The effect of maturation on in-vitro erosion of glass-ionomer and other dental cements.

The clinical durability of restorations made using water-based materials depends upon the type of material used. Current specification tests cannot predict durability, possibly because these are carried out on samples matured for 24 hours whereas longer maturation times may be more relevant. The lactic acid jet test was selected as a test method, being believed capable of ranking materials in the same order of erosion resistance in vitro as found in vivo. The powder/liquid interaction (glass or zinc oxide with polymeric or phosphoric acid) was investigated by selecting glass-ionomer, zinc polycarboxylate, silicate and zinc phosphate cements, with emphasis placed on glass ionomers. Two test times, 24 hours and 2 months, were chosen, with eight samples for each material tested at each time. All glass ionomers showed a significant reduction in erosion rate with time; two zinc polycarboxylates also showed some reduction but not to a significant degree. The silicate and zinc phosphate cements increased in erosion rate but not significantly. It was concluded that materials using polymeric acids had erosion rates which reduced with time, significantly so for glass ionomers. This might explain their longevity over silicate cements.