The effects of drying techniques on the compr-essive strength of gypsum products

الملخص EN

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.

Specimens were divided into six groups of 10 identical .25 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.