The influence of shelf life and storage conditions on some properties of composite resins.

This study demonstrated that the rate of strengthening and the ultimate strength of composite resins depend on the storage record of the material before polymerization. It is likely that both properties are related to the concentration of an effective initiator at the moment of use. For dental practice a somewhat delayed setting is inconvenient but acceptable. A decrease of ultimate strength, however, is an indication of less effective polymerization. Thus, premature disintegration may be expected from such material. Because no specification offers a measure for the shelf life of a composite resin, a reduction of the diametral tensile strength (for example, 20%) may be a useful test to indicate decomposition.