Biomedical subjects

V Pattijn

Publications and source records attributed to V Pattijn.

4 recordsLinked to original sources

PubMed2006

Resonance frequency analysis of implants in the guinea pig model: influence of boundary conditions and orientation of the transducer.

The goal of this study was to identify the parameters that must be controlled during in vivo resonance frequency measurements with a custom Osstell transducer for custom implants in the guinea pig animal model. A numerical study and in vitro measurements were performed to determine the influence of the boundary conditions as well as the transducer orientation on the resonance frequency measured by the custom Osstell transducer. In the reported guinea pig model, the type of boundary condition, the orientation of the transducer (parallel or perpendicular to the long axis of the bone) and the length of the modelled bone have a large influence on the resonance frequency values. This implies that a follow-up in time of the stability of an implant requires the boundary conditions applied to the bone in which the implant is installed as well as the orientation of the transducer to be highly repeatable. Applying controlled boundary conditions during in vivo measurements had a highly positive influence on the repeatability of the Osstell measurements. This improves the possibility of the technique to measure changes in the implant-bone interface during healing of the implant.

Animals↗

PubMed2006

The resonance frequencies and mode shapes of dental implants: Rigid body behaviour versus bending behaviour. A numerical approach.

The purpose of this study was to evaluate the modal behaviour of the bone-implant-transducer (Osstell) system by means of finite element analyses. The influence of different parameters was determined: (1) the type of implant anchorage being trabecular, cortical, uni-cortical, or bi-cortical, (2) the implant diameter, (3) the length of the implant embedded in the bone, and (4) the bone stiffness. The type of anchorage determines the resulting modal behaviour of the implant-transducer system. A rigid body behaviour was found for a uni-cortical anchoring and for a homogeneous anchoring with low bone stiffness (< or =1000 MPa), whereas a bending behaviour was found for a homogeneous anchoring with a high bone stiffness (> or =5000 MPa) and for a bi-cortical anchorage. The implant dimensions influence the values for the resonance frequencies. Generally, an increase in implant diameter or implant length (in bone) results in higher resonance frequencies. This study also showed that resonance frequencies in case of rigid body behaviour of the implant-transducer system are more sensitive to changes in bone stiffness than resonance frequencies in case of bending behaviour. In conclusion, it seems that the Osstell transducer is suited for the follow-up in time of the stability of an implant, but not for the quantitative comparison of the stability of implants.

Anisotropy↗

PubMed2002

Medical image based, preformed titanium membranes for bone reconstructions: design study and first clinical.

The currently used intralesional or marginal surgical treatment of a bone tumour in the extremities shows some shortcomings in providing a restoration of the mechanical strength of the bone and the containment of the used filling materials. The use of a medical image based, preformed and custom-made titanium membrane screwed onto the periosteal side of the bone is introduced. This study looks in detail into the design process and the biomechanical evaluation of such a membrane. The buckling strength of the membrane, the strength at the perforation holes and the strength of the screw-bone fixation are tested experimentally. The two latter experiments are performed with different screw types. From the performed tests it appears that a titanium membrane without a wave pattern, of 0.3 mm thickness, fixed to the bone with seven trabecular bone screws (4 mm diameter and 28 mm length) is capable of carrying the anticipated mechanical loads on the reconstructed tibia. The medical image based design methodology and the first clinical application of such a preformed and custom-made titanium membrane are reported and discussed. The feasibility of preformed titanium membranes for bone reconstruction in tumour surgery is demonstrated.

Biocompatible Materials↗

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↗