Effects of adhesive systems and luting agents on bonding of fiber posts to root canal dentin

The study evaluated the influence of different luting materials on the microtensile bond strength of glass fiber posts to root canal dentin. Thirty extracted maxillary premolars were endodontically treated, and the roots were prepared for post cementation using the FRC Postec system (Vivadent). Two luting materials (Multilink, Vivadent and Clearfil Photo Core, Kuraray) were used in combination with three adhesive: Multilink Primer (Vivadent), Clearfil Photo Bond, and Clearfil New Bond (Kuraray). A composite build-up was performed around the root to provide adequate gripping during testing. Specimens were cut to obtain beams with the post in the center and with the radicular dentin overlaid by the composite build-up on each side. Microtensile testing was performed with a universal testing machine at a cross-head speed of 0.5 mm/min. The failure mode was classified under a stereomicroscope and four representative beams of each group were selected for SEM analysis. Bond strength data that were analyzed with two-way ANOVA and Student-Newman-Keuls multiple comparisons tests revealed that adhesive systems, luting materials, and the interaction between these two factors significantly influenced the bond strength results (p < 0.01). Multilink applied with its own adhesive system obtained the best results, while the lowest bond strength was achieved with clearfil photo core in combination with multilink primer.     

Single-bottle adhesives behave as permeable membranes after polymerisation. II. Differential permeability reduction with an oxalate desensitiser

OBJECTIVES: This study examined the changes in hydraulic conductance and ultrastructure of dentine bonded with simplified etch-and-rinse adhesives to oxalate desensitiser pre-treated acid-etched dentine. METHODS: Human dentine disks were acid-etched, treated with an oxalate desensitiser (BisBlock, Bisco), and bonded with One-Step (OS), Single Bond (SB), OptiBond Solo Plus (OB) or Prime and Bond NT (PB). Similar disks from each group were acid-etched, and bonded without oxalate pre-treatment. Hydraulic conductance of the specimens was measured at 20 cm of water pressure and analysed with nonparametric statistical methods. Epoxy resin replicas of the smear layer-covered dentine and bonded dentine were examined with SEM for the extent of fluid transudation. Specimens bonded under perfusion were examined with TEM after tracer immersion. RESULTS: OB and PB exhibited a highly significant reversal of the reduced hydraulic conductance obtained with BisBlock on unbonded acid-etched dentine. Profuse water transudation across the bonded dentine was observed from the replicas. Adhesive interfaces were covered with spherical globules that interfered with dentine hybridization. Conversely, no significant difference in hydraulic conductance was observed in SB, between Bisblock pre-treated, unbonded and bonded acid-etched dentine. Significantly lower hydraulic conductance was shown on application of OS to Bisblock-treated acid-etched dentine. Water transudation was sparse, interfering surface globular structures were absent, and only angular subsurface crystals were seen in the dentinal tubules. CONCLUSIONS: Convective water fluxes through dentine may be reduced by applying Bisblock to acid-etched dentine before bonding with One-Step or Single Bond. However, reducing adhesive permeability with the use of oxalate desensitiser is not applicable to low acidity adhesives such as OptiBond Solo Plus and Prime and Bond NT.     

The adhesive strength of non-spherical particles mediated by specific interactions

The specific adhesive interaction between a non-spherical particle and a cell layer under a linear shear flow is analyzed. The effect of the characteristic particle size, expressed in terms of the volume V, and shape, expressed in terms of the aspect ratio gamma, on the adhesive strength is investigated. It is shown that for a fixed shape, there exists an optimal volume V(opt) for which the adhesive strength has a maximum. A surprisingly accurate relationship has been derived between the optimal volume V(opt) and the ratio microS/m(r) (wall shear stress to the receptors surface density) having the form V(opt)=alpha(m(r)/microS)(beta). Also, oblate particles have been shown to adhere more effectively to the biological substrate than classical spherical particles for the same volume V. As a consequence, non-spherical particles can carry a larger amount of drugs and contrast agents than classical spherical particles with the same adhesive strength, improving the therapeutic and imaging efficacy. The formulae and the procedures described in the present work can guide the optimal design of intravascularly injectable micro/nano carriers.     

Hippocampal cell proliferation across the day: increase by running wheel activity, but no effect of sleep and wakefulness

The present study investigated whether proliferation of hippocampal progenitors is subject to circadian modulation. Mice were perfused using 3h intervals throughout the light-dark cycle and brains were stained for Ki-67. Since Ki-67 is not expressed during the G0 phase of the cell cycle, we expected a decline in Ki-67 expression at the moment cells synchronously exit the cell cycle. However, despite the fact that various hippocampal factors fluctuate across the day, the number of dividing cells remained constant. In a second experiment, we studied whether disturbance of normal sleep affected the stable rate in cell proliferation. Our data show that 12h of sleep deprivation during the light phase did not influence proliferating cell number. A third experiment investigated whether physical activity, a condition known to enhance hippocampal cell proliferation, caused an elevation of the steady baseline number of proliferating progenitors, or a peak directly following the active phase of the animals. Mice were housed with a running wheel for 9 days. On the last day, animals were sacrificed either directly before or directly after the active phase. Exercise significantly promoted cell proliferation and this effect appeared to be strongest directly after the active period and to disappear during the resting phase. Our data suggest that hippocampal cell proliferation is not synchronized under basal conditions and is unchanged by sleep deprivation. However, running affected cell proliferation differentially at two times of day. These data demonstrate that the steady rate in cell proliferation is not indispensable, but can be changed by behavioral activity.     

Tertiary gain and disability syndromes

Since the introduction of the concept of tertiary gain by Dansak in 1973, there has been little further publication or research on this topic. Yet, tertiary gain is often the subject of debate amongst physicians, therapists, insurers, the media, and even at times the general public. Much of the controversy of disability syndromes and the health and economic burden they present has focused on secondary gain and illness behaviour. The role of tertiary gain in illness behaviour is likely also relevant, and a model of tertiary gain is needed to begin further understanding the implications of this phenomenon for patients and those who treat them. This article introduces a phraseology for tertiary gain, and models the effects of tertiary gain on illness behaviour and the interactions of secondary and tertiary gain in the setting of disability syndromes.     

Baseline-Dependent Effects of Cocaine Pre-Exposure on Impulsivity and D2/3 Receptor Availability in the Rat Striatum: Possible Relevance to the Attention-Deficit Hyperactivity Syndrome

We have previously shown that impulsivity in rats predicts the emergence of compulsive cocaine seeking and taking, and is coupled to decreased D_2/3 receptor availability in the ventral striatum. As withdrawal from cocaine normalises high impulsivity in rats, we investigated, using positron emission tomography (PET), the effects of response-contingent cocaine administration on D_2/3 receptor availability in the striatum. Rats were screened for impulsive behavior on the five-choice serial reaction time task. After a baseline PET scan with the D_2/3 ligand [¹⁸F]fallypride, rats were trained to self-administer cocaine for 15 days under a long-access schedule. As a follow-up, rats were assessed for impulsivity and underwent a second [¹⁸F]fallypride PET scan. At baseline, we found that D_2/3 receptor availability was significantly lower in the left, but not right, ventral striatum of high-impulsive rats compared with low-impulsive rats. While the number of self-administered cocaine infusions was not different between the two impulsivity groups, impulsivity selectively decreased in high-impulsive rats withdrawn from cocaine. This effect was accompanied by a significant increase in D_2/3 receptor availability in the left, but not right, ventral striatum. We further report that D_2/3 receptor availability was inversely related to baseline D_2/3 receptor availability in the ventral striatum of high-impulsive rats, as well as to the left and right dorsal striatum of both low-impulsive and high-impulsive rats. These findings indicate that the reduction in impulsivity in high-impulsive rats by prior cocaine exposure may be mediated by a selective correction of deficient D_2/3 receptor availability in the ventral striatum. A similar baseline-dependent mechanism may account for the therapeutic effects of stimulant drugs in clinical disorders such as ADHD.     

Probing the Binding Site of Bile Acids in TGR5

相似文献   

Leveraging nanochannels for universal,zero-order drug delivery in vivo

Drug delivery is essential to achieve effective therapy. Herein we report on the only implantable nanochannel membrane with geometrically defined channels as small as 2.5 nm that achieves constant drug delivery in vivo. Nanochannels passively control the release of molecules by physico-electrostatic confinement, thereby leading to constant drug diffusion. We utilize a novel design algorithm to select the optimal nanochannel size for each therapeutic agent. Using nanochannels as small as 3.6 and 20 nm, we achieve sustained and constant plasma levels of leuprolide, interferon α-2b, letrozole, Y-27632, octreotide, and human growth hormone, all delivered at clinically-relevant doses. The device was demonstrated in dogs, rats, and mice and was capable of sustaining target doses for up to 70 days. To provide evidence of therapeutic efficacy, we successfully combined nanochannel delivery with a RhoA pathway inhibitor to prevent chronic rejection of cardiac allografts in a rat model. Our results provide evidence that the nanochannel platform has the potential to dramatically improve long-term therapies for chronic conditions.