Csaba Dobó-Nagy

Distortional effect of beam-hardening artefacts on microCT: a simulation study based on an in vitro caries model

OBJECTIVE The aim of this study was to assess quantitatively the degrading effect of artefacts caused by beam hardening on the microscopic computerized tomography (microCT) measurements of an in vitro caries model. STUDY DESIGN A simulation-based method was described, with which the degrading effect of microCT artefacts on certain parameters of the observed structure could be determined. Simulations were carried out with polychromatic and monochromatic X-ray source, and a linearization method with a second-order polynomial fit algorithm was used in specific cases to correct the beam hardening artefact. The virtual test object was a half-crown of a tooth with an artificial caries lesion. RESULTS For simulation with monochromatic X-ray source, the relative error of lesion depth and thickness measurements of the remineralized layer was found to be 1%-2%. For polychromatic X-ray source, and omitting beam hardening correction, the relative error exceeded 6%. After appropriate beam-hardening correction, the relative error of the measurement could be reduced to 1%-2%. CONCLUSION With the adjustment simulated in this study, microCT having polychromatic X-ray source resulted in the same level of error as with monochromatic source if the linearization method to correct the beam hardening was used. The presented simulation-based method is a useful way to determine artefact-caused distortions for other studies testing objects with different material and geometry.

Phospholipase Cγ2 is required for basal but not oestrogen deficiency–induced bone resorption

Eur J Clin Invest 2012; 42 (1): 49–60

Atomic and vibrational origins of mechanical toughness in bioactive cement during setting

Bioactive glass ionomer cements (GICs) have been in widespread use for ∼40 years in dentistry and medicine. However, these composites fall short of the toughness needed for permanent implants. Significant impediment to improvement has been the requisite use of conventional destructive mechanical testing, which is necessarily retrospective. Here we show quantitatively, through the novel use of calorimetry, terahertz (THz) spectroscopy and neutron scattering, how GICs developing fracture toughness during setting is related to interfacial THz dynamics, changing atomic cohesion and fluctuating interfacial configurations. Contrary to convention, we find setting is non-monotonic, characterized by abrupt features not previously detected, including a glass–polymer coupling point, an early setting point, where decreasing toughness unexpectedly recovers, followed by stress-induced weakening of interfaces. Subsequently, toughness declines asymptotically to long-term fracture test values. We expect the insight afforded by these in situ non-destructive techniques will assist in raising understanding of the setting mechanisms and associated dynamics of cementitious materials.

Serum albumin coating of demineralized bone matrix results in stronger new bone formation

Blood serum fractions are hotly debated adjuvants in bone replacement therapies. In the present experiment, we coated demineralized bone matrices (DBM) with serum albumin and investigated stem cell attachment in vitro and bone formation in a rat calvaria defect model. In the in vitro experiments, we observed that significantly more cells adhere to the serum albumin coated DBMs at every time point. In vivo bone formation with albumin coated and uncoated DBM was monitored biweekly by computed tomography until 11 weeks postoperatively while empty defects served as controls. By the seventh week, the bone defect in the albumin group was almost completely closed (remaining defect 3.0 ± 2.3%), while uncoated DBM and unfilled control groups still had significant defects (uncoated: 40.2 ± 9.1%, control: 52.4 ± 8.9%). Higher density values were also observed in the albumin coated DBM group. In addition, the serum albumin enhanced group showed significantly higher volume of newly formed bone in the microCT analysis and produced significantly higher breaking force and stiffness compared to the uncoated grafts (peak breaking force: uncoated: 15.7 ± 4 N, albumin 46.1 ± 11 N). In conclusion, this investigation shows that implanting serum albumin coated DBM significantly reduces healing period in nonhealing defects and results in mechanically stronger bone. These results also support the idea that serum albumin coating provides a convenient milieu for stem cell function, and a much improved bone grafting success can be achieved without the use of exogenous stem cells.

Remineralization of demineralized bone matrix in critical size cranial defects in rats: A 6-month follow-up study.

The key drawback of using demineralized bone matrix (DBM) is its low initial mechanical stability due to the severe depletion of mineral content. In the present study, we investigated the long-term regeneration of DBM in a critical size bone defect model and investigated the remineralization after 6 months. Bone defects were created in the cranium of male Wistar rats which were filled with DBM or left empty as negative control. In vivo bone formation was monitored with computed tomography after 11, 19, and 26 weeks postoperatively. After 6 months, parietal bones were subjected to micro-CT. Mineral content was determined with spectrophotometric analysis. After 11 weeks the DBM-filled bone defects were completely closed, while empty defects were still open. Density of the DBM-treated group increased significantly while the controls remained unchanged. Quantitative analysis by micro-CT confirmed the in vivo results, bone volume/tissue volume was significantly lower in the controls than in the DBM group. The demineralization procedure depleted the key minerals of the bone to a very low level. Six months after implantation Ca, P, Na, Mg, Zn, and Cr contents were completely restored to the normal level, while K, Sr, and Mn were only partially restored. The remineralization process of DBM is largely complete by the 6th month after implantation in terms of bone density, structure, and key mineral levels. Although DBM does not provide sufficient sources for any of these minerals, it induces a faster and more complete regeneration process.

Endodontic and microsurgical treatments of maxillary lateral incisor dens invaginatus in combination with cone-beam-computed tomography fusion imaging

In this case report, we present the endodontic treatment and microsurgical intervention of dens invaginatus affecting a lateral incisor using cone-beam-computed tomography (CBCT). A 26-year-old woman visited us with a diagnosis of acute apical periodontitis in the upper right lateral incisor (tooth 12). Endodontic treatment of the tooth was carried out. Intraoral radiography provided limited information on the unusual anatomy of the pulp chamber and root canal system; therefore, preoperative CBCT was performed. At the 3-month recall, a radiograph revealed a 5-mm-diameter lateral transparency, and CBCT was, therefore, repeated to facilitate microsurgery treatment planning. A medical image-processing program was used to demonstrate the changes between the CBCT images obtained before and after root canal preparation. In conclusion, endodontic treatment of dens invaginatus is challenging even for endodontic specialists, because the therapy sometimes requires surgical intervention. The currently available novel three-dimensional imaging modalities may have importance in planning and following up the root canal treatment in such cases, especially when unforeseen complications arise.

Comparison of hand and semiautomatic tracing methods for creating maxillofacial artificial organs using sequences of computed tomography (CT) and cone beam computed tomography (CBCT) images

Introduction The aim of this study was to compare the paranasal sinus volumes obtained by manual and semiautomatic imaging software programs using both CT and CBCT imaging. Methods 121 computed tomography (CT) and 119 cone beam computed tomography (CBCT) examinations were selected from the databases of the authors’ institutes. The Digital Imaging and Communications in Medicine (DICOM) images were imported into 3-dimensonal imaging software, in which hand mode and semiautomatic tracing methods were used to measure the volumes of both maxillary sinuses and the sphenoid sinus. The determined volumetric means were compared to previously published averages. Results Isometric CBCT-based volume determination results were closer to the real volume conditions, whereas the non-isometric CT-based volume measurements defined coherently lower volumes. By comparing the 2 volume measurement modes, the values gained from hand mode were closer to the literature data. Furthermore, CBCT-based image measurement results corresponded to the known averages. Conclusions Our results suggest that CBCT images provide reliable volumetric information that can be depended on for artificial organ construction, and which may aid the guidance of the operator prior to or during the intervention.

Identification of the Root Canal and Its Centreline from Dental Cone Beam CT Records

Abstract This paper presents a novel image processing procedure dedicated to the automated detection of the medial axis of the root canal from dental cone beam CT records. The 3D model of root canal is built up from several dozens of parallel cross sections, using image enhancement and a fuzzy chain based segmentation algorithm, center point detection in the segmented slice, three dimensional inner surface reconstruction and curve skeleton extraction in three dimensions. The central line of the root canal can finally be approximated as a 3D spline curve. Several visualization methods have been developed using 3D surfaces, planar sections and 3D curves. The proposed procedure can help prepare several kinds of endodontic interventions.

Identification of the root canal from dental Micro-CT records

This paper presents a novel semi-automated image processing procedure dedicated to the identification and characterization of the dental root canal, based on high-resolution micro-CT records. After the necessary image enhancement, parallel slices are individually segmented via histogram based quick fuzzy c-means clustering. The 3D model of root canal is built up from the segmented cross sections using the reconstruction of the inner surface, and the medial line is extracted by a 3D curve skeletonization algorithm. The central line of the root canal can finally be approximated as a 3D spline curve. The proposed procedure may support the planning of several kinds of endodontic interventions.

Identification of the Dental Root Canal from Micro-CT Records Using 3D Curve Skeleton Extraction

Abstract This paper presents a novel image processing procedure dedicated to the automated detection of the medial axis of the root canal from dental micro CT records. The 3D model of root canal is built up from several hundreds of parallel cross sections, using image enhancement and an enhanced fuzzy c-means based partitioning, center point detection in the segmented slice, three dimensional inner surface reconstruction and curve skeleton extraction in three dimensions. The central line of the root canal can finally be approximated as a 3D spline curve. The proposed procedure can help prepare several kinds of endodontic interventions.