The intrinsic viscosities of fractions of poly(ethylene oxide) in the molecular weight range 1.5 × 103 to 106 have been measured at 25°C in benzene, carbon tetrachloride, and acetone; at 35°C in 0.45M aqueous potassium sulfate; and at 50°C in methyl isobutyl ketone and diethylene glycol diethyl ether. The latter three are practically theta solvents. The value of (r02/M)1/2 for poly(ethylene oxide) is calculated to be 0.84 Å from the molecular weights of the high molecular weight fractions, and their intrinsic viscosities in the theta solvents and acetone. Erroneous values result if the usual methods of determination are applied to the data obtained for the low molecular weight (<104) fractions or to the intrinsic viscosities in the very good solvents, benzene and carbon tetrachloride.

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A method for accelerating the dissolution and erosion of 'acidic' dental cements has been developed which gave relative solubilities in accordance with in vivo observations, in contrast to the conventional test. It involves subjecting 24-h-old specimens to a jet of dilute acid (lactic or citric) and determining weight loss. The relative ranking for 'acidic' cements in the apparatus and in vivo was: glass ionomer less than silicophosphate less than zinc phosphate less than polycarboxylate. The method was not valid for reinforced zinc oxide/eugenol/EBA cements. Of the two polycarboxylate cements studied, a brand which has the acid in the powder was found to be more soluble than the conventional material. It is proposed that the method be the basis of a new solubility/erosion test in national and international standards for 'acidic' dental cements.

A technique for measuring the shear bond strength of composites to etched enamel was developed. The importance of thorough washing of the enamel surface to remove deposits formed during etching was demonstrated by measurements of bond strength and by scanning electron microscopy. One of three orthodontic adhesive systems showed a highly significant increase in bond strength after immersion in water for three months. Etching times as short as five seconds gave a bond strength not significantly different from that obtained after a one-minute etch.