Effects of water-aging for 6 months on the durability of a novel antimicrobial and protein-repellent dental bonding agent

Biofilms at the tooth-restoration bonded interface can produce acids and cause recurrent caries. Recurrent caries is a primary reason for restoration failures. The objectives of this study were to synthesize a novel bioactive dental bonding agent containing dimethylaminohexadecyl methacrylate(DMAHDM) and 2-methacryloyloxyethyl phosphorylcholine(MPC) to inhibit biofilm formation at the tooth-restoration margin and to investigate the effects of water-aging for 6 months on the dentin bond strength and protein-repellent and antibacterial durability. A protein-repellent agent(MPC) and antibacterial agent(DMAHDM) were added to a Scotchbond multi-purpose(SBMP) primer and adhesive. Specimens were stored in water at 37 °C for 1, 30, 90, or 180 days(d).At the end of each time period, the dentin bond strength and protein-repellent and antibacterial properties were evaluated. Protein attachment onto resin specimens was measured by the micro-bicinchoninic acid approach. A dental plaque microcosm biofilm model was used to test the biofilm response. The SBMP + MPC + DMAHDM group showed no decline in dentin bond strength after water-aging for 6 months, which was significantly higher than that of the control(P < 0.05). The SBMP + MPC + DMAHDM group had protein adhesion that was only 1/20 of that of the SBMP control(P < 0.05). Incorporation of MPC and DMAHDM into SBMP provided a synergistic effect on biofilm reduction. The antibacterial effect and resistance to protein adsorption exhibited no decrease from 1 to 180 d(P > 0.1). In conclusion, a bonding agent with MPC and DMAHDM achieved a durable dentin bond strength and long-term resistance to proteins and oral bacteria. The novel dental bonding agent is promising for applications in preventive and restorative dentistry to reduce biofilm formation at the tooth-restoration margin.

Monthly Seasonality in the Top 50 Australian Stocks

We studied monthly seasonality in the top 50 Australian stocks across different industry sectors. Unlike other Australian studies, we examined monthly seasonality using stock return data of individual companies for the period of January 1980 through to August 2010. We found that stock returns of over half of the 50 companies are significantly positive in April and December, and most companies have low stock returns in October. Seven companies have higher returns in April than in other months of the year, most of which are banking and financial services companies, while six companies have lower returns in February than in other months. Although Australia has a July-June taxation cycle, we found that only three stocks have a July anomaly. The findings are inconsistent with the tax-loss selling hypothesis and other studies on the Australian equity markets （e.g., Brown, Keim, Kleidon, ＆ Marsh, 1983; Brailsford ＆ Easton, 1991）. However, our findings are generally consistent with Bonin and Moses （1974） on individual stock seasonality