Formation of crystals on the surface of calcium hydroxide-containing materials in vitro

The purpose of the present study was to examine the surface of calcium hydroxide-containing materials when treated in different in vitro conditions. Five calcium hydroxide-containing materials (Dycal, Nu-Cap, Life, Sealapex, and Apexit) and two control calcium hydroxide-free materials (Roth 811 and AH26) were tested. The materials were placed onto Teflon discs or root dentin samples; maintained in distilled water or phosphate-buffered saline, or culture medium supplemented or not supplemented with fetal calf serum; incubated at 37 degrees C in humidified atmosphere containing or not containing 5% CO2; and examined by scanning electron microscope. The results demonstrated precipitation of simple crystal units or organized crystalline structures in the calcium hydroxide-containing specimens treated in all experimental conditions, except those maintained in distilled water without 5% CO2. X-ray elemental microanalysis of the different crystalline structures showed one or two peaks corresponding to calcium or calcium and phosphorus. These data indicate that the crystals formed by reactions of calcium ions released from the calcium hydroxide-containing materials with the environmental ions might modify the material surface, especially in the presence of substrate adhesion molecules, such as fibronectin. This modification might play an important role in the regulation of cell adhesion and the initiation of new matrix synthesis.