Long-term hygroscopic dimensional changes of core buildup materials in deionized water and artificial saliva.

The dimensional stability of core buildup materials plays an important role in clinical application. In this study, hygroscopic dimensional changes of four commercial core buildup materials were investigated in deionized water and artificial saliva for up to 150 days. Specimens were made within a customized cylindrical mold. The initial mass and the apparent mass in liquids were measured. All the tested materials showed hygroscopic expansion after a 150-days immersion time. Hygroscopic expansion of these four materials can partly compensate for the polymerization shrinkage. SDR showed the lowest hygroscopic expansion of the four tested materials when immersed in deionized water and artificial saliva. PC showed the highest hygroscopic expansion in deionized water, while LC showed the highest hygroscopic expansion in artificial saliva. In the case of different immersion solvents, osmotic pressure should be considered. For hygroscopic dimensional changes, the hydrophilicity of monomers and changes of intermolecular forces may be crucial factors.