An Optimized Injectable Hydrogel Scaffold Supports Human Dental Pulp Stem Cell Viability and Spreading.

Introduction. HyStem-C™ is a commercially available injectable hydrogel composed of polyethylene glycol diacrylate (PEGDA), hyaluronan (HA), and gelatin (Gn). These components can be mechanically tuned to enhance cell viability and spreading. Methods. The concentration of PEGDA with an added disulfide bond (PEGSSDA) was varied from 0.5 to 8.0% (w/v) to determine the optimal concentration for injectable clinical application. We evaluated the cell viability of human dental pulp stem cells (hDPSCs) embedded in 2% (w/v) PEGSSDA-HA-Gn hydrogels. Volume ratios of HA : Gn from 100 : 0 to 25 : 75 were varied to encourage hDPSC spreading. Fibronectin (Fn) was added to our model to determine the effect of extracellular matrix protein concentration on hDPSC behavior. Results. Our preliminary data suggests that the hydrogel gelation time decreased as the PEGSSDA cross-linker concentration increased. The PEGSSDA-HA-Gn was biocompatible with hDPSCs, and increased ratios of HA : Gn enhanced cell viability for 14 days. Additionally, cell proliferation with added fibronectin increased significantly over time at concentrations of 1.0 and 10.0 µg/mL in PEGDA-HA-Gn hydrogels, while cell spreading significantly increased at Fn concentrations of 0.1 µg/mL. Conclusions. This study demonstrates that PEG-based injectable hydrogels maintain hDPSC viability and facilitate cell spreading, mainly in the presence of extracellular matrix (ECM) proteins.

Study of Pd-Ag dental alloys: examination of effect of casting porosity on fatigue behavior and microstructural analysis.

The goals of this study were to investigate the fatigue limits of two Pd-Ag alloys (Ivoclar Vivadent) with differing mechanical properties and varying proportions of secondary alloying elements, examine the effect of casting porosity on fatigue behavior, and determine the effect of casting size on microstructures and Vickers hardness. The alloys selected were: IPS d.SIGN 59 (59.2Pd-27.9Ag-8.2Sn-2.7In-1.3Zn); and IS 64 (59.9Pd-26.0Ag-7.0Sn-2.8Au-1.8 Ga-1.5In-1.0Pt). Tension test bars, heat-treated to simulate dental porcelain application, were subjected to cyclic loading at 10 Hz, with R-ratio of -1 for amplitudes of compressive and tensile stress. Two replicate specimens were tested at each stress amplitude. Fracture surfaces were examined with a scanning electron microscope (SEM). Sectioned fatigue specimens and additional cast specimens simulating copings for a maxillary central incisor restoration were also examined with the SEM, and Vickers hardness was measured using 1 kg load. Casting porosity was evaluated in sectioned fatigue fracture specimens, using an image analysis program. The fatigue limit (2 × 10(6) loading cycles) of IS 64 was approximately 0.20 of its 0.2% yield strength, while the fatigue limit of d.SIGN 59 was approximately 0.25 of its 0.2% yield strength. These relatively low ratios of fatigue limit to 0.2% yield strength are similar to those found previously for high-palladium dental alloys, and are attributed to their complex microstructures and casting porosity. Complex fatigue fracture surfaces with striations were observed for both alloys. Substantial further decrease in the number of cycles for fatigue failure only occurred when the pore size and volume percentage became excessive. While the heat-treated alloys had equiaxed grains with precipitates, the microstructural homogenization resulting from simulated porcelain firing differed considerably for the coping and fatigue test specimens; the latter specimens had significantly higher values of Vickers hardness.

Alteration of dentin-enamel mechanical properties due to dental whitening treatments.

The mechanical properties of dentin and enamel affect the reliability and wear properties of a tooth. This study investigated the influence of clinical dental treatments and procedures, such as whitening treatments or etching prior to restorative procedures. Both autoclaved and non-autoclaved teeth were studied in order to allow for both comparison with published values and improved clinical relevance. Nanoindentation analysis with the Oliver-Pharr model provided elastic modulus and hardness across the dentin-enamel junction (DEJ). Large increases were observed in the elastic modulus of enamel in teeth that had been autoclaved (52.0 GPa versus 113.4 GPa), while smaller increases were observed in the dentin (17.9 GPa versus 27.9 GPa). Likewise, there was an increase in the hardness of enamel (2.0 GPa versus 4.3 GPa) and dentin (0.5 GPa versus 0.7 GPa) with autoclaving. These changes suggested that the range of elastic modulus and hardness values previously reported in the literature may be partially due to the sterilization procedures. Treatment of the exterior of non-autoclaved teeth with Crest Whitestrips, Opalescence or UltraEtch caused changes in the mechanical properties of both the enamel and dentin. Those treated with Crest Whitestrips showed a reduction in the elastic modulus of enamel (55.3 GPa to 32.7 GPa) and increase in the elastic modulus of dentin (17.2 GPa to 24.3 GPa). Opalescence treatments did not significantly affect the enamel properties, but did result in a decrease in the modulus of dentin (18.5 GPa to 15.1 GPa). Additionally, as expected, UltraEtch treatment decreased the modulus and hardness of enamel (48.7 GPa to 38.0 GPa and 1.9 GPa to 1.5 GPa, respectively) and dentin (21.4 GPa to 15.0 GPa and 1.9 GPa to 1.5 GPa, respectively). Changes in the mechanical properties were linked to altered protein concentration within the tooth, as evidenced by fluorescence microscopy and Fourier transform infrared spectroscopy.

Renal impairment in cystic fibrosis patients due to repeated intravenous aminoglycoside use.

Although there are reports of cases of acute renal failure occurring in cystic fibrosis (CF) patients, usually in association with the use of nephrotoxic antibiotic therapy, there have been no studies of renal function in this patient group. We hypothesized that long-term use of intravenous (IV) nephrotoxic antibiotics (aminoglycosides and colistin sulphomethate) may contribute to renal disease in CF patients. In a prospective study, we assessed creatinine clearance as an index of renal function with two techniques (24-hr urine collections and the Cockroft-Gault formula) in a group of 80 stable adult CF outpatients chronically infected with Pseudomonas aeruginosa but with no history of preceding renal disease. Using a multiple linear regression model, we evaluated their renal function in terms of their lifetime IV use of aminoglycosides and colistin. Between 31% (Cockroft-Gault formula method) and 42% (24-hr urine collection method) of patients had a creatinine clearance below normal range. Using either method, there was a strong correlation between aminoglycoside use and diminishing renal function (r=- 0.32, P=0.0055), which was potentiated by the coadministration of colistin (r=- 0.42, P <0.0002). However, there was no correlation with colistin when used in combination with other antibiotics alone (r=0.18, P=NS). Repeated IV aminoglycoside use in CF is associated with long-term renal damage. Although this effect is potentiated by colistin, colistin on its own in moderate doses does not appear to be nephrotoxic. IV aminoglycosides should be used cautiously in CF patients, with regular monitoring of renal function.

When to suspect ischemic colitis. Why is this condition so often missed or misdiagnosed?

Ischemic colitis is one of the most often seen disorders of the large intestine in the elderly. Common predisposing factors are atherosclerosis, shock, and congestive heart failure, but often, elderly patients have no obvious predisposing or precipitating factors. The typical clinical presentation is acute sudden abdominal pain and distention with bloody diarrhea. Common early radiographic signs are bowel-wall thickening with thumbprinting, and later, ulceration and strictures may be found. Endoscopy is valuable in revealing the sharp demarcation between viable and necrotic colonic mucosa that is a strong indicator of ischemia. Within 48 hours, most patients show favorable response to conservative measures consisting of intravenous hydration, bowel rest, antibiotic therapy, and correction of precipitating processes. Vasoconstricting drugs and corticosteroids are contraindicated. When surgical intervention is indicated, it usually consists of resection of the ischemic segment and exteriorization of the remaining ends of the bowel.