An investigation into the compatibility of some irreversible hydrocolloid impression materials and dental gypsum products

Part I of this study considered the ability of alginate and gypsum combinations to reproduce a line on a test block. Part II describes a refined discriminatory procedure in the evaluation of the compatible combinations. Statistical analysis showed this procedure to be consistent, and that it could be expected to be repeatable. On the basis of this analysis, it was found that one alginate was clearly superior to all others, and that it was possible to distinguish a further group of combinations within the group that reproduced the 0.050 mm line. Surface treatment of the alginates by fixing solutions showed that none of the treated materials could be improved to the extent of equating them with the best of the naturally compatible combinations. It is recommended that manufacturers pay more strict adherence to the requirements of the ISO Standard with regard to the availability and recommendation of suitable compatible gypsum products, and also that perhaps the actual Standard should be modified to be more realistic in its demands, and more discriminatory in its evaluation procedure.