The tensile strength of the union between various glass ionomer cements and various composite resins*

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Abstract
Increasing use is being made of the glass ionomer cements as a lining for composite resin restorations, particularly when restoring posterior teeth. It has been suggested that it is possible to obtain a mechanical union between the two materials by etching the surface of the cement. This paper discusses the result of testing a broad variety of combinations of different glass ionomer cements and composite resins that have been reported on previously, and suggests that a number of factors need to be taken into account if the optimum physical properties are to be achieved from the union. There would appear to be four main factors which dictate the final strength of the union. The tensile strength of the cement itself is of primary importance and it seems the wettability of the resin bonding agent is also significant. When using some of the less heavily filled composite resins, the stresses set up by the setting contraction of the resin may be too great and, finally, the more heavily filled composite resins for restoration of posterior teeth often prove difficult to adapt to the underlying cement. With careful clinical handling, the so-called 'sandwich' technique is very useful. However, not all combinations of glass ionomer cement and composite resin will unite with sufficient strength to be successful clinically.