Setting characteristics of five autopolymerizing resins measured by an oscillating rheometer

Statement of problem. Ease of handling and the working time of autopolymerizing resins are directly associated with the setting characteristics during polymerization. Purpose. This study assessed the setting characteristics of autopolymerizing resins by measuring viscosity changes and tested the hypotheses that: (1) different products have different viscosity increase patterns during polymerization, and (2) the increased rate of viscosity is not proportional to the length of the setting time. Material and methods. Viscosity change during polymerization was measured in 5 test materials (Unifast II, ADFA, META FAST, Miky, and Trim) with an oscillating rheometer. The working time was defined as the time required for a 5% reduction in the amplitude of the rheometer trace. The setting time was measured as the time required to reach zero amplitude on the rheometer trace. Results. The order of working times from longest to shortest was Trim, Unifast II and META FAST, ADFA, Miky (ANOVA, P<.0001). The order of setting times from longest to shortest was Trim, META FAST, Miky, ADFA, Unifast II. Materials that had rapid setting times did not necessarily have short working times. Unifast II showed well-balanced setting properties that satisfied both longer working time and faster setting time. Conclusion. Autopolymerizing resins have setting characteristics specific to 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.