Setting characteristics of five autopolymerizing resins measured by an oscillating rheometer

Statement of problem. Ease of handling and the working time of autopolymeri zing resins are directly associated with the setting characteristics during polymerization. Purpose. This study assessed the setting characteristics of autopolymerizin g resins by measuring viscosity changes and tested the hypotheses that: (1) different products have different viscosity increase patterns during polym erization, and (2) the increased rate of viscosity is not proportional to t he length of the setting time. Material and methods. Viscosity change during polymerization was measured i n 5 test materials (Unifast II, ADFA, META FAST, Miky, and Trim) with an os cillating rheometer. The working time was defined as the time required for a 5% reduction in the amplitude of the rheometer trace. The setting time wa s measured as the time required to reach zero amplitude on the rheometer tr ace. Results. The order of working times from longest to shortest was Trim, Unif ast II and META FAST, ADFA, Miky (ANOVA, P<.0001). The order of setting tim es from longest to shortest was Trim, META FAST, Miky, ADFA, Unifast II. Ma terials that had rapid setting times did not necessarily have short working times. Unifast II showed well-balanced setting properties that satisfied b oth longer working time and faster setting time. Conclusion. Autopolymerizing resins have setting characteristics specific t o the brand. Knowledge of these characteristics is essential for selection of the appropriate resin product depending on the purpose of clinical usage and the individual dentist's technique.