Effect of surface condition and storage time on the repairability of temporary crown and fixed partial denture materials.

OBJECTIVES: The aim of the present study was to investigate which parameters (chemical nature, time after mixing, surface characteristics) might affect the repair strength of temporary crown and bridge materials (t-c&b). METHODS: Four different t-c&bs (Cool Temp Natural, Protemp 3 Garant, Structur Premium, Trim) were investigated using a shear-bond strength (SBS) setup. A cylinder (2 mm x 2.37 mm) of identical t-c&b (n=10) was bonded onto a specimen surface of either freshly set t-c&b (10 min after mixing) or onto specimens that were stored for 24h (37 degrees C, distilled water) and 7 days (thermocycling x 5,000, 5-55 degrees C=TC), respectively. The specimen surface was roughened with SiC paper (grit size 320) or left as it was (specimens stored for 10 min) prior to repair to retain the oxygen-inhibition layer. In addition, mono-block specimens were fabricated as control. The thickness of the oxygen-inhibition layer and the surface morphology was determined. Statistical analysis was carried out with an ANOVA followed by parametric tests (p=0.05). RESULTS: SBS values ranged from 10 to 40 MPa. Trim showed lowest SBS values for most storage conditions. Material, surface characteristics and time after mixing significantly affected the SBS (ANOVA p<0.001). TC significantly reduced the SBS (p<0.05) for all t-c&bs except for Trim (p>0.05). CONCLUSIONS: In case of monomethacrylates, storage and surface condition do not affect the repair strength. In contrast, the repair quality of dimethacrylates greatly depends on the material. In any case, roughening the surface is recommended, even if an oxygen-inhibition layer is present.

Clearance of low levels of HCV viremia in the absence of a strong adaptive immune response.

Spontaneous clearance of hepatitis C virus (HCV) has frequently been associated with the presence of HCV-specific cellular immunity. However, there had been also reports in chimpanzees demonstrating clearance of HCV-viremia in the absence of significant levels of detectable HCV-specific cellular immune responses. We here report seven asymptomatic acute hepatitis C cases with peak HCV-RNA levels between 300 and 100,000 copies/ml who all cleared HCV-RNA spontaneously. Patients were identified by a systematic screening of 1176 consecutive new incoming offenders in a German young offender institution. Four of the seven patients never developed anti-HCV antibodies and had normal ALT levels throughout follow-up. Transient weak HCV-specific CD4+ T cell responses were detectable in five individuals which did not differ in strength and breadth from age- and sex-matched patients with chronic hepatitis C and long-term recovered patients. In contrast, HCV-specific MHC-class-I-tetramer-positive cells were found in 3 of 4 HLA-A2-positive patients. Thus, these cases highlight that clearance of low levels of HCV viremia is possible in the absence of a strong adaptive immune response which might explain the low seroconversion rate after occupational exposure to HCV.

High rate of spontaneous clearance of acute hepatitis C virus genotype 3 infection.

Treating acute hepatitis C with interferon alpha prevents chronicity in nearly all cases when therapy is initiated within 3 months after infection. However, 15-50% of untreated patients may clear the hepatitis C virus (HCV) spontaneously. Therefore, factors are needed to identify patients prior to therapy who have a higher or lower risk for developing a chronic course to avoid unnecessary treatment. The role of the HCV genotype for spontaneous recovery from acute hepatitis C has been discussed controversially. In the year 2002, all 1,176 new incoming prisoners in a Northern German prison for young men (age 16-24) were screened for anti-HCV antibodies and 92 tested positive. Ninety eight percent of these reported i.v.-drug abuse for a median of 32 months prior to imprisonment. HCV-RNA negative individuals (21%) were serotyped and HCV-RNA positive patients were genotyped. The prevalence of HCV genotype 3 was significantly higher among individuals who had cleared HCV spontaneously as compared to chronically infected patients (86% vs. 38%; P = 0.002). Ninety three percent of individuals exposed to HCV genotype 1 but only 63% of individuals exposed to genotype 3 experienced a chronic course of the infection (P = 0.006). Thus, acute infection in young Caucasian men with HCV genotype 3 leads more often to spontaneous clearance than infection with HCV genotype-1. Considering also the high chance of successful treatment of chronic HCV genotype 3 infection with pegylated-interferon in combination with ribavirin, we suggest not to treat acute hepatitis C genotype 3 infection early but rather to wait at least 3 months after the onset of symptoms when chronicity becomes likely.

Binding analysis of 1alpha- and 17alpha-dihydrotestosterone derivatives to homodimeric sex hormone-binding globulin.

Binding studies of the interaction of immobilized 1alpha- and 17alpha-aminoalkyl derivatives of 5alpha-dihydrotestosterone (DHT) with purified N-deglycosylated homodimeric human sex hormone-binding globulin (SHBG) were performed using a surface plasmon resonance biosensor. These 1alpha- and 17alpha-derivatives with spacers of appropriate lengths between the amine function and the steroid ring skeleton enabled privileged, sterically undisturbed, interactions of either the 17- or 3-characteristic functional groups of DHT with SHBG. The association constants (K(a)1) for the binding of these immobilized DHT derivatives to the first binding site of SHBG, determined by SPR measurements, were 0.16 x 10(7) M(-1) for 17alpha-aminopropyl-17beta-hydroxy-5alpha-androstan-3-one (1), 1.64 x 10(7) M(-1) for 17alpha-aminocaproyl-17beta-hydroxy-5alpha-androstan-3-one (2), and 1.2 x 10(8) M(-1) for 1alpha-aminohexyl-17beta-hydroxy-5alpha-androstan-3-one (3). These values were compared with global K(a) data for the corresponding nonimmobilized DHT derivatives from equilibrium measurements using competitions with a tritiated testosterone tracer: the K(a) values were 1.25 x 10(7) M(-1) for 1, 1.50 x 10(7) M(-1) for 2, and 140 x 10(7) M(-1) for 3, confirming a remarkably high binding affinity of this latter compound for SHBG. A global fitting analysis of the biosensor data revealed that the interaction of the three immobilized steroids with SHBG was best described by a kinetic model assuming two structurally independent binding sites. This hypothesis of a bivalent binding model was also directly suggested by a dual fluorescent signal observed by the flow cytometry analysis of SHBG immobilized as a hybrid complex binding simultaneously two 1alpha-aminohexyl DHT ligands, one formed by 3, covalently coupled to phycoerythrin-labeled latex microspheres, and the other by the same DHT derivative, coupled to a fluorescein derivative (4).