Comparison of Elastomer Tear Strengths Immediately and After 24 Hours

Objectives: We studied immediate and 24 hour tear strengths of five currently-used elastomers. Marginal tearing of an elastomer damages the accuracy of a dental impression. During mouth removal and/or cast separation by dental personnel, impression material may tear, causing a repeated impression procedure or an ill-fitting restoration. Thus, elastomer tear strength must be robust enough to present providers with predictable and reliable attributes.
Methods: Five low viscosity, fast set materials were tested: Impregum Soft Quick Step LB (3M Oral Care), VPS Hydro LB (Henry Schein), Take 1 Advanced LB Wash Super Fast (Kerr), Imprint 4 Super Quick Light (3M Oral Care), and Aquasil Ultra+ LV Fast Set (Dentsply Sirona). Axial notch specimens measuring 102 mm x 19 mm with a central notch of 120 µm were made in a proprietary stainless steel injection mold. The mold was conditioned at oral cavity temperature, ~35 ^oC, the materials were quickly injected into the mold which was plunged into a 35 ^oC water bath. For the “immediate group,” at the stated mouth removal time, the mold was removed from the bath; it was opened and the specimen was retrieved and immediately installed into grips in a universal testing machine at a gauge length of 50 mm. At 508 mm/min, the specimen was elongated in tensile mode until failure. For the 24 hour group, the same testing was completed the following day after bench aging at 25 ^oC overnight. Five specimens were made for material/test time groups. Load at failure was recorded and used to calculate the tear strengths in MPa. Statistical analysis (α = 0.05) was carried out by ANOVA techniques and the Tukey-Kramer HSD test identified differences among materials.
Results: Tear strengths of the two conditions are given in the following table. The strongest material was Aquasil Ultra+. The immediate group was weaker than the 24 hour group (p ≤ 0.001) and the individual materials were uniquely different from each other (p ≤ 0.0001.) Additionally, Impregum showed a 20% increase in strength after 24 hours, while the other products slightly improved by ~5%.
Conclusions: Aquasil Ultra+ was the strongest material tested herein and 24 hour aging improves tear strengths.