A vertical measuring apparatus was devised by Fusayama and used for measuring the free setting expansion of hydrocal. This apparatus is very easy to use and is accurate enough.
Perfect curves of dimension, temperature and hardness of hydrocal during setting were made and compared in fig. 2. Plastone and Duroc were used as hydrocal material.
Their setting expansions occured at the time of the initial setting. The maximum expansion of Plastone was +0.54% 1 day after pouring, and that of Duroc was +0.05% 6 hours after pouring.
The maximum temperature rise from room temperature in the center of a 23×23×50 mm³ block of Plastone was 7.5°C 30 minutes after pouring. That of Duroc was 16°C 13 minutes after pouring. The times requested to reach to these peaks substantially corresponded with those of the highest piches of their setting expansions.
At first the hardness increased generally parallel to the curves of their setting expan-sions, and then continued to increase during their drying shrinkage also. They reached B. H. N 7 after 50 minutes in the case of Plastone and B. H. N 8.5 after 30 minutes in the case of Duroc. These results were about 60% of their final hardness measured after 1 week.
Elastic hydrocolloid impressions restricted the setting expansion of hydrocal poured in them to some extent. Harder impression colloid supported closer by tray walls restricted it more.
The Plastone models poured in various hydrocolloid impressions expanded after one day. This is illustrated in the following data :
Technicol-Plastone model +0.26 (±0.06) %
Algix-Plastone model +0.51 (±0.10) %
Deelastic-Plastone model +0.27 (±0.07) %
D. P. Im. Col.-Plastone model +0.35 (±0.09) %