Microstructural investigation of hybrid CAD/CAM restorative dental materials by micro-CT and SEM

Objectives: An increasing number of CAD/CAM (computer-aided design/computer-aided manufacturing) hybrid materials have been introduced to the dental market in recent years. In addition, CAD/CAM hybrid materials for additive manufacturing (AM) are becoming more attractive in digital dentistry. Studies on material microstructures using micro-computed tomography ($\mu$-CT) combined with scanning electron microscopy (SEM) have only been available to a limited extent so far. Methods: One CAD/CAM three-dimensional- (3D-) printable hybrid material (VarseoSmile Crown plus) and two CAD/CAM millable hybrid materials (Vita Enamic; Voco Grandio), as well as one direct composite material (Ceram.x duo), were included in the present study. Cylindrical samples with a diameter of 2 mm were produced from each material and investigated by means of synchrotron radiation $\mu$-CT at a voxel size of 0.65 $\mu$m. Different samples from the same materials, obtained by cutting and polishing, were investigated by SEM. Results: The 3D-printed hybrid material showed some agglomerations and a more irregular distribution of fillers, as well as a visible layered macrostructure and a few spherical pores due to the printing process. The CAD/CAM millable hybrid materials revealed a more homogenous distribution of ceramic particles. The direct composite material showed multiple air bubbles and microstructural irregularities based on manual processing. Significance: The $\mu$-CT and SEM analysis of the materials revealed different microstructures even though they belong to the same class of materials. It could be shown that $\mu$-CT and SEM imaging are valuable tools to understand microstructure and related mechanical properties of materials.Comment: 22 pages, 3 tables, 11 figures including supplementary materia

Molecular biology of breast cancer metastasis Molecular expression of vascular markers by aggressive breast cancer cells

During embryogenesis, the formation of primary vascular networks occurs via the processes of vasculogenesis and angiogenesis. In uveal melanoma, vasculogenic mimicry describes the 'embryonic-like' ability of aggressive, but not nonaggressive, tumor cells to form networks surrounding spheroids of tumor cells in three-dimensional culture; these recapitulate the patterned networks seen in patients' aggressive tumors and correlates with poor prognosis. The molecular profile of these aggressive tumor cells suggests that they have a deregulated genotype, capable of expressing vascular phenotypes. Similarly, the embryonic-like phenotype expressed by the aggressive human breast cancer cells is associated with their ability to express a variety of vascular markers. These studies may offer new insights for consideration in breast cancer diagnosis and therapeutic intervention strategies

Remineralization of artificial enamel caries lesions by calcium coacervate emulsions

Der in den letzten Jahren beobachtete Kariesrückgang bei Kindern und Jugendlichen, stellt Therapiekonzepte in den Vordergrund, die auf eine Manipulation der kariösen Zahnhartsubstanz verzichten und stattdessen auf eine Remineralisation von initialen kariösen Läsionen abzielen. In der vorliegenden Studie wird erstmals in der Zahnmedizin eine Calcium-Coacervat-Emulsion als Präkursor zur Remineralisation von künstlich kariösen Läsionen im Zahnschmelz getestet. Das Ziel dieser Studie war, eine Remineralisation von künstlich kariösen Läsionen im Zahnschmelz durch eine zuvor bestimmte optimale Konzentration der Calcium-Coacervat-Emulsion zu erzielen. Die Calcium-Coacervat-Emulsionen wurden mittels Infiltration in die künstlich kariösen Läsionen eingebracht. Das Prinzip ist vergleichbar mit der Kariesinfiltration, bei der ein niedrig-viskoser Kunststoff als Infiltrationsmedium, nach entsprechender Vorbehandlung der kariösen Läsionen, verwendet wird. Kapillarkräfte ermöglichen ein schnelles Eindringen des niedrig-viskosen Kunststoffes in die kariöse Läsion. Der Begriff „Infiltration“ wurde in der vorliegenden Studie bewusst gewählt, da es sich um eine Weiterentwicklung der Kariesinfiltration handelt. Calcium-Coacervat-Emulsionen wurden ebenfalls mit Hilfe von Kapillarkräften in die künstlich kariösen Läsionen infiltriert. In einem ersten Versuch wurden künstlich kariöse Läsionen in kariesfreien bovinen Schmelzproben erzeugt. Diese wurden anschließend mit 37 % Phosphorsäuregel für 5 Sekunden geätzt. Nach Reinigung und Trocknung wurden die Schmelzproben mit gesättigter Dikaliumhydrogenphosphat-Lösung (1 M) infiltriert. Anschließend wurde das optimale Verhältnis von Calciumchlorid-Dihydrat und Polyacrylsäure-Natriumsalz ermittelt. Dabei sollte eine opake, calciumreiche, niedrig-viskose Calcium-Coacervat-Emulsionslösung entstehen, die keinen Niederschlag ausbildete und sofort in die künstlich kariösen Läsionen infiltriert werden konnte, um diese zu remineralisieren. Mit Hilfe der Transversalen Mikroradiografie (TMR) wurden alle Schmelzproben in Bezug auf ihren Mineralverlust untersucht. Nur in einer Gruppe konnte eine signifikante Reduktion des Mineralverlustes im Sinne einer Remineralisation nachgewiesen werden. In einem weiteren Versuch sollte nachgewiesen werden, welches Mineral sich in den künstlich kariösen Läsionen nach der Infiltration der Calcium-Coacervat-Emulsion bildete. Bei zwei infiltrierten Schmelzproben wurde die Zusammensetzung der Kristallstruktur mittels Röntgendiffraktion analysiert. Diese Proben wurden zuvor mit einer Calcium-Coacervat-Emulsion infiltriert, die in der TMR eine signifikante Reduktion des Mineralverlustes gezeigt hatte. Die Analyse der Röntgendiffraktion zeigte eine homogene Zusammensetzung des Zahnschmelzes mit Hydroxylapatit. In einer infiltrierten künstlich kariösen Läsion wurden Anteile von Oktacalciumphosphat nachgewiesen. Die vorliegende Studie belegt die Remineralisation des Zahnschmelzes durch Calcium-Coacervat-Emulsionen und das Vorhandensein von Apatitverbindungen nach Infiltration in die Effektflächen.The decline of caries in young individuals observed in recent years emphasizes therapeutic concepts that do not require manipulation of tooth structure and instead aim at a remineralization of initial carious lesions. In the present study, a calcium coacervate emulsion was tested for the first time in dentistry as a precursor for remineralization of artificial carious lesions in enamel. The aim of this study was to prove that a calcium coacervate emulsion formed calcium phosphate nanocrystals via various intermediate steps, which cause remineralization of the enamel. Calcium coacervate emulsions were infiltrated into the artificial carious lesions. The principle is similar to the resin infiltration technique, in which a low-viscous resin is used as an infiltration medium, after appropriate pretreatment of the carious lesions. Capillary forces allow the resin to penetrate rapidly into the carious lesion. The term "infiltration" was chosen deliberately in the present study to underline the further development of caries infiltration. Calcium coacervate emulsions were also infiltrated into the artificial carious lesions by capillary forces. Firstly, artificial carious lesions were generated in caries free bovine enamel specimens. These were then etched (37 % phosphoric acid gel, 5 seconds), cleaned, dried and stored in a saturated dipotassium hydrogen phosphate solution (1 M, 60 minutes). The optimum ratio of calcium chloride dihydrate and poly(acrylic acid) sodium salt was investigated. An opaque, calcium-rich, low-viscous calcium coacervate emulsion was developed. The infiltration emulsion was applied straight after mixing to the artificial carious lesions excessively. Transverse Microradiography (TMR) was used to examine the degree of mineral loss. Only in one group a significant reduction of mineral loss could be shown. Another attempt was to demonstrate what kind of mineral was created in the artificial carious lesions after infiltration of the calcium coacervate emulsion. In order to perform an accurate crystal structure analysis of the lesions, two specimens, that had shown a significant decline in mineral loss in the TMR after infiltration of a calcium coacervate emulsion (group 8) before, were examined by X-ray diffraction analysis. X-ray diffraction showed a homogeneous composition of the enamel with hydroxyapatite. Shares of octacalcium phosphate could be detected in one effect segment. The present study demonstrates the remineralization of enamel by calcium coacervate emulsions and the presence of apatite compounds after infiltration into the artificial carious lesions

Visual Versus Digital Color Determination of 3D-Printed Teeth as an Exercise in Dental Students’ Education

Visual color determination is part of the daily routine in dental practice. However, it is not a part of dental education so far. The aim of this study was to evaluate whether visual or digital tooth color determination of 3D-printed teeth is a reliable tool for inexperienced dentistry students. Preclinical dental students evaluated eleven 3D-printed, tooth-shaped samples (VarseoSmile Crown plus, BEGO, Bremen, Germany) of different color shades. Visual shade determination using a reference scale (3D-Master Toothguide (3DM_TG), VITA Zahnfabrik, Bad Säckingen, Germany), followed by a digital color determination using a spectrophotometer (VITA Easyshade V, (ES_V), VITA Zahnfabrik), was performed. Color deviation was calculated in the Lab* color space (ΔE00) and converted into CIELAB 2000. The results were evaluated using the Mann–Whitney U test and the Wilcoxon Rank Sum test (α = 0.05). Significant differences between visual and digital color determination were proven (p < 0.001). Visual color determination (3DM_TG) showed a mean deviation (ΔE00 ± 95%CI) of 6.49 ± 0.47. Digital color determination (ES_V) showed significantly lower mean deviations of ΔE00 of 1.44 ± 0.58. Digital tooth color measurement using a spectrophotometer was a more reliable tool for the color determination of 3D-printed teeth for inexperienced dentistry students

Mechanical properties of 3D-printed and milled composite resins for definitive restorations

Objective: To evaluate the flexural strength and fatigue behavior of a novel 3D-printed composite resin for definitive restorations. Materials and Methods: Fifty disc-shaped specimens were manufactured from each of a nanohybrid composite resin (NHC), polymer-infiltrated ceramic network (PICN), and 3D-printed composite resin (3D) with CAD-CAM technology. Biaxial flexural strength (σ$_{in}$) (n = 30 per group) and biaxial flexural fatigue strength (σ$_{ff}$) (n = 20 per group) were measured using piston-on-three-balls method, employing a staircase approach of 105 cycles. Weibull statistics, relative-strength degradation calculations, and fractography were performed. The results were analyzed with 1-way ANOVA and Games-Howell post hoc test (α = 0.05). Results: Significant differences in σ$_{in}$ and σ$_{ff}$ among the groups (p < 0.001) were detected. The NHC group provided the highest mean ± standard deviation σ$_{in}$ and σ$_{ff}$ (237.3 ± 31.6 MPa and 141.3 ± 3.8 MPa), followed by the PICN (140.3 ± 12.9 MPa and 73.5 ± 9.9 MPa) and the 3D (83.6 ± 18.5 MPa and 37.4 ± 23.8 MPa) groups. The 3D group exhibited significantly lower Weibull modulus (m = 4.7) and up to 15% higher relative strength degradation with areas of nonhomogeneous microstructure as possible fracture origins. Conclusions: The 3D-printed composite resin exhibited the lowest mechanical properties, where areas of nonhomogeneous microstructure developed during the mixing procedure served as potential fracture origins

Role of Helicobacter pylori in conjunctival mucosa-associated lymphoid tissue lymphoma

Objective: Conjunctiva-associated lymphoid tissue is the conjunctival equivalent to mucosa-associated lymphoid tissue (MALT). Mucosa-associated lymphoid tissue lymphoma has been shown to be associated with Helicobacter pylori. In this study, the prevalence and possible role of H. pylori infection in conjunctival MALT lymphoma were evaluated. Design: Retrospective noncomparative case series. Participants: Thirteen cases of conjunctival MALT lymphoma were investigated. Five samples of conjunctival lymphoid hyperplasia and 20 biopsies of normal conjunctiva served as controls. Methods: The specimens were investigated for the presence of H. pylori with immunohistochemistry (IHC) and nested polymerase chain reaction (PCR) techniques. For each case of conjunctival MALT lymphoma, information regarding gender, age at presentation, conjunctival localization, and information of generalized MALT lymphoma were collected. Main Outcome Measures: Detection of H. pylori and patient characteristics. Results: The 13 conjunctival MALT lymphomas originated from 8 women and 5 men with an average age of 62 years (range, 25-87). Only 1 patient had evidence of systemic MALT lymphoma. H. pylon could not be identified in any of the conjunctival MALT lymphomas, in conjunctival lymphoid hyperplasia, or in normal conjunctival biopsies using IHC and PCR techniques. Conclusions: An association between H. pylori and localized conjunctival MALT lymphoma could not be verified. Antigens other than H. pylon may take part in the development of conjunctival MALT lymphoma