By means of a reometer the changing flow properties of many dental materials during setting may be monitored.

With Wilson's reometer this is done the following way. The numbers in parentheses refer to the numbers in the photos. The shaft (2), which extends from the upper part, ends a small (adjustable) distance above the glass mixing pad (1) makes a very small twisting motion. The material under test is applied between the shaft and the mixing pad.
As the material is setting, the twisting motion is increasingly damped. From the output connector at the rear panel a voltage is available, which varies with the twisting motion between approximately -400 and +400 mV, as long as no damping occurs. 
In most cases this output is connected to a strip chart recorder to monitor the setting process in time.

In specific cases, which are not relevant to the Dental Materials Workshop, the twisting motion can be switched on or off with switch (3) and varied in speed from 10 to 60 cycles per minute (0.167 to 1 Hz) with dial (4).
During the Workshop the twisting is switched on permanently on its lowest frequency, i.e. switch (3) down and dial (4) completely to the left. To make sure that the setting process is influenced as little as possible the amplitude of the twisting motion is so small that it is invisible to the naked eye.

In many cases the setting reaction is rather sensitive to temperature. This requires that the reometer be switched on and set to the correct temperature a few minutes before it will be used (power switch on the rear panel) to allow for some time for the mixing pad to warm up. The LCD screen (6) indicates the temperature of the mixing pad. With switch (7) held to the left, the screen indicates the temperature set by dial (5).
The shaft (2) is not heated or cooled. To make sure that its temperature stays close to that of the mixing pad (1), the upper part should be kept hinged-down (as in the lower picture) as much as possible. Only during mixing or cleaning the upper part is raised.

The strip chart recorder is set to an input sensitivity of 1 Volt. The zero offset shift is adjusted to center the oscillating motion of the pen in the middle of the paper. The paper speed is set to 1 cm/min. Because of the constant speed of the paper it is not necessary to use a stopwatch with this test. At (0) the mixing started. Time (1) indicates the end of the mixing. For obvious reasons this moment cannot be read from the plot. (2) Marks the end of the working time. At (3) the material is completely set. 

It is usually possible to put the measured portions of the components of the tested material on the mixing pad, to the left and right of the shaft, so that these can adapt to the correct temperature, before mixing is started. Just before mixing you raise the upper part. As much as possible you do the mixing at and around the area where the shaft will be. To avoid air entrapment the material should be piled up with a convex top surface.
The reometer should be kept clean. Especially the container of the glass mixing pad should be perfectly clean to guarantee a good quality of the thermal contact.