The determination of working time and gelation time of temporary soft lining materials.

OBJECTIVE: The purpose of this study was to establish a new method for the determination of working time and gelation time of temporary soft lining materials using a displacement rheometer. METHOD: A displacement rheometer (The Dental School, University of Newcastle, Newcastle upon Tyne, UK) was used to apply a rapid displacement of 0.25 mm held for 1 s at intervals of 60 s to samples of four temporary soft lining materials. Material displacement and elastic recovery at each test time was recorded. The test procedure was repeated three times at 23 degrees C and at 37 degrees C for each material. For one material, the displacement time was varied (1, 5, 10 s). The working time was defined as the time corresponding to the initial observation of elastic recovery at 23 degrees C. Gelation time was the time when a material achieved 95% of its maximum elastic recovery at 37 degrees C. Values were compared between materials using one-way analysis of variance and Student-Newman-Keuls test at the 5% level of significance. RESULTS: The gelation rate of all materials increased with increasing temperature although the extent of this influence varied between materials. The development of elastic recovery in the materials during gelation accurately fitted asymmetric sigmoids. The correlation coefficient (r) ranged from 0.982 to 0.999. Statistically significant variations in both the working and gelation times of the test materials were established. The time of displacement affected both the rate of development of elasticity and the value of elastic recovery but this effect was only statistically significant when the displacement time was increased to 10 s. SIGNIFICANCE: The displacement rheometer may be suited for use as a standard test method for the determination of the working time, gelation time and elastic behavior of temporary soft lining materials.