Undercut reproducibility of functional impression materials (tissue conditioners).

Impressions of a laboratory model of an edentulous ridge were made with three commercial tissue conditioners (FITT, Hydro-Cast and Coe-Comfort). Combinations of undercut dimensions and tray relief were tested by using three different sized trays with each tissue conditioner. Greater tray relief increased the accuracy of all materials tested; increasing ageing time from 7 to 24 h resulted in little change of accuracy of the stone models poured from the impressions taken.