Crack closure on rehydration of glass-ionomer materials

Moisture‐sensitivity of immature glass‐ionomer cements suggests that hydration‐induced volumetric expansion might close and potentially heal established cracks. Crack closure in glass‐ionomer cements (GICs) was observed following rehydration. Circular cavities were prepared in 15 teeth: 10 were restored with resin‐modified GICs (5 with Fuji II LC and 5 with Photac‐Fil) and 5 were restored with a conventional GIC (Fuji IX); all were dehydrated for 1 min with air and imaged immediately by confocal microscopy. Crack formation in each was located, after which water was placed on the surface and observed for 15 min via a CCD camera. Dehydration caused cracks with measurable gaps, while rehydration resulted in varying degrees of closure: closure was limited in the conventional GIC, and complete or near complete along part/s of the crack in the resin‐modified GICs. In all, closure movement became imperceptible after the first 10 min. Statistical analysis indicated no significant difference between the closure behavior of all materials. However, the resin‐modified GICs appeared to show a greater potential for closure of established cracks than the conventional GIC upon rehydration.