Abstract
Excess water in set dental stone decreases its strength.
So different methods were used to expel excess water but the
compressive strength may be affected by drying technique.
The purpose of this study was to evaluate the compressive strength
of two types of set dental stone after air, conventional
oven and microwave drying techniques.
A total of 60 stone specimens (30 specimens made from
Silky Rock stone and 30 Zeta stone) were prepared by the aid
of an acrylic split mold according to ADA Specification No.
25. Specimens were divided into six groups of 10 identical
specimens for each. Then groups were either dried by air,
conventional oven or microwave oven. Using Unconfined
Compression Machine, the specimens were loaded by a cross
head speed of 1 mm/minute till the specimen being fractured.
The load required to fracture the stone specimens was recorded
and analyzed using analysis of variance followed by Duncan’s
Multiple Range Test for the statistical comparisons between
drying techniques at a significance level of p< 0.05, and
Student’s t–test was used to compare between the two stone
types.
The results revealed that high significant differences
were present between the different drying techniques
(p<0.0001) with air dried specimens were significantly stronger
than others and microwave dried specimens were significantly
stronger than conventional oven dried specimens. Silky
Rock (type IV) stone was significantly stronger than Zeta
(type III) stone (p<0.001).
From this study, it could be concluded that the highest
compressive strength can be obtained by air drying of the stone
for 24 hours, while microwave drying technique give better
results than conventional oven drying technique with the
advantage of time saving over the two other drying techniques.