Abstract The presence of an interface gap around the periphery of old amalgam restorations in extracted teeth was confirmed by scanning electron microscopy (SEM) and light microscopy. Two fissure sealant resins (Concise White Sealant and Delton Fissure Sealant) were placed over amalgam margins in vitro and were found to occlude this gap. SEM studies permitted assessment of the integrity of the resin in the interface defect and degree of sealant penetration toward the enamel/dentine junction. Microleakage studies using dye immersion techniques confirmed the efficacy of sealants in limiting dye penetration. This study indicates that margins of amalgams may be sealed in vivo by this method, delaying the need for replacement of the old amalgam and potentially providing protection for the tooth from secondary marginal caries.