ACCURACY OF IRREVERSIBLE HYDROCOLLOIDS (ALGINATES) FOR FIXED PROSTHODONTICS - A COMPARISON BETWEEN IRREVERSIBLE HYDROCOLLOID, REVERSIBLE HYDROCOLLOID, AND ADDITION SILICONE FOR USE IN THE SYRINGE-TRAY TECHNIQUE

One reversible, seven irreversible hydrocolloids and two addition sili cones were examined. The aim was to study their ability to reproduce s ix differently shaped abutments of a full arch stainless steel master model correctly, by measuring: 1) the accuracy of irreversible hydroco lloid impressions with different storage periods of 15 min, 2 h, 24 h and 95 h, reversible hydrocolloid stored 15 min and 2 h, and Type III addition silicones stored 24 h when the syringe-tray technique was use d; and 2) whether mixing technique or tray design had any influence of the accuracy of irreversible hydrocolloid impressions. All the tested impression materials had difficulties in producing full arch casts, w here the six abutments were correctly reproduced, because 58% of the h eights and 45% of the diameters of the occlusal surfaces were shorter than the corresponding distances of the master model. Storage time, mi xing technique and tray design were of significant importance for the irreversible hydrocolloids. Concerning the accuracy at the gingival ma rgin, a shorter storage time resulted in improved accuracy, and mechan ical mixing without a vacuum and a tray designed similar to a perforat ed stock tray gave most accurate impressions.