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- Rheological characterization of thermoplasticized injectable gutta percha and resilon
- Juhea Chang, Seung-Ho Baek, In-Bog Lee
- J Korean Acad Conserv Dent 2011;36(5):377-384. Published online September 30, 2011
- DOI: https://doi.org/10.5395/JKACD.2011.36.5.377
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Abstract
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ePub Objectives The purpose of this study was to observe the change in the viscoelastic properties of thermoplasticized injectable root canal filling materials as a function of temperature and to compare the handling characteristics of these materials.
Materials and Methods Three commercial gutta perchas and Resilon (Pentron Clinical Technologies) in a pellet form were heated in the Obtura-II system (Obtura Spartan) at 140℃ and 200℃, and the extrusion temperature of the thermoplasticized materials was measured. The viscoelastic properties of the materials as a function of temperature were evaluated using a rheometer. The elastic modulus
G' , viscous modulusG" , loss tangenttan δ, and complex viscosity η* were determined. The phase transition temperature was determined by both the rheometer and a differential scanning calorimeter (DSC). The consistency of the materials was compared under compacting pressure at 60℃ and 40℃ by a squeeze test.Results The three gutta perchas had dissimilar profiles in viscoelastic properties with varying temperature. The phase transition of softened materials into solidification occurred at 40℃ to 50℃, and the onset temperatures obtained by a rheometer and a DSC were similar to each other. The onset temperature of phase transition and the consistency upon compaction pressure were different among the materials (
p < 0.05). Resilon had a rheologically similar pattern to the gutta perchas, and was featured between high and low-flow gutta perchas.Conclusions The rheological characteristics of the thermoplasticized root canal filling materials changed under a cooling process. The dissimilar viscoelastic properties among the materials require different handling characteristics during an injecting and compacting procedure.
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Original Article
- The change of the initial dynamic visco-elastic modulus of composite resins during light polymerization
- Min-Ho Kim, In-Bog Lee
- J Korean Acad Conserv Dent 2009;34(5):450-459. Published online September 30, 2009
- DOI: https://doi.org/10.5395/JKACD.2009.34.5.450
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Abstract
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The aim of this study was to measure the initial dynamic modulus changes of light cured composites using a custom made rheometer. The custom made rheometer consisted of 3 parts: (1) a measurement unit of parallel plates made of glass rods, (2) an oscillating shear strain generator with a DC motor and a crank mechanism, (3) a stress measurement device using an electromagnetic torque sensor. This instrument could measure a maximum torque of 2Ncm, and the switch of the light-curing unit was synchronized with the rheometer.
Six commercial composite resins [Z-100 (Z1), Z-250 (Z2), Z-350 (Z3), DenFil (DF), Tetric Ceram (TC), and Clearfil AP-X (CF)] were investigated. A dynamic oscillating shear test was undertaken with the rheometer. A certain volume (14.2 mm3) of composite was loaded between the parallel plates, which were made of glass rods (3 mm in diameter). An oscillating shear strain with a frequency of 6 Hz and amplitude of 0.00579 rad was applied to the specimen and the resultant stress was measured. Data acquisition started simultaneously with light curing, and the changes in visco-elasticity of composites were recorded for 10 seconds. The measurements were repeated 5 times for each composite at 25±0.5℃. Complex shear modulus
G *, storage shear modulusG ', loss shear modulusG " were calculated from the measured strain-stress curves. Time to reach the complex modulusG * of 10 MPa was determined. TheG * and time to reach theG * of 10 MPa of composites were analyzed with One-way ANOVA and Tukey's test (α= 0.05).The results were as follows.
1. The custom made rheometer in this study reliably measured the initial visco-elastic modulus changes of composites during 10 seconds of light curing.
2. In all composites, the development of complex shear modulus
G * had a latent period for 1~2 seconds immediately after the start of light curing, and then increased rapidly during 10 seconds.3. In all composites, the storage shear modulus
G ' increased steeper than the loss shear modulusG " during 10 seconds of light curing.4. The complex shear modulus of Z1 was the highest, followed by CF, Z2, Z3, TC and DF the lowest.
5. Z1 was the fastest and DF was the slowest in the time to reach the complex shear modulus of 10 MPa.
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