Abstract
A new measuring method for mechanical pressure was recently developed by Fuji Film Company and was quickly introduced into the dental profession. It consists of two sheets, each having a different formation. When these sheets are pressed together, one of them develops a red color pattern measuring the density in proportion to the intensity of pressure exerted. At present three types of sheets are available-low, intermediate and highpressure sheets.
A study was made to determine the effects of this method on measuring pressure. The results indicated that pressure from 8 to 450 kg/cm2 can be measured with an accuracy of 2.0 kg/cm2 in low-pressure sheet, 8.0 kg/cm2 in intermediate and 20.0 kg/cm2 in high and that humidity had to be precisely controlled during the measurement. For instance, the same loading of 44 kg/cm2 against low-pressure sheet brought various values of color density from 0.94 (22.0°C, 50%) to 1.35 (23.5°C, 83%) in accordance with the grade of humidity.
The sheets didn't keep their original color density, but changed, espcially within the first 5-10 days after loading. During this change there was a specific density area near 1.25 where there was only a slight change in its density. Density thicker than this value became thinner and density thinner than 1.25 became thicker. After this changing period the sheets kept their concentration for 4 months.
