Study of the bismuth oxide concentration required to provide
Portland cement with adequate radiopacity for endodontic
use
Carlos Eduardo da Silveira Bueno, DDs, MSc, PhD, Eduardo Gregatto Zeferino, DDS,
Luiz Roberto Coutinho Manhães, Jr., DDS, MSc, PhD,
Daniel Guimarães Pedro Rocha, DDS, MSc, Rodrigo Sanches Cunha, DDS, MSc, PhD, and
Alexandre Sigrist De Martin, DDS, MSc, PhD, Campinas, Brazil
SÃO LEOPOLDO MANDIC UNIVERSITY
Objective: The purpose of this study was to determine the ideal concentration of bismuth oxide in white Portland
cement to provide it with sufficient radiopacity for use as an endodontic material (ADA specification #57).
Study design: 2-mm thick standardized test specimens of white MTA and of white Portland cement, as controls, and
of white Portland cement with the experimental addition of 5%, 10%, 15%, 20%, 25% or 30% of bismuth oxide were
radiographed and compared with various thicknesses of pure aluminum, using optic density to determine the observed
grayscale levels of radiopacity in a scale ranging from 0 to 255. The data was submitted to ANOVA (p⬍0.05) and the
Ryan-Einot-Gabriel-Welch and Quiot test (REGWQ) for multiple comparison of the means.
Results: White Portland cement with 0%, 5%, 10%, 15%, 20%, 25% and 30% of bismuth oxide presented mean
readings of 63.3, 95.7, 110.7, 142.7, 151.3, 161.0 and 180.0 respectively. MTA presented a mean reading of 157.3.
The readings of MTA and white Portland cement with 15% bismuth oxide did not differ significantly from the reading
observed for a thickness of 4 mm of aluminum (145.3), which is considered ideal for a test specimen by ADA
specification #57 (2 mm above the thickness of the test specimen).
Conclusion: White MTA and white Portland cement with 15% bismuth oxide presented the radiopacity required for
an endodontic cement. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009;107:e65-e69)
Mineral trioxide aggregate (MTA) is a material that
was developed at the University of Loma Linda in the
1990s.1 Use of this material has yielded favorable results for cases of root perforation compared with other
materials because of its good sealing ability.2,3 MTA
has also been used for capping of pulps with reversible
pulpitis, for apexification, for repair of root perforations
nonsurgically and surgically, as a root-end filling material, to protect the dental pulp directly in pulpotomies,
as a coronal plug after complete obturation of the root
canal system, and before internal bleaching of discolored teeth.4
Suitable physical and biologic properties have been
associated with this material, such as good tolerability
in contact with bone and conjunctive tissues,1,5-10 low
cytotoxicity and genotoxity,1,11,12 good sealing ability,2,3,13-15 antimicrobial action,16-18 low solubility,19
good setting and working time,19 and radiopacity suitable for use as an endodontic material.19
Endodontic Area, Center for Dental Research.
Received for publication Jul 24, 2008; returned for revision Aug 11,
2008; accepted for publication Sep 22, 2008.
1079-2104/$ - see front matter
© 2009 Mosby, Inc. All rights reserved.
doi:10.1016/j.tripleo.2008.09.016
Various studies have demonstrated that MTA and
Portland cement have a very similar chemical composition,1,11,20,21 except for the presence of bismuth oxide, which is contained in MTA and imparts radiopacity
to the material.
Other studies have compared Portland cement with
MTA and observed that they had the same sealing
ability in root-end fillings,13,14 in perforations of the
tooth’s middle third,22 and in furcation regions.15
Both materials also produced good cellular responses
in studies of subcutaneous and intrabone implantations
in animals.6-8,10
Studies comparing genotoxity and cytotoxicity6,11,12
and studies of their use in the dental pulps of animals5,9
and their antimicrobial action16-18 also provided similar
results for both MTA and Portland cement.
Radiopacity is an important property of an endodontic material for it to be distinguishable from that of
either cortical bone or dentin,23 so much so that the
American Dental Association (ADA) establishes standards for researching the radiopacity of endodontic
cements, set down in specification no. 57 (1984).23 The
ADA specifications state that because 1 mm of cortical
bone or dentin has a radiopacity equivalent of 1 mm of
1100 aluminum alloy, and comparisons can be made
with step wedges of this material, a clear image is
e65
e66
Bueno et al.
producible with at least 2 mm of aluminum equivalent
differential. Because the test specimens used in the
present study were 2 mm thick, we adopted the radiopacity obtained with a thickness of 4 mm of aluminum as an equivalence standard.
The aim of the present study was to determine what
concentration of bismuth oxide must be added to white
Portland cement to provide the cement with adequate
radiopacity, as measured by the grayscale levels of
digitized radiographic images, to comply with ADA
specification no. 57.23
MATERIALS AND METHODS
The methodology used in this study was based on
ADA specification no. 57,23 which determines the requirements for endodontic cements, one such requirement being radiopacity. This specification determines
that research undertaken to determine radiopacity must
be conducted by comparing the materials under study
with different thicknesses of pure aluminum.
Initially, standardized portions of each material under study were obtained: white MTA (Angelus Indústria de Produtos Odontológicos, Londrina, PR, Brazil), white Portland cement (Irajazinho Votorantim;
Cimento Rio Branco, Rio de Janeiro, RJ, Brazil), and
white Portland cement with 5%, 10%, 15%, 20%, 25%,
and 30% bismuth oxide (Neon Comercial, São Paulo,
SP, Brazil). Three portions of each material were obtained, all weighing 500 mg; they were weighed on an
electronic analytic balance (Ohaus Corp., Pine Brook,
NJ).
Standardized test specimens of the materials were
obtained by mixing them with one-third of the material’s weight in distilled water (from the MTA kit), using
a spatula. A syringe with 0.5 mL capacity was used to
measure the water. The dimensions of the resulting test
specimens were standardized to 10 mm in diameter and
2 mm in thickness. Standardization was performed using standard metal matrixes which were filled with the
tested materials. Three test specimens were made for
each material.
After adequate drying, the test specimens were radiographed with occlusal films (Kodak Insight Speed E;
Eastman Kodak Company, Rochester, NY) at a distance of 40 cm from the radiation source, using an
apparatus (Gendex 765DC; Gendex Dental X-Ray Division, Dentsply International, Des Plaines, IL) set to
work at 65 kV, 7 mA, and an exposure time of 0.25 s.
Radiographic processing was performed with an automatic processing unit (Gendex GXP; Gendex Corporation, Des Plaines, IL).
The test specimens were placed over the radiographic film in such a way that there was a test specimen of each material and a scale with different thick-
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January 2009
nesses (1-8 mm) of pure aluminum in each radiograph.
Three radiographs were taken (each with a different test
specimen of each material). The radiographs were then
digitized using a digital camera (Sony W5; Tokyo,
Japan). The photographs were obtained in macro mode
(resolution of 5 megapixels) by placing the film on a
light box and superimposing a totally black paper frame
slightly overlapping the outside borders of the film to
prevent any light from invading the area not covered by
the frame. The camera was then maintained at a standard distance from the film so that only the film and an
adjacent black paper strip were included in the picture.
On the digital photographs, areas with a standardized
size for each test specimen as well as each thickness of
the aluminum scale were measured in grayscale levels
(0 to 255) with the Adobe Photoshop computer program, version 7.0.1 (Adobe Systems, San Jose, CA).
Because there were 3 test specimens of each material, one for each X-ray, an arithmetic mean of the
values obtained for these 3 samples was calculated. The
results were subjected to statistical analysis.
RESULTS
Initially, analysis of variance was applied to assess
the differences between the means of the grayscale
levels of the materials evaluated. The null hypothesis
was rejected by the analysis of variance, which strongly
indicated significant differences in the grayscale levels
of the materials. The Ryan-Einot-Gabriel-Welch and
Quiot test was applied to allow multiple comparisons of
the means (at a level of significance of 5%), by comparing them 2 by 2. The standard deviations and the
highest and lowest interval of 95% confidence limits for
each sample were also compared.
The results of the study are presented in Table 1.
Regarding MTA, it was observed that there were no
statistically significant differences in the grayscale levels of the material in relation to the thicknesses of 4 mm
and 5 mm of aluminum. Neither was there any statistically significant difference between MTA and the
white Portland cement with additions of 20% and 25%
bismuth oxide.
No statistically significant difference was observed
between the radiopacity obtained with white Portland
cement with the addition of 15% and 20% bismuth
oxide and that obtained with a 4-mm thickness of
aluminum.
A regression analysis (P ⬍ .01) performed for bismuth oxide content (Fig. 1) mathematically represented
the development of radiopacity as a function of the
amount of bismuth oxide present. This analysis showed
that 96.91% of the variation in radiopacity can be
credited to bismuth oxide content. It also showed that a
theoretic addition of 21.51% of bismuth oxide in white
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Bueno et al. e67
Table I. Results and statistical analysis
Limits of the interval of
confidence (95%)
Group
Mean
Standard deviation
Upper
Lower
Test of REGWQ alpha 5%
(␣ ⫽ .05)*
8 mm Al
7 mm Al
6 mm Al
WPC/30%BO
5 mm Al
WPC/25%BO
MTA
WPC/20%BO
4 mm Al
WPC/15%BO
3 mm Al
WPC/10%BO
WPC/5%BO
2 mm Al
WPC
1 mm Al
208.0
197.7
184.3
180.0
166.3
161.0
157.3
151.3
145.3
142.7
118.7
110.7
95.7
86.0
63.3
54.0
2.0000
2.5166
3.5119
9.6437
3.5119
6.2450
3.7859
10.5040
3.5119
4.5092
2.5166
4.0415
1.1547
1.7321
1.1547
1.7321
213.0
203.9
193.1
204.0
175.1
176.5
166.7
177.4
154.1
153.9
124.9
120.7
98.5
90.3
66.2
58.3
203.0
191.4
175.6
156.0
157.6
145.5
147.9
125.2
136.6
131.5
112.4
100.6
92.7
81.6
60.4
49.6
A
AB
BC
CD
DE
EF
EFG
FGH
GH
H
I
I
J
K
L
M
Al, aluminum; BO, bismuth oxide; MTA, mineral trioxide aggregate; REGWQ, Ryan-Einot-Gabriel-Welch and Quiot; WPC, white Portland
cement.
*Simple statistics and the 95% confidence interval of the means of the original data and the REGWQ test applied to the resulting data according
to the method recommended by the study of assumptions. Means with the same letters do not differ among themselves according to the REGWQ
test, with a 5% alpha level (␣ ⫽ .05) of significance.
Radiopacity (Grayscale levels)
200
180
160
140
120
y = -0.0667x2 + 5.7238x + 65.048
(p < 0.01 - R2:96.91%)
100
80
60
Grayscale value
40
MTA (157.3)
20
4 mm of aluminum (145.3)
0
0
5
10
15
20
25
30
35
Bismuth Oxide (%)
Fig. 1. Polynomial quadratic regression to represent radiopacity (grayscale level) as a function of added bismuth
oxide content. MTA, Mineral trioxide aggregate.
Portland cement provided a radiopacity (grayscale
level) equivalent to the mean observed for white MTA,
and that a theoretic addition of 17.65% of bismuth
oxide in white Portland cement provided a mean radiopacity equivalent to that obtained with a thickness of
4 mm of aluminum.
DISCUSSION
The aim of this study was to determine the concentration of bismuth oxide that must be added to Portland
cement to give it the radiopacity needed to be used as
an endodontic material.
A recently published study24 evaluated the radiopac-
ity of Portland cement with the addition of different
proportions of bismuth oxide (4:1, 6:1, and 8:1). The
authors observed that with 20% bismuth oxide the
material presented a radiopacity not significantly different from that of MTA, and they concluded that this
proportion of bismuth oxide rendered Portland cement
with a greater potential for being used as a root-end
filling material compared with Porland cement with less
bismuth oxide. Statistically similar cell viability was
also observed for the different groups. Another study25
demonstrated the adequate radiopacity of MTA and
inadequate radiopacity of Portland cement for endodontic use, suggesting that this difference is due to the
presence of bismuth oxide in MTA, but the concentration of bismuth oxide that should be added to Portland
cement to produce adequate radiopacity in this material
was not determined. Cellular responses in animals to
subcutaneous implantations of MTA and Portland cement with additions of 20% and 30% bismuth oxide
have been proven to be similar.8 A study comparing
tissue response to MTA and to Portland cement with
the addition of iodoform found similar results for the
experimental groups, suggesting the addition of iodoform to Portland cement as a radiopacity agent rather
than bismuth oxide because of the greater availability
of the former than of the latter.10
Radiopacity is an important property of an endodontic material for it to be distinguishable from that of
either cortical bone or dentin.23 The ADA specification
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January 2009
Bueno et al.
no. 5723 establishes other properties required for endodontic materials in addition to radiopacity, such as the
possibility of being sterilized, pureness of the material,
biocompatibility, working time, setting time, resistance
to the forces of compression and traction, dimensional
stability, and resistance to solubility. Regarding radiopacity, this specification determines that the tests of
the materials must be performed comparatively with
different thicknesses of pure aluminum. However, the
specification is not clear regarding the material dimensions of the test specimen or to the aluminum thicknesses with which the specimens must be compared.
In the present study, a thickness of 2 mm was
adopted for preparing the test specimens, as in other
studies.26-29 Regarding the comparison procedure, an
aluminum thickness of 4 mm was adopted.26,27 However, some authors had used test specimens with different thicknesses, such as 1 mm24,30 or 1.5 mm.31
There is also divergence regarding the comparison with
aluminum, considering that some authors made comparisons with an aluminum thickness of 3 mm.28-30 The
use of 3 test specimens of each material instead of only
1 sample reduced the possibility of an operational error.
Radiography was performed in the present study
with a direct-current apparatus (that does not undergo
variations of electrical current, guaranteeing stability to
the radiation emission). The appliance also had a high
voltage (65 kV), which allows better discrimination of
grayscale levels (contrast) in the radiographic film.31
Although many studies have demonstrated the similarity between MTA and Portland cement, the clinical
use of Portland cement has not yet been accepted on
human beings, owing to lack of quality control in
producing Portland cement and the absence of radiopacity of this material. The major difference between MTA and Portland cement is the presence of
bismuth oxide, which ensures the radiopacity of
MTA.20,21,25
Based on the results of the present study, new research on the physical and biologic aspects of MTA and
Portland cement with bismuth oxide is recommended to
assess whether the addition of bismuth oxide modifies
the physical and biologic properties of the material and
also to eventually authorize the use of Portland cement
with the addition of bismuth oxide as an endodontic
material in clinics.
CONCLUSIONS
Based on the methodology used and on the results
obtained in this study, and based on the recommendations of ADA specification no. 57, it can be concluded
that:
1. White MTA has a radiopacity (measured in grayscale levels) that allows it to be used as an endodontic material.
2. White Portland cement does not have sufficient
radiopacity for it to be used as an endodontic material.
3. The addition of at least 15% of bismuth oxide to
white Portland cement gives it sufficient radiopacity for it to be used as an endodontic material.
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Reprint requests:
Carlos Eduardo da Silveira Bueno
Endodontic Area
Center for Dental Research
São Leopoldo Mandic University
Rua Antônio Lapa, 854
Campinas, São Paulo
Brazil
[email protected]