The purpose of the present study was to examine the effects of a newly developed water-soluble reduced chitosan on Streptococcus mutans, plaque regrowth, and biofilm vitality. A 1.0%, water-soluble reduced chitosan, with pH ranging from 6.0 to 6.5, molecular weights between 3,000 and 5,000 Da, and 70% degree of deacetylation, was used. To determine antibacterial and antiplaque potency of chitosan, minimal inhibitory concentrations (MICs) for S. mutans and S. sanguinis (formerly S. sanguis), short-term exposure to S. mutans, and clinical trial of plaque regrowth and biofilm vitality were conducted. Twelve dental students volunteered to participate in the 6-week, double blind, randomized clinical trial using the classical 4-day plaque regrowth design. The MIC of water-soluble reduced chitosan for S. mutans was 1.25 g/l. While the cells exposed to distilled water (DW) grew rapidly, with a maximum turbidity reached by 16 h postinoculation, S. mutans exposed to chitosan (5.0 g/l) exhibited a substantial delay in growth and reached a maximum turbidity by 32 h postinoculation. The chitosan solution reduced the plaque index and the vitality of the plaque flora significantly when compared to DW, but this was less than the reductions found with the positive control of 0.1% chlorhexidine solution. The water-soluble reduced chitosan exhibited potent antibacterial effect on S. mutans, and displayed a significant antibacterial and plaque-reducing action during the 4-day plaque regrowth.

There is no single standardised method of measuring the orientation of the acetabular component on plain radiographs after total hip arthroplasty. We assessed the reliability and accuracy of three methods of assessing anteversion of the acetabular component for 551 THAs using the PolyWare software and the methods of Liaw et al, and of Woo and Morrey. All measurements of the three methods had excellent intra- and inter-observer reliability. The values of the PolyWare software, which determines version of the acetabular component by edge detection were regarded as the reference standard. Although the PolyWare software and the method of Liaw et al were similarly precise, the method of Woo and Morrey was significantly less accurate (p < 0.001). The method of Liaw et al seemed to be more accurate than that of Woo and Morrey when compared with the measurements using the PolyWare software. If the qualified lateral radiograph was selected, anteversion measured using the method of Woo and Morrey was considered to be relatively reliable.

The effect of the molecular weight and acrylonitrile (AN) content of the styrene-acrylonitrile copolymer ( SAN ) on the morphology, mechanical properties, and rheological properties of acrylonitrile-butadiene-styrene terpolymer/poly ( I NTRO DU CTlO NBeing a most successful rubber-toughened thermoplastic, the acrylonitrile-butadiene-styrene terpolymer (ABS) is manufactured mainly by graft polymerization of acrylonitrile and styrene onto polybutadiene ( P B ) ( SAN-g-PB, or g-ABS ) , followed by blending it with free styrene-acrylonitrile copolymer (SAN) to form a multiphase polymer blend where rubber particles, viz., g-ABS forms a dispersed domain in the SAN matrix.'s2In the ABS resin, properties, notably the toughness, depend on a number of factors including the type, size, concentration of the rubber, and the adhesion between the rubber and m a t r i~.~-~ The effect of the grafting ratio6 and AN content7 of graft SAN on ABS properties was also extensively studied.ABS has certain limitations such as the lack of flame retardance, poor resistance to UV and ketone, in addition to relatively low use temperature. These limitations have been overcome to some extent by blending with other polymers including poly (vinyl chloride ) and polycarb~nates.~-'~ In our earlier studies of ABS/poly (methyl methacrylate) (PMMA) blends, 13*14 where three types of ABS having different AN content of matrix SAN ( 24,27, and 35% ) were used, it was found that ABS containing 24 and 27% AN formed miscible blends and the one containing 35% AN formed immiscible blends with PMMA. The miscibility of ABS/ PMMA blends seems to follow that of SAN/PMMA blends that show lower critical solution temperature at 7 I AN I 2%. In immiscible blends, synergism in terms of mechanical properties was obtained in ABS-rich compositions. The present work considers the ABS/PMMA blend at a specific composition of 60/40 by weight. Three types of base SAN having different molecular weights and/or different AN content were used. Combinations of these SANS led to the 13 different types of SAN, which are different in molecular weight and/or AN content. The difference in interaction with the rubber (AN content of graft SAN is 30%) and with the PMMA, in addition to the molecular weight effect, is considered with regard to morphological, mechanical, and rheological points of view.

To investigate die filling from a semisolid melt, a die was designed to cast a two-part test sample with restrictions in one part and steps of different thicknesses in the other. Several defect types were observed including surface eutectic segregation, gas holes with eutectic segregation, oxide flaws, and shrinkage porosity. The effect of melt injection velocity on liquid segregation in the cast parts was investigated using macro-microstructural observation and computer simulation. Process parameters to reduce liquid segregation were obtained by computer simulation. The effect of injection speed of the plunger tip on liquid segregation was most significant after the semisolid material had filled the runner. According to experimental and simulation results, liquid segregation could be removed by controlled high plunger speed (more than 0.3m/s).

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