Biomedical subjects

Guy Willems

Publications and source records attributed to Guy Willems.

At least 19 recordsLinked to original sources

PubMed2006

Implantation of an RFID-tag into human molars to reduce hard forensic identification labor. Part I: working principle.

Recently the tsunami disaster, the London bombings and the landfall of hurricane Katrina demonstrated once more the need for an accurate, quick and easy to handle identification system. The implantation of a radio frequency identification (RFID) tag into a human tooth and the read-out of its information may give an answer to this problem. A description is given of the modification of an existing RFID-tag that was made for veterinary use. This modified system was implanted in human molars using directly bonded resin composites. A protocol for tooth preparation and tag implantation was developed. A study of tag read-out patterns, revealed their accurate read-out distance range, the optimal site of RFID-tag implantation, assemblage of its components, and dimensions of the primary coil. It was found that disassembling the commercial RFID-tags was practically feasible and resulted in a properly working set-up. Further research is needed to optimize the design and the stability of RFID-tags for human identification purposes.

Disasters↗

PubMed2006

Dental age estimation through volume matching of teeth imaged by cone-beam CT.

A custom-made voxel counting software for calculating the ratio between pulp canal versus tooth volume based on cone-beam CT tooth images was developed and evaluated. The aim of this study was to attempt establishing a correlation between the chronological age of a certain individual and the pulp/tooth volume ratio of one of the teeth. Twenty-eight single rooted teeth of 19 individuals with well-known chronological age were scanned by the cone-beam CT (3D Accuitomo, J. Morita, Kyoto, Japan). Next the images were analyzed using the custom-made software. Linear regression analysis was performed. The results of the analysis showed a moderate correlation between the pulp/tooth volume ratio and biological age with a coefficient of determination (R2) of 0.29. Although the present work was limited to a pilot study, the developed technique showed promising results for dental age estimation in a non-invasive manner using cone-beam CT images in living individuals.

Adult↗

PubMed2006

Racemization of aspartic acid from human dentin in the estimation of chronological age.

The estimation of chronological age in cadavers, human remains and in living human beings by various methods is discussed. These methods, which are based on the age dependent non-enzymatic changes of l-form amino acids to d-form amino acids, mainly aspartic acid, are among the most reliable and accurate methods to date. Most of these methods use gas chromatography (GC). In this review, results of aspartic acid racemization in dentin at different targets are discussed. In addition, pre-considerations and guidelines are given for the selection of dentin from teeth. A pilot project was run to evaluate the efficiency of high performance liquid chromatography (HPLC) coupled with fluorescence detection. New buffer conditions were found to obtain stable derivatives of aspartic acid enantiomers for the estimation of racemization.

Adolescent↗

PubMed2006

Implantation of an RFID-tag into human molars to reduce hard forensic identification labor. Part 2: physical properties.

Modifying and implanting existing RFID-tags into extracted human molars was described previously [P. Thevissen, G. Poelman, B. Puers, M. De Cooman, G. Willems, Implantation of RFID-tag into human molars to reduce hard forensic identification labor. Part 1. Working principle, Forensic Sci. Int. 156 (2006)]. Maximal vertical occlusal load during which the implanted RFID-tags remain active was evaluated in vitro. The temperature dependency of the implanted RFID-tags was studied on the extracted teeth to find out the maximal obtainable temperature before failure and a test with embedded thermistors to verify temperature distributions. The maximal working temperature of the implanted RFID-tags was revealed and gave indications for the set-up of measuring intra oral and intra tooth temperature during the cremation of a human body. Fatigue was induced on the implanted teeth by thermocycling. The results of this investigation showed the need of putting an extra insulating layer around the modified tags before implantation. The different in vitro tests indicated that the implanted RFID-tags can support certain oral and forensic circumstances.

Disasters↗

PubMed2006

Craniofacial reconstruction using a combined statistical model of face shape and soft tissue depths: methodology and validation.

Forensic facial reconstruction aims at estimating the facial outlook associated with an unidentified skull specimen. Estimation is generally based on tabulated average values of soft tissue thicknesses measured at a sparse set of landmarks on the skull. Traditional 'plastic' methods apply modeling clay or plasticine on a cast of the skull, approximating the estimated tissue depths at the landmarks and interpolating in between. Current computerized techniques mimic this landmark interpolation procedure using a single static facial surface template. However, the resulting reconstruction is biased by the specific choice of the template and no face-specific regularization is used during the interpolation process. We reduce the template bias by using a flexible statistical model of a dense set of facial surface points, combined with an associated sparse set of skull-based landmarks. This statistical model is constructed from a facial database of (N = 118) individuals and limits the reconstructions to statistically plausible outlooks. The actual reconstruction is obtained by fitting the skull-based landmarks of the template model to the corresponding landmarks indicated on a digital copy of the skull to be reconstructed. The fitting process changes the face-specific statistical model parameters in a regularized way and interpolates the remaining landmark fit error using a minimal bending thin-plate spline (TPS)-based deformation. Furthermore, estimated properties of the skull specimen (BMI, age and gender, e.g.) can be incorporated as conditions on the reconstruction by removing property-related shape variation from the statistical model description before the fitting process. The proposed statistical method is validated, both in terms of accuracy and identification success rate, based on leave-one-out cross-validation tests applied on the facial database. Accuracy results are obtained by statistically analyzing the local 3D facial surface differences of the reconstructions and their corresponding ground truth. Identification success rate is obtained by comparing, based on correlation, Euclidean distance matrix (EDM) signatures of the reconstructed and the original 3D facial surfaces in the database. A subjective identification success rate is quantified based on face-pool tests. Finally a qualitative comparison is made between facial reconstructions of a real-case skull, based on two typical static face models and our statistical model, showing the shortcomings of current face models and the improved performance of the statistical model.

Adolescent↗

PubMed2006

Computerized craniofacial reconstruction using CT-derived implicit surface representations.

In forensic craniofacial reconstruction, facial features of an unknown individual are estimated from an unidentified skull, based on a mixture of experimentally obtained guidelines on the relationship between soft tissues and the underlying skeleton. In this paper, we investigate the possibility of using full 3D cross-sectional CT images for establishing a reference database of densely sampled distances between the external surfaces of the skull and head for automated craniofacial reconstruction. For each CT image in the reference database, the hard tissue (skull) and soft tissue (head) volumes are automatically segmented and transformed into signed distance transform (sDT) images, representing for each voxel in this image the Euclidean distance to the closest point on the skull and head surface, respectively, distances being positive (negative) for voxels inside (outside) the skull/head. Multiple craniofacial reconstructions are obtained by first warping each reference skull sDT maps to the target skull sDT using a B-spline based free form deformation algorithm and subsequently applying these warps to the reference head sDT maps. A single reconstruction of the target head surface is defined as the zero level set of the arithmetic average of all warped reference head sDT maps, but other reconstructions are possible, biasing the result to subject specific attributes (age, BMI, gender). Both qualitative and quantitative tests (measuring the similarity between the 3D reconstructed and corresponding original head surface) on a small (N = 20) database are presented to proof the validity of the concept.

Databases as Topic↗

PubMed2006

In-vitro evaluation of the material characteristics of stainless steel and beta-titanium orthodontic wires.

INTRODUCTION: The exact composition and material properties of the metal alloys used in orthodontics are usually not identified by or even available from manufacturers. This makes meaningful comparisons between wires impossible and is unacceptable with regard to biocompatibility issues. The aim of this study was to investigate the material characteristics of contemporary stainless steel (SS) and beta-titanium (beta-Ti) wires, also known as titanium-molybdenum alloy (TMA), for comparison. METHODS: Twenty-two different SS and beta-Ti wires, preferably straight wires sized 0.43 x 0.64 mm, (0.017 x 0.025 in) were tested blindly for wire dimensions, chemical compositions, bending and tensile properties, and surface characteristics. RESULTS: Four chemical compositions were found for the beta-Ti wires: titanium-11.5, molybdenum-6, zirconium-4.5 tin; titanium-3, aluminum-8, vanadium-6, chromium-4, molybdenum-4, zirconium; titanium-6, aluminum-4, vanadium, and titanium-45 niobium. The SS wires were of AISI type 304 or the nickel-free variant BioDur 108. All beta-Ti wires showed high surface roughness values. TMA 02 significantly had the highest E-modulus, TMA 02 and TMA 11 had the highest 0.2% yield strength, TMA 02 had the highest hardness, and TMA 12 was the most ductile wire of the beta-Ti wires. All SS wires showed high 0.2% yield strength, SS 10 significantly had the lowest E-modulus and was the most ductile wire, and SS 08 significantly showed the lowest hardness values of all SS wires. CONCLUSIONS: Significant differences were found between SS and beta-Ti wires, but there was little or no difference between the mechanical and physical characteristics tested in each subgroup. However, the morphological analysis clearly demonstrated that the finishing phase (annealing, polishing) of the wires' production process lacks the quality one would expect with regard to good mechanical properties and biocompatibility issues. Accurate specifications are urgently needed concerning the quality of orthodontic wires on the market.

Analysis of Variance↗

PubMed2006

Tribological behaviour of orthodontic archwires under dry and wet sliding conditions in-vitro. I--Frictional behaviour.

OBJECTIVE: To evaluate the frictional behaviour of orthodontic archwires in dry and wet conditions in-vitro. METHODS: Two types of archwire materials were investigated: stainless steel and NiTi. A fretting wear tribometer fitted with an alumina ball was operated at 23 degrees C in three different environments: ambient air with 50 per cent relative humidity, 0.9 wt. per cent sodium chloride solution, and deionised water. RESULTS: NiTi archwires sliding against alumina exhibited high coefficients of friction (about 0.6) in the three environments. Stainless steel archwires sliding against alumina had relatively low coefficients of friction (0.3) in the solutions, but high coefficients (0.8) in air. CONCLUSION: The low frictional forces of the stainless steel wires sliding against alumina in the solutions were due to a lubricating effect of the solutions and corrosion-wear debris. The high frictional forces between the NiTi wires and alumina are attributed to an abrasive interfacial transfer film between the wires and alumina.

Air↗

PubMed2006

Tribological behaviour of orthodontic archwires under dry and wet sliding conditions in-vitro. II--Wear patterns.

OBJECTIVE: To evaluate the wear patterns of orthodontic archwires in dry and wet conditions in-vitro. METHODS: The patterns of wear of stainless steel and NiTi orthodontic archwires were investigated with a fretting wear tribometer fitted with an alumina ball. The tribometer was operated at 23 degrees C in three different environments: ambient air with 50 per cent relative humidity (RH), 0.9 wt. per cent sodium chloride solution and deionised water. Differences in the wear characteristics of the archwires were investigated by scanning electron microscopy. Energy Dispersive X-ray Analysis and Inductively Coupled Plasma Analysis were used to investigate the surface composition of the wires, the wear debris generated during fretting and the corrosion products in the test solutions. RESULTS: Both archwire materials were degraded by oxidational wear in ambient air. The NiTi wires were more resistant to wear than the stainless steel wires. In the aqueous media the stainless steel wires were degraded by abrasive wear, while the NiTi wires were degraded by adhesive wear. CONCLUSION: In ambient air with 50 per cent RH, NiTi wires were more resistant to wear than stainless steel wires. Both archwire materials exhibited higher wear rates in the solutions than in air, indicating some synergism between the wear and corrosion processes. In the solutions the stainless steel archwires had a much lower corrosion-wear resistance than the NiTi archwires.

Aluminum Oxide↗

PubMed2005

Three-dimensional cranio-facial reconstruction in forensic identification: latest progress and new tendencies in the 21st century.

Three-dimensional (3D) cranio-facial reconstruction can be useful in the identification of an unknown body. The progress in computer science and the improvement of medical imaging technologies during recent years had significant repercussions on this domain. New facial soft tissue depth data for children and adults have been obtained using ultrasound, CT-scans and radiographies. New guidelines for facial feature properties such as nose projection, eye protrusion or mouth width, have been suggested, but also older theories and "rules of thumbs" have been critically evaluated based on digital technology. New fast, flexible and objective 3D reconstruction computer programs are in full development. The research on craniofacial reconstruction since the beginning of the 21st century is presented, highlighting computer-aided 3D facial reconstruction. Employing the newer technologies and permanently evaluating and (re)questioning the obtained results will hopefully lead to more accurate reconstructions.

Face↗

PubMed2005

[Determination of dental age].

A review of the most commonly used dental age estimating techniques is generated. The most important issue for the forensic odontologist involved in dental age estimation is to employ as many of these methods as possible by performing repetitive measurements and calculations of different age-related parameters. That is the only way in order to try and establish reliable dental age estimations. In particular, a special chapter is attributed to the complex problem of determining the age of majority.

Adolescent↗

PubMed2005

[Analysis of bite marks].

Precise photographs, supplemented by impressions are used to research and compare bite marks. Different materials for impressions are available to the forensic odontologist. Subsequently, the acquired information of the bite mark will be compared with the dentition of a suspect through photographs, intra- and extra oral examination and impressions. The overlay, which can be created using a variety of methods, allows the comparison between the bite mark and the dentition of the suspect. Among the most commonly used are hand-tracing of study models, wax bites or photocopies, or the radio-opaque wax bite method. Thanks to modern technology and the use of computers, analyses of bite marks have gradually become more accurate. Current research carried out at the Katholieke Universiteit Leuven will demonstrate whether the computer program ForensicIQ is able to offer an even more precise comparison between a given bite mark and the dentition of a suspect. By no means should bite mark analysis alone be allowed to lead to a guilty verdict, but it will offer the opportunity to exclude a suspect from a crime when the data do not correspond.

Bites, Human↗

PubMed2005

[Computer-assisted facial reconstruction: recent developments and trends].

Three-dimensional (3D) craniofacial reconstruction can be a useful tool in the identification of an unknown body. The progress in computer science and the improvement of medical imaging technologies during recent years has had a significant impact on this domain. New facial soft tissue depth data have been obtained. New guidelines for facial feature properties such as nose projection, eye protrusion or mouth width, have been suggested, but also older theories and "rules of thumbs" have been critically evaluated based on digital technology. New fast, flexible and objective 3D reconstruction computer-based programs are in full development. Employing the newer technologies and permanently evaluating the obtained results will hopefully lead to more accurate reconstructions.

Algorithms↗

PubMed2005

Semi-automated ultrasound facial soft tissue depth registration: method and validation.

A mobile and fast, semi-automatic ultrasound (US) system was developed for facial soft tissue depth registration. The system consists of an A-Scan ultrasound device connected to a portable PC with interfacing and controlling software. For 52 cephalometric landmarks, the system was tested for repeatability and accuracy by evaluating intra-observer agreement and comparing ultrasound and CT-scan results on 12 subjects planned for craniofacial surgery, respectively. A paired t-test evaluating repeatability of the ultrasound measurements showed 5.7% (n = 3) of the landmarks being significantly different (p < 0.01). US and CT-scan results showed significant differences (p < 0.01) using a Wilcoxon signed rank test analysis for 11.5% (n = 6) of the landmarks. This is attributed to a difference in the volunteer's head position between lying (CT) and sitting (US). Based on these tests, we conclude that the proposed registration system and measurement protocol allows relatively fast (52 landmarks/20 min), non-invasive, repeatable and accurate acquisition of facial soft tissue depth measurements.

Adult↗

PubMed2005

Treatment protocol for unilateral cleft lip and palate patients: questioned by two case reports.

BACKGROUND: The types and severity of clefts as well as palatal development and growth in children with repaired cleft lip and palate deformities can vary greatly. Independent of the technique used surgery produces scar tissue, which restricts palatal growth so that by the second decade many patients have an underdeveloped maxilla. Experience has shown that the maxillary retrognathism found in many cleft patients is not amenable to nonsurgical correction. Few long-term studies have evaluated the procedures, sequencing and timing of the treatment methods found to give the best results. This lack of reliable information means there is a serious gap in our ability to assess the value of different treatment modalities. AIMS AND METHODS: From the viewpoint of orthodontics, this article describes the treatment protocol used by the cleft lip and palate team at the University Hospitals of the KU Leuven. The present treatment protocol is illustrated and questioned by two cases. The roles of prediction of facial growth and distraction osteogenesis are discussed.

Alveoloplasty↗

PubMed2004

The application of Kvaal's dental age calculation technique on panoramic dental radiographs.

INTRODUCTION: Literature reports on a method for dental age calculation which is based only on radiological measurements on periapical dental radiographs: the relationship between chronological age and the two-dimensional dental pulpal size was analysed by means of multiple regression analyses. The purpose of the present study was to evaluate whether this approach could be feasible and could lead to statistically sound results with adequate repeatability when applied on panoramic radiographs. MATERIALS AND METHODS: One hundred and ninety seven panoramic radiographs were collected at random from patients of whom the age ranged from 19 to 75 years. According to the reported technique, six teeth were selected on the panoramic radiograph: in the maxilla the central and lateral incisor and second bicuspid, and in the mandibula the lateral incisor, cuspid and first bicuspid. The same exclusion criteria as in the original paper were respected. Statistical analysis was carried out in order to spot significant differences between the chronological age and the calculated age. RESULTS: When the age was calculated based on measurements of all six teeth or of all three mandibular teeth, no significant differences were found between the real age and the calculated one. In all other instances using the individual teeth separately or using all three maxillary teeth statistical analysis revealed significant differences. CONCLUSION: There appears to be no significant difference between applying the original technique on standard long-cone periapical radiographs or on orthopantomograms, especially when carrying out measurements on all six selected teeth.

Adult↗

PubMed2004

Periodontal parameters around implants anchoring orthodontic appliances: a series of case reports.

BACKGROUND: Implants replacing missing teeth provide advantages over clinical orthodontic treatment as compensation for reaction forces is no longer necessary and the lack of teeth is immediately resolved. METHODS: A total of 38 two-stage implants were inserted (16 in maxilla, 22 in mandible) in 10 partially edentulous patients with orthodontic problems. Osseointegration and marginal bone levels were assessed via intra-oral radiographs taken at the abutment stage and at the completion of the orthodontic treatment and also via probing depth, measurement of recession toward the implant/abutment (I/A) interface, and sulcus bleeding index, recorded after completion of orthodontic treatment. RESULTS: In the maxilla, the cumulative survival rate was 87.1% after 2 years; for the mandible, it remained 100%. Mean amount of bone loss was 1.6 mm for maxilla and 0.8 mm for mandible. No correlation could be found between directions of orthodontic forces and marginal bone loss. Mean percentage of bleeding sites was 38.5% and 25%, respectively, for implants in the maxilla and mandible. Attachment level was 1.2 mm (SD: 1.2) below I/A interface after completion of the orthodonic treatment. CONCLUSION: No significant marginal bone loss was present. Using implants during orthodontics can result in an easier and more predictable treatment.

Adolescent↗

PubMed2004

Age calculation using X-ray microfocus computed tomographical scanning of teeth: a pilot study.

To correlate dental age with an individual's chronological age based on the calculated volume ratio of pulp versus tooth volume measured, an X-ray microfocus computed tomography unit (microCT) with 25 microm spatial resolution was used to non-destructively scan 43 extracted single root teeth of 25 individuals with well-known chronological age. Custom-made analysis software was used by two examiners to obtain numerical values for pulpal and tooth volume. The ratio of both was calculated and statistically processed. No significant intra- or inter-examiner differences were found. In fact, a very strong concordance correlation coefficient was found. Linear regression analysis showed a coefficient of determination (r) of 0.31 which suggests that there is a rather weak correlation between the volume ratio of pulp versus tooth and biological age. Although rather time consuming, this technique shows promising results for dental age estimation in a non-destructive manner using X-ray microfocus computed tomography.

Adult↗