Veerle Pattijn

Accuracy and surgical feasibility of a CBCT-based stereolithographic surgical guide aiding autotransplantation of teeth: in vitro validation

The aims of this study were to determine the accuracy of a 3D computer model and stereolithographic (STL) replica when compared to the real tooth and to develop a cone beam computed tomography (CBCT)-based planning technique including surgical guide fabrication. A STL surgical guide and a tooth replica were fabricated using SimPlant Pro 12.1. To validate this process, tooth segmentation and replica design were prepared for comparison to an optical scan of the corresponding tooth. For surgical intervention, a dry dentate mandible was scanned using a Scanora CBCT and the donor tooth was segmented. The donor tooth was repositioned, and two guides were designed. These tooth replica and guides were used in socket preparation of the dry mandible. The 3D computer model of the segmented teeth and related STL models showed satisfactory results with an acceptable accuracy. The surfaces were within 0·25mm distance, but in some areas up to 2·5mm deviation were seen. The results showed that 79% of the points was between 0·25 and -0·25mm, 3% was overestimated (>0·25mm) and 18% was underestimated (<-0·25mm). The computer-based repositioning of the donor tooth and construction of tooth replica and guide allowed socket preparation before donor tooth extraction and optimization of the STL procedure for in vivo planning of CBCT-based autotransplantation.

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

AbstractTrabecular 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 Youngs 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 μCT-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 Youngs modulus EUS determined from the ultrasound measurement is highly correlated with the maximal stress σ max (R2=0.88) but not with the mechanically determined Youngs modulus Emech (R2=0.67). The maximal stress σ max correlates well with the density parameters (R2 varies between 0.76 and 0.86). On the contrary the mechanically determined Youngs 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 σ max (R2=0.83). The inclusion of structural parameters besides a density related parameter did improve the prediction of the Youngs 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.

Medical image based, preformed titanium membranes for bone reconstructions: Design study and first clinical evaluation

Abstract 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.

Structural and radiological parameters for the characterization of jawbone

The success of dental implants has been highly correlated with the jaw bone quantity and quality. In contrast to a precise determination of bone volume, bone quality is usually assessed by a crude grading method (Lekholm and Zarb 1985). A new pre-operative classification of bone quality is mandatory. As CT is becoming a standard procedure in the pre-operative planning of dental implants, the Hounsfield units of the selected implant sites are available and a classification like the one proposed by Norton and Gamble proposed in 2001 seems most suitable. The question remains how these Hounsfield values relate to the structural and mechanical properties of the jawbone. The aim of this study was to determine the Hounsfield values of selected bone sites on a CT scan of the jaw and to investigate the relationship between this radiological parameter and structural parameters.