Influence of Water Exposure on the Tensile Strength of Composites

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Abstract
The objective of this study was to investigate whether water storage causes permanent damage to composites by determining how the tensile strength of nine different composite materials changes with both water storage and water storage followed by dehydration. Eighteen samples (ASTM-D Specification 1708-66) of each of the nine materials were prepared and divided into three groups of six samples each. Group I was stored dry at 60°C, while Groups II and III were stored in distilled water at 60°C. After six months, Groups I and II were subjected to tensile testing, while Group III was transferred to a desiccator and dehydrated for two weeks at 60°C before this group was tested in tension. Mean values, pooled by storage group independent of material, revealed a significant (p<0.05) reduction in strength for both Groups II and III relative to Group I. These findings prove that water has an irreversible effect on most dental composites. A comparison of Group II with Group III data revealed that the samples which were aged in water and tested (Group II) were significantly (p<0.05) weaker than the dehydrated samples (Group III). However, some products within Group III did not show any tendency to recover their strength after dehydration.