A marginal gap exists between the amalgam restoration and the cavity walls. At this interface, there is a constant percolation of fluid containing ions, molecules and bacteria. With time, corrosion products of the amalgam components seal the gap at the amalgam/tooth interface. The corrosion processes for conventional and high copper amalgam and factors affecting the corrosion deposits are reviewed. Better amalgam adaptation to the cavity walls improves the chances of sealing the restoration by corrosion products. The effectiveness of cavity varnish in preventing microleakage until corrosive deposits are formed is discussed.
Temporary fillings are commonly used to seal endodontic access cavities between visits. IRM and Cavidentin were selected to represent two widely used groups of temporary filling materials. The first is a reinforced zinc oxide-eugenol preparation that is mixed at chairside, whereas the second is a ready-to-use calcium sulfate-based material that gained popularity due to its convenience of application. The seal provided by the aforementioned materials was studied using a radioactive tracer quantitative assay. When compared as passive temporary filling, the two provided a similar quality of seal. However, when subjected to repetitive "occlusal" cyclic loading of 4 kg, IRM was clearly superior to the calcium sulfate-based material. Whereas IRM maintained a reasonable seal, the calcium sulfate-based fillings deteriorated and lost the ability to seal. These results suggest that even though calcium sulfate-based materials may be useful when not subjected to any occlusal forces, IRM should be preferred whenever occlusal loads may be applied. Furthermore it is demonstrated that testing such materials for microleakage with no reference to mastication forces may be of limited value.
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