The Influence Of Tubule Density And Area Of Solid Dentin On Bond Strength Of Two Adhesive Systems To Dentin

Purpose: To determine the correlation between the tubule density (TD) and the area occupied by solid dentin (ASD) with the bond strength of one conventional and one self-etching adhesive system to dentin. Materials and Methods: The crown of extracted human third molars was transversally sectioned with a diamond saw to expose either superficial, middle, or deep dentin. The three groups of dentin surfaces were randomly divided and bonded with either Clearfil Liner Bond 2V (LB) or Prime & Bond 2.1 (PB) adhesive systems according to manufacturer's directions. Resin composite buildup crowns (10.0 mm high) were incrementally constructed on the bonded surfaces and the teeth stored in water at 37°C. After 24 h of storage, the teeth were vertically, serially sectioned in both x and y directions to obtain several bonded sticks of approximately 0.7 mm2 cross-sectional area. Each stick was tested in tension in a EMIC DL-500 tester at 0.5 mm/min until failure. After testing, the dentin side of the fractured specimen was gently abraded with a 1000-grit SiC paper, etched with 37% phosphoric acid for 15 s and allowed to air dry. SEM micrographs at 1000X and 4000X magnification were taken to permit calculation of the TD (number of tubules/mm2) and ASD (% of total area) at the site of fracture. Correlation between TD and ASD with the bond strength data was performed by linear regression. All statistical analysis was done with a = 0.05. Results: Overall bond strength (MPa) for LB was 26.0 ± 10.2, and 42.6 ± 15.2 for PB. There was a significant direct relationship between bond strength and ASD for both materials (r2 = 0.20, p < 0.05 and r2 = 0.66, p < 0.01, respectively for LB and PB). PB bond strength dropped significantly as the TD increased (r2 = 0.63, p < 0.05), while LB was not sensitive to TD (r2 = 0.05, p > 0.05). Mean bond strength of PB was significantly higher than LB for both superficial and middle dentin (p < 0.05), while there was no significant difference for deep dentin (p > 0.05). Conclusion: Regional variations in TD and ASD may modify bond strength of both conventional and self-etching adhesive systems. 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Application of a bubble column for evaporative cooling and a simple procedure for determining the latent heat of vaporization of aqueous salt solutions

In this work we have studied the evaporative cooling effect produced in a continuous flow air bubble column, containing water and salt solutions. We have established that, at equilibrium, a significant reduction in temperature is produced in an insulated, continuous flow, bubble column. For example, with a continuous flow of inlet air at 22 °C, a water bubble column cools to about 8 °C, at steady state equilibrium. The cooling effect observed in a continuous bubble column of concentrated aqueous salt solution could be used for commercial applications, such as for evaporative cooling systems. We have developed a simple method, based on the steady state thermal energy balance developed in a bubble column, to determine the latent heat of vaporization of the liquid in the column. Only the equilibrium temperature of the bubble column, the temperature of the inlet gas and the hydrostatic pressure across the column need to be measured. This analysis has been used to determine the heat of vaporization for water and some concentrated salt solutions

A study of oil droplet coalescence

Oil droplets dispersed in water can be readily studied when they are coated with surfactants, which lower their interfacial tension and enhance their stability. Pure oil droplets are more difficult to study because of their high interfacial tension, which facilitates coalescence and the adsorption of contaminants. In this study, we have characterised the surface charging properties of a water insoluble oil, bromododecane, which has a density close to water. The small density difference allows us to study relatively large drops of this oil and to analyse its coalescence behaviour. The results obtained with this simple, surfactant-free, system suggest that an additional attractive force, such as the long range hydrophobic interaction, might be required to explain oil droplet coalescence behaviour

The effect of de-gassing on the efficiency of reverse osmosis filtration

Water permeated porous membranes, under a large hydrostatic pressure differential, are likely to create opportunities for vapour and dissolved gas cavitation, which will restrict water flow through the membrane void spaces. The formation of cavities within the voids may be facilitated by the presence of dissolved gases in water. Removal of these gases might, therefore, reduce or prevent cavitation and thereby increase the flow rate through the porous membranes used to purify water. Reverse osmosis (RO) membranes operate under high pressure differentials and will be very susceptible to cavitation reduced flow. It is well established that RO membranes have a lower water flux than expected and the reasons for this have yet to be identified. This study presents direct experimental evidence, obtained with a commercial RO unit, in support of an average increase in product flow-rate of up to 3-5%, on de-gassing the feed water, consistent with the proposed cavitation model

Further studies into oil droplet size manipulation

Recent work has shown that heating degassed oil-in-water emulsions causes a significant reduction in the oil droplet size. The results presented here report further work on the effect of changes in salt concentration, oil/water ratio, pH and heating, on the oil droplet sizes of dispersions produced by the de-gassing process. The change in particle or droplet size for long, straight chain hydrocarbon oils, dispersed in water by degassing, is also reported here. These oils, of 20-24 carbon units in length, are liquid when heated above 50 °C but are solid at room temperature. The particle size of these dispersions was also monitored during the phase transition from liquid to solid, on cooling

The effect of de-gassing on the efficiency of reverse osmosis filtration

Water permeated porous membranes, under a large hydrostatic pressure differential, are likely to create opportunities for vapour and dissolved gas cavitation, which will restrict water flow through the membrane void spaces. The formation of cavities within the voids may be facilitated by the presence of dissolved gases in water. Removal of these gases might, therefore, reduce or prevent cavitation and thereby increase the flow rate through the porous membranes used to purify water. Reverse osmosis (RO) membranes operate under high pressure differentials and will be very susceptible to cavitation reduced flow. It is well established that RO membranes have a lower water flux than expected and the reasons for this have yet to be identified. This study presents direct experimental evidence, obtained with a commercial RO unit, in support of an average increase in product flow-rate of up to 3-5%, on de-gassing the feed water, consistent with the proposed cavitation model

A study of oil droplet coalescence

Oil droplets dispersed in water can be readily studied when they are coated with surfactants, which lower their interfacial tension and enhance their stability. Pure oil droplets are more difficult to study because of their high interfacial tension, which facilitates coalescence and the adsorption of contaminants. In this study, we have characterised the surface charging properties of a water insoluble oil, bromododecane, which has a density close to water. The small density difference allows us to study relatively large drops of this oil and to analyse its coalescence behaviour. The results obtained with this simple, surfactant-free, system suggest that an additional attractive force, such as the long range hydrophobic interaction, might be required to explain oil droplet coalescence behaviour

Unusual properties of water: Effects on desalination processes

Recent research on the fundamental properties of liquid water has been applied to demonstrate potential new improvements to the three main technologies for desalination. They have demonstrated that the so-called 'inert' atmospheric gases, oxygen and nitrogen, have a significant influence, even at their relatively low level of solubility. For example, the almost complete removal of these dissolved gases enhances the dispersion of fine oil droplets in water, simply by shaking, without the need for added surfactants. Even more importantly, the almost complete degassing of liquid water significantly enhances its natural electrical conductivity. These discoveries have recently been applied to the development of ideas for the improvement of reverse osmosis and electrodialysis. In addition, investigations of the effect of salt on the dispersion of bubbles in water have allowed the construction of a high density air bubble column to transfer water vapour under controlled sub-boiling conditions

Changing the size of oil droplets dispersed in water without added surfactants

Electrophoresis studies on pure hydrocarbon oil droplets, dispersed in water, have established that a significant charge is naturally developed on the droplets surface due to the spontaneous adsorption of hydroxyl ions. It has subsequently been pointed out that this charge should ensure the meta-stability of fine, micron-sized oil droplets dispersed in water. Further studies have demonstrated that such dispersions can be produced by the vigorous shaking of de-gassed mixtures of oil and water. De-gassing appears to enhance the dispersion process and the natural charging of the oildroplets ensures their meta-stability. Using this enhanced dispersion process, we have found that subsequent heating and cooling cycles, carried out over several minutes, can alter the average droplet size and the droplet size distribution, in some cases producing narrower distributions