Elke Van de Casteele

3D volumetric displacement and strain analysis of composite polymerization

OBJECTIVE The present study aimed at a better understanding of the internal shrinkage patterns within different cavity sizes. METHODS Ten cylindrical cavities in two sizes were filled with a flowable composite and scanned using X-ray micro-computed tomography (μ-CT) before filling, before and after polymerization. Three-dimensional (3D) non-rigid image registration was applied to sets of two subsequent μ-CT images, before and after polymerization in order to calculate the displacements and strains caused by polymerization shrinkage. RESULTS 3D volumetric displacement analysis disclosed a main vertical component for both the small and large cavities, however in the latter the downward direction reversed to an upward direction from a depth of approximately 2mm due to debonding at the bottom. Air bubbles and voids in the restorations increased upon polymerization, causing a reverse in strain in the surrounding areas. SIGNIFICANCE Polymerization-induced shrinkage stress in composite restorations cannot be measured directly. This exploratory study revealed more information on cavity-size dependent shrinkage patterns and opens the way to more extensive studies using different composite materials and varying geometric cavity configurations.

Validation of cone beam computed tomography–based tooth printing using different three-dimensional printing technologies

OBJECTIVE Our aim was to determine the accuracy of 3-dimensional reconstructed models of teeth compared with the natural teeth by using 4 different 3-dimensional printers. STUDY DESIGN This in vitro study was carried out using 2 intact, dry adult human mandibles, which were scanned with cone beam computed tomography. Premolars were selected for this study. Dimensional differences between natural teeth and the printed models were evaluated directly by using volumetric differences and indirectly through optical scanning. Analysis of variance, Pearson correlation, and Bland Altman plots were applied for statistical analysis. RESULTS Volumetric measurements from natural teeth and fabricated models, either by the direct method (the Archimedes principle) or by the indirect method (optical scanning), showed no statistical differences. The mean volume difference ranged between 3.1 mm(3) (0.7%) and 4.4 mm(3) (1.9%) for the direct measurement, and between -1.3 mm(3) (-0.6%) and 11.9 mm(3) (+5.9%) for the optical scan. A surface part comparison analysis showed that 90% of the values revealed a distance deviation within the interval 0 to 0.25 mm. CONCLUSIONS Current results showed a high accuracy of all printed models of teeth compared with natural teeth. This outcome opens perspectives for clinical use of cost-effective 3-dimensional printed teeth for surgical procedures, such as tooth autotransplantation.

Classification of microcalcifications using micro-CT

Microcalcifications are tiny spots of calcium deposit that often occur in female breasts. Microcalcifications are common in healthy woman, but they often are an early sign of breast cancer. On a mammogram; the current standard of care for breast screening; calcifications appear as tiny white dots. They may occur scattered throughout the breast or grouped in clusters. Radiologists determine the suspiciousness based upon several factors, including position, frequency, grouping, evolution compared to prior studies and shape. In this paper, we study micro-CT images of biopsy samples containing microcalcifications. The scanner delivers 3D images with a voxel size of 8.66 μm, i.e. ca. 8 times the spatial resolution of a contemporary digital mammogram. We propose an automated binary classification method of the samples, based upon shape analysis of the microcalcifications. The study is performed on a set of 50 benign and 50 malign samples preserved in paraffin. The ground truth of the classification is based upon anapathological investigation of the paraffin blocks. The results show a sensitivity, i.e. the percentage of correctly classified malign samples, of up to 98% with a specificity of 40%.

Evaluation of Dimensional Changes of 3D Printed Models After Sterilization: A Pilot Study

Objectives: To assess the effect of two of the most commonly used sterilization techniques on 3D printed clinical objects. Materials & Methods: The two sterilization methods used in our hospital and investigated in this paper are: Steam heat and Gas plasma. Three objects were printed and tested in this study: a tooth replica, an orthognathic final splint, a surgical cutting guide for the purpose of mandible reconstruction. For each of the 3 objects, 4 copies were made: one original STL object, one copy of the object pre-sterilization, one copy of post-steam heat sterilization, and one copy of post-gas plasma sterilization. Each printed object was scanned using a high resolution CBCT protocol and the compared (morphologically and volumetrically). Results: At the level of volumetric changes, no difference was found between pre and post-sterilization for both methods evaluated. As for the morphological changes, only differences were noticed with the orthognathic splint object indicating deformation of the printed splints after sterilization. Larger differences were observed with heat sterilization, making it less reliable. Conclusion: Sterilization of dental objects to be used in a clinical setting may lead to deformation of the printed model, especially for heat sterilization. Further investigations are needed to confirm these findings.

Shape-Based Clustering and Classification of Breast Microcalcifications in Micro-CT Images

This paper presents a novel classification approach for microcalcifications extracted from core biopsy tissue samples digitized using micro-CT, a high-resolution 3D imaging modality. Microcalcifications are tiny spots of calcium that may occur in the female breast. Although they are common in healthy woman, they are often an early sign of breast cancer. In case of suspiciousness, a biopsy is conducted and the extracted tissue is pathologically analyzed for the presence of cancer cells. The calcifications themselves however are mostly not analyzed. As a result, there is a ground truth for the tissue samples but not for the individual calcifications. Therefore, this paper presents an approach where the calcifications are first classified according to shape-based clusters before predicting a label for the tissue samples.