Photopolymerization of dental composite matrices.

The kinetic behaviour of dental composite is traditionally studied, considering only the isothermal behaviour, whereas a fast and highly non-isothermal bulk polymerization is expected as a consequence of the significant heat developed due to the exothermic nature of the polymerization reaction. In this paper the photopolymerization kinetics of a commercial dental composite activated by visible light are analysed by differential scanning calorimetry. This technique is applied to determine the degree of reaction and the glass transition temperature of thin layers of the composite matrix, at different isothermal cure temperatures. A phenomenological kinetic model is then integrated with an energy balance in order to analyse the cure behaviour of thicker composite layers. The full model results indicate that non-isothermal cure conditions may be achieved, obtaining higher values for the glass transition temperature and the degree of reaction.

[Annual usage in a general hospital of antimicrobials and frequency of resistant bacterial strains (author's transl)]. / Consumo di antibiotici e resistenza batterica in ambiente ospedaliero.

The data concerning annual usage in a general hospital and the frequency of resistant bacterial strains, isolated from patients with urinary tract's infection from 1975 to 1977 were collected and statistically processed. It was noticed that the year by year variation of resistance were mainly confined to E. coli and P. mirabilis. Increasing resistance with time was found for E. coli with Co-trimoxazole, P. mirabilis with Cephaloridin and Gentamicin, Proteus indole-positive with Rifampicin. Reducing resistance with time was found for E. coli with Colistin and Rifampicin, and Klebsiella-Enterobacter with Rifampicin. Trende with usage were found for E. coli and Klebsiella-Enterobacter with Rifampicin (decreasing) and P. mirabilis with Cephalorin (increasing). Naturally, none of the above trends imply cause and effect.