Studies in vitro on the effects of rhein on the chemotaxis of human leukocytes

Rhein (R: 1,8-dihydroxy-3-carboxyanthraquinone) is the active metabolite of the drug diacetylrhein (DAR), an anthraquinone molecule which has recently been proposed for the long-term treatment of osteoarthrosis. Its action mechanism in rheumatic pathology has not been fully explained. It is known that DAR, while not inhibiting the formation of prostaglandins, inhibits certain proteolytic enzymes, and acts on phlogistic cells by lysosomal enzymic and superoxide-anion modifications. Moreover DAR modifies phagocytic functions and the motility of cells. This paper is a contribution to the clarification of the last point, namely the effect of rhein on cell motility. It reports that in vitro no effect of R on random migration was found, but instead a double inhibiting effect on chemotaxis (i.e. a low-dosage and a high-dosage effect). Furthermore, R did not modify the inhibition or induce modification of chemotaxis by vinblastine. Finally R cancelled the stimulating effect of ionic potassium. The results thus indicate that R acts on the chemotaxis of the leukocytes with a complex action at different doses. The action mechanism is probably due to a membrane effect, since rhein (R) did not modify the chemotaxis-inhibiting activity of vinblastine but did interfere with the stimulating effect of K+.     

Three-dimensional finite element modelling of all-ceramic restorations based on micro-CT

ObjectivesTo describe and apply a method of modelling dental crowns and three-unit fixed partial dentures (FPD) for finite element analyses (FEA) from 3D images obtained using a micro-CT scanner.MethodsA crown and a three-unit fixed partial denture (FPD) made of a ceramic framework (Y-TZP) and veneered with porcelain (VM9) were scanned using an X-ray micro-CT scanner with a pixel size of 6.97 μm. Slice images from both structures were generated at each 0.034 mm and processed by an interactive image control system (Mimics). Different masks of abutments, framework and veneer were extracted using thresholding and region growing tools based on X-ray image brightness and contrast. 3D objects of each model were incorporated into non-manifold assembly and meshed simultaneously. Volume meshes were exported to the FEA software (ABAQUS), and the load-generated stress distribution was analyzed.ResultsFEA models showed great shape resemblance with the structures. The use of non-manifold assembly ensured matching surfaces and coinciding nodes between different structural parts. For the crown model, tensile stresses were concentrated in the internal surface of the core, near to the applied load. For the FPD model, the highest tensile stresses were located in the framework, on the cervical area of connectors and pontic.ConclusionsValid 3D models of dental crown and FPD can be generated by combining micro-CT scanning and Mimics software, emphasizing its importance as design tool in dental research.Clinical significanceThe 3D FEA method described in this work is an important tool to predict the stress distribution, assisting on structural design of dental restorations.     

Evolution of endodontic medicine: a critical narrative review of the interrelationship between endodontics and systemic pathological conditions

Odontology - Endodontics has gained emphasis in the scientific community in recent years due to the increase in clinical and in animal models studies focused on endodontic medicine, which aims to...     

Ischemia-reperfusion model in rat spinal cord: cell viability and apoptosis signaling study

This work aimed at determining the ideal ischemia time in an in vitro ischemia-reperfusion model of spinal cord injury. Rat spinal cord slices were prepared and then exposed or not to oxygen deprivation and low glucose (ODLG) for 30, 45, 60, 75 and 90 minutes. Cell viability was assessed by triphenyltetrazolium (TTC), lactate dehydrogenase (LDH) release, and fluorochrome dyes specific for cell dead (ethidium homodimer) using the apotome system. Glutamate release was enzymatically measured by a fluorescent method. Gene expression of apoptotic factors was assessed by real time RT-PCR. Whereas spinal cord slices exposed to ODLG exhibited mild increase in fluorescence for 30 minutes after the insult, the 45, 60, 75 and 90 minutes caused a 2-fold increase. ODLG exposure for 45, 60, 75 or 90 minutes, glutamate and LDH release were significantly elevated. nNOS mRNA expression was overexpressed for 45 minutes and moderately increased for 60 minutes in ODLG groups. Bax/bcl-xl ratio, caspase 9 and caspase 3 mRNA expressions were significantly increased for 45 minutes of ODLG, but not for 30, 60, 75 and 90 minutes. Results showed that cell viability reduction in the spinal cord was dependent on ischemic time, resulting in glutamate and LDH release. ODLG for 45 minutes was adequate for gene expression evaluation of proteins and proteases involved in apoptosis pathways.     

Effect of supporting substrate on the failure behavior of a polymer-infiltrated ceramic network material

Statement of problemRestorative materials are cemented on different types of substrates, such as dentin, metal, and glass-fiber posts with composite resin cores.PurposeThe purpose of this in vitro study was to evaluate the failure behavior after cycling fatigue of a polymer-infiltrated ceramic network material (PICN; VITA ENAMIC) cemented on different supporting substrates.Material and methodsPICN plates (N=80) were obtained from computer-assisted design and computer-assisted manufacturing (CAD-CAM) blocks and cemented with a resin cement to 4 different supporting substrates (n=20): (1) human dentin (PICNDen); (2) dentin analog (PICNDenAn); (3) nickel-chromium alloy (PICNNiCr); and (4) composite resin plus fiberglass post (PICNRc). For comparison, the fracture behavior of a feldspathic ceramic (FelDenAn; VITABLOCS Mark II) and an indirect composite resin (ResDenAn; Opallis LAB Resin) cemented to the DenAn substrate was investigated (n=20). Thus, specimens were composed of the restorative material layer (1-mm thick) resin cemented (0.1-mm-thick layer) to a 2-mm-thick supporting substrate. All specimens were subjected to mechanical cycling (MC) using a pneumatic cycling machine (500 000 cycles, 2 Hz, 50 N). Specimens that did not fracture during cycling were tested under compression using a universal testing machine at a cross-head speed of 0.5 mm/min until the sound of the first crack was detected using an acoustic system. Failure data were statistically evaluated using Weibull distribution. Failures were classified as radial crack, cone crack, combined, and catastrophic fracture.ResultsAll FelDenAn specimens were fractured during MC. Only 4 PICNRc specimens survived MC, so their fracture load data were not statistically analyzed. PICNNiCr showed the greatest characteristic load (L₀) value, followed by ResDenAn. Groups PICNDenAn and PICNDen showed lower and similar L₀ but statistically different Weibull modulus (m). There was a significant relationship between experimental group and failure mode (P<.001). FelDenAn and PICNRc had a higher frequency of radial cracks, whereas PICNNiCr failed from cone cracking.ConclusionsThe supporting substrate influenced the failure behavior of PICN. When the substrate had a higher elastic modulus than the restorative material, better mechanical behavior was observed.     

The Number of Bleaching Sessions Influences Pulp Tissue Damage in Rat Teeth

Introduction

Hydrogen peroxide tooth bleaching is claimed to cause alterations in dental tissue structures. This study investigated the influence of the number of bleaching sessions on pulp tissue in rats.

Methods

Male Wistar rats were studied in 5 groups (groups 1S–5S) of 10 each, which differed by the number (1–5) of bleaching sessions. In each session, the animals were anesthetized, and 35% hydrogen peroxide gel was applied to 3 upper right molars. Two days after the experimental period, the animals were killed, and their jaws were processed for light microscope evaluation. Pulp tissue reactions were scored as follows: 1, no or few inflammatory cells and no reaction; 2, <25 cells and a mild reaction; 3, between 25 and 125 cells and a moderate reaction; and 4, 125 or more cells and a severe reaction. Results from each experimental group were compared between groups and within groups to the corresponding unbleached upper left molars and analyzed for significant differences using the Kruskal-Wallis test (P < .05).

Results

All tissue sections showed significant bleaching-induced changes in the dental pulp. After 1 bleaching session, necrotic tissue in the pulp horns and underlying inflammatory changes were observed. The extent and intensity of these changes increased with the number of bleaching sessions. After 5 sessions, the changes included necrotic areas in the pulp tissue involving the second third of the radicular pulp and intense inflammation in the apical third.

Conclusions

The number of bleaching sessions directly influenced the extent of pulp damage.     

Analysis of thermal distributions in veneered zirconia and metal restorations during firing

Objective

The present work evaluated the thermal behavior of porcelain–metal and porcelain–zirconia restorations during fast and slow firing and cooling.

Methods

All-ceramic (porcelain on zirconia) and porcelain-fused-to-metal (PFM) molar crowns were fabricated with 1 or 2 mm porcelain thickness. Thermocouples were attached to the cementation (T1) and occlusal (T4) surfaces of the restoration and embedded at the framework–porcelain interface (T2) and inside the porcelain (T3) to acquire temperature readings by time. Slow heating was set as 45 °C/min and fast heating as 140 °C/min. For fast cooling, the furnace was opened immediately after the holding time. Slow cooling was effected by opening the furnace when it reached 50 °C below the T_g. Porcelains T_g were calculated for each cooling rate.

Results

Slow heating rate was measured at T4 as being 30 °C/min while fast heating at T4 was 100 °C/min. The measured cooling rates within the porcelain (T2) around the T_g range were 20 °C/min and 900 °C/min for slow and fast cooling, respectively. During slow cooling, similar temperatures were found for both zirconia and metal crowns. Remarkable temperature gradients were observed for the fast cooled all-ceramic crown (T1–T4 = 100 °C) and, of lower magnitude for PFM (T1–T4 = 30 °C). T_g of porcelains increase with faster cooling rates.

Significance

Slow cooling appears to be especially important for all-ceramic crowns to prevent high magnitude thermal gradients, which could influence cracking and fracture of the porcelain.