Commentary. Tear strength of five elastomeric impression materials at two setting times and two tearing rates.

UNLABELLED PROBLEM/AIMS: Thin sections of impression materials are susceptible to tearing in gingival crevices and interproximal spaces. This study measures the tear strength of six fast and regular set impression materials after different setting times and at different tearing rates. MATERIALS/METHODS Tear strength specimens were prepared of four addition silicone materials: Aquasil (Dentsply, Konstanz, Germany), Imprint 3 (3M ESPE, Seefeld, Germany), Stand Out (Kerr, Orange, CA, USA), Virtual (Ivoclar Vivadent, Schaan, Liechtenstein); one polyether material: Impregum (3M ESPE); and a new hybrid material: Senn (GC, Aichi, Japan) using a split mold. Specimens were divided into four groups (N = 5). Groups 1 and 2 were immediately removed from the mold and loaded in tension until failure using an Instron testing device (Instron Corp., Canton, MA, USA). Groups 3 and 4 were tested 24 hours after fabrication. Groups 1 and 3 were tested at 1 mm/minute, and groups 2 and 4 were tested at 500 mm/minute. RESULTS A two-factor analysis of variance (ANOVA) and Tukey's test revealed differences among material brands (alpha = 0.05) in all experimental groups. The polyether and hybrid material were in the lowest statistically significant ranking group for all experimental groups. A three-factor ANOVA determined that a 500 mm/minute tearing rate and a 24-hour set time produced higher tear strengths and that fast set materials produced greater tear strength than regular set materials. CONCLUSIONS Most addition silicone materials provide higher tear strengths than polyether and hybrid materials. Materials display higher tear strengths after longer set times and at faster tearing rates. Impressions should be removed from the mouth with the fastest possible speed. CLINICAL SIGNIFICANCE Addition silicone materials should be used in impressions requiring replication of gingival crevices or interproximal spaces to prevent tearing of thin sheets of material. Impressions should be removed from the mouth and separated from the model with the fastest possible speed.