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function.1,2 Fiber posts that are used after

endodontic treatment have some addition-

al advantages, including biocompatibility,

mechanical strength, resistance to corro-

sion, improvement of light transmission, and

the optical effects of esthetic restorations.3

An important characteristic of fiber posts

is a modulus of elasticity similar to dentin,

resin cement, and resin core materials4

so that the occlusal loads can be better

distributed along the root.5 In addition,

the restoration of endodontically treated

teeth with metal-free materials eliminates

the potential hazards of corrosion and aller-

gic hypersensitivity.6 Fiber-reinforced posts

also have the advantage of easy removal if

with prefabricated fiber post-and-core sys-

tems has been widely accepted as a treat-

ment option that offers both esthetics and

1Associate Professor, Department of Prosthodontics, Faculty of

Dentistry, Ondokuz Mayıs University, Samsun, Turkey.

2Assistant Professor, Department of Prosthodontics, Faculty of

Dentistry, Ondokuz Mayıs University, Samsun, Turkey.

3Research Assistant, Department of Prosthodontics, Faculty of

Dentistry, Ondokuz Mayıs University, Samsun, Turkey.

4Private Practice, Ankara, Turkey.

5Professor, Department of Prosthodontics, Faculty of Dentistry,

Selçuk University, Konya, Turkey.

Correspondence: Dr Ahmet Umut Güler, Ondokuz Mayıs

University, Faculty of Dentistry, Department of Prosthodontics

55139, Kurupelit, Samsun, Turkey. Email: auguler@omu.edu.tr

Effects of different acids and etching times on the bond strength of glass fiber–reinforced composite root canal posts to composite core materialAhmet Umut Güler, DDS, PhD1/Murat Kurt, DDS, PhD2/Ibrahim Duran, DDS3/

Altay Uludamar, DDS, MSc, PhD4/Ozgur Inan, DDS, PhD5

Objective: To investigate the effects of different acids and etching times on the bond

Method and Materials:

in the other groups were acid etched with 35% phosphoric acid and 5% and 9.6% hydro-

polytetrafluoroethylene mold was placed around the treated posts and filled with dual-cure

After 24 hours of water storage, the specimens were sectioned perpendicularly to the

bonded interface under water cooling to obtain 2-mm post-and-core specimens. Eight

specimens were made from each group. Push-out tests were performed at a crosshead

speed of 0.5 mm/min using a universal testing machine. Data were analyzed by one-way

α Results: The

Pthe highest bond strength values (P Conclusion: -

ing procedures tested showed significantly increased bond strength when compared with

the control group. Acid-etching with 5% hydrofluoric acid and 9.6% hydrofluoric acid for 2

minutes and with 35% phosphoric acid for 3 minutes (groups H5-120, H9-120, and P-180,

composite core material. Although the bond strength was increased by prolonged acid

(Quintessence Int 2012;43:e1–e8

Key words: acid etching, bond strength, composite core material, etching time,

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Güler et al

endodontic retreatment is required. These

systems can reduce the incidence of nonre-

trievable root fractures when compared with

prefabricated metallic posts or conventional

cast posts.9,10

If the bonding of the interface is poor,

debonding and/or fracturing of the core

and post can occur.11 A good adaptation

and reliable bonding between the post

surface and core buildup material must be

achieved.12

-

cal studies of fiber-based post systems that

present clinical failure rate. Glazer13 pub-

lished results of a study in which the results

for 52 teeth in 42 patients were analyzed.

-

cal pathology, while an additional two were

mechanical failures of the restoration. A

published prospective investigation14 dem-

onstrated a failure rate of glass fiber posts

of 12.8% after 24 months. The most frequent

types of failure were post fractures or loss

of retention. A retrospective study evaluat-

ing 1,304 teeth restored with three different

types of fiber posts from 1 to 6 years without

recording the loss of coronal tooth structure

reported a failure rate of 3.2%.15

smooth surface that limits mechanical inter-

is often recorded at the post-composite

guarantee a strong and durable fiber post-

to-composite bond.16 Therefore, several

methods for conditioning the post surface

were investigated, including infiltration of

bonding, silanization followed by bonding

of the post surface,11,18–21 airborne-particle

abrasion with corundum,20–23 tribochemi-

5,23 acid etching using

5% hydrofluoric acid followed by silani-

zation,5,23,24 and surface activation using

acetone, chloroform, hydrogen peroxide, or

hydrochloric acid followed by silanization.24

These treatments result in surface micro-

between the two surfaces and/or exposure

of the fiber by removal of the matrix, per-

mitting silanization with a silane coupling

agent. Some of these treatments may cause

detrimental effects when the treatment is

performed over a long period of time, such

as etching with hydrofluoric acid or blasting

with aluminum oxide particles.25 Mechanical

pretreatment of the glass fiber–reinforced

only is the matrix removed, but the fibers

might also be damaged, depending on the

particle size and abrasion time.26

To optimize the bonding of resin cements

the posts have been proposed, such as

etching with phosphoric or hydrofluoric

acid. The effect of etching varied depend-

ing on the acid-etching time and acid type.

The aim of this study was to investigate

the effects of different acids and etching

times on the bond strength of glass fiber–

reinforced composite root canal posts to

composite core material. It was hypoth-

esized that the bond strength achieved at

the post-core interface was affected by the

various acids and acid-etching times.

METHOD AND MATERIALS

Twenty-six fiber-reinforced composite root

being a control group that received no

The specimens in group P-30 were acid

etched with 35% phosphoric acid gel (Ultra-

30 seconds, the specimens in group P-60

were acid etched for 60 seconds, the speci-

mens in group P-120 were acid etched for

2 minutes, and the specimens in group

P-180 were acid etched for 3 minutes. After

the acid-etching procedures, all specimens

were rinsed with water for 30 seconds and

dried with oil-free air spray for 30 seconds.

The specimens in group H5-30 were

acid etched with 5% hydrofluoric acid gel

-

mens in group H5-60 were acid etched

for 60 seconds, the specimens in group

H5-120 were acid etched for 2 minutes, and

the specimens in group H5-180 were acid

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Güler et al

etched for 3 minutes. After the acid-etching

procedures, all specimens were rinsed with

water for 30 seconds and dried with oil-free

air spray for 30 seconds.

The specimens in group H9-30 were

acid etched with 9.6% hydrofluoric acid

in group H9-60 were acid etched for 60

seconds, the specimens in group H9-120

were acid etched for 2 minutes, and the

specimens in group H9-180 were acid

etched for 3 minutes. After the acid-etching

procedures, all specimens were rinsed with

water for 30 seconds and dried with oil-free

air spray for 30 seconds.

-

allel in the coronal and tapered in the apical

part of its design. A polytetrafluoroethylene

tapered part of the posts. The tapered sec-

tion was placed in the PTFE mold, while

the parallel section was used for the core

foundation to simplify the calculation of

the surface area. Only the upper cylindric

the larger diameter of 2 mm was used. It is

ideal for the post diameter to be constant

throughout the post length. A cylindric PTFE

mold was placed around the coronal part of

Photoactivation was performed by using

a light-emitting diode unit with 1,550 mW/

cm2

The tip of the light unit was initially placed

at the top of the PTFE mold for 20 seconds

and then through the mold on each side for

20 seconds, for a total exposure of 60 sec-

-

tilled water, the specimens were attached

to the arm of a low-speed saw (IsoMet,

the bonded interface into 2-mm post-and-

core segments under water cooling. Four

segments were obtained from each post-

and-core specimen—each group of eight

post-and-core specimens provided a total

of 104 post-and-core segments. The exact

was measured using a digital micrometer

was calculated using the formula: A = 2r

× ∏ × h where r is the post radius, ∏ is the

constant 3.14, and h

coronal sections were used for core foun-

dations, the bonding area was equal for all

post segments and calculated as 2 × 3.14

× 1 × 2 = 12.56 mm2.

Push-out tests were performed at a

crosshead speed of 0.5 mm/min using a

loaded with a 1.5-mm–diameter cylindric

stainless steel plunger. The tip of the equip-

ment was positioned to contact only the

of extrusion of the post segment from the

Push-out bond strength values in MPa were

then calculated by dividing this force by the

bonded area of the post segment.

using statistical software (SPSS for Windows

effect of acid-etching procedures on bond

core material. The means were then com-

-

α

each group was prepared and evaluated by

observed for surface irregularity under a

scanning electron microscope at 250× and

500× magnification.

Tip ofapparatus

FRC Postec Plus

MultiCore Flow

Fixation apparatusof sample

Space for displacedfilling material

F

Fig 1 Schematic drawing of push-out test of the specimens.

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Güler et al

RESULTS

The bond strengths were shown to be sig-

P <

standard deviations, and group differences

for the 13 groups are shown in Table 2.

In the study groups, the lowest bond

Group P-30 demonstrated a high-

P -

cant difference was observed among group

P

groups demonstrated higher bond strength

values when compared with group P-30

-

ference was observed among group H5-60

P

groups demonstrated higher bond strength

values when compared with the above

mentioned groups (P

significant difference was observed among

(P

the highest bond strength values in this

study. The differences among all groups

are listed in Table 2.

The SEM studies revealed that the

surface irregularities of the glass fiber–

reinforced composite root canal post corre-

sponded to the results of the bond strength

DISCUSSION

Within the limitations of the present study,

it can be concluded that our hypothesis

was confirmed—that the bond strengths of

significantly affected by the investigated

acid-etching procedures.

Flowable and hybrid composites have

been reported to have good adaptation at

-

ical properties of flowable composites are

generally inferior to those of conventional

composites. Therefore, a dual-cure com-

also recommended as an adhesive luting

agent and core buildup material was used

in the present study.

Table 1 One-way ANOVA table for study groups

Variable (source) df Sum of squares Mean squares F P

12 88.036 .001*

Within groups 91 51.405 0.565

Total 103

df, degrees of freedom. *Significant difference at P < .05.

Table 2 Mean bond strengths (MPa),

standard deviation (SD) values,

and group differences for the

study groups (each n = 8)

Group Mean (MPa) SD Difference*

12.51 a

P-30 13.85 .95 b

H5-30 15.38 .99 c

H9-30 15.64 .88 c

P-60 c

P-120 16.14 .43 c

H5-60 .83 d

H9-60 .59 d

H5-180 .64 d

H9-180 18.10 .53 d

H5-120 20.31 .66 e

H9-120 20.55 .54 e

P-180 .94 e

*Different letters indicate dissimilarity of groups (P

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Güler et al

A number of studies focused particularly

on the possibility to improve adhesion at the

fiber post–composite interface through vari-

ous treatments of the post surface.1,6,28–30

Mechanical and chemical treatments of

the post surfaces and changes in the

post matrix composition seemed to affect

the bond strength of resin materials to

been evaluated to dissolve the epoxy resin

matrix or methacrylate-based resin matrix

and expose fibers and filler particles so that

silanization could be effective.

Use of hydrogen peroxide24 and differ-

ent chemical agents (followed by silaniza-

resin core materials with dissolving of the

resin matrix of the post’s surface and con-

comitant exposure of undamaged fibers.31

The use of hydrofluoric acid and tribo-

chemical coating followed by silanization

resulted in damaged fibers at the surface of

24,32

Different concentrations and etching

times of acid agents were used in the

studies investigating the effect of surface

with hydrofluoric acid5,24,33,34 and phosphor-

ic acid5,35 since clear information regarding

the most appropriate etching conditions is

In the present study, 35% phosphoric

acid and 5% and 9.6% hydrofluoric acid

Fig 2 (right) SEM images of untreat-ed specimen (control) at 250× magni-fication. The undamaged glass fibers and resin matrix around the fibers can be seen (a, glass fiber; b, resin matrix).

Fig 3 (below) SEM images of treated specimens at 500× magnification. The cracks and damages on the glass fibers and dissolved resin matrix around the remaining fibers due to the different acid treatments can be seen.

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Güler et al

gel with four different etching times (30,

evaluate time and concentration effects on

the bond strength of glass fiber–reinforced

composite root canal posts to composite

core material. Even though there is no sta-

tistical significance between 5% and 9.6%

hydrofluoric acid treatments for all etching

times, the hydrofluoric acid groups showed

greater bond strength values than phos-

phoric acid groups with the exception of the

180-second etching time. According to the

images obtained with SEM, the post surface

etched with phosphoric acid was not modi-

epoxy matrix and fibers was observed on

the surfaces etched with hydrofluoric acid

This is a minority finding: The study

indicated that conditioning with hydroflu-

oric acid seemed to be very aggressive

5 Acid-

etching treatment resulted in roughness

of the post surface, which might have

the luting cement and post surfaces. The

authors attributed the roughness to frac-

tured glass fibers and partial removal of the

epoxy matrix.35

The bond strength values of the phos-

phoric acid groups increased with longer

etching times. This was also similar for

the 30- and 60-second etching hydroflu-

oric acid groups. Hydrofluoric acid–treated

groups for 120 seconds showed higher

bond strength values than those of groups

treated for 180 seconds.

Schmage et al stated that previously

performed pretests with 120-second hydro-

fluoric acid etching had shown that the

described effect of increased surface tex-

ture could be observed with increased

etching time.36 However, any conditioning

method including prolonged acid etch-

ing would reduce the post diameter and

cause misfitting posts with a wider cement

gap, resulting in lower retentive bond

strengths.26,36

while other chemical conditioning methods

affect only the glass fibers.18 This is due to

the corrosive effect of hydrofluoric acid on

the glass phase of a ceramic matrix. These

findings were confirmed when hydrofluoric

acid was used for conditioning methacry-

late-based fiber posts. Despite the improve-

ment in post-to-composite bond strength, a

noteworthy surface alteration ranging from

fiber layer was detected.16,24

Although the bond strength was increased

with longer etching times, the microstructure

thus also damaging its physicomechanic

properties. Hence, even though this method

of conditioning improved the bond strength,

other studies to evaluate the effects of this

surface treatment on the physicomechanic

-

bility and integrity of the posts.

The current study is limited to one

better understanding of the effects of dif-

ferent acids and acid-etching times on the

bond strength of core buildup materials to

-

ating the effects of different post and core

materials using artificial aging methods are

recommended. To assess long-term dura-

bility and for improved simulation of the in

vivo environment, further treatments such

as mechanical loading and thermal cycling

could be applied.

CONCLUSION

Within the limits of the present study, it was

concluded that both the different acids

and acid-etching times significantly influ-

enced the push-out bond strength between

the composite core buildup material and

P

posts, all acid-etching procedures tested

significantly increased bond strength when

compared with the control group. Although

the bond strength was increased by pro-

longed acid etching, the microstructure of

The use of acid treatments seems to be

more practical than the other applications.

However, type and concentration of acid

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Güler et al

gels and application time is an essential

factor to achieve optimal bond strength

application. Additionally, acid etching the

need for additional chairside treatments.

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