Assessment of microhardness and color stability of micro-hybrid and nano-filled composite resins.

BACKGROUND AND AIMS: Composite resins are among the most popular restorative dental materials because of the strength and esthetic properties. The goal of this study was to assess the effect of commonly consumed beverages on microhardness and color stability of microhybrid (MH) and nanofilled NF) composite resins. MATERIAL AND METHODS: 240 samples were prepared from the composite material [MH = 120 (material I) and NF = 120 (material II)] and allocated into eight groups of 30 samples. In each group, half of the samples were tested for microhardness and another-half for color stability. After baseline measurements, the samples were immersed in test media, that is, distilled water and beverages (tea, cola, and coffee) for 15 days. Microhardness and color stability measurements were carried out after 15 days to assess the effect of beverages. The color stability and microhardness values were compared and evaluated by analysis of variance (ANOVA) using Tukey's alteration test. RESULTS: It was reported that the microhardness decreased for both the materials after immersion in all the beverages. Percentage change in microhardness was considerably higher in material II in comparison to the material I in cola drink. Color change was significantly higher in material II compared to material I in water and coffee. Cola drink caused the maximum change in microhardness among all the beverages and coffee caused the maximum color change among all the beverages. CONCLUSION: Both composite materials (I and II) showed a reduction in microhardness and change in color after immersion in a different type of test media.

Investigations of some aspects of the spray process in a single wire arc plasma spray system using high speed camera.

A high speed camera has been used to record and analyze the evolution as well as particle behavior in a single wire arc plasma spray torch. Commercially available systems (spray watch, DPV 2000, etc.) focus onto a small area in the spray jet. They are not designed for tracking a single particle from the torch to the substrate. Using high speed camera, individual particles were tracked and their velocities were measured at various distances from the spray torch. Particle velocity information at different distances from the nozzle of the torch is very important to decide correct substrate position for the good quality of coating. The analysis of the images has revealed the details of the process of arc attachment to wire, melting of the wire, and detachment of the molten mass from the tip. Images of the wire and the arc have been recorded for different wire feed rates, gas flow rates, and torch powers, to determine compatible wire feed rates. High speed imaging of particle trajectories has been used for particle velocity determination using time of flight method. It was observed that the ripple in the power supply of the torch leads to large variation of instantaneous power fed to the torch. This affects the velocity of the spray particles generated at different times within one cycle of the ripple. It is shown that the velocity of a spray particle depends on the instantaneous torch power at the time of its generation. This correlation was established by experimental evidence in this paper. Once the particles leave the plasma jet, their forward speeds were found to be more or less invariant beyond 40 mm up to 500 mm from the nozzle exit.

Regeneration of plantlets in Sapindus trifoiatus L.

Continuous production of healthy plantlets of Sapindus trifoliatus L. was achieved via somatic embryos from long term cultures of an embryogenic mass (EM). A highly embryogenic culture of S. trifoliatus L. was obtained by recurrent embryogenesis from somatic embryos cultured on Murashige and Skoog's (MS) medium supplemented with kinetin (2.3 microM) and benzyladenine (8.8 microM). The cultures could be maintained without reduction of embryogenic competence for more than 20 months by subculture at 4 week intervals. About 90% mature somatic embryos on transfer to basal MS medium, germinated to plantlets, of which more than 70% survived when transferred to a sand and soil mixture in green house.