibility during chin osteotomy. Both incisions were 3 cm wide. Maximal incision lengthening between two skin hooks was recorded with a ruler before closure, and there was no significant difference between the two. The maximum wound area between three skin hooks was photographed and computed, and showed a mean difference of 188.75 mm2 (t-test, P < 0.001), which corroborated the clinical findings that access and visibility were superior in the W-shaped incision group. Complications were few in both groups. We now use the high labial royal incision about 3.5 cm wide, with 90 degrees limb angle for complicated chin osteotomies and ostectomies. A smaller curvilinear high labial incision is used for simple advancement osteotomies.

Adult↗