Volume contraction in photocured dental resins: the shrinkage-conversion relationship revisited.

Polymerization shrinkage and degree of conversion (DC) of resin composites are closely related manifestations of the same process. Ideal dental composite would show an optimal degree of conversion and minimal polymerization shrinkage. These seem to be antagonistic goals, as increased monomer conversion invariably leads to high polymerization shrinkage values. OBJECTIVES: This paper aims at accurately determining the polymerization volume contraction of experimental neat resins and to link it to the number of actual vinyl double bonds converted in single ones instead of, as generally done, to the degree of conversion. METHODS: Different mixtures of Bis-GMA/TEGDMA (traditionally used monomers) were analyzed. Contraction of the polymers was determined by pycnometry and the use of a density column. DC was determined by the use of Raman spectrometry. RESULTS: An univocal relationship has been found between the volume contraction and the actual number of vinyl double bonds converted into single ones. A contraction value of 20.39 cm3/mole (of converted C=C) was deduced from 27 measurements. SIGNIFICANCE: This relationship helps in finding solutions to the polymerization shrinkage problem. A reduction of the polymerization shrinkage due to the chemical reaction may obviously be expected from the addition of molecules allowing a decrease in the number of double bonds converted per unit volume of resin matrix, while maintaining the degree of conversion (of Bis-GMA and TEGDMA) and thus the mechanical properties. Further research will be directed at this objective.     

Drug-induced vitiligo: a case/non-case study in Vigibase®, the WHO pharmacovigilance database

Vitiligo is a common depigmenting disorder ensuing the loss of epidermal melanocytes. It is a multifactorial disease with immunological, genetic and environmental factors including drug exposure. The purpose of the study was to investigate the drugs and therapeutic subclasses associated with vitiligo occurrence reported in VigiBase^®, the WHO pharmacovigilance database. A case/non-case study was carried out by defining cases as vitiligo reports and non-cases as all other reports. The reporting odds ratio (ROR) was calculated for the ‘suspected’ drugs and drug classes according to ATC level 4. During the study period, 741 cases of vitiligo were registered. Mean age was 49 ± 20 years. The disproportionality analysis showed an association between vitiligo and pembrolizumab (ROR 116.9, 95% Confidence Interval (CI) 94.8, 144.3), nivolumab (ROR 22.6, 95% CI 15.8, 32.4), ipilimumab (ROR 41.7, 95% CI 25.0, 69.7), imiquimod (ROR 152.8, 95% CI 103.0, 226.7), adalimumab (ROR 3.8, 95% CI 2.5,5.8), infliximab (ROR 2.6, 95% CI 1.65, 4.01), alemtuzumab (ROR 27.8, 95% CI 17.6, 43.9), and ustekinumab (ROR 9.3, 95% CI 5.6, 15.6). Concerning the pharmacological classes ATC level 4, a significant association was found with monoclonal antibodies, interferons, selective immunosuppressants, TNF-alpha inhibitors, interleukin inhibitors, and topical antivirals. This study confirmed the expected associations between vitiligo and immune checkpoint inhibitors and strengthened the emerging signal about the association between vitiligo and imiquimod, TNF-alpha inhibitors and interferons. New signals were shown with selective immunosuppressants including alemtuzumab and interleukin inhibitors.     

The effect of antigen deprivation on thymus-dependent and thymus-independent lymphocytes in the small intestine of the mouse

Isografts of foetal small intestine, implanted under the kidney capsules of adult mice grow normally and, despite the lack of intraluminal antigenic stimulation, are populated by thymus-dependent and thymus-independent lymphocytes. The Peyer's patches in these grafts are very small, lack germinal centres and can be shown to have small thymus-dependent areas.

Quantitative intraepithelial lymphocyte counts were carried out in normally sited small intestine of immunologically intact and thymus-deprived mice, and in grafts implanted in intact and thymus-deprived mice. Counts were also performed in a group of neonatally thymectomized and control mice. The results show a significant depletion of intraepithelial lymphocytes in neonatally thymectomized mice, and a profound reduction in numbers of intraepithelial lymphocytes in grafts, deprived of antigen, when compared with normally sited intestine of the same age.

     

Toxoplasma gondii infection can regulate the expression of tumour necrosis factor-alpha receptors on human cells in vitro

The in vitro regulation of tumour necrosis factor (TNF)-alpha receptors during Toxoplasma gondii infection of human MRC5 fibroblasts and human myelomonocytic THP-1 cells was investigated. Cells were infected with the virulent RH of T. gondii. TNFR membrane receptors were analysed by flow cytometry with biotinylated TNF-alpha. Shedding of the soluble form of TNFR1 and TNFR2 in cell culture supernatants was measured by enzyme-linked immunosorbent assay, and expression of mRNA production of TNFR1 and TNFR2 was analysed by quantitative real-time polymerase chain reaction, 1 h after infection. In the MRC5 cell line, T. gondii infection did not induce any up- or down-regulation of membrane TNFRs, soluble TNFRs or mRNA of TNFRs. However, THP-1 cell infection with living parasites induced a significant soluble TNFR1 release by THP-1 cells after 1 h. We detected an approximately 50% up-regulation (P < 0.01) of soluble TNFR1 in infected THP-1 cells compared to controls. No change in soluble TNFR2 levels was observed in the same conditions. Moreover, infection decreased the level of TNF membrane receptors, but had no effect on TNFR1 and TNFR2 mRNA levels. TNFR modulation by T. gondii infection, in vitro, depends on the cell type. Furthermore, our data suggest that living parasites control the shedding of the soluble form of TNFR1. This mechanism may influence the role of TNF-alpha in toxoplasmosis.