Results of many trials have shown that fissure sealants can have a highly significant effect in the prevention of occlusal caries. The ultraviolet light cured materials appear to produce the most succesful and reproducible results. No evidence of caries or demineralization has been reported which could be related to acid etching of enamel. Several studies have shown that etched enamel, not covered by resin, will be remineralized on contact with oral fluid. There is evidence to support the argument that a small amount of undiagnosed caries at the base of the fissure would be arrested by the application of sealant. Larger carious lesions must be restored with a suitable material. Microleakage occurs at the margins of restorations as demonstrated in vitro by the use of an artificial caries technique in which 'outer' and 'cavity wall' lesions are produced. The incidence of cavity wall lesions is less if a composite material, rather than amalgam, is used. Microleakage may be decreased further by application of resin to the composite/enamel margins.