Fatigue of dental ceramics in a simulated oral environment.

Fatigue in ceramics refers to the subcritical growth of cracks, aided by the combined influence of water and stress. The dynamic fatigue (constant stressing rate) method was used to obtain subcritical crack growth parameters for three dental ceramics: a feldspathic porcelain, an aluminous porcelain, and a fine-grain, polycrystalline core material. The constant stressing rate experiments were carried out at 37 degrees C for all three ceramics in distilled water, and, for the feldspathic porcelain, in artificial saliva as well. Considerable differences were found in the value of the crack growth exponent (n) among the three ceramics. The feldspathic porcelain was lowest in n-value, while the fine-grain ceramic had the highest n-value. No differences were found for the feldspathic porcelain with respect to n measured in water and in the artificial saliva. Lifetime prediction curves in 37 degrees C water, constructed from the n-values and inert strengths, showed that fatigue failure within five years is a good possibility for feldspathic porcelain specimens at stress levels which can reasonably be anticipated to occur in the oral environment. Little likelihood of failure was perceived for the fine-grain ceramic. The aluminous porcelain was intermediate between these two materials with respect to failure probability.

[Carbamazepine-induced agranulocytosis. Apropos of 2 cases]. / Agranulocitosi indotta da carbamazepina. A proposito di due casi.

Carbamazepine-induced agranulocytosis (CIA) is a rare event. We report on two cases, highlighting the wide variability of the bone marrow, which may show pseudohypercellularity with disappearance of neutrophils and excess of immature cells (myeloblasts and promyelocytes), thus mimicking the features of acute myeloid leukemia. Although its pathogenesis is still unclear, CIA must be considered as an idiosyncratic hemopathy and moreover it appears to be an unpredictable complication among patients taking the drug. It should be clearly distinguished from the benign neutropenia frequently associated with carbamazepine therapy and often self-limiting. Anyhow a careful clinical and hematological monitoring is the only mean to recognize promptly this life-threatening disease and to treat it with the withdrawal of the drug and the administration of an adequate anti-infectious therapy.

Fluoride-tolerant mutants of Aspergillus niger show enhanced phosphate solubilization capacity.

P-solubilizing microorganisms are a promising alternative for a sustainable use of P against a backdrop of depletion of high-grade rock phosphates (RPs). Nevertheless, toxic elements present in RPs, such as fluorine, can negatively affect microbial solubilization. Thus, this study aimed at selecting Aspergillus niger mutants efficient at P solubilization in the presence of fluoride (F-). The mutants were obtained by exposition of conidia to UV light followed by screening in a medium supplemented with Ca3(PO4)2 and F-. The mutant FS1-555 showed the highest solubilization in the presence of F-, releasing approximately 70% of the P contained in Ca3(PO4)2, a value 1.7 times higher than that obtained for the wild type (WT). The mutant FS1-331 showed improved ability of solubilizing fluorapatites, increasing the solubilization of Araxá, Catalão, and Patos RPs by 1.7, 1.6, and 2.5 times that of the WT, respectively. These mutants also grew better in the presence of F-, indicating that mutagenesis allowed the acquisition of F- tolerance. Higher production of oxalic acid by FS1-331 correlated with its improved capacity for RP solubilization. This mutant represents a significant improvement and possess a high potential for application in solubilization systems with fluoride-rich phosphate sources.

Glass transition temperatures of dental porcelains at high heating rates.

The glass transition temperature (Tg) of a dental porcelain is a factor in determining the magnitude of residual stresses introduced in a dental porcelain during cooling of a porcelain-fused-to-metal prosthesis. Tg is known to vary with changes in heating or cooling rate. However, available commercial instrumentation does not permit Tg to be obtained at the very high cooling rates commensurate with actual dental laboratory practice. Tg values are reported here for a number of commercial dental porcelains and other materials. These data were obtained by the bending beam technique, employing a special low thermal-mass furnace to permit rapid heating and cooling rates. Measurements were made at rates as high as 600 degrees C/min. Coefficients of determination (r2) for 1/Tg vs. ln (heating rate) were excellent. This relation is consistent with previously reported low rate Tg data obtained by a different technique.

In vitro IgE inhibition in B cells by anti-CD23 monoclonal antibodies is functionally dependent on the immunoglobulin Fc domain.

CD23, the low affinity receptor for IgE (FcvarepsilonRII), is involved in regulation of IgE synthesis by B-lymphocytes. Five monoclonal antibodies to human CD23 were generated from cynomolgus macaques immunized with purified soluble CD23 (sCD23). Four of the five primate antibodies blocked the binding of IgE complexes to CD23 positive cells and also inhibited the production of IgE in vitro by IL-4 induced human peripheral blood mononuclear cells (PBMC). The variable domains of several primate antibodies were utilized to construct chimeric macaque/human (PRIMATIZED((R))) monoclonal antibodies. PRIMATIZED((R)) p5E8G1, containing human gamma 1 constant region, inhibited IgE production in vitro as efficiently as the parent primate antibody, but the human gamma 4 constant version, PRIMATIZED((R)) p5E8G4, was not as effective in IgE inhibition. An F(ab')(2) of p5E8G1 did not inhibit IgE production but did interfere with IgE inhibition by the intact anti-CD23 antibody in a dose dependent fashion. The murine monoclonal antibody MHM6 recognizes human CD23 at a different epitope than primate antibody 5E8, and inhibits IgE production by IL-4 induced PBMC. As with the F(ab')(2) of p5E8G1, the F(ab')(2) of MHM6 also failed to inhibit IgE production. These data imply that the mechanism by which anti-CD23 antibodies inhibit IgE production requires cross-linking of CD23 to an IgG receptor. These data also imply that neither bivalent cross-linking of CD23 alone or inhibition of CD23 binding to its natural ligands is sufficient to inhibit IgE production.