1. Effect of Chemical Materials on
the Properties of Dental Stone
DR.AMER A.TAQA * MSC . PhD (Professor)
NADA Z. MOHAMMED, MSC(Assistant Professor)
TARIK Y. KASSAB Bash DBs, MSC, (Professor)

2. ABSTRACT
Aims: To determine the effect of some chemical materials on the compressive strength
and surface hardness of dental stone. Material: three types of chemical materials(rosin,
nigella stavia oil and sodium lauryl sulfate)were incorporated into three kinds of type III
dental stone (Zeta, Elite and Dental stone) at four concentrations (0.5%, 1%, 1.5% and
2%).The collected data of compressive strength and surface hardness were subjected to
the descriptive analysis (mean and stander deviation), student T test(to evaluate the
difference between standard and experimental groups) and one way analysis of
variance(ANOVA)(to show if there are significant differences among experimental
groups). Also the FTIR was measured to show the effect of the additives on the chemical
structure of the stone. Results:revealed that the incorporation of these chemical
materials into each type of dental stone resulted in changing their evaluated physical
properties;this change varies with the type, concentration of the added chemical material
and type of dental stone being used. Conclusion:The highest values of compressive
strength and surface hardness were recorded with the addition of rosin in each of Zeta,
Dental stone(at a concentration of 1%)and Elite stone(at a concentration of 1.5%).Also the
addition of nigella sativa stone oil increases in the compressive strength and surface
hardness of Zeta and Dental stone when this materials added at a concentration of 1%
and at a concentration of 0.5%when it is added to Elite.

3. The compressive strength values wereThe compressive strength values were
determined according to ADAdetermined according to ADA
specification No.25 (1975).specification No.25 (1975). A special splitA special split
mold was used to prepare threemold was used to prepare three
cylindrical specimens.cylindrical specimens. The compressive
strength was determined from the value
of the maximum load at the point of
specimen fracture according to the
following formula:
20mm
40mm
Compressive StrengthCompressive Strength
Load (Kg)
Area (cm²)

4. The Surface Hardness was evaluated withThe Surface Hardness was evaluated with
“microhardness tester”“microhardness tester”
Rockwell hardness test was used with minorRockwell hardness test was used with minor
load of 10 Kg and major load of 50 Kg (El-load of 10 Kg and major load of 50 Kg (El-
Tannir and Imam, 1970; Combe and Smith, 1971;Tannir and Imam, 1970; Combe and Smith, 1971;
Kasier ana Nicholls, 1976; Mohammed, 1983).Kasier ana Nicholls, 1976; Mohammed, 1983).
30mm
20mm
Initially, the indenter is
placed under a static load of a
given magnitude (minor load),
and the dial gauge is set at zero.
The load is then increased by a
given amount (major load) and
maintained for a certain
period. The depth of
indentation is measured after
the major load is again reduced
to the minor load (Phillips,
1982).

5. 0
50
100
150
200
250
300
350
400 Rosin
Nigella Stavia oil
Sodium Lauryl Sulfate
-ve Zeta Elite Dental +ve
control stone control

6. 0
20
40
60
80
100
120 Rosin
Nigella Stavia oil
Sodium Lauryl Sulfate
-ve Zeta Elite Dental +ve
control stone control

7. change the chemical composition of these stones and
from comparing ir-spectra of those modified stones
with ir-spectra of rosin alone we can note the
disappearing of some bands that present in ir-spectra
rosin specially at 2560, 1250, 1300, 1600 cm-¹
region .Also this figure shows new bands in the ir-
spectra of these modified stone at 600, 500, 1450,
1550,3000,3200cm-¹region.
The ir-spectra of sodium lauryl sulphate show bands
at 450, 850, 1000, 1100, 1250, 1850, 2400, 2500 cm-
¹region. Some of these bands disappear when
sodium lauryl sulphate mixed with each type of
dental stone, especially at 850, 1100, 1250, 1850,
2400, 2500 cm-¹region.
Throughout comparing the ir-spectra chart of nigella
stavia oil alone with the ir-spectra chart of the three
types of dental stone after the addition of nigella
stavia oil), we can note the disappearing of some
bands at 1100, 1150, 1400, 1700, 2800, 2850 cm-
¹region in negllia stavia oil spectra. And the
appearance of new bands at 600, 1600, 1850, 2100,
3400 cm-¹region in the modified stone spectra.

9. This increase in a compressive strength may be attributed to the reduction:This increase in a compressive strength may be attributed to the reduction:
in the water-powder ratio that achieved after the addition of these chemicalin the water-powder ratio that achieved after the addition of these chemical
materials which indicate a densermaterials which indicate a denser
and to the effect of these additives on the chemical structure of theand to the effect of these additives on the chemical structure of the
experimental dental stones.experimental dental stones.
material.El-Tannir and Imam (1969) reported that the basis of physical
properties of gypsum is the function of the crystals structure and the
crystal rate of formation
However, there is a decrease in compressive strength with increasing the
concentration of the added chemical materials); this may be partially
attributed to the action of the added chemical materials as an adulterant
and to the reduction in the intercrystalline cohesion (Anusavice, 1996).
significant reduction in the compressive strength that is achieved after thesignificant reduction in the compressive strength that is achieved after the
addition of the sodium lauryl sulfate (despite the reduction in the water-addition of the sodium lauryl sulfate (despite the reduction in the water-
powder ratio).powder ratio).
This was advocated by Mori and Yamane (1982) reported that the water-powder
ratio alone dose not necessarily determine the strength of cast gypsum. So
this reduction in the compressive strength could be attributed to:
the reduction in the intercrystalline cohesion between the crystals
to the change in the chemical composition of these stones after the addition of
these chemical materials.

10. The change in the surface hardness as a result of the incorporation of the
chemical materials into the experimental dental stones is recorded in
terms of the change in the Rockwell hardness number.
In the present study, different types and concentrations of added the chemical
materials render different results on the surface hardness of the
experimental dental stones. Improving the surface hardness of the
experimental dental stones is achieved after the addition of rosin and
nigella stavia oil, while the addition of sodium lauryl sulfate resulted in
the reduction of the surface hardness.
This was advocated by Craig( 1997) Surface hardness of gypsum
products stated to be related to their compressive strength, the
higher the compressive strength, the higher being the hardness,
but disagreeing with Combe and Smith (1964) who reported that
there is no clear relation detected between the values of both
hardness and compressive strength, since the conditions in the
surface layer determine the former.
The effect of chemical additives used in this study on the hardness has
been reported to correlate with the effect of these chemicals on the
compressive strength.

11. The differences in the examined properties of the dental stone relatedThe differences in the examined properties of the dental stone related
to the different chemical interactions between the added chemicalto the different chemical interactions between the added chemical
materials and the calcium sulfate hemihydrate crystals. Incorporatingmaterials and the calcium sulfate hemihydrate crystals. Incorporating
of suitable chemical additives can produce dental stone with superiorof suitable chemical additives can produce dental stone with superior
mechanical properties. The highest values of compressive strengthmechanical properties. The highest values of compressive strength
and surface hardness were recorded with the addition of rosin intoand surface hardness were recorded with the addition of rosin into
each of Zeta, Dental stone (at a concentration of 1%) and Elite stoneeach of Zeta, Dental stone (at a concentration of 1%) and Elite stone
(at a concentration of 1.5%). Also the addition of nigella sativa stone(at a concentration of 1.5%). Also the addition of nigella sativa stone
oil increases in the compressive strength and surface hardness ofoil increases in the compressive strength and surface hardness of
Zeta and Dental stone when this materials added at a concentration ofZeta and Dental stone when this materials added at a concentration of
1% and at a concentration of 0.5%when it is added to Elite.1% and at a concentration of 0.5%when it is added to Elite.