Print ISSN: 1812-1217

Online ISSN: 1998-0345

Keywords : compressive strength

The Effect of Formaldehyde Disinfectant on Compressive Strength of Dental Stone (Type IV)

Musab M Ibrahim; Munther Najeeb Kazanji; Salwa H Mohammed

Al-Rafidain Dental Journal, Volume 16, Issue 1, Pages 1-9
DOI: 10.33899/rden.2016.160857

Aims: The purpose of this study is to evaluate the effect of 2% formaldehyde on compressive strength of dental stone (type IV), and to evaluate its antibacterial effect. Materials and methods: To study the effect of 2% formaldehyde on compressive strength of dental stone (type IV), ten samples of stone were prepared in cylindrical blocks and divided into two groups, each group contain of (5) samples. First group composed of stone and distilled water as (control group) and the second group composed of stone and (2%) formaldehyde solution. after (1h) the samples were tested for compressive strength using digital compression machine(ALFA Company, Turkey).To study the bacterial effect of formaldehyde 60 stone discs prepared and mixed with formaldehyde 2% divided into 12 group (each group consist of 5 discs) and stored for different intervals between 1-12 days, antibacterial effect against salivary sample for each interval day using disc diffusion test. Results: The statistical analysis of data by analysis of t-test reveals significant different in compressive strength between control group and stone-2% formaldehyde group at (P<0.05). The result showed that second group which contains 2%formaldehydehad higher values compared with control group. Also the results showed that the antibacterial effect of stone-formaldehyde discs continued till 12thday. Conclusions: Adding 2% formaldehyde as chemical disinfectant to dental stone increase the compressive strength in addition of the antibacterial activity of stone - formaldehyde disc continued till 12th day.

Evaluation of compressive strength for refractory casts made from different investment materials

Ahmed A Al-Ali

Al-Rafidain Dental Journal, Volume 7, Issue 2, Pages 166-172
DOI: 10.33899/rden.2007.45483

Aims: To compare the compressive strength of refractory casts made from investments for cobalt–
chromium and investment for titanium and to study the effect of mixing fluid on compressive strength.
Materials and Methods: Three types of investments were used, one for titanium and two for cobalt–
chromium, each one is mixed with three types of mixing fluids; tap water, distilled water and special liquid,
to produce refractory casts. Compressive strength test was carried out using compression testing machine.
Results: Showed significant differences in compressive strength between the types of investments, with
titanium investment mixed with special liquid showed the highest value. There were significant differences
between subgroups of the same type by changing mixing fluid type. Conclusions: Refractory casts made
from titanium investment showed significantly higher compressive strength than refractory casts made
from Co–Cr investments, and there was a difference between the two special liquids used, and tap water in
which it produced casts with higher compressive strength than distilled water in two out of the three
investment materials tested.

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.