Forensic Microscope

Water uptake and water loss have been studied in a commercial resin-modified glass-ionomer cement, Fuji II LC, under a variety of conditions. Uptake was generally non-Fickian, but affected by temperature. At room temperature, the equilibrium water uptake values varied from 2.47 to 2.78% whereas at low temperature (12°C), it varied from 0.85 to 1.18%. Cure time affected uptake values significantly. Water uptake was much lower than in conventional glass-ionomer restorative cements exposed to water vapor. Loss of water under desiccating conditions was found to be Fickian for the first 5 h loss at both 22 and 12°C. Diffusion coefficients were between 0.45 and 0.76 x 10 ^-7 cm²/s, with low temperature diffusion coefficients slightly greater than those at room temperature. Plotting water loss as percentage versus s^-1/2 allowed activation energies to be determined from the Arrhenius equation and these were found to be 65.6, 79.8, and 7.7 kJ/mol respectively for 30, 20, and 10 s cure times. The overall conclusion is that the main advantage of incorporating HEMA into resin-modified-glass-ionomers is to alter water loss behavior. Rate of water loss and total amount lost are both reduced. Hence, resin-modified glass-ionomers are less sensitive to water loss than conventional glass-ionomers.

The paper describes the structure, growth and vitality of natural oak regeneration in relation to stand density. To gain a better understanding of regeneration strategies, the investigation was carried out in oak forest flood plains in Poland, which were flooded in the summer of 1997. To study the stand structure and regeneration, 108 circular plots were established in stands managed using the shelterwood system. In addition, five gaps were chosen in a stand managed using the group cutting system (Legnica forest district). The results of the study showed that oak regenerated spontaneously in all stands. The abundance and vitality of oak seedlings and saplings were very high. The number of oak seedlings and saplings significantly depended on stand density. The greatest maximum height was found in gaps (146.0 cm) and in a stand with open canopy (88.9 cm) in Wolów. In Wolów and Miekinia, the shortest oaks grew in the worst light conditions. To regenerate naturally, oak stands in preparatory cutting should be reduced in the number of trees per hectare to ~150 and decreased in basal area to ~26 m² ha^–1. The group cutting system can be used in oak stands growing on flood plain sites, but there is the danger of ground vegetation development in openings.