Comparison of mineral trioxide aggregate's composition with Portland cements and a new endodontic cement.

Abstract

The aim of this study was to compare the compositions of mineral trioxide aggregates (MTAs), Portland cements (PCs), and a new endodontic cement (NEC). Our study also investigated the surface characteristics of MTA and NEC root-end fillings when immersed in normal saline. For part I, we prepared samples of 9 brands of MTAs, PCs, and NEC. The materials were imaged and analyzed by scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDXA). In part II, 3-mm-deep root-end preparations were filled with MTA or NEC and stored in normal saline for 1 week. Samples were imaged and analyzed by SEM and electron probe microanalysis (EPMA). EDXA investigations revealed differences in the dominant compounds of NEC, PCs, and MTAs. The major components of MTA and PC are the same except for bismuth. The most significant difference was the presence of higher concentrations of Fe (minor element) in gray MTA and PC when compared with white ones. EPMA results revealed remarkably different elements in MTA compared with surrounding dentin, whereas in the NEC group the distribution patterns of calcium, phosphorous, and oxygen were comparable. NEC differs chemically from MTAs and PCs and demonstrates comparable surface composition with adjacent dentin as a root-end filling material.

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Comparison of Mineral Trioxide Aggregate’s Composition
with Portland Cements and a New Endodontic Cement
Saeed Asgary,* Mohammad Jafar Eghbal,* Masoud Parirokh,†Jamileh Ghoddusi,‡
Sanam Kheirieh,§and Frank Brink?
Abstract
The aim of this study was to compare the compositions
of mineral trioxide aggregates (MTAs), Portland ce-
ments (PCs), and a new endodontic cement (NEC). Our
study also investigated the surface characteristics of
MTA and NEC root-end fillings when immersed in nor-
mal saline. For part I, we prepared samples of 9 brands
of MTAs, PCs, and NEC. The materials were imaged and
analyzed by scanning electron microscopy (SEM) and
energy dispersive x-ray analysis (EDXA). In part II,
3-mm-deep root-end preparations were filled with MTA
or NEC and stored in normal saline for 1 week. Samples
were imaged and analyzed by SEM and electron probe
microanalysis (EPMA). EDXA investigations revealed
differences in the dominant compounds of NEC, PCs,
and MTAs. The major components of MTA and PC are
the same except for bismuth. The most significant
difference was the presence of higher concentrations of
Fe (minor element) in gray MTA and PC when com-
pared with white ones. EPMA results revealed remark-
ably different elements in MTA compared with sur-
rounding dentin, whereas in the NEC group the
distribution patterns of calcium, phosphorous, and ox-
ygen were comparable. NEC differs chemically from
MTAs and PCs and demonstrates comparable surface
composition with adjacent dentin as a root-end filling
material. (J Endod 2009;35:243–250)
Key Words
Chemical composition, electron probe, MTA, new den-
tal material, Portland cement, x-ray microanalysis
O
Food and Drug Administration (FDA) approval, ProRoot MTA (Dentsply Tulsa Dental,
Tulsa,OK)becamecommerciallyavailablein1998asgrayMTA(GMTA).Becauseofthe
potentialdiscolorationeffectofGMTA,white-coloredformulaofProRootMTA(WMTA)
was introduced in 2002 for the same clinical purposes (3). These dental filling mate-
rials consisting of fine hydrophilic particles harden in oral environment 4 hours after
mixing(4)andactasasealantforcommunicationsbetweenrootcanalsystemandthe
external tooth surfaces (5). According to the manufacturer, MTA is a mechanical
mixture of 3 powder ingredients: Portland cement (PC), bismuth oxide, and gypsum
(6). Portland cement is the major component of MTA and is composed of dicalcium
silicate, tricalcium silicate, tricalcium aluminate, and tetracalcium aluminoferrite (7).
ReducingtheamountofironinWMTA’scompositionaccountsforitslightercolorwhen
compared with GMTA (8).
Since then, other kinds of MTA have been introduced (Table 1). The overall
compositionofgrayPC(GPC)andwhitePC(WPC)issimilartothatofGMTAandWMTA
except for the presence of bismuth oxide in PCs (9, 10). A recent study has shown that
the sealing ability of PC was similar to that of MTA when used in furcation perforation
repair (11).
Inarecentprospectiveclinicalstudy,MTAshowedahighsuccessratewhenused
as root-end filling material (12). MTA has gained widespread use as a result of its
excellentbiocompatibility(13);however,MTAhasadelayedsettingtime(4)andpoor
handling characteristics (14) and is expensive to use.
New root-end filling materials have constantly been introduced to overcome the
shortagesofthepreviousones(15,16).Recently,anewendodonticcement(NEC)has
been developed with similar clinical uses to tooth-colored ProRoot MTA but different
chemicalcomposition(17).Thismaterialhasacceptablephysicalproperties(18)(ie,
settingtimelessthan1hour,moreflowandlessfilmthicknessthanMTA)andiscapable
of hydroxyapatite formation over material in normal saline solution (19). An in vivo
studycarriedoutondogsshowedthatMTAandNEChavethesamefavorableresultsas
pulp capping materials and were even preferred over calcium hydroxide (20).
Oneoftheprincipalcharacteristicsofbioactivematerialsistheirabilitytoforman
apatite-like layer on their surface when in contact with bodily fluids (21) or with
simulated body fluids such as phosphate-buffered saline (19).
In recent years many studies have been carried out on the clinical and biologic
characteristics of the numerous brands of MTA as well as PCs; less research has been
performed on the chemical properties of original and branded MTAs and how they
might be compared with white and gray PCs. Moreover, investigating the composition
andsizeoftheparticlesaswellasthechemicalpropertiesofamaterialcanrevealwhy
itworkssoeffectivelywheninteractingwithbodytissues.Hencethecompositioncanbe
changed to obtain more favorable results in different situations.
The objectives of this study were (1) to analyze and compare the elemental con-
stituents of MTAs, PCs, and NEC cements by using energy dispersive x-ray analysis
(EDXA)and(2)toevaluateandcomparethedistributionoftheelementsinGMTA,NEC,
and also OMTA by using a combination of backscattered electron (BSE) imaging and
digital compositional mapping.
riginalmineraltrioxideaggregate(OMTA)wasintroducedin1993byLomaLinda
University for root-end fillings and the repair of lateral perforations (1, 2). After
From the *Department of Endodontics, Iranian Center for
Endodontic Research, Dental Research Center, Dental School,
Shahid Beheshti University M.C., Tehran, Iran;†Department of
Endodontics, Dental School, Kerman University of Medical
Sciences, Kerman, Iran;‡Department of Endodontics, Dental
School, Mashad University of Medical Sciences, Mashad, Iran;
§Iranian Center for Endodontic Research, Shahid Beheshti Uni-
versity M.C., Tehran, Iran; and?ANU Electron Microscopy Unit,
Research School of Biological Sciences, Australian National
University, Canberra, Australia.
Address requests for reprints to Professor Saeed Asgary,
Department of Endodontics, Iranian Center for Endodontic
Research, Shaheed Beheshti Dental School, Evin, Tehran, Iran.
E-mail address: saasgary@yahoo.com.
0099-2399/$0 - see front matter
Copyright © 2008 American Association of Endodontists.
doi:10.1016/j.joen.2008.10.026
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Materials and Methods
This study was approved by the Ethics Committees of Dental Re-
searchCenterofShahidBeheshtiMedicalUniversity,Tehran,Iran,and
Australian National University, Canberra, Australia. The study was di-
vided into 2 parts. In part I, nine cementswereusedaccordingtoTable1.
Samples were mounted in individual, pre-prepared 25.4-mm diameter
resin disks (Araldite 502?Epon 812; ProSciTech, Kirwan, QLD, Aus-
tralia) to ensure compatibility with the electron probe microanalyzer.
Each disk contained 3 holes, drilled to a depth of 3 mm by using a no.
4 round bur. Each cement powder was mixed with appropriate liquid
according to the manufacturer’s instruction. They were placed in cavi-
ties and condensed with a modified condenser. The samples were then
immersedinastandardsalinesolutionandallowedtosetcompletelyin
anincubatorat37°Cfor48hours.Afterwardsallsampleswerepolished
with 1 ?m diamond paste followed by a ?20-nm coating of carbon by
using a Dynavac CS300 (Dynavac, Sydney, Australia) coating unit.
A JEOL JSM6400 (JEOL, Tokyo, Japan) scanning electron micro-
scope (SEM), equipped with an Oxford Instruments light element dis-
persive spectrometer detector (Oxford Instruments, Cambridge, UK),
was used for imaging and determining the composition. All analyses
were carried out at 15 kV and 1 nA of probe current, with well-charac-
terized minerals as calibration standards (Astimex MINM25–53; As-
timex Scientific Limited, Toronto, Ontario, Canada). Atomic number,
absorption, and fluorescence corrections were applied throughout the
study(22).Becauseoftheheterogeneityofthesamples,intermsofboth
mineral composition and surface texture (Figs. 1and 2), each analysis
was carried out by using an area scan taken at ?200 magnification to
provideanaveragevaluefortheoverallcomposition.Thefinalresultfor
each sample was based on the average of 12 analyses (4 analyses for
eachofthe3cavitiesinthedisk),withtheoverallerrorprovidedbythe
standarddeviation.Carbonconcentrationswerenotmeasuredbecause
of the hydrous nature of the sample(s) and the presence of a carbon
coat, as well as inherent difficulties associated with the quantitative
analysis of carbon. Therefore, the amount of carbon and water was
measured by their difference.
In part II, sixteen extracted human teeth were used. Crowns were
removedatthecementoenameljunction.Therootcanalswerecleaned
andshapedbyusingstandardstep-backtechnique.Afterfinalirrigation,
canals were dried and obturated with gutta-percha (Ariadent, Tehran,
Iran)andRoth801rootcanalsealer(RothInternationalLtd.,Chicago,
IL).Root-endresectionswerecutineachrootbyremoving3mmofthe
apex at a 90-degree angle to the long axis of the root with a cylindrical
carbide bur (D&Z, Germany) by using a high-speed handpiece with
water coolant spray. The 3-mm-deep class I root-end preparation was
made by using an ultrasonic power unit (miniPiezon; EMS, Nyon, Swit-
zerland) with ultrasonic retrotips (DT-043; EMS). Finally, they were
irrigated with 5.25% NaOCl, 17% ethylenediaminetetraacetic acid, and
salinesolutions,respectively.Thecavitiesweredried,andsampleswere
randomly divided into 2 groups, each composed of 8 roots. In each
group, cavities were filled with GMTA or NEC. The excess material was
removed, and the roots were immersed in saline solution at 37°C for 1
week. Afterwards, the samples were removed from the solution and
used for compositional imaging. They were coated with ?20 nm of
carbon. A JEOL JSM6400 SEM, equipped with an EDXA system (Oxford
Instruments), used Isis software (Isis Inc, Richmond, VA) to perform
the digital compositional mapping. The SEM operating condition was
15-kV accelerating voltage, 39-mm working distance, and 1-nA probe
current. We collected energy dispersive x-ray spectra, secondary (SE)
and BSE images from each sample at ?600 magnification. The digital
x-ray images were collected at 256 ? 200 resolution.
TABLE 1. Cements Used in This Study
Cement (abbreviation)
GMTA
WMTA
FMTA
IMTA
NEC
IGPC
AGPC
IWPC
AWPC
Commercial name
ProRoot MTA
ProRoot MTA
Angelus MTA
Root MTA
Company Country
USA
USA
Brazil
Iran
Iran
Iran
Australia
Iran
Australia
Dentsply Tulsa Dental
Dentsply Tulsa Dental
Soluçöes em Odontologia
Salami-far
S. Asgary (Inventor)
Abyek
Melcann
Saveh
Melcann
—
Abyek cement
Melcann cement
Saveh white cement
Melcann white cement
Figure 1. Scanning electron micrograph of different brands of MTA revealed their different surfaces. Bar, 0.1 mm.
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Results
SEMofdifferentbrandsofMTAshowed2specificphasesthrough-
out the materials. All the observed samples contained a complex mix-
ture of mineral phases with highly visible randomly distributed 5- to
40-?m particles of bismuth oxide, which were added to the composi-
tionwiththepurposeofradiopacity(Figs.1and2).Themineralphases
of original and commercial types of MTA and also Iranian gray PC
(IGPC) and NEC specimens revealed the presence of coarse crystalline
Figure3. Scanningelectronmicrographofcalcium-enrichedmixturecementshowsthepresenceofcoarsecrystallineparticlesinagroundmassoffineramorphous
material. Bar: left, 0.1 mm; right, 0.01 mm.
Figure2. Complexmixof2mineralphasesofdifferentbrandsofMTAandaPC.PresenceofbismuthoxidewhiteparticlesinMTAsisshown.SimilartextureofGMTA
and IGPC except bismuth oxide particles in GMTA is clearly visible. Bar, 0.1 mm.
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particlesinageneralgroundmassoffineramorphousmaterial(Figs.2
and 3).
Careful inspection of the overall texture shown in Fig. 2 indicated
that the approximate size distribution (5–70 ?m) of the crystalline
particlesobservedinGMTAwasbiggerthaninfastsettingMTA(FMTA)
(5–65 ?m), Iranian MTA (IMTA) (5–60 ?m), WMTA (5–50 ?m),
and OMTA (5–30 ?m), respectively, but it was similar to IGPC (5–70
?m).
The resultsofEDXAareshowninTable2.Thisanalysisrevealedthat
forGMTA,WMTA,FMTA,andIMTA,lime(CaO),silica(SiO2),andbismuth
oxide (Bi2O3) formed the bulk of detected oxides, making up 73.33%,
81.57%,76.04%,and75.36%oftheanalytictotal,respectively.
Theconcentrationvaluesofstudiedcompoundswerecomparable
when the error in the measurement was taken into account (Table 2).
Oxides of sulfur, phosphorus, titanium, and sodium as well as ele-
mentalchlorinewerefoundattracelevels(?0.99wt%)indifferent
types of MTA, except for the sodium oxide in FMTA, which was
detected in minor amounts (1–5 wt%).We observed considerable
variabilityintheconcentrationsofAl2O3,MgO,andparticularlyFeO.
For example, the measured concentration of Al2O3in FMTA was
approximately 237% higher compared with WMTA (Table 2). When
comparing GMTA with FMTA, the concentration of FeO ranged from
anondetectableamountto4.39wt%(a?%increase);alsoMgOwas
found to be 486% higher.
Figure 4. Scanning electron micrograph and compositional imaging of OMTA. BSE photomicrograph and digital compositional images of elements Bi, Ca, Si, O, Fe,
Al, and Mg. Note the very similar x-ray pattern of distribution of “Ca and Si” and “Fe and AL” particles.
TABLE 2. Electron Probe Microanalysis Results for Different Brands of MTA, PC, and NEC
GMTA
40.42 (2.82)
17.02 (1.62)
15.89 (1.97)
4.28 (0.99)
3.11 (0.46)
4.40 (0.74)
0.49 (0.12)
0.19 (0.11)
0.07 (0.09)
0.04 (0.06)
0.41 (0.07)
13.68
100
WMTA
44.16 (3.25)
21.25 (1.59)
16.13 (4.85)
1.87 (0.19)
1.36 (0.12)
0.39 (0.19)
0.55 (0.12)
0.27 (0.11)
0.09 (0.09)
0.03 (0.03)
0.39 (0.11)
13.51
100
FMTAIMTA IGPCAGPC IWPCAWPC
54.03 (3.29)
22.33 (1.41)
ND
4.61 (0.51)
1.22 (0.13)
0.26 (0.11)
3.34 (0.41)
0.14 (0.10)
0.25 (0.09)
0.29 (0.19)
0.31 (0.05)
13.22
100
NEC
CaO
SiO2
Bi2O3
Al2O3
MgO
FeO
SO3
P2O5
TiO2
Na2O
Cl
H2O & CO2
Total
49.20 (1.50)
18.58 (1.19)
8.26 (1.19)
4.48 (0.42)
0.64 (0.70)
ND
0.19 (0.09)
ND
ND
1.32 (0.38)
0.51 (0.08)
16.82
100
41.64 (3.26)
18.54 (1.43)
15.18 (3.49)
3.41 (0.34)
2.08 (0.29)
0.35 (0.13)
0.55 (0.14)
0.15 (0.08)
0.12 (0.09)
0.64 (0.22)
0.52 (0.14)
16.82
100
50.19 (1.02)
18.51 (0.75)
ND
4.72 (0.84)
3.69 (0.59)
3.91 (0.91)
0.86 (0.12)
0.24 (0.06)
0.43 (0.06)
0.60 (0.18)
0.11 (0.03)
17.19
100
50.99 (3.46)
18.01 (1.90)
ND
4.29 (0.55)
2.16 (0.23)
2.61 (0.28)
1.50 (0.22)
0.31 (0.14)
0.22 (0.11)
0.22 (0.15)
0.41 (0.17)
19.28
100
52.69 (3.82)
21.92 (1.77)
ND
4.11 (0.16)
1.12 (0.12)
0.34 (0.11)
1.39 (0.11)
0.14 (0.06)
0.09 (0.11)
0.71 (0.31)
0.12 (0.06)
17.37
100
51.75 (1.27)
6.32 (0.77)
ND
0.93 (0.32)
0.24 (0.10)
ND
9.53 (1.42)
8.49 (0.39)
ND
0.34 (0.09)
0.21 (0.07)
22.19*
100
GMTA,GrayMTA;WMTA,WhiteMTA;FMTA,FastsettingMTA;IMTA,IranianMTA;IGPC,IraniangrayPC;AGPC,AustraliangrayPC;IWPC,IranianwhitePC;AWPC,AustralianwhitePC;NEC,newexperimentalcement;
ND, not detected.
Most data are shown as mean (standard deviation).
*Water, carbon dioxide, and other not mentioned elements.
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The results of the EDXA revealed that each of the various kinds
of PCs predominantly consisted of lime and silica, with minor amounts
of Al2O3, MgO, FeO, and SO3(Table 2). Although the concentration of
Al2O3was comparable, data showed a major difference in the concen-
trationsofMgO,SO3,andespeciallyFeObetweengrayandwhitekinds.
Trace amounts of P2O5, TiO2, NaO2, as well as elemental Cl were also
found to be present in each specimen.
As Table 2 shows, the results of the EDXA revealed that lime is the
predominant component of NEC cements, and the concentration of
other constituents, except some trace elements, considerably differed
from MTAs or PCs.
Fig.4showsdigitalcompositionalimagesofOMTA,displayingthe
distribution of major and minor elements. The distribution patterns of
CaandSicolocalizein2majorphasesofthematerial.Thesamedistri-
butionpatternisobservableforFeandAl.ParticlesofMgaredenseand
do not colocalize with other elements.
Fig 5 shows digital compositional image of a tooth with GMTA
root-end filling. The distribution patterns of Bi, P, and Fe in the GMTA
comparedwithsurroundingdentinareconsiderablydifferent,whereas
Ca and O have even distribution (Fig. 5). In the case of NEC root-end
filling, the distribution patterns of Ca, P, and O in the material and
surrounding dentin are comparable (Fig. 6).
Discussion
The principal research on chemical properties of MTA has been
carried out by Torabinejad et al. (4). They reported that MTA exhibits
both crystalline and amorphous phases after setting, which concurs
with the present study (Figs. 1, 2, and 4). All MTA specimens clearly
showed the presence of the intentionally added bismuth oxide, which
can be seen as the areas of higher intensity in Figs. 1 and 2. These
particlesareentrappedintheamorphousphaseofdifferenttypesofthe
MTA and provide radiopacity for clinical purposes.
Compositional image of oxygen in Fig. 4 shows its distribution
throughout the crystalline and amorphous phases of OMTA. This re-
vealed that all other compositional elements are present in their oxide
form.QualitativestudiesofWMTAandGMTAwithcompositionalimag-
ing (23) showed similar distribution pattern to the above finding.
Figure 5. Backscattered electron photomicrograph (BSE) and digital compositional images of elements of a tooth with GMTA root-end filling: Bi, Ca, P, O, and Fe.
Note the presence of bismuth and iron in GMTA and phosphorous in the surrounding dentin (D). Bar, 0.1 mm.
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The EDXA results showed that the predominant elements in the
different brands of MTA are calcium, silicon, and bismuth oxides, con-
curring with our previous findings (24). In contrast, the study by Tor-
abinejad et al. (4) did not report the actual amount of elements, al-
though the amounts were reported as 2 separate amorphous and
crystalline phases. Furthermore, because the proportion of phases is
unknown, the data cannot refer to the proportion of elements in the
whole cement. It was reported that calcium and phosphorous were the
main components of MTA (4). The present study, however, demon-
strated that the observed concentrations of phosphorus were close to
the limit of detection (Table 2). These results are entirely consistent
with a previous study (24) as well as the information supplied by
DentsplyTulsaDentalCompany,inwhichphosphorusisnotreportedas
a significant element in MTA (25).
The greatest disadvantage of GMTA is its color (26), which led to
theintroductionofdifferentbrandsofWMTAthathaveahueinharmony
with tooth color. It is well-known that many of the late transitional
elements (eg, Fe, Mn, Cu), which have free d-electrons, have strong
colors in their oxide forms; these d-electrons can be readily excited by
light in the visible spectrum. On the other hand, the oxides of elements
thatdonothaveeasilyexcitedelectrons(Ca,Si,Al,Mg,andS)tendtobe
colorless or white, whereas the heavier element Bi has a yellow oxide
(27). The EDXA results of this study revealed that most of the
changes occur in the concentrations of FeO (black), SO3 and MgO
(white), when white brands of MTA are compared with GMTA. Sim-
ilar results can be seen between white and gray PCs (Table 2).
Therefore, the color change from gray to white when OMTA and
GMTA are compared with WMTAs (or even between gray and white
PCs) is likely to be due to the absence of significant amounts of iron
oxide in white brands.
It has been shown that the behavior of cells in contact with the
surface of WMTA and GMTA is very different (28). Researchers found
that GMTA demonstrated significantly less leakage than WMTA when
appliedasanapicalbarrier(29).InarecentstudyGMTA,whenusedas
a root canal filling material, leaked less than WMTA, although the dif-
ference was not statistically significant (30). It seems that the differ-
encesinchemicalcompositionbetweenMTAsrepresentdifferentchar-
acteristicsandreactionsofthematerial.Ontheotherhand,otherinvivo
studies showed comparable tissue response for gray and white MTA.
When researchers implanted dentin tubes filled with gray and white
MTA into the connective tissue of rats, both groups demonstrated very
similar biocompatibility (21). Furthermore, when used in pulp cap-
ping, both white and gray MTA stimulated dentinal bridge formation
(31,32).TheosteogenicactivityofMTAisduetoitsreleaseofabundant
amounts of Ca?2ions, which interact with phosphate groups in the
surrounding tissue fluid to form hydroxyapatite crystals on their sur-
faces (33). Therefore, clinical success of MTA can be attributed to its
biocompatibility.
This study showed that all MTAs, unlike different PCs and NEC,
containasignificantquantityofbismuthoxide.Thechemicalproperties
and biologic effects of GMTA and GPC have been investigated in several
studies(9,10,34,35).IthasbeenreportedthatMTAandPCappearto
be almost identical chemically, macroscopically, microscopically, as
well as according to x-ray analysis, except for bismuth (36). The com-
positional structure of WMTA has also been compared with WPC (10).
These studies concur with ours and have demonstrated similar differ-
ences.
Many research studies have been performed to analyze MTA sur-
face (37), particle size, and shape (38, 39). It has been shown that
crystalsizecanaffectthephysicalpropertiesofPCs,ie,smallerparticle
size increases the surface available for hydration and enhances early
strength(40).Researchersshowedthatplacingthesmoothersurfaceof
anindividualdentalmaterialindirectcontactwithlivingtissuesresults
inlessirritation(41).Henceasmallparticlesizeisanimportantaspect
Figure 6. Backscattered electron photomicrograph (BSE) and digital compositional images of elements of a tooth with calcium-enriched mixture (CEM) root-end
filling: O, Ca, and P. Note the same presence of oxygen, calcium, and phosphorous in new endodontic cement (NEC) and surrounding dentin. Bar, 0.1 mm.
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of a reasonable material in endodontic treatment. Observation of
smaller size distribution of crystals in the WMTA suggests that their
setting time might be less than that of GMTA, and application of WMTA
might be more appropriate in endodontic treatment procedures. Be-
causethereisnopublishedreportontheseissues,furtherinvestigation
is recommended.
The errors in Table 2 are more than expected, especially when
majorcomponentsintheanalyticresultsareconsidered(eg,?30%
and ?23% for Bi2O3in WMTA and IMTA, respectively). This is a
direct consequence of the heterogeneous nature of the samples in
which Bi2O3particularly showed areas of distinct higher concentra-
tions under SEM examination. For a routine analysis with a well-
calibrated system on homogeneous samples, percentage of relative
errors is typically ?2%–3% for concentrations greater than 10
wt% (42).
ThepatentbyTorabinejadandWhite(7)disclosedthatMTAorig-
inatedfromPCwithaspecificBlainenumber.Carefulinspectionofthe
x-rayintensitymapsof“CaandSi,”“CaandAl,”andalso“Ca,Fe,andAl”
in OMTA reveals similar distribution pattern of these elements in the
cement (Fig. 4). The data suggest the presence of calcium silicate
(CaO.SiO2), calcium aluminate (CaO.Al2O3), and calcium aluminofer-
rite (CaO.Al2O3.Fe2O3) compounds as the major component of PC in
the MTA.
The x-ray intensity maps of the minor and major elements Ca, O,
Bi, P, and Fe, shown in Fig. 5, indicate that their distribution is signifi-
cantly different when the root-end filling (GMTA) is compared with
surrounding dentin. In each case the x-ray intensity maps revealed
absence of P in GMTA and Bi and Fe in surrounding dentin, whereas
majorelementsCaandOshowedapproximatelyanevendistributionin
the material and dentin. In the case of NEC root-end filling, the x-ray
intensity maps of Ca, P, and O showed a comparable distribution of
these elements in the surface of the material and surrounding dentin.
Thisfindingindicatesthatthecompositionofthematerialoritssetform
is similar to dentin (hydroxyapatite [HA]). The results of recent re-
search revealed that NEC produced HA precipitation and covered the
surfaceofthisroot-endfillingmaterialwhenthetoothwasimmersedin
normal saline (19).
Torabinejadetal.(43)haveshownthatcementumcangrowover
MTAincasesofroot-endresection.Sarkaretal.(33)suggestedthatHA
formation over MTA might be a reason for producing biologic seal. It
seems that human tissue cannot recognize HA as an antigen, and as a
result, cementum can grow over it. HA is a main component of dentin;
therefore, similarity between NEC and dentin might help the human
body to produce natural tissue over it (19).
Taking the limitations of this in vitro study into consideration, it
wasconcludedthat(1)themajorcomponentsofdifferenttypesofMTAs
and PCs are similar except for bismuth oxide; (2) the color difference
betweengrayandwhiteMTAsandPCsisduetothelessconcentration
of iron in white types; (3) NEC differs chemically from MTAs and
PCs; (4) phosphorous is the major component of NEC, whereas in
MTAs and PCs this element is close to the detection limit; and (5) in
contrast with MTA, NEC shows surface composition similar to sur-
rounding dentin.
Acknowledgments
This study was supported by Iranian Center for Endodontic
Research, Shahid Beheshti University M.C., Tehran, Iran. The au-
thors wish to thank Dr Sally Stowe and the staff members of the
Electron Microscopy Unit of the Australian National University,
Canberra,Australiafortheirassistancewithscanningelectronmi-
croscopy.
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