Print ISSN: 1812-1217

Online ISSN: 1998-0345

Keywords : dental stone

Evaluation of the Effect of Physically Magnetized Water on Some Properties of Dental Stone

Ahmed I. Jasim Al-Khyeat

Al-Rafidain Dental Journal, Volume 19, Issue 1, Pages 32-41
DOI: 10.33899/rden.2019.163420

Aims: to study the effect of interaction of dental stone with tap water and physically magnetized water on two periods of time 24h. and 12h to study the change in the physical properties of final product. Materials and Methods: We started prepair no. of control samples and other of samples interacted with physically magnetized water for two periods of time 24h and 12h, then we studied the liner setting expansion and compressive strength.. Results: results obtained from comparing control sample with that treated with physically magnetized water showed an increase in the compressive strength of physically magnetized group and decrease of linear setting expansion in comparison with that of control sample. Conclusion: Reaction of dental stone with physically magnetized water lead to change in some physical properties of dental stone.

Evaluation of Some Physical Properties of Locally Prepared Alpha-calcium Sulfate Hemihydrate

Lamia T Rejab

Al-Rafidain Dental Journal, Volume 13, Issue 1, Pages 14-20
DOI: 10.33899/rden.2013.84673

Aims: Aim of the study is to evaluate some physical properties of locally prepared dental stone form natural gypsum by two different calcination methods with autoclave with and without adding crystal habit modifier during calcination procedure for different periods of time. Materials and methods: The values of some physical properties that include specific gravity, water/ powder ratio and linear setting expansion of the prepared dental stone with autoclave with and without adding crystal habit modifier during calcination procedure for different periods of time and compared with that of commercial den-tal stone. ANOVA and Duncan's multiple range test were performed to determine the significant differ-ence among the tested groups at p ≤ 0.05%. Results: Results showed that there were significant differ-ences of the values of the physical properties between the locally prepared dental stone with autoclave and the commercial one at p≤ 0.05 in specific gravity, water/ powder ratio and linear setting expansion. Conclusions :The results appeared the alpha- calcium sulfate hemihydrates dental stone that prepared in autoclave with adding crystal habit modifier has superior properties than of that prepared without modifier, but still not reach the properties of the commercial product. All values of the tested proper-ties were in accordance with ADA Specification

The Effect of Mixing Technique and Methods on Some Physical Properties of Dental Stone

Alaa N Al-Saraj

Al-Rafidain Dental Journal, Volume 13, Issue 1, Pages 170-175
DOI: 10.33899/rden.2012.84766

Aims: The study aims to evaluate the effect of mixing techniques and water powder ratio on the compres-sive strength and surface hardness of dental stone. Materials and Methods: The samples of compressive strength and surface hardness testes were prepared by 2 water powder ratio the ratio recommended by manufacture and that used by dentists and 2 mixing methods rubber bowl and spatula and zip-lock bag. The collected data analyzed using one sample t-test, ANOVA and Duncans' multiple range test at p≥0.5. Re-sults: The results showed statistically significant difference in compressive strength and surface hardness among tested groups. Conclusion: Mixing by rubber bowl and spatula and using water powder ratio rec-ommended by manufacturer gives the highest compressive strength value while using zip-lock bag give a higher surface hardness value than rubber bowl and spatula.

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

Radhwan H Hasan; Kasim Mohammad

Al-Rafidain Dental Journal, Volume 5, Issue 1, Pages 63-68
DOI: 10.33899/rden.2005.45514

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
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.