The effect of storage media upon the surface microhardness and abrasion resistance of three composites

The effects of various storage media [distilled water, lactate (pH 4.0), and citrate (pH 6.0) buffers] upon the hardness and wear factor values of three composites [Occlusin (O), P-30 (P), and Fulfil (F)] were studied. Over the one-year storage period, the hardness of all three materials stored in citrate buffer was unchanged. In the case of P in water and all materials stored in lactate buffer, a reduction was observed. There was no significant difference (P greater than 0.05) between the wear factors of specimens after one year or one week of water storage. Specimens of F stored in citrate buffer had a wear factor (P less than 0.01) higher than that of those stored in water. The other materials were not affected by storage in the lactate or citrate buffers. A reduction in surface hardness for some materials did not result in an increase in wear rate. This indicates that the softening effect was limited to a thin surface layer. Although not significant in vitro, this effect would probably increase the rate of in vivo wear, since the softened material would be lost, exposing a fresh surface to further attack. This would adversely prejudice the material's long-term clinical durability by impairing its resistance to abrasion.