AbstractPurposeThe objective of this preliminary laboratory study was to explore whether bioactive dental cements have the ability to seal marginal gaps as compared with other classes of dental cements.Materials and MethodsTooth discs (dentin/enamel) were positioned adjacent to a second disc of one of five possible dental cements (two bioactive and three conventional) and separated by a 50‐μm Mylar film, creating a controlled gap between the two discs. The edges of the tooth segments were abraded to expose dentin such that the dentin interface was positioned opposite the cement. The artificial gap assembly was stabilized with adhesive and composite resin. Artificial gap assemblies for each cement type were immersed in a phosphate‐containing, simulated body fluid (phosphate buffered saline) for up to 8 months. Occlusion of artificial marginal gaps (including deposition of crystal‐like, mineralized deposits within the gaps) was observed and scored categorically during the observation period. Deposition of radiodense material within the artificial marginal gap space was confirmed by micro‐computerized tomography analysis.ResultsThere was no evidence of marginal gap occlusion for the three conventional control cements, whereas both bioactive, surface apatite‐forming cements demonstrated occlusion of the artificial marginal gaps.ConclusionsThe preliminary findings of this initial study suggest the possible capability of surface apatite‐forming, calcium‐based, bioactive dental cements to seal or reseal artificial marginal gaps in simulated aqueous physiological conditions.Clinical SignificanceThe results of this laboratory study, although preliminary in nature, suggest a new functional property for bioactive dental materials, namely the ability to significantly improve marginal stability with tooth/restorative material interface. Such behavior in a restorative material could improve the survival and serviceability of dental restorations.