Influence on dimensional accuracy of volume of wash material introduced into pre-spaced putty/wash impressions

This study compared the accuracy of stone models obtained from two-stage, pre-spaced putty/wash impressions under conditions in which known volumes of wash material were introduced during the second stage of the impression: Group I, a quantity of wash material corresponding to the space provided; Group II, double the quantity of wash material as the space provided; Group III, double the quantity of wash material, but with V-shaped vents in the putty for escape of excess material. Percentage deviations of the vertical dimensions of stone dies with respect to the master model were significantly different between Groups I and II (the latter being shorter) (p < 0.05). For horizontal dimensions, differences were less consistent, although the deviations for Groups I and II and Groups II and III, with respect to the master model, were significantly different from each other for two of the three dimensions measured (Group II inter-abutment distances were generally larger) (p < 0001 and p < 0.05, respectively). It is concluded that putty recoil, resulting from compression by excess wash material, plays a significant role in the undersizing of working dies, although the level of clinical relevance is less clear.