J Bagh College Dentistry Vol. 26(1), March 2014 Effect of disinfectant
Restorative Dentistry 24
Effect of disinfectant agents on certain physical and
mechanical properties of type IV dental stone
Hanan Abdul- Rahman Khalaf, B.D.S., M.Sc. (1)
Mithaq Radhi Mohammed, B.D.S., M.Sc. (2)
ABSTRACT
Background: Dental stone casts come into contact with impression materials and becomes susceptible to cross
contamination from saliva and blood. This study was done to evaluate the physical and mechanical properties of
dental stone type IV after treatments with various disinfecting agents and regimes (methods).
Materials and Methods: Type IV dental stone and different types of disinfecting agents were used and divided into
seven groups: G1: dental stone without disinfection (control group), G2: dental stone mixed with silver nitrate powder
0.5% , G3: dental stone mixed with silver nitrate powder 1%, G4: dental stone mixed with copper sulfate powder 0.5%,
G5: dental stone mixed with copper sulfate powder 1% ,G6: dental stone immersed in propanol 70% and G7: dental
stone immersed in ethanol 70%.Setting time, linear setting expansion, surface detail reproduction, compressive
strength of type IV dental stone as well as compatibility with auto mixing addition silicone impression material were
evaluated. The statistical analysis were conducted by ANOVA test followed by LSD test (p<0.05), also chi square test
was used.
Results: The compressive strength, linear setting expansion, surface detail reproduction and compatibility of stone
specimens was affected to a higher extent by mixing with silver nitrate powder 1%, copper sulfate powder 1% while
treating the stone specimens with the disinfecting powders at low concentrations as well as immersion of stone
specimens in either ethanol or propanol for 15 minutes produce less effect on the previous tested properties.
Conclusion: Silver nitrate 0.5%, copper sulfate 0.5% powders as well as 15 minutes immersion in 70% ethanol or 70%
propanol did not promote adverse alterations in most of evaluated properties of type IV dental stone.
Key Words: Gypsum products, metallic disinfectants, ethanol, propanol. (J Bagh Coll Dentistry 2014; 26(1):24-31).
INTRODUCTION
The need for an infection control program is
felt because a number of bacteria, fungi, and
viruses present in the dental environment have
been linked to debilitating and life-threatening
diseases. Every effort, therefore, must be made to
avoid cross contamination of these
microorganisms and to prevent the potential
transfer of disease in the dental setting. One
common dental procedure that may cause cross
contamination, especially between patients and
dental laboratory personnel, is transfer of
infectious agents from blood and saliva to the
casts through impressions, record bases, occlusion
rims, and trial dentures (1,2).
Gypsum products have been considered to be
among the most widely used model and die
materials. Modifications of these materials by
adding chemicals or salts result in a change in
their structure (2,3).. American Dental Association
(ADA) and the Center for disease control and
prevention (CDC) have suggested methods for the
disinfection of dental casts including immersion
in or spraying with a disinfectant (3) .Several
studies have been attempted to come up with an
improved system for models and die constructions
(4), other studies attempted to improve the
mechanical properties of gypsum products and
oriented mainly towards the decrease of water
requirement (5).
(1)Assistant Professor. Department of Prosthodontics,
College of Dentistry, University of Baghdad
(2)Lecturer. Department of Prosthodontics, College of
Dentistry, University of Baghdad
In order to improve gypsum materials many
attempts have been made by the use of various
additives to gain several modification related to
the chemical, mechanicals, physical and other
properties of gypsum material (6,7) .
Chemical disinfectants can also be added
directly to the dental stone (8,9). However, adding
disinfectant in dental stone, have been reported to
compromise critical properties of the cast such as
compressive strength, setting time and
dimensional accuracy (10,11).
This study was done to develop a dental stone
with disinfecting properties and still has adequate
physical and mechanical properties.
MATERIALS AND METHODS
In this study type IV dental stone (elite stone,
NAVY BLUE. Rovigo- Italy) was used. Ten
specimens were prepared for each tested property
following the water powder ratio recommended
by the manufacturer instructions (powder water
ratio 100gm/25ml). The dental stone was
immediately poured in the molds with the aid of a
mechanical vibrator, the stone specimens were
separated from the molds 45 minutes after the
starting of the mix and left to dry for 24 hours at
(23±2)ºc before testing. Two different disinfection
methods (incorporation and 15 minutes
immersion for the set gypsum specimens) were
applied and four disinfectant agents were used
0.5% , 1% silver nitrate (SCRC, China: sinopharm
chemical reagent company) ,0.5% , 1% copper
sulphate (Barcelona, Espana), 70%propanol and
J Bagh College Dentistry Vol. 26(1), March 2014 Effect of disinfectant
Restorative Dentistry 25
70% ethanol .The following physical and
mechanical properties were evaluated for the
prepared stone specimens:
1. Setting time
According to ADA specification no.25, metal
ring (2.5 cm inside diameter and 2.5 cm high) was
used to test the setting time of the disinfected
stone specimens using apparatus with 1 ± 0.05
mm needle diameter and 240 g weight (B.S.12:
part 2:1971). Standard mix of 200g powder and
50 ml distilled water according to manufacturers
instruction was prepared and immediately
transferred to the cylindrical mold painted with
separating medium (SHANGHAI NEW
CENTURY DENTAL MATERIAL CO.LTD)
then the needle tip brings in contact with the
surface of the tested material locking it in position
with the thumb screw, the needle was released and
allowed to penetrate the sample at 15 second
intervals.
After each penetration the needle was cleaned
and the mold moved to allow another penetration
in a new area, the average value for two tests was
measured as initial setting time, figure (1).
2. Linear setting expansion
To evaluate and compare linear setting
expansion of conventional type IV dental stone
(control group) and the experimental groups
(disinfected specimens), 10 Stone specimens were
prepared for the control and the experimental
groups. Metallic model with of seven slots with
widths ranging from 0.025 to 0.300 mm and 2.5
mm of distance between the grooves according to
ADA specification No. 25 for dental gypsum
products was used (22) , figure (2). Rubber ring 30
mm in diameter and 15 mm high was placed on
the test block so that the intersection of a cross
line and a groove 0.050 mm depth is in the center
of the ring , the stone powder was weighed on an
electronic balance (±0.2%) and mixed with
distilled water that measured by using a graduated
cylinder according to the ratios recommended by
the manufacturer. After mixing the stone mix was
poured inside rubber ring under vibration then the
ring and the gypsum material was separated from
the test block at 45 minutes according to
manufacturer's instructions, AB distance (which
represent the distance between groove 0.050 mm
and groove 0.150 mm) was measured by using
computerized soft ware program (Corel Draw x4),
figure (3).
Figure 1: Vicat device for measuring Fig. 2: Metal block for linear expansion test
the setting time of gypsum products
B
Fig. 3: Gypsum sample prepared for linear expansion test
(AB: represent the distance between four lines carved on the metal block)
J Bagh College Dentistry Vol. 26(1), March 2014 Effect of disinfectant
Restorative Dentistry 26
3. Surface detail reproduction
To evaluate and compare Surface detail reproduction of conventional type IV dental stone (control
group) with the disinfected gypsum specimens (experimental groups), 10 specimens for each gypsum group
were prepared on the test block previously used for linear setting expansion test. Rubber ring (15 mm high
and 30 mm in diameter) was used and the stone specimens were separated from the test block at 45 minutes
according to manufacturer's instructions , the stone specimens were tested under X5 magnification
microscope (Olympus BX51M with digital camera mounted on the microscope and connected to the
computer) with low angle lighting, figure (4) .The surface detail reproduction will be satisfactory if the
0.050 mm depth groove is continuous for the length inside diameter of the plastic ring, figure (5).
Fig.4: Low lighting microscope Fig.5: Optical microscope illustrates the
used for surface roughness evaluation continuity of 0.050 mm line regarding surface
detail reproduction test
The following scoring system with rating
values from one to four was used as follows (2):
Rating 1: well defined, sharp detail and
continuous line.
Rating 2: continuous line but with some loss of
sharpness.
Rating 3: poor detail or loss of continuity of line.
Rating 4: marginally or completely discernible
line.
4. Compatibility with addition silicone
impression material
Compatibility of type IV dental stone with the
elastomeric impression material was conducted
according to ADA specification No.19, 10 stone
samples were prepared for the same metallic
block that used for the linear setting expansion
test, a plastic ring (30 mm diameter and 15 mm
high) was placed on the test block so that the
groove 0.025 mm wide was reproduced on the
gypsum surface, 10 vinyl polysiloxane (syringe
type) elastic impressions were taken for the test
block, figure (6) .Boxing was done for these
impressions and the stone was poured inside the
waxed impressions then after 45 minutes
(according to manufacturer's instructions) stone
samples were removed from the waxed
impressions and the surface area was examined by
using optical microscope with X5 magnification
power. The gypsum compatibility is considered
satisfactory if the 0.025 mm width groove is
continuous for the length inside diameter of the
plastic ring.
Fig. 6: Auto mix elastic impression material
5. Compressive strength
For Compressive strength test 10 stone
samples were prepared using split mold 20 mm in
diameter and 40 mm high according to ADA
specification No.25, the split mold was placed on
a glass plate so that the ends of the samples
remained flattened and vibrated gently while the
stone mix was poured inside the mold then the
overfilled mold was covered with a second glass
plate and pressed firmly. The specimens were
removed from the split mold at 45 minutes
(according to manufacturer's instructions) from
the start of the mix, stored for 24 hours, then the
stone samples figure (7) were crushed at a loading
of 7.5 KN. the test was performed with hydraulic
press testing machine, figure (8), the compressive
strength was calculated according to the following
formula: compressive strength = load (N) /
surface area (mm2). The average value of the 10
readings was dependent for the compressive
strength test.
J Bagh College Dentistry Vol. 26(1), March 2014 Effect of disinfectant
Restorative Dentistry 27
Fig. 7: Gypsum samples for compressive Fig 8: Hydraulic press machine
strength test
RESULTS
The addition of AgNO3 and CuSO4
disinfectant powders to the type IV dental stone
showed a clear reduction in the initial setting time
in comparison to the control group.
Table 1: Setting time for the control and experimental groups
Groups
Setting time
Minutes Seconds
Control 11 00
Ag No30.5 % 10 10
AgNO3 1 % 8 30
CuSO4 0.5 % 4 33
CuSO4 1 % 6 50
The results of this study showed that the
disinfectant agents produced a significant
reduction in the mean value of the linear setting
expansion in comparison to the control group, this
result was found by ANOVA test but LSD test
revealed a non significant difference between
G1& G2, G1&G4 also between G1&G7 regarding
the linear expansion mean values as shown in
table (2)& table (3).
Table 2: Descriptive statistical analysis and ANOVA test of setting expansion for the control and
experimental groups
Table 3: LSD analysis test of setting expansion for the control and experimental groups
**P<0.01 Highly significant.
Groups
Setting expansion (mm) Groups’ comparison
N Mean SD df F-test P value Sig.
(G1) control 10 7.9285 0.0111
29
6.591
0.005 **HS (G2) AgNO3 0.5 % 10 7.8776 0.0067
(G3) AgNO3 1 % 10 7.7619 0.1808
(G1) control 10 7.9285 0.0111
29
31.749
0.000 **HS (G4) CuSO4 0.5 % 10 7.8700 0.0718
(G5) CuSO4 1 % 10 7.7760 0.0158
(G1) control 10 7.9285 0.0111
29
7.312
0.003 **HS (G6) Ethanol 70 % 10 7.8520 0.0759
(G7) Propanol 70 % 10 7.9250 0.0406
Studied groups P- value Sig.
G1 & G2 0.171 NS
G1 & G3 0.000 HS
G2 & G3 0.002 HS
G1 & G4 0.115 NS
G1 & G5 0.000 HS
G4 & G5 0.010 HS
G1 & G6 0.040 S
G1 & G7 0.971 NS
G6 & G7 0.043 S
J Bagh College Dentistry Vol. 26(1), March 2014 Effect of disinfectant
Restorative Dentistry 28
The addition of AgNO3 and CuSO4 to the type
IV dental stone resulted in a statistically
significant reduction in the mean values of
compressive strength in comparison to the control
group while a statistically in significant difference
in the mean values of compressive strength was
observed for the stone specimens after immersion
in alcohols for 15 minutes (ethanol or propanol) in
comparison to the control group, table (4).
Table 4: Descriptive statistical analysis and ANOVA test of compressive strength (MPa) for the
control and experimental groups
** P<0.01 Highly significant.
Further analysis using LSD test revealed that
no significant differences were found between the
control group and the experimental groups (G2,
G6, G7), also a non significant difference was
observed between G4 and G5 groups regarding
the compressive strength of dental stone used in
this study, table (5).
Table 5: LSD analysis test of compressive strength (MPa) for the control and experimental
groups
Table (6) showed that mixing high
concentrations of AgNO3 and CuSO4 adversely
affected the surface detail reproduction of type IV
dental stone. None of the examined casts showed
grade 4 surface quality.
Table 6: Presents the results of chi-square analysis (the percentage values) of the surface detail
reproduction of the control and the experimental groups.
X2= 38.719, df =12, p-value = 0.000(HS), Likelihood ratio=46.135, df = 12, p-value=0.000(HS)
Groups
Compressive strength
N/m2 (MPa)
Groups’ comparison
N Mean SD df F value P value Sig.
(G1) control 10 19.8465 0.8877
29 334.740 0.000 **HS (G2) AgNO3 0.5 % 10 19.6485 0.4263
(G3) AgNO3 1 % 10 13.4964 0.4454
(G1) control 10 19.8465 0.8877
29 24.430 0.000 **HS (G4) CuSO4 0.5 % 10 17.0330 1.0860
(G5) CuSO4 1 % 10 16.9170 1.1882
(G1) control 10 19.8465 0.8877
29 1.112 0.344 NS (G6) Ethanol 70 % 10 18.6670 2.4183
(G7) Propanol 70 % 10 17.5655 4.9473
Studied groups P- value Sig.
G1 & G2 0.484 NS
G1 & G3 0.000 HS
G2 & G3 00000 HS
G1 & G4 0.000 HS
G1 & G5 0.000 HS
G4 & G5 0.908 NS
Groups
Rankings
I II III Total
Control 8 (80%) 2 (20%) 0 (0%) 10 (100%)
AgNO3 0.5% 8 (80%) 2 (20%) 0 (0%) 10 (100%)
AgNO3 1% 0 (0%) 6 (60%) 4 (40%) 10 (100%)
CuSO4 0.5% 2 (20%) 6 (60%) 2 (20%) 10 (100%)
CuSO4 1% 1 (10%) 7 (70%) 2 (20%) 10 (100%)
Ethanol 70% 8 (80%) 2 (20%) 0 (0%) 10 (100%)
Propanol 70% 8 (80%) 2 (20%) 0 (0%) 10 (100%)
Total 35(50%) 27(38.6%) 8(%11.4) (100%)00
J Bagh College Dentistry Vol. 26(1), March 2014 Effect of disinfectant
Restorative Dentistry 29
Table 7 showed that mixing high
concentrations of disinfectant agents (AgNO3,
CuSO4) with gypsum powder adversely affected
the compatibility of type IV dental stone. None of
the examined casts showed grade 4 surface
quality.
Table 7: Presents the results of chi-square analysis (the percentage values) of the surface detail
reproduction of the control and the experimental groups.
X2= 45.718, df=12, p-value = 0.000(HS), Likelihood ratio= 54.179, df= 12, p-value= 0.000(HS)
DISCUSSION
In Prosthodontics, objects potentially
contaminated with pathogenic microorganisms are
transported between dental laboratory and dental
clinic. It has been claimed that to avoid cross
contamination, specific disinfection measures
should be followed. In the literature, the usual
solution to this problem has been to chemically
disinfect either the impressions or gypsum casts
(1).
In this study, gypsum specimens disinfected
with either incorporation or immersion in
disinfectant agents revealed the following results
regarding the evaluated properties:
Setting time
The time elapsing from the beginning of
mixing until the material hardens is called the
setting time; certain penetrometers are dependant
for measuring setting time of gypsum products
like Gilmore needle and Vicat needle (11).
Following ADA specification No.25, the setting
time was obtained using standardized Vicat
apparatus. Regarding the result of this study it
could be found that the disinfectant powders in
the evaluated concentrations promoted a clear
reduction in the Vicat setting time in comparison
to the control group, this can be explained that
AgNO3 in high concentration increased the rate of
dissolution of hemihydrates and subsequently
made the hemihydrates more soluble. The setting
reaction of gypsum products is affected by the
type and the concentration of the chemical
modifiers which are added within the gypsum
materials, this finding is in agreement with Hatim
et al. (12) While the addition of CuSO4 in low
concentration (0.5%) has shown a greater
reduction the setting time of dental stone in
comparison to 1%, this could be explained that
some modifiers in high concentrations may
precipitate and poison the nuclei of crystallization
either by reducing the rate of solubility of
hemihydrates or by inhibiting the growth of
dihydrate crystals (11).
Linear setting expansion
The setting expansion of the dental stones is an
important factor for many dental applications. The
casts must have slightly larger dimensions to
offset the impression material shrinkage and then
ensure that the dental pieces are adequately
manufactured, under ordinary conditions high
strength dental stone has 0.08% to 0.10 % linear
setting expansion (6,17). Many factors may affect
the setting expansion of gypsum products among
them the technique of spatulation, condition of
water (deionozed or not), the composition of the
gypsum product (6). In this study, the addition of
disinfectant powders in low concentrations to the
dental stone or immersion of stone specimens in
70% propanol did not adversely affect the
dimensional stability of dental stone, Regarding
the addition of disinfectant powders in high
concentrations to the dental stone, the reduction in
the linear setting expansion could be due to the
changes in the morphology of the resulted
gypsum crystals as a result to the disinfectant
treatment and subsequently produce changes in
the crystals thrust and tendency for expansion,
this finding is in agreement with the finding of
Hatim et al. (12).While for stone specimens
immersed in 70% ethanol for 15 minutes, the
change in the linear setting expansion could be
due to interaction between the solution and dental
stone (22) also this finding is in agreement with
Sarma et al. (24) who found that immersion of
Groups
Rankings
I II III Total
Control 8 (80%) 2 (20%) 0 (0%) 10(100%)
AgNO3 0.5% 7 (70%) 3 (30%) 0 (0%) 10(100%)
AgNO3 1% 0 (0%) 4 (40%) 6 (60%) 10(100%)
CuSO4 0.5% 3 (30%) 6 (60%) 1 (10%) 10(100%)
CuSO4 1% 0 (0%) 6 (60%) 4 (40%) 10(100%)
Ethanol 70% 8 (80%) 2 (20%) 0 (0%) 10(100%)
Propanol 70% 8 (80%) 2 (20%) 0 (0%) 10(100%)
Total 34(48.6%) 25(35.7%) 11(15.7%) 70(100%)
J Bagh College Dentistry Vol. 26(1), March 2014 Effect of disinfectant
Restorative Dentistry 30
stone specimens 2% gluteraldehyde for 10-30
minutes showed negative shrinkage and relate the
change to the erosion of the reproduced lines,
surface erosion is perhaps the best measure of the
reaction of the stone. Immersion of stone
specimens in 70% propanol for 15 minutes
showed no statistical significant difference in
comparison to the control group, this is similar to
the study of Abdelaziz et al. (15).
Compressive strength
The strength of gypsum – based products is
usually expressed in terms of compressive
strength, which is directly related to the material's
ability to fracture resistance when subjected to
compressive tensions. Thus the dental stone
compressive strength is an important factor in the
rehabilitation work in dentistry (13). In the set
gypsum material, the number of crystals formed
during setting and their inter-meshing and
enlargement determines the strength. Of the set
material (14), the prepared dental stone specimens
with the additives have shown a reduction in
compressive strength in comparison to the control
specimens, this could be either related to the
presence of additional excess water in the mixture
or to the decrease interaction (inter crystallization
cohesion) between the gypsum crystals related to
decreased amount of gypsum crystals as a result
of Increased concentration of additives in a given
volume of gypsum material. 1% AgNO3 and 1%
CusO4 produce great reduction in compressive
strength than the control group and other
experimental groups, this may be related to the
increase in the rate of reaction so that some of the
hemihydrates crystals does not get hydrated to
form dihydrate crystals, this increase the un
reacted hemihydrates contents in the materials and
thereby produces a weaker product (13).
Detail reproduction
The incorporation of disinfectant powders
(AgNO3, CuSO4) in high concentrations adversely
affected the detail reproduction of stone cast, this
could be due to several alteration in the crystals
formed during the stone setting reaction or could
be attributed to the change in the water
requirement of dental stone as a result of
incorporation of the disinfectant powders leading
to change in the recommended consistency for
satisfactory detail reproduction (13,16). The
immersion of stone samples in 70% ethanol or
70% propanol for 15 minutes did not affect their
surface detail reproduction; this finding is in
contrast with Sarma et al. (24) who found that
immersion of stone specimens in 2%
gluteraldehyde for 10-30 minutes showed
alteration.
Gypsum compatibility with silicone impression
materials
Mixing the dental stone with high
concentrations of disinfectant powders did harm
the compatibility of dental stone while 15 minute
immersion of stone specimens in either 70%
ethanol or 70% propanol did not affect the
compatibility of dental stone ,this finding is in
agreement with Abbas and Ibrahim (16) and
Marcos et al. (17) , it could be due to some kind of
interaction of disinfectant powders with that of
impression material leading to reduction in the
sharpness of the line reproduced also could be due
to low wetting behaviors of the disinfected dental
stone against the surface of silicone impression
material.
As conclusion; within the limitations of this
study, the newly introduced mixing method
revealed that 0.5% silver nitrate powder as well as
15 minutes immersion of the set stone specimens
in 70% ethanol or 70% propanol did not appear to
have an adverse effect on the tested physical and
mechanical properties
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