Prominence of Cu in a plasmonic Cu-Ag alloy decorated SiO2@S-doped C3N4 core-shell nanostructured photocatalyst towards enhanced visible light activity.

A series of Cu-Ag bimetal alloys decorated on SiO2 and the fabrication of few-layer S-doped graphitic carbon nitride (SC) warped over it to form a core-shell nanostructured morphology have been demonstrated and well characterized through various physiochemical techniques. HRTEM data confirmed the formation of a compact nanojunction between the SiO2 and SC, where Cu-Ag is embedded uniformly with an average particle size of 1.3 nm. The Ag : Cu (1 : 3) between SiO2 and SC produces 1730 µmol h-1 g-1 of H2 under visible light illumination. Moreover, 6.2-fold current enhancement in the case of Ag : Cu (1 : 3) as compared to the Ag-loaded core-shell nanostructured photocatalyst indicates higher electron-hole-pair separation. The excellent activity was due to the synergistic alloying and plasmonic effect of Ag and Cu. DFT studies reveal that the Cu atom in the Cu-Ag bimetal alloy plays a pivotal role in the generation of H2, and the reaction proceeds via a 4-membered transition state. The mechanistic insight proceeds from the generation of hot electrons due to the LSPR effect and their transfer to the SC layer via a compact nanojunction.

Flexural behavior of visible light-cured composites as a function of temperature under water immersion test conditions.

OBJECTIVES: The purpose of this study was to investigate the effect of temperature of the flexural behavior for four visible light-cured hybrid composite materials. METHODS: Light-cured samples were post-cured for 24 h at 37 degrees C in 100% relative humidity prior to testing. Flexural tests were performed at the following water immersion temperatures: 5, 15, 25, 37, 45 and 55 degrees C, as well as in the dry condition which served as control. The following flexural property parameters were obtained as a function of test temperature: flexural strength, sigma fs, flexural modulus, Efs, flexural stress at 0.06% total offset strain, 0.06% (yield stress), and the total displacement at fracture, delta fs. Statistically significant differences (p < 0.01) in flexural parameters were noted for all the materials as a function of test temperature. RESULTS: The yield stress, sigma 0.06% was found to be most sensitive to thermomechanical changes. The results of this study indicate significant softening due to temperature under wet immersion test conditions for all materials. The temperature range at which two of the materials show significant reduction in yield stress compare well with "Wet Tg" values obtained by dynamic thermal mechanical analysis (Culbertson et al., 1990; 1991). SIGNIFICANCE: The effect of damage accumulation on surface or subsurface microstructure due to transient thermomechanical loads needs to be taken into account in the correlation of in vitro and in vivo wear or creep behavior.

Removal of intrinsic enamel stains with vital bleaching and modified microabrasion.

This study utilized a vital bleaching agent as well as an enamel microabrasion compound with low hydrochloric acid concentration to remove intrinsic stains on the facial surfaces of anterior teeth. In addition, scanning electron microscopic analyses of enamel from extracted teeth compared the etching pattern of the commercial compound used in this study to 18% hydrochloric acid. Type 1 and Type 2 etch patterns were observed with 18% hydrochloric acid after 5 and 20 seconds, respectively. Milder and more diffuse etch patterns were observed with the enamel microabrasion compound. A conservative form of treatment to remove intrinsic stains would employ the use of a vital bleaching agent, followed by an enamel microabrasion compound.

Evaluation of a no-rinse enamel conditioning prior to sealant application: an in vitro study of comparison to traditional etching technique.

Moisture contamination is a major factor in sealant application, often determining clinical success or failure. A new enamel conditioner using HNO3 (2.5%) has been introduced that does not require a water rinse after etching. The aim of this study is to compare etching characteristics using sealant retention from shear bond strength tests for traditional etch conditioning using H3PO4 (37%) and the HNO3 (2.5%) conditioner with and without a water rinse. We used 28 crown-intact extracted human teeth. We evaluated eight shear bond strength tests per group, on cylindrical sealant stubs (3.24 mm diameter x 3 mm height) for 12 groups (three etch conditions, two prophylactic methods, and two enamel surface type). The highest mean values of shear bond strength of 22.0 MPa was measured for H3PO4, and the lowest of 12.7 MPa for HNO3 (2.5%) without water wash. No significant differences (P < 0.05) were found between water rinse and air blast post-treatment groups after HNO3 conditioning.

At-home bleaching system: effects on enamel and cementum.

An analysis by scanning electron microscopy was undertaken to investigate the effects of bleaching on enamel-cementum surface morphology. Teeth were investigated in five groups: control; vital bleached for 5, 15, and 30 days; and 37 percent phosphoric acid gel etched for 20 seconds. Only the gel-etched group exhibited etching patterns. Shade change in vital bleached teeth was noted in the group vital bleached for 30 days.

Addition of fresh amalgam to existing amalgam: microleakage study.

The purpose of this in vitro study was to determine whether adhesive lining materials reduce microleakage in amalgam restorations, and to observe the degree of microleakage at the interface between freshly placed (new) and existing (old) amalgam. Forty-eight specimens were used in the experimental groups. The materials used to study microleakage in this investigation were: copal varnish, a dentin bonding agent (Clearfil New Bond), and a 4-META adhesive (Amalgambond). No significant difference in microleakage was found at the interfaces between freshly placed and existing amalgam. Significantly less microleakage was noted in specimens using the 4-META adhesive and the dentin bonding agent as compared to specimens in which no lining material was placed. Significantly less microleakage was noted in specimens using the 4-META adhesive compared to specimens using cavity varnish.

Bonding fresh amalgam to existing amalgam: a shear and flexural strength study.

The purpose of this study was to compare the shear and flexural strength obtained when various adhesives or liners were used to bond freshly placed amalgam to existing amalgam. The adhesives used in this study were the following: cavity varnish, 4-META adhesive (Amalgambond), and a dentin bonding agent (Clearfil New Bond). After samples were fabricated, shear bond strengths were determined by using an Instron Testing Machine, and flexural strengths determined using a Material Test System (MTS) testing machine. All test groups produced shear and flexural strengths less than one half of the control group. The dentin bonding agent and the 4-META adhesive produced significantly higher shear and flexural strengths than the test group in which no lining material was used.

The effect of three polishing systems on the surface roughness of four hybrid composites: a profilometric and scanning electron microscopy study.

A highly polished composite restoration is necessary to help promote a plaque-free environment. In this study the polishability of four hybrid composites (Pertac, APH, Herculite, and Z100) was compared after finishing and polishing with the Caulk Enhance polishing kit, Kerr composite finishing kit, and the ESPE MFS/MPS polishing kit. Profilometric evaluation revealed that the MFS/MPS polishing system gave a superior polish for Z100, Herculite, and Pertac; the Enhance polishing system demonstrated the poorest polish with all four composites tested. There were no significant differences among the four composites when polished with each of the three polishing systems.

Flexural behaviour of post-cured composites at oral-simulating temperatures.

Post-curing treatments have been known to improve the mechanical stability of visible light-cured composites. After individual post-curing treatment, the flexural strength (FS) of four commercial direct/indirect placement composite materials which differ greatly in composition [oligocarbonate dimethacrylate (OCDMA)-based Conquest C & B (CQT), Bisphenol-A glycidyl dimethacrylate (BisGMA)-based Charisma, urethane dimethacrylate (UDMA)-based Concept (CCT), and BisGMA/UDMA-based Dentacolor] was evaluated under water in the temperature range of 12-50 degrees C. A control series was tested in air at room temperature (25 +/- 1 degrees C). Data were analysed using ANOVA and Duncan's test. Flexural strengths overall decreased (20-40%, P < 0.01) with increasing temperatures except with Conquest C & B. Surprisingly, higher FS values were found in wet conditions than in dry conditions at 25 degrees C. UDMA-based materials much more easily undergo softening in water and by temperature change than do BisGMA- or OCDMA-based materials. Post-cured composites can be significantly affected by exposure to oral environments. Different composition determines the degree of influence.