Kinetic studies of the effect of varnish on water loss by glass-ionomer cements.
OBJECTIVE
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 (6mmdiameterx2mm depth) were prepared and cured for 10min at 37 degrees C. They were exposed to a desiccating environment over H(2)SO(4) 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 6h, 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.


CONCLUSIONS
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.
Nicholson
John W
JW
Department of Chemical and Pharmaceutical Sciences, University of Greenwich, Medway Campus, Chatham, Kent ME4 4TB, United Kingdom. J.W.Nicholson@gre.ac.uk
Czarnecka
Beata
B
D003890:Desiccation; D005899:Glass Ionomer Cements; D007700:Kinetics; D008422:Materials Testing; D010150:Paint; D014867:Water / Q000737:chemistry*
D005899:Glass Ionomer Cements; D014867:Water