The objective of this clinical study was to determine the ability of an ultraconservative, sealed composite resin restoration, without a traditional cavity preparation and without the removal of the carious lesion, to arrest Class I caries. Tooth preparation was limited to placing a bevel in the enamel. These restorations were compared, over 6 years, with (10 ultraconservative, localized, sealed amalgam restorations with no extension for prevention and (2) traditional, unsealed amalgam restorations with the usual extension for prevention outline form. Caries was arrested by the ultraconservative, sealed composite resin restorations for 6 years. Complete sealant retention on the sealed amalgam restorations was somewhat lower than that on the sealed composite resin resotrations; conversely, p artial sealant retention was higher for the sealed amalgam group. The marginal integrity of the sealed amalgam restorations was significantly superior to that of the unsealed amalgam restorations. The sealant also protected Class I posterior composite resin restorations against wear.