The effect of sandblasting on adhesion of a dual-cured resincomposite to methacrylic fiber posts: Microtensile bondstrength and SEM evaluation

Ivana Radovic a,b,*, Francesca Monticelli c, Cecilia Goracci b, Alvaro Hafiz Cury b,d,Ivanovic Coniglio b, Zoran R. Vulicevic a, Franklin Garcia-Godoy e, Marco Ferrari b

aClinic for Pediatric and Preventive Dentistry, Faculty of Dentistry, University of Belgrade, Dr. Subotica 11, Beograd 11000, SerbiabDepartment of Dental Materials and Restorative Dentistry, Policlinico ‘‘Le Scotte’’, University of Siena, Viale Bracci, Siena, ItalycDental Materials, University of Granada, 18071 Granada, SpaindBauru Dental School, University of Sao Paulo, BrazileBioscience Research Center, Biomaterials Research Center, and Clinical Research Center, College of Dental Medicine,

Nova Southeastern University, 3200 South University Drive, Fort Lauderdale, FL 33328, United States

j o u r n a l o f d e n t i s t r y 3 5 ( 2 0 0 7 ) 4 9 6 – 5 0 2

a r t i c l e i n f o

Article history:

Received 28 June 2006

Received in revised form

24 January 2007

Accepted 26 January 2007

Keywords:

Fiber posts

Microtensile bond strength

Sandblasting

Silane coupling

a b s t r a c t

Objectives: To evaluate the influence of different surface treatments on the microtensile

bond strength of a dual-cured resin composite to fiber posts.

Methods: Thirty-two glass methacrylate-based fiber posts (GC Corp.) were used in the study.

Posts were divided into two groups, according to the surface pretreatment performed. Group

1: sandblasting (Rocatec-Pre, 3 M ESPE). Group 2: no pretreatment. In each of the two groups

posts received three types of additional ‘‘chair-side’’ treatments. (1) Silane application

(Monobond S, Ivoclar Vivadent); (2) adhesive application (Unifil Core self-etching bond,

GC); (3) no treatment was performed. A dual-cured resin composite (Unifil Core, GC) was

applied on the posts to produce cylindrical specimens. Specimens were cut to obtain

microtensile sticks that were loaded in tension at a cross-head speed of 0.5 mm/min until

failure. The morphology of the post/composite interface and the post surface morphology

were evaluated under SEM. Statistical analysis was performed with two-way ANOVA and

Tukey test for post hoc comparisons (p < 0.05).

Results: Post surface pretreatment did not prove to be a significant factor in post-composite

bond strength ( p = 0.08), whereas ‘‘chair-side’’ treatment modalities and the interaction

between pretreatment and treatment showed a significant influence on bond strength

( p < 0.001). When no ‘‘chair-side’’ treatment was performed, bond strength was signifi-

cantly higher on sandblasted posts. Additional adhesive application resulted in significantly

lower bond strength on sandblasted posts. When no pretreatment was performed, silane

application resulted in higher bond strength than adhesive application.

Conclusions: Sandblasting may give an increase in microtensile strength to methacrylate-

based glass fiber posts, eliminating the need for additional ‘‘chair-side’’ treatments. Redu-

cing the number of clinical steps could contribute to simplify the clinical procedures.

# 2007 Elsevier Ltd. All rights reserved.

avai lable at www.sc iencedi rec t .com

journal homepage: www. int l .e lsev ierhea l th .com/ journals / jden

* Corresponding author at: Clinic for Pediatric and Preventive Dentistry, Faculty of Dentistry, University of Belgrade, Dr. Subotica 11,Beograd 11000, Serbia. Tel.: +381 112684581.

E-mail address: ivana.radovic@iritel.com (I. Radovic).

0300-5712/$ – see front matter # 2007 Elsevier Ltd. All rights reserved.doi:10.1016/j.jdent.2007.01.009

j o u r n a l o f d e n t i s t r y 3 5 ( 2 0 0 7 ) 4 9 6 – 5 0 2 497

1. Introduction

Reconstructing endodontically treated teeth with prefabricated

fiber post and core systems has been widely accepted as a

treatment option offering both esthetics and function.1,2 The

advantages of fiber post and core restorations have been

demonstrated in in vitro studies.3–9 These systems can reduce

the incidence of non-retrievable root fractures when compared

to prefabricated metallic posts or conventional cast posts.3–9

Retrospective10–12 and prospective13–18 clinical studies have

shown overall satisfactory performance of endodontically

treated teeth restored with fiber post and core systems.

An important characteristic of fiber posts is a modulus of

elasticity similar to dentin, resin cements and resin core

materials.19 This feature is most beneficial in the presence of a

homogeneous post-composite-dentin structure that would

allow optimal stress distribution.20 Therefore, the importance

of optimal coupling between fiber post system components

has been recognized and investigated. A number of studies

focused particularly on the possibility to improve adhesion at

the fiber post-composite interface through various treatments

of post surface.21–29

An increase in bond strength to flowable composites was

observed when fiber posts were silanized,24 treated with a

combination of hydrogen peroxide etching and silanization,28

as well as when chemical pretreatment with potassium

permanganate followed by silanization was employed.29

Furthermore, application of the silane/adhesive coupling

was shown to improve bond strength to hybrid composite.27

Adhesion of dual-cure resin composite to epoxy resin-based

fiber posts was improved when the post surface was treated

with a dual cured bonding agent or was silanized.30

The possibility of improving the adhesion between fiber

posts and resin cements has been investigated to a somewhat

lesser extent. Sandblasting followed by silane coating,

sandblasting alone and tribochemical treatment (CoJet) sig-

nificantly increased shear bond strength of resin cements to

methacrylate based glass fiber posts.26 CoJet treatment

significantly increased the resistance to cyclic loading of teeth

restored with adhesively luted glass fiber posts, which was

assumed to derive from an effective bonding of resin cement

Table 1 – Composition, batch numbers and the application mo

Material Composit

Rocatec-Pre Aluminum oxide (particle s

Monobond S (Ivoclar Vivadent).

Batch no. F68158

1% 3-methacryloxypropyltr

(3-MPS), ethanol/water-bas

Unifil Core self-etching bond

(GC Corporation). Batch no. 0511251

Liquid A: ethanol, water, 4-

silica, catalyst. Liquid B: eth

Unifil Core resin cement/core material

(GC Corporation). Batch no. 0511251

Pastes A and B: urethane d

dimethacrylate, photo/chem

fluoro-amino silicate glass

GC fiber post (GC Corporation).

Batch no. 21700BZZ00408000

Glass fibers (77 vol%), meth

resin matrix (23 vol%)

a Information from the manufacturers.b Manufacturer’s recommended procedure is: sandblast from the dista

Considering the size of fiber posts, the sandblasting time was reduced to

to the posts with a reinforcing effect on the teeth.31

Sandblasting of the surface of the glass-fiber epoxy resin

posts significantly improved the retention of posts adhesively

luted with a dual cured resin cement.22

Sandblasting is routinely applied in general industry to

provide surface roughening making materials more bondable.

It is commonly employed in ceramic32 and composite repair

procedures,33–35 indirect composite bonding,36 for pretreat-

ment of metal surface in metal–ceramic restorations,37 or as a

part of a tribochemical silica-coating process.38

Nevertheless, the information on the effect of sandblasting

alone or combined with additional ‘‘chair-side’’ treatments on

bond strength to fiber posts is lacking. Therefore, the aim of

this investigation was to evaluate the influence of sandblast-

ing pretreatment and different ‘‘chair-side’’ treatments of

methacrylate based fiber posts on the microtensile bond

strength with a dual-cured resin composite. The null hypoth-

esis tested was that various combinations of surface

pre-treatment and ‘‘chair-side’’ treatment did not influence

the adhesion of methacrylate based fiber posts to dual-cured

resin composite.

2. Materials and methods

Thirty-two translucent methacrylate-based glass fiber posts

(GC Corporation, Tokyo, Japan) with a diameter of 1.6 mm

were used in the study. Posts were divided into two groups,

according to the surface pretreatment performed. Group 1:

sandblasting with 110 mm aluminum oxide particles (Rocatec-

Pre, 3 M ESPE, St. Paul, MN, USA) for 5 s at 2.8 bar (0.28 MPa)

from a distance of 1 cm. In Group 2 no pretreatment was

performed. Each group was further divided into three

subgroups (n = 5), according to the additional ‘‘chair-side’’

treatment performed. Subgroup 1: silane application (Mono-

bond S, Ivoclar Vivadent, Schaan, Liechtenstein); subgroup 2:

adhesive application (Unifil Core self-etching bond, GC

Corporation); subgroup 3: no additional ‘‘chair-side’’ treat-

ment. The materials were used according to the manufac-

turers’ instructions. The chemical composition, batch

numbers and the application modes are reported in Table 1.

de of the materials used in the study

iona Application mode

ize: 110 mm) Sandblasting from a distance of 1 cm at

2.8 bar (0.28 MPa) for 5 sb

imethoxysilane

ed solvent

Apply to the post surface. Air dry

after 60 s

MET, dimethacrylate,

anol, catalyst

Mix liquid A and liquid B; (1:1) apply

mixture to the post surface for 1–2 s;

gently air dry; light cure

imethacrylate,

ical initiator,

Mix components; seat the post

immediately; light cure

acrylate –

nce of 1 cm at 2.8 bar for 15 s for the area of approximately 1 cm2.

5 s.

j o u r n a l o f d e n t i s t r y 3 5 ( 2 0 0 7 ) 4 9 6 – 5 0 2498

2.1. Composite build-up and microtensile bond strengthtest procedures

A dual-cured resin composite (Unifil Core, GC Corporation)

was applied on the posts to produce cylindrical specimens

with the post in the center, using a transparent plastic matrix.

The procedure previously described by Goracci et al. for core

build-up materials was followed.24 All specimens were

prepared by the same investigator to ensure standardization.

Each post was positioned upright on a glass slab, and secured

with a drop of sticky wax. A cylindrical plastic matrix was

placed around the post and adjusted so that the post would be

exactly in the middle. The matrix was 10 mm in diameter. In

height, the matrix was extended only to the cylindrical portion

of the post (about 10 mm), since for an appropriate cutting of

the microtensile specimens, it is desirable that the post

diameter is constant throughout the post length. The two

components of resin composite were mixed, applied on the

post filling the matrix completely, and light cured for 40 s with

a halogen curing light (600 mW/cm2 output; VIP; Bisco,

Schaumburg, IL, USA) directly from the open upper side of

the matrix and through the post. Additional 40 s irradiations

were performed from each side of the cylinder prior to the

removal of the matrix to ensure optimal polymerization of the

composite material.

Cylinders were mounted in a cutting machine (Isomet 1000,

Buehler, Lake Bluff, IL, USA) and sectioned under water cooling

to obtain a slab of uniform thickness, with the post in the

center and composite on each side. From each slab, 6–8 sticks

of 1-mm in thickness were obtained, resulting in the multiple

specimens (32 on average per subgroup) that were available for

microtensile bond strength testing. Beams were glued (Super

Attak Gel, Henkel Loctite Adesivi S.r.l., Milano, Italy) to the two

free sliding components of a jig, which was mounted on a

universal testing machine (Triax, Controls S.P.A., Milano, Italy)

and loaded in tension at a crosshead speed of 0.5 mm/min

until failure occurred at either side of the post-composite

interface. The dimensions of the interface on each beam were

measured with a digital caliper to the nearest 0.01 mm. No

pretesting failures occurred during cutting and testing

procedures. Schematic drawing of specimen preparation for

microtensile testing is shown in Fig. 1.

Failure modes were evaluated with a stereomicroscope

(Nikon SMZ645, Tokyo, Japan) at 40� magnification and

recorded as adhesive (at the post/composite interface),

cohesive (within the post or the composite) or mixed (a

Fig. 1 – Schematic drawing of specimen preparation for

microtensile bond strength testing. C, composite; P, post.

combination of the two modes of failure in the same

interface). Bond strength was expressed in MegaPascals

(MPa), dividing the load at failure in Newtons by the bonding

surface area. As the bonded interface was curved, its area was

calculated using a mathematical formula previously applied

by Bouillaguet et al.39

2.2. SEM evaluation

One post was randomly selected from each of the two main

groups for SEM examination of the surface morphology. The

posts were ultrasonicated in 96% alcohol for 2 min and air

dried. Following core build-up procedure, one post-composite

cylinder from each subgroup was randomly chosen for the

SEM evaluation of the bonded interface. Samples were cut into

1.5 mm thick cross-sections (Isomet 1000; Buehler). Sections

were polished with wet abrasive SiC papers, cleaned with

orthophosphoric acid for 15 s, rinsed with water, ultrasoni-

cated in 96% alcohol for 2 min and air dried. Each specimen

was mounted on a metallic stub, sputtered with gold–

palladium (Polaron Range SC7620; Quorum Technology, New-

haven, UK), and observed under an SEM (JSM 6060 LV, JEOL,

Tokyo, Japan) at different magnifications.

2.3. Statistical analysis of the microtensile bond strengthdata

A preliminary linear regression analysis showed that the post-

composite cylinder did not have a significant influence on the

measured bond strength; therefore, the sticks were considered

as independent within each group. After analyzing the bond

strength data for the normality of data distribution (Kolmo-

gorov–Smirnov test) and homogeneity of variances (Levene’s

test), a two-way ANOVA was applied with bond strength as the

dependent variable, and types of surface pretreatment and

‘‘chair-side’’ treatment as factors. The Tukey test was used for

post hoc comparisons. In all the tests, the level of significance

was set at p < 0.05 and calculations were handled by the SPSS

13.0 software (SPSS Inc.; Chicago, IL, USA).

3. Results

3.1. Microtensile bond strength

Results of microtensile bond strength testing are summarized

in Table 2 and Fig. 2. Statistical analysis revealed that post

surface pretreatment was not a significant factor ( p = 0.08),

while ‘‘chair-side’’ treatment had a significant influence on

bond strength (p < 0.001). When the results were pooled for

each ‘‘chair-side’’ treatment regardless of the pretreatment,

post hoc comparisons (Tukey test) revealed that no ‘‘chair-

side’’ treatment and silanization resulted in comparable bond

strengths while the values were significantly lower when the

adhesive was applied. The interaction of the two factors was

also significant (p < 0.001). This lead to post hoc comparisons

(Tukey test) in which all six groups were compared to assess

which group means differed from which others. The Tukey

test revealed that sandblasting significantly improved bond

strength when no ‘‘chair-side’’ treatment was performed

Table 2 – Post-composite microtensile bond strength[MPa]

Treatment Pretreatment

Sandblasting None

Monobond S 19.76 [6.16]AB 21.67 [7.13]AB

Unifil Core self-etching bond 14.29 [6.02]C 14.12 [4.90]C

None 23.97 [6.82]A 17.67 [5.31]BC

Numbers are means. Values in brackets are standard deviations.

Different superscript letters (A–C) indicate statistically significant

differences.

Fig. 2 – Post-composite microtensile bond strength.

Fig. 4 – Representative SEM micrographs of a post surface.

After sandblasting (A) the surface appeared more retentive

compared to the conventional post surface (B).

j o u r n a l o f d e n t i s t r y 3 5 ( 2 0 0 7 ) 4 9 6 – 5 0 2 499

(Table 2). The values in this group were comparable to

experimental groups ‘‘sandblasting/Monobond S’’ and ‘‘no

pretreatment/Monobond S’’. Adhesive application resulted in

significantly lower bond strength on sandblasted posts, while

on conventional posts results were comparable with no

‘‘chair-side’’ treatment. Application of silane had no influence

on bond strength, regardless of the pretreatment. In group

‘‘sandblasting/Monobond S’’ and ‘‘sandblasting/no treat-

ment’’ cohesive failures within the fiber post occurred in 47

and 35% of tested beams, respectively. In the other groups the

most frequent type of failure was adhesive (Fig. 3).

Fig. 3 – Failure d

3.2. SEM evaluation

Sandblasting created a rough surface along the entire post

length (Fig. 4A), providing additional spaces for micromecha-

nical retention compared to the surface of a conventional post

istribution.

j o u r n a l o f d e n t i s t r y 3 5 ( 2 0 0 7 ) 4 9 6 – 5 0 2500

(Fig. 4B). Cross-sections of the post-composite interfaces

exhibited a good adaptation of the resin composite to the

post surface in groups: ‘‘sandblasting/Monobond S’’, ‘‘sand-

blasting/no treatment’’, ‘‘no pretreatment/Monobond S’’ and

‘‘no pretreatment/no treatment’’ (not shown). No defects and

no discontinuities occurred along the interface, and no

significant differences in the morphology of the interface

between these groups were noticed. In groups where adhesive

was applied, gaps between the post surface and the adhesive

layer were frequently observed, both on sandblasted and

conventional posts (not shown), without significant differ-

ences in gap occurrence and morphological appearance.

4. Discussion

Unifil Core belongs to the group of materials that are

formulated to be used both for cementation and core-build-

up procedures. However, the experimental set-up employed in

this investigation has limitations that render it more appro-

priate for simulating a core-build-up procedure than a luting

procedure. The amount of material that was placed around the

posts is considerably thicker than the cement layer between

the fiber post and root canal. In the clinical situation, a much

higher C-factor is present, as well as an unfavorable interac-

tion between C-factor and shrinkage stress that could

interfere with bond strength values.40 However, microtensile

tests allow bond strength measurements between resin

cements or core materials and surface of fiber posts. Assessing

fiber post-resin cement bond strength with conventional

shear bond strength tests required the post surface to be

removed,26 while tensile bond strength tests have been

conducted with discs of post materials.41,42 Therefore, micro-

tensile bond strength values measured after bonding to the

original post surface may be advantageous and more clinically

relevant.

Significant differences in bond strength were found

between experimental groups, which led to the rejection of

the null hypothesis. The highest bond strength was recorded

on sandblasted posts with no additional ‘‘chair-side’’ treat-

ment. Results in this group were significantly better than the

results on conventional posts with no additional treatment.

SEM evaluation supported bond strength data (Fig. 4A),

revealing a more retentive surface created by sandblasting.

This finding is in accordance with others demonstrating the

beneficial influence of sandblasting on retention of epoxy

resin based fiber posts.22 Significantly higher bond strengths of

resin cements to sandblasted posts were also observed on

methacrylate26 and epoxy resin-based fiber posts (Wang et al.,

unpublished data, 2006).

Application of silane did not result in increase in bond

strength, regardless of the pretreatment. This finding is in

contrast with previous studies that reported beneficial

influence of silanization on bond strength to conventional24

and sandblasted fiber posts.26 The mechanism of silane action

relies on formation of bonds between its functional alkoxy

groups and OH-covered inorganic substrates. Since the resin

matrix of fiber posts contains highly cross-linked monomers,

only the exposed fibers on the post surface could provide sites

for chemical bonding with the silane molecules. As the

contribution of such a chemical interaction to fiber post-

composite bond strength is considered to be fairly low, it is

assumed that the increase in surface wettability induced by

silane application plays a more important role.24 However, it

was shown that surface energy characteristics of adherend

and adhesive determine fiber post-composite bond strength in

the minor part, while the other factors remained to be

identified.21 Bond strength of Unifil Core to epoxy resin fiber

posts silanized with Monobond S was noticeably lower than in

the present investigation.43 Since GC fiber post is methacrylate

based, it can be speculated that the dual-cured resin

composite bonded to the organic matrix of fiber posts,

consequently influencing bond strength to a greater extent

than the potential surface wetting capacity of the silane

applied. Nevertheless, bond strength to conventional silanized

posts (‘‘no pretreatment/Monobond S’’) was comparable to

bond strength to sandblasted posts (‘‘sandblasting/no treat-

ment’’) (Table 2).

Monobond S is a single component pre-hydrolyzed silane.

On the other side, two-component systems have been

introduced for ‘‘on-demand’’ hydrolysis. In these systems

the silane is rapidly hydrolyzed when mixed with the acidic

phosphate monomers like 10-methacryloloxydecyl dihydro-

genphosphate (10-MDP), which are present in the water-

containing dentin adhesives. It would be of interest to

investigate whether the beneficial effect of a two-component

system on epoxy resin-based fiber posts27,30 could be observed

using fiber posts that contain methacrylate matrix.

Coating the posts with the proprietary self etching adhesive

(Unifil Core self-etching bond) resulted in the lowest bond

strengths, regardless of the pretreatment. Moreover, gaps

were frequently observed between the post and the adhesive

layer. No discontinuities were seen between the adhesive

layer and the cement. In contrast to these findings, the

application of a dual cured bonding agent significantly

improved adhesion to epoxy resin based fiber posts.30 The

authors speculate that the water content and acidity of the

self-etching adhesive used in this study may have influenced

bonding to fiber post surface. A possible mechanism involved

could be the phase separation of adhesive monomers from

water upon evaporation of ethanol solvent, that was demon-

strated to occur in HEMA-free (2-hydroxyethyl methacrylate)

one-step self-etching adhesives.44 Remnants of water may

have affected the polymerization of the adhesive, decreasing

bond strength and influencing gap formation at the adhesive-

post interface.

In general, higher bond strengths resulted in a superior

percentage of cohesive failures (Fig. 3), correlating with

previous investigations of other authors.41,42 The vast majority

of cohesive failures occurred within the fiber post, which may

be the result of an unfavorable coupling between glass fibers

and methacrylate matrix of the fiber post.

Although sandblasting may give an increase in micro-

tensile strength to methacrylate-based glass fiber posts, its

effects should be further investigated. Concern was raised

regarding the possible volume loss induced by sandblasting or

tribochemical coating procedures.45 Therefore, further

research is necessary in order to agree on the optimal particle

size, distance, pressure and time of application. Additional

application of a self-etching adhesive to methacrylate-based

j o u r n a l o f d e n t i s t r y 3 5 ( 2 0 0 7 ) 4 9 6 – 5 0 2 501

fiber posts should be avoided, since no increase in bond

strength could be observed. Moreover, long term durability of

fiber post-composite bonds following various treatments of

post surface under clinical and laboratory conditions remains

to be determined.

5. Conclusion

Sandblasting may give an increase in microtensile strength to

methacrylate-based glass fiber posts, eliminating the need to

apply additional ‘‘chair-side’’ treatments. Reducing the num-

ber of clinical steps could contribute to simplify the clinical

procedures.

Acknowledgements

The authors thank the manufacturers for the generous

donation of the materials used in the study.

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