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Niobium pentoxide as a new filler formethacrylate-based root canal sealers
V. C. B. Leitune1, A. Takimi2, F. M. Collares1, P. D. Santos1, C. Provenzi1, C. P. Bergmann2
& S. M. W. Samuel1
1Dental Materials Laboratory, School of Dentistry Porto Alegre, RS; and 2Ceramic Materials Laboratory, Federal University of
Rio Grande do Sul Porto Alegre, RS, Brazil
Abstract
Leitune VCB, Takimi A, Collares FM, Santos PD,
Provenzi C, Bergmann CP, Samuel SMW. Niobium
pentoxide as a new filler for methacrylate-based root canal
sealers. International Endodontic Journal, 46, 205210, 2013.
Aim To evaluate the influence of several niobium
pentoxide (Nb2O5) concentrations on the radio-opacity,
flow, film thickness, microhardness and degree of
conversion of an experimental root canal sealer.
Methodology An experimental dual-cured root
canal sealer was produced with a methacrylate-based
comonomer blend. Nb2O5 was added at four different
concentrations: 0, 80, 100 and 120 wt%. Radio-
opacity was evaluated according to ISO 6876 using a
digital system (n = 5). Flow and film thickness weredetermined in accordance with ISO 6876 (n = 3).Microhardness was evaluated with 50 g for 15 s
(n = 5). Degree of conversion was evaluated withFTIR immediately after photocuring and after 1, 7
and 14 days. The data were analysed using ANOVA
and Tukeys test. The degree of conversion over time
was evaluated using RM-ANOVA (a = 0.05).
Results The groups with 80 wt% and 100 wt% of
filler showed no significant difference in radio-opacity
from that of equivalent 2 mmAl (P > 0.05). The addi-tion of 120 wt% resulted in radio-opacity values
higher than 2 mmAl (P < 0.05). The flow was notsignificantly different amongst the different groups
(P > 0.05). All groups had a film thickness of
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The materials used for a root filling come in direct
contact with dentine and periapical tissues. Therefore,
the materials should not be cytotoxic and would ideally
be biological stimulators. Root canal materials that are
capable of ionic delivery have been proposed to produce
increased sealing in the apical region (Alani et al.
2009). However, these materials have high solubility
and degrade over time. Some inorganic fillers with a
monoclinic phase (e.g. niobium pentoxide) appear to be
less prone to degradation (Khan et al. 1992) and could
possess bioactive properties (Karlinsey et al. 2006).
Niobium pentoxide (Nb2O5) is an oxide of a transition
metal (atomic number of 41) with suitable properties
for biomedical uses (Khan et al. 1992, Karlinsey et al.
2006). This oxide has never been used as filler for poly-
meric-based root canal sealers.
The purpose of this study was to evaluate the
effects of several Nb2O5 concentrations on the radio-
opacity, flow, film thickness, microhardness and
degree of conversion of an experimental dual-cured
methacrylate-based root canal sealer. The null
hypothesis was that the addition of niobium pentoxide
will not influence the properties of the experimental
methacrylate-based root canal sealer.
Materials and methods
The monomers used to produce an experimental root
canal sealer were urethane dimethacrylate (UDMA),
glycerol 1,3-dimethacrylate (GDMA), ethoxylated
bisphenol A glycol dimethacrylate (BISEMA6), cam-
phorquinone (CQ), N,N-dihydroxyethyl-para-toluidine
(DHEPT) and benzoyl peroxide (BP), which were sup-
plied by Esstech Inc (Essington, PA, USA). These mate-
rials were used without further processing. Nb2O5,
with a mean particle size of 38.16 lm (Leitune et al.2012), was obtained from Companhia Brasileira de
Mineracao e Metalurgia (CBMM, Araxa, MG, Brazil).
The filler was silanized using gamma-methacryloxypro-
pyltrimethoxysilane (c-MPTS; Aldrich Chemical Co.,Milwaukee, WI, USA). The filler was added to an ace-
tone (Labsynth Ltda., Diadema, SP, Brazil) solution
containing c-MPTS (5% of the filler wt) to form aslurry. The mixture was stored for 24 h at 37 C toensure complete solvent removal (Sideridou & Karabela
2009).
The experimental root canal sealers were made by
mixing 70 wt% UDMA, 15 wt% BISEMA6 and 15 wt%
GDMA. CQ, DHEPT and BP were added to produce
a dual-cure root canal sealer (Collares et al. 2012).
The filler particles were used in four different
concentrations (0, 80, 100 and 120 wt%). Consider-
ing the weight of the co-monomer blend, a relative
amount of filler was added (e.g. to 1 g of resin 1.2 g
of Nb2O5 was added in the group with 120 wt%).
The density of niobium pentoxide is 4.6 g cm3, ofUDMA is 1.12 g cm3, of GDMA is 1.12 g cm3 andof BisEMA6 is 1.10 g cm3. Consequently, the volu-metric concentrations of the experimental groups
were 0, 19.44, 24.25 and 29.16 vol%. The mixture
(resin/particles) was hand-mixed for 120 s, sonicated
for 480 s and hand-mixed for another 120 s. To per-
form sealer photo-activation, a light-emitting diode
activation unit (Radii Cal; SDI, Bayswater, Vic.,
Australia) was used. An irradiation value of
1200 mW cm2 was confirmed with a digital powermeter (Ophir Optronics, Danvers, MA, USA). Radio-
opacity, flow and film thickness were tested according
to ISO 6876 (Standardization 2001).
Radio-opacity
The radio-opacity of the experimental sealers was eval-
uated using five specimens per group. The specimens
were 6.0 mm (0.5 mm) in diameter and 1.0 mm(0.2 mm) in thickness. X-ray images were obtainedby a digital system with phosphorous plates (VistaScan;
Durr Dental GmbH & CO. KG, Bietigheim-Bissingen,
Germany) with an exposure time of 0.4 s and a focus-
film distance of 400 mm. The X-ray source (DabiAtlante
model Spectro 70X) was operated with a tungsten
anode at 70 kV and 8 mA. For each film, one specimen
from each group with the same concentration was
used, resulting in a total of five films per concentration.
For all images, an aluminium step-wedge was exposed
simultaneously with the specimens. The thickness of
the aluminium step-wedge ranged from 0.5 to 5.0 mm
in increments of 0.5 mm. The aluminium alloy used
contained Al, 99.12; Fe, 0.47; Mg, 0.41; and < 0.1 ofCu (mass%), and met ISO 6876 standards (Standardi-
zation 2001). The images were saved in TIFF format
and analysed using Photoshop software (Adobe Sys-
tems Incorporated, San Jose, CA, USA). The means and
standard deviations of the grey levels (pixel density) of
the aluminium step-wedge and the specimens were
measured in a standardized area of 1.5 mm2 (Collares
et al. 2010).
Flow test
The flow test was conducted according to ISO 6876
(Standardization 2001). A total of 0.5 mL of each
Nb2O5 for root canal sealers Leitune et al.
2012 International Endodontic JournalInternational Endodontic Journal, 46, 205210, 2013206
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experimental sealer was placed on a glass plate
(40 9 40 9 5 mm) with a graduated 1.5-mL syr-
inge. At 180 5 s after mixing was started, anotherplate with a mass of 20 2 g and a load of 100 gwas placed on top of the material. Ten minutes after
mixing had been started, the load was removed, and
the major and minor diameters of the compressed
material were measured using a digital calliper. If
both measurements were within 1 mm of each other,
the results were recorded. If the major and minor
diameter discs were not uniformly circular or did not
fall within 1 mm of each other, the test was repeated.
The test was conducted three times for each experi-
mental group, and the mean value was recorded.
Film thickness
The film thickness was evaluated according to ISO
6876 (Standardization 2001). Two glass plates that
measured 5 mm in thickness and 10 mm in length
were placed together and their combined thickness
was measured. The centre of one of the plates was
covered with 0.5 mL of experimental sealer, and a
second plate was placed on top of the material. At
180 5 s after the start of mixing, a load of 150 Nwas applied vertically on top of the glass plate. Ten
minutes after the mixing had been started, the thick-
ness of the two glass plates and the interposed sealer
film was measured using a digital calliper. The differ-
ence in the thickness of the two glass plates, with and
without sealer, was recorded as the film thickness of
the experimental sealer material. The mean value of
three measurements for each sealer was recorded as
the film thickness of the material.
Knoop microhardness
The specimens used for the evaluation of radio-
opacity were also used to determine the Knoop
microhardness. For each experimental sealer, five
specimens were embedded in acrylic resin and
polished using a manual polisher (Model 3v; Arotec,
Cotia, SP, Brazil) with a felt disc saturated with in an
alumina suspension (Alumina 1.0 lm; Arotec). Thesamples were then dried at 37 C and stored for 24 hThe specimens were subjected to a microhardness test
in which five indentations (50 g 15 s1), which wereplaced 100 lm apart from each other, were assessedusing a digital microhardness tester (HMV 2; Shimadzu,
Tokyo, Japan). The calculation of the hardness
value was carried out using the following equation:
Knoop microhardness 14228 cd2
Where 14228 is a constant, c is the load in grams, d
is the length of the larger diagonal, in micro meter.
The Knoop microhardness number (KHN) was the
mean of the five indentations for each specimen.
Degree of conversion
The degree of conversion of the experimental root canal
sealers was evaluated using real-time Fourier transform
infrared spectroscopy (RT-FTIR) with a Vetrex 70
(Bruker Optics, Ettlingen, Germany) spectrometer
equipped with an attenuated total reflectance device
composed of a horizontal diamond crystal with a mir-
ror angle of 45 degrees. A support was coupled to the
spectrometer to fix the light-curing unit and standard-
ize the distance between the fibre tip and sample at
5 mm. Opus software (Bruker Optics) was used in the
monitoring scan mode, with Blackman-Harris 3-Term
apodization in a range of 4000400 cm1 and resolu-tion of 4 cm1. With this setup, one spectrum wasobtained prior to photocuring and one immediately
after photocuring. The same samples were analysed on
days 1, 7 and 14. The samples (3 lL) were directly dis-pensed onto the diamond crystal and light-activated for
40 s (n = 3). The degree of conversion was calculatedas described in a previous study (Collares et al. 2011),
considering the intensity of carbon-carbon double bond
stretching vibration (peak height) at 1635 cm1, andusing the carbonyl group at 1720 cm1 from the poly-merized and unpolymerized samples as an internal
standard (Stansbury & Dickens 2001).
Statistical analysis
The normality of the data was evaluated using the
KolmogorovSmirnov test. Statistical analysis was
performed using one-way ANOVA (Nb2O5 concentra-
tion) and Tukeys post hoc test. The degree of conver-
sion over time was evaluated using repeated
measures ANOVA at the 0.05 level of significance.
Results
The radio-opacity data, measured in pixels, are shown
in Table 1. The group with a ratio of 80 wt% and
100 wt% showed no significant difference from that of
equivalent 2 mm of Al (P > 0.05). The addition of120 wt% increased the radio-opacity, resulting in
Leitune et al. Nb2O5 for root canal sealers
2012 International Endodontic Journal International Endodontic Journal, 46, 205210, 2013 207
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values >2 mmAl (P < 0.05), but 0.05).*Indicates that was not possible to perform the flow test for group with 0% of Nb2O5.
Nb2O5 for root canal sealers Leitune et al.
2012 International Endodontic JournalInternational Endodontic Journal, 46, 205210, 2013208
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because the ability to create a thin film of sealer could
promote a better seal (de Deus et al. 2003). Although
the group containing 120 wt% of Nb2O5 had flow
values that were not in accordance with ISO 6876
(Standardization 2001), a commercially available and
widely used resin-based root canal sealer has lower
values than established by standardization (Almeida
et al. 2007). The flow property could determine the
effectiveness of filling accessory canals and voids
between core materials (McMichen et al. 2003).
The radio-opacity of root canal sealers is essential
for clinical use (Collares et al. 2010); the clinician has
to be able to distinguish the filling material from hard
and soft tissues that surround the root (Krejci et al.
1991). For this purpose, the ISO standardization
(Standardization 2001) established the reference
value of 3 mm Al. In this study, all groups had val-
ues that were significantly different from 3 mm Al.
The groups contained large weight-based amounts of
filler material; however, when considering the volu-
metric fraction of Nb2O5 relative to resin, there was a
relatively low volumetric concentration of Nb2O5(max 29.16 vol%). However, greater amounts of
Nb2O5 could not be used without compromising the
flow of the sealer (Table 1). A viable alternative could
be the addition of a second filler with the goal to
increase radio-opacity without losing the biological
properties provided by Nb2O5 (Karlinsey et al. 2006).
The addition of inorganic particles to the polymeric
matrix could change its properties, including the degree
of conversion and microhardness, because the refrac-
tive index of a given substance may decrease the avail-
ability of light energy within the polymer (Shortall
et al. 2008). In this study, the addition of filler particles
to the root canal sealer led to an increase in microhard-
ness in all groups. The degree of conversion in groups
containing Nb2O5 was lower than that in groups with-
out added filler. However, considering the methacry-
late-based sealers, the values for degree of conversion
are similar to those reported previously (Lee et al.
2011). The evaluation of degree of conversion of the
experimental root canal sealers within a specific time is
important because chemical initiators (e.g. benzoyl per-
oxide) were used in these formulations and could
increase the degree of conversion of the sealer. The
group containing 80 wt% filler was less influenced
than groups with 100 wt% and 120 wt% because the
initial value of degree of conversion showed no signifi-
cant difference compared with days 1, 7 and 14. The
presence of less filler (80 wt%) could lead a more avail-
ability of light and consequently promote a higher ini-
tial degree of conversion than groups with 100 wt%
and 120 wt%.
Niobium pentoxide was added to improve the prop-
erties of methacrylate-based sealers and introduces a
new filler with bioactive properties (Karlinsey et al.
2006). In the oral environment, methacrylate resins
degrade over time (Ferracane 2006). This degradation
is thought to be a limiting factor because it could lead
to gap formation, fluid infiltration (Kim et al. 2010)
and leaching of monomers, resulting in undesirable
tissue reactions (Yamanaka et al. 2011). Theoreti-
cally, Nb2O5 could be deposited at the root canal sur-
face during the degradation process, thereby
increasing the biocompatibility of the sealer. Further-
more, some substances are known to have the capac-
ity to induce crystal growth on material surfaces,
such as octacalcium phosphate (Barrere et al. 2001),
amorphous calcium phosphate (Johns et al. 2010),
bioglass (Hashimoto et al. 2010) and ionomer cement
(Hashimoto et al. 2010). In the present study, Nb2O5was shown to be a novel filler material, especially
with the knowledge that this oxide could promote
crystal growth and biomimetic mineralization of the
surrounding tissues because of its known bioactive
properties (Karlinsey et al. 2006).
Conclusion
The addition of Nb2O5 increased radio-opacity and
microhardness and may be a promising filler for the
production of new endodontic sealers.
Acknowledgements
The authors gratefully acknowledge CAPES (Corde-
nacao de Aperfeicoamento de Pessoal de Nvel Supe-
rior) for the scholarship, the CBMM (Companhia
Brasileira de Metalurgia e Mineracao) for providing the
niobium pentoxide and the Durr Dental Brazil for pro-
viding the VistaScan Digital Radiograph System. This
article represents a part of a PhD thesis (V.C.B.L.)
References
Alani A, Knowles JC, Chrzanowski W, Ng YL, Gulabivala K
(2009) Ion release characteristics, precipitate formation
and sealing ability of a phosphate glass-polycaprolactone-
based composite for use as a root canal obturation mate-
rial. Dental Materials 25, 40010.
Almeida JF, Gomes BP, Ferraz CC, Souza-Filho FJ, Zaia AA
(2007) Filling of artificial lateral canals and microleakage
Leitune et al. Nb2O5 for root canal sealers
2012 International Endodontic Journal International Endodontic Journal, 46, 205210, 2013 209
-
and flow of five endodontic sealers. International Endodontic
Journal 40, 6929.
Barrere F, Layrolle P, Van Blitterswijk CA, De Groot K
(2001) Biomimetic coatings on titanium: a crystal growth
study of octacalcium phosphate. Journal of Material Science
Materials in Medicine 12, 52934.
Camilleri J (2009) Evaluation of selected properties of min-
eral trioxide aggregate sealer cement. Journal of Endodontics
35, 14127.
Collares FM, Leitune VCB, Ogliari FA, Piva E, Fontanella VR,
Samuel SM (2009) Influence of the composition of an exper-
imental adhesive on conversion kinetics, flexural strength
and radiodensity. Revista Odonto Ciencia 24, 4149.
Collares FM, Ogliari FA, Lima GS, Fontanella VR, Piva E,
Samuel SM (2010) Ytterbium trifluoride as a radiopaque
agent for dental cements. International Endododontic Journal
43, 7927.
Collares FM, Ogliari FA, Zanchi CH, Petzhold CL, Piva E,
Samuel SM (2011) Influence of 2-hydroxyethyl methacry-
late concentration on polymer network of adhesive resin.
Journal of Adhesive Dentistry 13, 1259.
Collares FM, Leitune VC, Rostirolla FV, Trommer RM,
Bergmann CP, Samuel SM (2012) Nanostructured
hydroxyapatite as filler for methacrylate-based root canal
sealers. International Endodontic Journal 45, 637.
Desai S, Chandler N (2009) Calcium hydroxide-based root
canal sealers: a review. Journal of Endodontics 35, 47580.
de Deus GA, Martins F, Lima AC, Gurgel-Filho ED, Maniglia
CF, Coutinho-Filho T (2003) Analysis of the film thickness
of a root canal sealer following three obturation tech-
niques. Brazilian Oral Research 7, 11925.
Duarte MA, Ordinola-Zapata R, Bernardes RA et al. (2010)
Influence of calcium hydroxide association on the physical
properties of AH Plus. Journal of Endodontics 36, 104851.
Ferracane JL (2006) Hygroscopic and hydrolytic effects in
dental polymer networks. Dental Materials 22, 21122.
Goncalves F, Kawano Y, Braga RR (2010) Contraction stress
related to composite inorganic content. Dental Materials
26, 7049.
Hanemann T (2008) Influence of particle properties on the
viscosity of polymer alumina composites. Ceramics Interna-
tional 34, 2099105.
Hashimoto M, Iijima M, Nagano F, Ohno H, Endo K (2010)
Effect of monomer composition on crystal growth by resin
containing bioglass. Journal of Biomedical Materials Research
B Applied Biomaterials 94, 12733.
ISO 6876(2001) Dental Root Canal Sealing Materials, 2nd
edn. Geneva, Switzerland: International Organization for
Standardization.
Johns JI, ODonnell JN, Skrtic D (2010) Selected physicochemi-
cal properties of the experimental endodontic sealer. Journal
of Material Science Materials in Medicine 21, 797805.
Karlinsey RL, Hara AT, Yi K, Duhn CW (2006) Bioactivity
of novel self-assembled crystalline Nb2O5 microstructures
in simulated and human salivas. Biomedical Materials 1,
1623.
Khan AM, Suzuki H, Nomura Y et al. (1992) Characteriza-
tion of inorganic fillers in visible-light-cured dental com-
posite resins. Journal of Oral Rehabilitation 19, 36170.
Kim YK, Grandini S, Ames JM et al. (2010) Critical review
on methacrylate resin-based root canal sealers. Journal of
Endodontics 36, 38399.
Krejci I, Lutz F, Sener B, Jenss J (1991) The x-ray opacity of
tooth-coloring inlay materials and composite cements.
Schweizer Monatsschrift fur Zahnmedizin 101, 299304.
Lee BS, Wang CY, Fang YY, Hsieh KH, Lin CP (2011) A
novel urethane acrylate-based root canal sealer with
improved degree of conversion, cytotoxicity, bond
strengths, solubility, and dimensional stability. Journal of
Endodontics 37, 2469.
Leitune VC, Collares FM, Takimi A et al. (2012) Niobium
pentoxide as a novel filler for dental adhesive resin. Journal
of Dentistry [Epub ahead of print].
McMichen FR, Pearson G, Rahbaran S, Gulabivala K (2003) A
comparative study of selected physical properties of five root-
canal sealers. International Endodontic Journal 36, 62935.
Salz U, Poppe D, Sbicego S, Roulet J-F (2009) Sealing proper-
ties of a new root canal sealer. International Endodontic
Journal 42, 10849.
Shortall AC, Palin WM, Burtscher P (2008) Refractive index
mismatch and monomer reactivity influence composite
curing depth. Journal of Dental Research 87, 848.
Sideridou ID, Karabela MM (2009) Effect of the amount of
3-methacyloxypropyltrimethoxysilane coupling agent on
physical properties of dental resin nanocomposites. Dental
Materials 25, 131524.
Stansbury JW, Dickens SH (2001) Determination of double
bond conversion in dental resins by near infrared spectros-
copy. Dental Materials 17, 719.
Versiani MA, Carvalho-Junior JR, Padilha MIAF, Lacey S,
Pascon EA, Sousa-Neto MD (2006) A comparative study
of physicochemical properties of AH PlusTM and Epiph-
anyTM root canal sealants. International Endodontic Journal
39, 46471.
Yamanaka Y, Shigetani Y, Yoshiba K, Yoshiba N, Okiji T
(2011) Immunohistochemical analysis of subcutaneous
tissue reactions to methacrylate resin-based root canal
sealers. International Endodontic Journal 44, 66975.
Nb2O5 for root canal sealers Leitune et al.
2012 International Endodontic JournalInternational Endodontic Journal, 46, 205210, 2013210