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 modulus G', loss shear modulus G" were calculated from the measured strain-stress curves. Time to reach the complex modulus G^* of 10 MPa was determined. The G^* and time to reach the G^* 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 modulus G" 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.

This study was aimed to develop an instrument for real-time measurement of fluid conductance and to investigate the hydrodynamics of dentinal fluid. The instrument consisted of three parts; (1) a glass capillary and a photo sensor for detection of fluid movement, (2) a servo-motor, a lead screw and a ball nut for tracking of fluid movement, (3) a rotary encoder and software for data processing.

To observe the blocking effect of dentinal fluid movement, oxalate gel and self-etch adhesive agent were used. BisBlock (Bisco) and Clearfil SE Bond (Kuraray) were applied to the occlusal dentin surface of extracted human teeth. Using this new device, the fluid movement was measured and compared between before and after each agent was applied.

The instrument was able to measure dentinal fluid movement with a high resolution (0.196 nL) and the flow occurred with a rate of 0.84 to 15.2 nL/s before treatment. After BisBlock or Clearfil SE Bond was used, the fluid movement was decreased by 39.8 to 89.6%.

Citations

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