Dimensional stability and weight changes of tissue conditioners

The dimensional stability of tissue conditioners characterizes the ability of the materials to yield accurate functional impressions of oral mucosa. This study evaluated the linear dimensional changes with time of six tissue conditioners (COE Comfort, FITT, GC Soft-Liner, Hydro-Cast, SR-Ivoseal and Visco-Gel) using a travelling microscope, and relationship between these changes and weight changes. The absorption and solubility of these materials were also determined. The percentage changes in dimension and weight in water storage were measured at 2 (baseline), 8 and 24 h, and 2, 4, 7, 14 and 21 days after specimen preparation. All materials except SR-Ivoseal exhibited shrinkage and weight loss during water storage, whilst SR-Ivoseal exhibited expansion and an increase in weight. The percentage solubility for all materials except SR-Ivoseal was higher than the percentage absorption. A positive linear relationship was found between the percentage changes in linear dimension and those in weight (r=0.797 - 0.986, P < 0.05). Water absorption and solubility of the materials were found to be associated with dimensional changes. The results suggest that the period recommended for forming functional impressions would be 24 h after insertion in the mouth. In addition, it is important to select tissue conditioners suitable for functional impressions because of the wide ranges of dimensional stability among the materials.