Mono-, di-, and trimethacrylates (monomers) are widely used in dentistry as restorative materials, adhesives, prosthetic devices, etc. It is known that the residual monomers released from the cured resin have been implicated in toxicological effects. In order to monitor the biological actions at the membrane level induced by monomers, we studied the changes in the phase transition temperature (T) and enthalpy (delta H) of dipalmitoyl-phosphatidylcholine liposomes induced by 37 different monomers using differential scanning calorimetry (DSC). The monomers that caused large changes in the T and delta H were vinyl monomers; acrylates; monomethacrylates that contain hydroxy, carbonyl, amino and phenyl groups; dimethacrylates with short-chain substituents; and aliphatic trimethacrylates. It is suggested that the changes in the T and delta H values may be due not only to hydrophobic interactions, but also to interactions induced by the double bonds or the functional groups in the monomers. On the other hand, methacrylates with simple alkyl ester linkage and dimethacrylates with bisphenol A groups exhibited the smallest changes. The changes in the T and delta H induced by highly hydrophobic methacrylates were small due to their slower interaction. These changes in transition properties of liposomes seem to be related to biological activities.

Acrylates↗

PubMedDate not supplied

Formyl-ended heterobifunctional poly(ethylene oxide): synthesis of poly(ethylene oxide) with a formyl group at one end and a hydroxyl group at the other end.

Well-defined poly(ethylene oxide) (PEO) with a formyl group at one end and a hydroxyl group at the other terminus was synthesized by the anionic ring opening polymerization of ethylene oxide (EO) with a new organometallic initiator possessing an acetal moiety, potassium 3,3-diethoxypropyl alkoxide. Hydrolysis of the acetal moiety produced a formyl group-terminated heterobifunctional PEO with a hydroxyl group at the other end.

Chromatography, Gel↗

PubMedDate not supplied

Comparative reduction of enamel demineralization by calcium and phosphate in vitro.

In theory, calcium and phosphate in the plaque fluid exert a large influence on the demineralization of enamel surface. In order to know the effect of increasing the concentration of either of these factors, the following in vitro experiment was conducted. Three thin sections, about 150 Im thick, were cut out from each of 13 human premolars. All surfaces of the sections, except for the original enamel surface, were coated with nail varnish. These sections were immersed into one of two sets of demineralizing solutions for 1 week at 25 degrees C. Each set, the 'calcium set' and the 'phosphate set', contained three solutions. The composition of these solutions differed mainly in calcium or phosphate concentrations. After 1 week, the degree of demineralization was determined by image analysis of contact microradiograms from each section. The subsurface demineralization in enamel was reduced by 95% by increasing the calcium concentration of the demineralizing solution from 7 to 21 mmol/l. A similar reduction (87%) was observed by increasing the phosphate concentration. However, the amount of phosphate needed was approximately 20 times more than that of calcium. The larger inhibitory effect that calcium has on enamel demineralization was related to the larger effect it has on the degree of saturation of the solution. Even though no statistically significant difference was found between the effect of calcium and phosphate on the demineralization of enamel (when the solutions had the same degree of saturation), the difference in the standard deviation of demineralization suggests the existence of some other factors which have an influence on the demineralization reaction.

Adolescent↗

PubMedDate not supplied

Permeation of lipophilic drugs through synthetic elastomers.

Permeability studies were carried out with three lipophilic drugs, namely, phenytoin and primidone (both widely used in the treatment of epilepsies and convulsive disorders), and dapsone (a sulfone antimicrobial agent used in the treatment of leprosy and to a lesser extent in dermatitis herpetiformis) through silica-filled poly(dimethyl siloxane) (Silastic) membranes, and anisotropic membranes of poly(ether-urethane)/poly(dimethyl siloxane) block copolymer (Avcothane, Cardiothane). These polymers are used in medical implants and in various cardiovascular devices. While both polymers were permeable to the drugs, the transport properties differed significantly. In the case of the poly(dimethyl siloxane) there was an initial large burst effect, followed by an exponential decrease in the rate of drugs released through the polymer films, although with dapsone the release rate became essentially constant between 100-180 h at 37 degrees C. In the case of the anisotropic films of the poly(ether-urethane)/poly(dimethyl siloxane) block copolymer, the permeabilities were much higher. Significantly, phenytoin exhibited essentially constant rate (zero-order) kinetics between 25-150 h, showing only a moderate burst effect that is probably not significant therapeutically. Importantly, dapsone showed neither a burst effect nor any significant time lag, and the release followed constant rate (zero-order) kinetics between 12-80 h, followed by only a moderate decrease in drug concentration up to 140 h (the experimental end-point). The diffusion coefficients calculated from initial desorption data at 37 degrees C for the poly(ether-urethane)/poly(dimethyl siloxane) block copolymer are as follows: phenytoin = 8.6 X 10(-9) cm2/s, primidone = 2.8 X 10(-9) cm2/s, and dapsone = 2.4 X 10(-8) cm2/s.(ABSTRACT TRUNCATED AT 250 WORDS)

Dapsone↗