Tear Strength and Density of Set Alginates: Influence of Mixing

Methods: Four alginate impression materials (Cavex CA37, Zhermack Hydrogum, GC Aroma fine, Dentsply Blueprint) were either hand mixed or machine mixed by two different groups of operators (dental assistants or undergraduate students). The mixed alginate was placed in a standard mould according to ISO CD 21563 by one experienced investigator. Density was determined (micro scale; Mettler Toledo Academica XS 205 DU) and tear strength measured (universal testing machine; Zwick 1454; crosshead speed 400 mm/min) after storing the specimens (n=10 per group) at 35 °C in water for the manufacturers' recommended intraoral setting time. Statistical analysis was performed using parametric test procedures to identify the influence of material, mixing technique and operator (α=0.05).

Results: Tear strength ranged from 0.45 to 0.91 N/mm and density from 1.15 to 1.20 g/mm3. For all materials tested, machine mixing lead to a higher density (significant for all materials, p<0.05) and a higher tear strength (significant only for Blueprint, p<0.05). CA37 showed significantly higher tear strength values compared to all other materials tested (p<0.05). The operator group had no influence on the parameters tested (p>0.05).

Conclusion: Under the limitations of the study it can be concluded that density and tear strength of alginates are more dependant on the material used than on the mixing procedure applied or the operator.