caracterizacion mecanica de cementos para postes de fibra de v
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7/29/2019 Caracterizacion Mecanica de Cementos Para Postes de Fibra de V
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d e n t a l m a t e r i a l s 2 3 ( 2 0 0 7 ) 100–105
a v a i l a bl e a t w w w . s c i en c e d i r e c t . co m
j o u r n a l h o m e p a g e : w w w . i n t l . e l s e v i e r h e a l t h . c o m / j o u r n a l s / d e m a
Mechanical characterization of resin cements used for luting
fiber posts by nanoindentation
Laura Ceballos a, Miguel Angel Garridob, Victoria Fuentes a, Jes ´ us Rodr´ ıguez b,∗
a Departamento de Ciencias de la Salud III, Universidad Rey Juan Carlos, C/Tulip ´ an s/n, 28933 M ´ ostoles, Madrid, Spainb Departamento de Ciencia e Ingenier´ ıa de Materiales, Universidad Rey Juan Carlos, C/Tulip ´ an s/n, 28933 M ´ ostoles, Madrid, Spain
a r t i c l e i n f o
Article history:
Received 29 July 2005
Accepted 6 December 2005
Keywords:
Resin cements
Fiber posts
Bonding
Mechanical properties
Nanoindentation
a b s t r a c t
Objectives. To evaluate the mechanical behavior of resin cements used for luting fiber post.
The influence of the curing mode is analysed.
Methods. Nanoindentationtechniques have beenapplied to determine hardness and Young’s
modulus of disc-shaped specimens of three types of cements: chemical- , photo- and
dual-cured, provided by Ivoclar-Vivadent. Results obtained have been compared with mea-
surements performed inside the post–cement–dentin system. Mechanical properties are
evaluated together with scanning electron micrographs showing the post–cement and
dentin–cement interfaces.
Results and Significance. Differences have been detected between mechanical measurements
performed inside the post–cement–dentin system and those carried out in laboratory disc-
shaped specimens. The close presence of post and dentin boundaries has a lot of influence
on the cement behavior. The nanoindentation measurements indicate that the photo-cured
cement exhibits a high hardness and stiffness, but with a more marked tendency to brittle
failure. The chemically cured cement is the material with higher ability to bear deformation
without damage, although its hardness and elastic modulus are significantly lower. Dual-
cured cements present the best combination of properties.
© 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
1. Introduction
The use of fiber posts to restore teeth with excessive loss
of coronal structure due to caries, trauma or overaggressive
endodontic procedures is gaining widespread acceptance with
dental clinicians [1–3]. Several characteristics of these postshave contributed to their popularity. They have comparable
elastic properties to dentin [4], inducing a stress field similar
to that of natural tooth [5]. This results in a reduction in the
incidence of root fractures, demonstrated in both in vitro [6]
and in clinical studies [2,7].
Moreover, the chemical nature of the posts allows them to
be bonded to canal walls with adhesive systems in combina-
tion with resin cements [8], avoiding friction between dentin
∗ Corresponding author. Tel.: +34 914887159.E-mail address: [email protected] (J. Rodrıguez).
walls and the post [4], and reinforcing the remaining tooth
structure [9].
However, adhesive technique performance in root canals
is a further challenge, due to the variable ability of bond-
ing systems to demineralize and infiltrate the dentin walls,
the poor control of moisture, the influence of differentdensity and orientation of dentin tubules along the root
canal, and the accessibility during handling of the materials
[8,11].
Regarding resin cements, an adequate polymerization is
utterly necessary to provide mechanical properties, such as
modulus of elasticity and hardness, good enough to reinforce
weakenedroots [12] and clinically ensure retentionof the post.
According to the curing mode, three possible alternatives may
0109-5641/$ – see front matter © 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.dental.2005.12.007
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be chosen: chemical-, photo- or dual-curing resin cements
[10].
The use of chemically cured resin cements guarantees
polymerization without the influence of post space depth, but
offers worse handling characteristics due to the absence of
control of the setting reaction. Photo-curing resin cements
allow sufficient time and control for proper seating of the post
into thecanal [12]. However,even whentranslucentfiber postsare supposed to transmit the light into the post space [8,13],
a reduction of resin cement hardness with depth has been
determined [12,13]. Dual-curing resin cements are expected to
combine favorable properties of both, auto- and photo-curing
systems.
The curing mode can also influence the amount of shrink-
age producedafter polymerization. Shrinkage stresses of resin
cements in root canals are especially relevant due to the unfa-
vorable factor of configuration that restricts the flow of resin
cement, which may affect the integrity of the adhesive inter-
face [10].
Traditionally, the mechanical properties of dental materials
on a small scale have been evaluated by means of micro-hardness tests. In recent years, the use of nanoindentation
has become very popular in several fields, mainly for its pos-
sibilities in the characterization of very small quantities of
material and, additionally, for providing simultaneous mea-
sures of hardness and elastic modulus [14].
In this work, the mechanical behavior of resin cements for
luting fiber posts has been evaluated by depth sensing inden-
tation. Three types of resin cement were studied (chemical-,
photo- and dual-curing) comparing the results obtained from
laboratory disc-shaped specimens with those derived from
actual restored teeth.
2. Materials and methods
The materials evaluated in the present study are shown in
Table 1.
Disc-shaped specimens were prepared for each resin
cement evaluated, Multilink, Variolink II Base and Variolink
II Base plus Catalyst (Ivoclar-Vivadent Schaan, Liechenstein)
using a metallic mold, 14mm in diameter and 1 mm thick.
The discs were placed over a glass plate and the materials
were inserted into thediscs. After insertion, themold wascov-
ered with a mylarsheetand a glass microscope slide. Multilink
resin cement was allowed to autocure, while Variolink II Base
Table 1 – Materials used in the study
FRC Postec (Ivoclar-Vivadent) Glass–fiber reinforced
composite posts
Multilink primer A and B
(Ivoclar-Vivadent)
Self-etching adhesive
Multilink resin cement
(Ivoclar-Vivadent)
Self-etching and self-curing
resin cement
Excite DSC (Ivoclar-Vivadent) Dual-curing adhesive
Variolink II Base
(Ivoclar-Vivadent)
Light-curing resin cement
Variolink II Base plus Catalyst
(Ivoclar-Vivadent)
Dual-curing resin cement
and Variolink II Base plus Catalyst mixture were photopoly-
merized for 30 s (Astralis 10, program ESC; Ivoclar-Vivadent).
After 20min, specimenswere removed from themoldsand
stored in darkness until evaluation.
Additionally, teeth were restoredwith fiberposts in order to
compare the mechanical behavior of the luting resin cements
in a situation similar to the clinical one. For this aim, single-
rooted teeth, free of caries and extracted for periodontal rea-sons were selected. The crowns of the teeth were eliminated
by cutting them 1mm coronally to the cementum–enamel
junction with a diamond bur mounted on a high-speed hand-
piece under water cooling.
Endodontic treatment was performed with stainless-steel
K-files (Dentsply-Maillefer, Paris, France) in combination with
2.5% sodium hypochlorite irrigation. The canals were filled
with laterally condensed guttapercha and TopSeal sealer
(Dentsply De-Trey GmbH, Konstanz, Germany).
The post space was prepared with the drills provided by
the manufacturer of the posts (FRC Postec, Size 1; Ivoclar-
Vivadent), leaving 4 mm of guttapercha in the apical portion.
The specimens were randomly allocated to three experi-mental groups according to the adhesive system and resin
cement applied. In all cases, the glass–fiber reinforced com-
posite posts FRC Postec (Size 1: length 15mm and a 0.8mm
diameter in the apical extreme; Ivoclar-Vivadent) were used.
They were all cleaned with alcohol after try-in and silanized
for 60 s (Monobond S, Ivoclar-Vivadent).
In group 1, the specimens were treated with Multilink
Primer A/B (Ivoclar-Vivadent) and the self-curing and self-
etching cement Multilink(Ivoclar-Vivadent) according to man-
ufacturer’s recommendations. Multilink Primer A and B were
mixed and applied into the root canal walls by means of a
microbrush. The excessive adhesive solution was removed
with a paper point and after 15 s, it was dried but not light-cured. Multilink cement was mixed and the post was coated
with it and inserted into the post space.
In group 2, the posts were luted with the dual-curing
adhesive Excite DSC (Ivoclar-Vivadent) and the light-curing
cement Variolink II Base (Ivoclar-Vivadent). The root canal
walls were etched with 35% phosphoric acid (Ultradent, South
Jordan) for 15 s, water rinsed and then gently dried with paper
points. This adhesive is offered in a single-dose vessel with
an applicator indicated for root canals. Excessive adhesive
was removed with a paper point. The adhesive was polymer-
ized for 10 s (Astralis 10 using ADH program; Ivoclar-Vivadent).
Then the posts were covered with Variolink II Base cement
and seated into place. The cement was light polymerizedthrough the post for 30 s (Astralis 10, program ESC; Ivoclar-
Vivadent).
Finally, in group3, theposts were also luted with ExciteDSC
adhesive (Ivoclar-Vivadent) and the dual-curing cement Var-
iolink II (Ivoclar-Vivadent). The adhesive system was applied
as previously described, but it was not light-cured. Variolink II,
Baseplus Catalyst, were mixedand applied covering the posts.
Fiber posts were seated and the cement was polymerized also
for 30 s (Astralis 10, program ESC; Ivoclar-Vivadent).
Samples were included in resin blocks and after 24 h sam-
pleswere sectioned perpendicularto theirlong axis(Accutom-
5, Struers, Copenhagen, Denmark), in order to obtain sections
from thecoronal andapical root areas. Surfaces were polished
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with alumina suspension slurry of 3 m and OP-A (Struers,
Copenhagen, Denmark).
Indentations were made on the disc-shaped specimens
and in different regions of the resin cement used to lute the
fiber post. Young’s modulus and hardnessof the cements were
determined from the load–displacement curves following the
Oliver–Pharr methodology [15].
2.1. Preparation of the samples for scanning electron
microscopy observation
Selected specimens from each group with their corresponding
posts were prepared for scanning electron microscope (SEM)
observation.
In order to observe hybrid layer formation, samples were
longitudinally sectioned, demineralized with 35% phosphoric
acid for 15 s, deproteinized with 2% sodium hypochlorite for
120 s and dehydrated with increasing concentrations of alco-
hol [8].
Other samples were immersed in a solution of 30% HCl for
24h and in2% sodiumhypochlorite for 10minin order to com-
pletely eliminate the dental tissues for better observation of
resin tags formation [8].
Finally, samples were mounted on aluminum stubs with
carbon cement and sputter coated with gold (Sputtercoater,
Baltec, SCD005) and observed under a Philips XL 30 environ-
mental scanning electron microscope (ESEM).
3. Results and discussion
3.1. Nanoindentation tests
Fig. 1 shows an example of the load–displacement curvesobtained from the nanoindenter for the disc-shaped speci-
mens. As can be appreciated, the nanoindentation technique
is quite sensitive to material behavior. Elaborate results are
includedin Table 2, where apart fromhardness, H, and Young’s
modulus, E, the ratios H /E and H2 /E are also included. The
magnitude H /E can be considered as a measure of the mate-
rial’s ability to bear elastic deformation. In other words, H /E
Table 2 – Nanoindentation data from disc-shapedspecimens
Cements E (GPa) H (GPa) H /E H2 /E(GPa)
Multilink (self-curing
cement)
4.9 (0.2) 0.21 (0.01) 0.042 0.009
Variolink II Base(light-curing cement) 8.8 (0.5) 0.31 (0.03) 0.035 0.011
Variolink II Base plus
Catalyst (dual-curing
cement)
7.4 (0.2) 0.31 (0.01) 0.042 0.013
Average values and standard deviations are in parentheses.
is related to the deformation limit before permanent dam-
age is caused. On the other hand, H2 /E can be understood
as a measure of the material’s ability to store elastic energy.
Both magnitudes are significant in the mechanical perfor-
mance of the resin cement within the tooth restored with a
fiber post. According to the results obtained, the chemically
cured cement, Multilink (Ivoclar-Vivadent), presents the low-est values of stiffness and hardness, although its ability to
being deformed without damage is superior to other cements.
Photo-cured cement, Variolink II Base(Ivoclar-Vivadent), is the
stiffest and hardest, but its low value of H /E is a warning of
brittle failure. Dual-cured cement, Variolink II Base plus Cata-
lyst(Ivoclar-Vivadent) seems to posses thebest combination of
properties. It is almostas stiffand hardas thephoto-cured ver-
sion, but with a much higher ability to be reversibly deformed.
One of the most valuable advantage of nanoindentation
is the possibility of testing the cements in situ, i.e., inside
the post–resin cement–dentin system. Obviously, the situa-
tion is clearly different from that in the disc-shaped speci-
mens, mainly due to the influence of viscosity, uncontrollablevoid formation, thickness, factor of configuration, etc. A very
thin layer of cement does not have to behave as the bulk
cement characterized from disc-shaped specimens. Table 3
summarized theresultsobtainedin each type of resincement,
measured in different regions. These results provide appeal-
ing conclusions. Multilink (Ivoclar-Vivadent), the chemically
cured cement, exhibited remarkable changes in the appar-
Fig. 1 – Nanoindentation load–displacement curves from disc-shaped specimens.
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ent hardness and Young’s modulus. The values of H and E
measured in situ increase by almost 100%. Interestingly, the
ratio H /E is not so severely altered, remaining constant at the
coronal region and exhibiting increases of 40% at the apical
zone.
Fig. 2 – ESEM micrograhs showing: (a) gap at the interface
obtained with Multilink Primer and resin cement ( ×1000);
(b) interface obtained with Excite DSC and Variolink II Base
( ×800); (c) interface detected for Excite DSC and Variolink II
Base plus Catalyst ( ×800).
Fig. 3 – ESEM micrographs showing: (a) resin tags at
coronal and mid-zones for Multilink Primer and resin
cement ( ×1200); (b) resin tags for Variolink II Base ( ×80); (c)
resin tags at coronal and mid-zones for Variolink II Base
plus Catalyst ( ×500).
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Table 3 – Nanoindentation data from in situ specimens
Cement Region E (GPa) H (GPa) H /E H2 /E (GPa)
Multilink (self-curing cement) Coronal 8.1 (0.4) 0.38 (0.01) 0.047 0.018
Apical 7.1 (0.3) 0.43 (0.02) 0.062 0.027
Variolink II Base (light-curing cement) Coronal 9.4 (0.6) 0.29 (0.04) 0.030 0.009
Apical – – – –
Variolink II Base plus Catalyst (dual-curing cement) Coronal 7.0 (0.3) 0.38 (0.02) 0.054 0.021
Apical 6.9 (0.3) 0.31 (0.02) 0.045 0.014
Average values and standard deviations are in parentheses.
Photo-cured Variolink II Base cement (Ivoclar-Vivadent) is
virtually unaltered in all the properties measured. It is worthy
of note to explain here, that an improper curingprocessmakes
it difficult to obtain consistent results in the apical region. The
difficulties of attainingcomplete photo-curinghave previously
been reported and it is one of the drawbacks of this type of
cement, confirmed in this work.
Finally, as is expected, the dualcement, Variolink II (Ivoclar-Vivadent) brings together the best properties of the other
cements. Itshardness andstiffness values areas high as those
of the photo-cured cement, but with a deformation capability
similar to that of thechemically curedcement. No appreciable
differences are observed between coronal and apical regions
in this case.
It is clear that the boundary conditions are decisive when
the thickness of the cement layer is quite low. The close prox-
imity of thepost andthe dentin surfacesplays a displacement
constraint role, leading to higher values of hardness and elas-
tic modulus. It would be very significant to analyse if cracks
and discontinuities between resin cement and post or dentin
are observed. The presence of this type of defect may partiallycancel the shrinkage stresses caused by polymerization.
3.2. Scanning electron microscopy observations
The interface obtained when Multilink adhesive and resin
cement were applied showeda discontinuousgap between the
resin cement and the infiltrated dentin, while this situation is
not observed in the other cements (Fig. 2).
Moreover, at this level, there were zones with no resin tags
and others where they only plugged the tubules, probably due
to the reduced density of tubules [16]. Also, many small and
few bigger voids in the resin cement were visible. In the coro-
nal and mid-zones, few areas were detected with long andnumerous resin tags. Generally, resin tags were short and no
adhesive lateral branches were observed (Fig. 3a).
Unlike self-etching adhesive Multilink, the density of the
resintagswas very high in coronal andmid-zones when Excite
DSC was applied after acid etching, regardless of the resin
cement used. Resin tags were also very long and numerous
lateral branches were observed (Fig. 3b). Probably phosphoric
acid is more effective in penetrating thick smear layers and
demineralizing the underlying dentin [10,11].
When light-curing Variolink II was used, areas were the
cement was detached from the post surface could be detected
in its apical extreme, being visible only in small areas. More-
over, short resin tags were observed in these areas. It may be
thatthe higher viscosityof thiscementrestricted itsflow along
the post space or that it was not properly polymerized due to
the attenuation of light with depth (Fig. 3c).
Posts bonded with Variolink II in dual-curing mode,
were completely covered with the resin cement. When the
dentin–cement interface was examined, the adhesive could
not be clearly detected, probably because it wasnot photopoly-
merized before post luting.The thickness of the cement layer changed according
to the different root canal morphologies. Some voids were
observed in the three resin cements evaluated, probably due
to their viscosity that restricts their placement inside the
post space and the mixing procedure of the base and catalyst
pastes.
Acknowledgements
Authors are indebted to the company Ivoclar-Vivadent for
providing the materials used in this study. Thanks are also
extended to the University Rey Juan Carlosfor partiallyfinanc-ing this work.
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