Kinetic studies of the effect of varnish on water loss by glass–ionomer cements

Objectives This paper reports a study of the water loss behaviour of two commercial glass–ionomer cements coated with varnishes. Methods For each cement (Fuji IX Fast or Chemflex), specimens (6 mm diameter × 2 mm depth) were prepared and cured for 10 min at 37 °C. They were exposed to a desiccating environment over H2SO4 either uncoated or coated with the appropriate varnish (Fuji Varnish, a solvent-based lacquer, or Fuji Coat, a light-cured varnish). Four specimens were prepared for each material. They were weighed at hourly intervals for 6 h, daily for up to 5 days, then weekly thereafter until equilibration. Results Unlike the uncoated specimens, water loss from varnished cements was not Fickian, but followed the form: mass loss = A/t + B, where t is time, A and B are constants specific to each cement/varnish combination. A varied from 1.22 to 1.30 (mean 1.26, standard deviation 0.04), whereas B varied from 1.54 to 2.09 (mean −1.83, standard deviation 0.29). At equilibrium, varnished specimens lost much less water than unvarnished ones (p > 0.01) but there was no significant difference between the solvent-based and the light-cured varnishes. Significance Varnishes protect immature glass–ionomer cements from drying out by altering the mechanism of water loss. This slows the rate of drying but does not necessarily change the total amount of water retained. It confirms that, in clinical use, glass–ionomer restoratives should be varnished to allow them to mature satisfactorily.