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Tanta Dental Journal 10 (2013) 116e122www.elsevier.com/locate/tdj

Effect of different surface treatments of luted fiber posts on push outbond strength to root dentin

S.E. Sultan*, A.M. Korsiel, M.S. Kamel, W.M. Etman

Conservative Dentistry Dep., Faculty of Dentistry, Tanta University, Egypt

Abstract

Purpose: The purpose of this in vitro study was to evaluate the influence of different post surface treatments on the micro push outbond strength of a luting agent to a fiber post.Materials and methods: Sixty freshly extracted single rooted upper central incisor teeth were selected, cut perpendicular to thelong axis at the labial cemento-enamel junction. All root canals were instrumented, obturated, the post spaces were prepared to adepth of 11 mm. The specimens were classified into five groups according to the surface treatment performed to the post. Group 1:-no surface treatments (control group), Group 2:-surface treatment with chloroform, Group 3:-surface treatment as in group 2 inaddition to the application of silane coupling agent (Calibra), Group 4:-surface treatment by sandblasting using 50 mm aluminaparticles, Group 5:-surface treatment as in group 4 in addition to the application of silane coupling agent (Calibra), A dual-polymerizing resin luting agent (Calibra) was used for cementation of posts. Three segments (1 mm each) from the cervical 1/3of each root were obtained. Micro push out test was performed on a universal testing machine at a cross-head speed of 1.0 mm/minuntil bond failure occurred. Data were analyzed with 1-way ANOVA.Results: Micro push out bond strength of the luting agent to the post was significantly affected by surface treatment (P < 0.05).Treating the surface of the post with airborne-particle abrasion followed by silanization resulted in the highest bond strengthcompared with other treatments. There was no significant difference in bond strength between the chloroform group before andafter silanization.Conclusions: Airborne-particle abrasion in addition to silanization provided the highest increase in bond strength between the fiberpost and the resin luting agent evaluated.� 2014, Production and Hosting by Elsevier B.V. on behalf of the Faculty of Dentistry, Tanta University.

Keywords: Fiber posts; Surface treatments; Sandblasting; Silane; Chloroform; Micro push out bond strength

Open access under CC BY-NC-ND license.

* Corresponding author.

E-mail address: dr_sherif82@yahoo.com (S.E. Sultan).

Peer review under the responsibility of the Faculty of Dentistry, Tanta

University

Production and hosting by Elsevier

1687-8574 � 2014, Production and Hosting by Elsevier B.V. on behalf of

http://dx.doi.org/10.1016/j.tdj.2013.11.0Open access under CC BY-NC-ND license.

1. Introduction

Endodontically treated teeth may be damaged bydecay, excessivewear, or previous restorations, resultingin a lack of coronal tooth structure.

The restoration of these teeth may require theplacement of a post to ensure adequate retention of acore foundation [1e3]. Cast metal posts and cores havebeen traditionally used in these situations to provide

the Faculty of Dentistry, Tanta University.

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117S.E. Sultan et al. / Tanta Dental Journal 10 (2013) 116e122

the necessary retention for the subsequent prostho-dontic restoration [3]. Many dentists prefer to useprefabricated post systems because they are morepractical, less expensive, and, in some situations, lessinvasive than cast metal post and core system [4].

Recently, the use of esthetic (tooth colored) postssuch as fiber and zirconia posts in the restoration ofendodontically treated teeth has increased in popularity[5,6]. Fiber posts are currently perceived as promisingalternatives to cast metal posts, as their elastic moduliare similar to that of dentin, producing a favorable stressdistribution [5]. These posts, also, increase the lighttransmission within the root and overlying gingival tis-sues, thereby, eliminating or reducing the dark appear-ance often associated with non-vital teeth and metalposts and cores [7].

A choice must be made between different types offiber posts based on their light-transmitting capacities,non-translucent posts block light passage, therefore,light-polymerizing luting materials must be substitutedwith auto polymerizing resin composites, and thesematerials are typically fluid and have a long polymer-ization time [8].

Selecting an appropriate adhesive and luting procedurefor bonding posts to root dentin is another challenge.Sealing is expected to be strong due to recent improve-ments in the sealing ability of adhesive resin luting agents[8]. Moreover, various types of bonding systems can beused in combination with different luting resin [8,9]. In arecent investigation, carbon fiber post and core founda-tions cemented with dentin bonding and resin lutingagents showed less microleakage than those luted withglass-ionomer and zincephosphate cements [10]. Resinluting agents may be polymerized through a chemicalreaction, a light-polymerization process, or a combinationof bothmechanisms [11].Most current resin luting agentspolymerize using a dual-polymerizing process that re-quires light exposure to initiate the reaction [11,12].

Failure of fiber post-and-core restorations oftenoccurs because of de bonding between the resin lutingagent (-fiber post and/or -root canal dentin) as a resultof inadequate bond strength [1,5,13,14].

One difficulty with some of the available pre-fabricated fiber posts is that the polymer matrix be-tween the post material fibers is highly cross-linkedand, therefore, less reactive. This makes it difficult forthese posts to bond to resin luting agents and toothstructure [2,15].

Although the adhesion in the root canal represents theweakest point of the post-endodontic restoration, the post/composite adhesion needs to be considered. Bonding offiber posts to composite materials relies only on the

chemical interaction between the post surface and theresinmaterial used for luting or building-up the core. In anattempt to maximize resin bonding to fiber posts severalsurface treatments have been recently suggested [16].

2. Materials & methods

Sixty freshly extracted human periodontallyinvolved, single straight rooted upper central incisorteeth with single canal were selected. To standardize theroot canal length for this study, the roots were cut (fromthe coronal end) to a uniform length of 16 mm. The rootcanals were instrumented to a working length of 1 mmfrom the apex up to #55Master apical file.All root canalswere instrumented by the same operator using a step-back technique with stainless steel K-files. The canalswere obturated with gutta-percha cones (Dentsply-Maillefer, Ballaigues, Switzerland) and sealer (AH-26,Dentsply DeTrey GmbH, Konstanz, Germany) usinglateral condensation technique. After complete end-odontic treatment, the cervical root canal openings werefilled with an eugenol free provisional restorative ma-terial (Orafil G, Prevest Denpro Limited, India). Theroots were then fixed in standardized self-cured cylin-drical acrylic blocks to facilitate handling of specimens.The temporary restorations were removed and the cav-ities were cleaned. The post spaces were prepared to adepth of 11 mm with special preparation drills suppliedfrom the manufacturer of the Easy Post systems(Dentsply-Maillefer, Switzerland) using a low speedstraight hand piece attached to bench drilling machine.

Number 3 Easy Posts with 1.6 mm diameter at thecoronal end and 20 mm length were used. The speci-mens were randomly classified into five equal groups(n ¼ 12) according to the type of treatment performedto the post surface:-

- Group I:-No post surface treatments, consideredas a control group.

- Group II:-Post surface treatment with chloroform,the post was immersed in the solvent (chloroform)for 1 h and then wiped with a chloroformimpregnated tissue for 1 min.

- Group III:-Post surface treatment as in group II inaddition to the application of silane coupling agentusing a brush then left undisturbed for 1 min andgently air-dried.

- Group IV:-Post surface treatment by extra oralsandblasting device using 50 mm alumina particles at2 Mpa air pressure for 10 s with the posts heldperpendicular to the incoming particle stream at20mmdistance. The sandblasted post is then cleaned

Fig. 2. Upper part.

118 S.E. Sultan et al. / Tanta Dental Journal 10 (2013) 116e122

5 min in an ultrasound bath to remove any looseparticles, cleaned with alcohol and air dried [17].

- Group V:-Post surface treatment as in group IV inaddition to the application of silane coupling agentusing a brush then left undisturbed for 1 min andgently air-dried. After surface treatment of posts,one specimen from each group was examined byscanning electron microscope (JEOLeJSM5200eLV) to show the effect of surface treatmentson the topography of tested posts. A dual-polymerizing resin luting agent (Calibra estheticresin cement, Dentsply-Maillefer, Switzerland) wasused for cementation of posts according manufac-turer instructions. Three segments from the cervical1/3 of each root were obtained by sectioning theroot under water coolant using an isomet saw, thesections were 1 mm in thickness, the coronal surfaceof each section was marked with an indeliblemarker, and the thickness of each specimen wasmeasured by using a caliper. For performing micropush out test a specially designed attachment wasfabricated and it consists of 3 parts, upper part (Figs.1 and 2).

Which is carrying 1.3 mm diameter cylindricalplunger that pushes the post segment, the plunger tipwas sized and positioned to touch only the post, withoutstressing the surrounding post space walls, lower part(Fig. 3). In which there is a large cavity that receives thepushed post fragment, and a movable part (Fig. 4).

That can be placed above or removed from the largecavity of the lower part, the upper end of this movablepart have a small cavity in which the root section isplaced, at the bottom of this cavity there is a hole with

Fig. 1. Specially designed attachment.

a 2 mm diameter which is slightly larger than the postspace diameter.

The load was applied in an apical-coronal directionon the apical aspect of the root slice. The load pushedthe post toward the larger part of the root slice to avoidany limitation to the post movement owing to the postspace taper. Loading was performed on a universaltesting machine at a cross-head speed of 1.0 mm/minuntil bond failure occurred. Failure was manifested as acomplete extrusion of the post segment. The force (N)required to debond the post from the dentin disc wasrecorded for all posts. To express the bond strength inMPa, the load (Newton) at failure point was divided bythe area of the bonded interface, which was calculatedwith the following formula:

A¼ 2prh

wherep is the constant 3.14, r is the post radius, and h isthe thickness of the slice in mm.

Fig. 3. Lower part.

Fig. 4. Movable part.

119S.E. Sultan et al. / Tanta Dental Journal 10 (2013) 116e122

All data was collected and tabulated to be statisti-cally analyzed using one way analysis of variance(ANOVA) test.

3. Results

Tables 1 and 2

3.1. Scanning electron microscope (SEM)observations

The following figures represent the topography ofthe posts after each surface treatment (Figs. 5e9).

4. Discussion

In this study the lowest bond strength values wereobtained in the control group (group I) because the postsurfaces were not altered by any treatment. Thus, thelower bond strength values may be attributed to poormechanical interlocking between the smooth surface ofthe post and the resin cement. The high crosslink densityin the epoxy polymer matrix of the Easy post makes itdifficult to bond the post to composite resin luting ce-ments. Monomers of the Calibra resin luting cementcannot penetrate into the crosslinked polymer matrix[18]. Therefore, an actual chemical bond between thecomposite resin and post surface may not be feasible.

Table 1

The push out bond strength mean values (Mpa) of the tested groups.

Gp I Gp II Gp III

m � s 23.4 � 0.39 28.8 � 0.66 29.4 � 0.42

a Highly significant at 0.05 level.

Chloroform is a strong organic solvent, which waschosen as a chemical surface treatment for fiber postsin the current study. The chloroform action increasedadherence values almost 20%, and the silane had thenlittle further positive effect on these values wheregroup II recorded a mean value of 28.8 Mpa versusgroup III with a mean value of 29.4 Mpa.

These results agreed with Cheleux et al., 2007 [17]who studied the effect of different surface treatmentson the push out bond strength of fiber posts. One ofthese treatments was the chloroform which increasedthe bond strength by 20%, which was explained by thecleaning action of the chloroform to the posts surfacesfrom all surface debris creating a well-defined surfacepattern with apparent fibers making them more avail-able for micro retention by bonding agent penetration.They also used silane after chloroform and found that ithad a little positive effect than chloroform alone.

In addition the results of the current study demon-strated that airborne-particle abrasion treatment of postsurfaces (group IV) produced higher post retention thannon-treated posts (control). These findings agreed withthose obtained by Soares et al., 2008 [19] who studiedSEM images of post surfaces after airborne-particleabrasion and observed roughness on their superficialstructures. The authors attributed the roughness to frac-tured glass fibers and partial removal of the epoxymatrix.

In the present study, the highest bond strength wasobtained in group V where the posts were sandblastedand then silanated, the overall bond strength wasimproved by 50% compared to the control group. Thismight be explained as sandblasting leads to rougheningof post surface by removing the resin matrix betweenthe silicon fibers making it more retentive in additionto the chemical reaction of silanes which relies on theformation of SieOeSi siloxane bonds and conversionof the mineral surface into a less polar surfacecompatible with organic bonding agent [5,6]. Thesefindings were matching with those obtained by Perdi-gao et al. (2004) [20], which concluded that the silicafiber surfaces need to be freshly exposed preferably byphysical abrasion (sandblasting) in order to benefitfrom silane coupling effects.

Concerning the current effect of silanation it wasfound that it effectively increased the micro push out

GpIV Gp V F (p)

28.6 � 0.48 34.6 � 0.47 1337 (0.00)a

Fig. 5. SEM micrograph �500 of untreated post surfaces (group 1)

showing solid void free surface and evenly distributed parallel oriented

fibers.

Fig. 6. SEM micrograph �500 of surface treatment with chloroform

(group 2) showing expansion of the polymer network.

Table 2

Pairwise test performed for the tested groups.

Gp II Gp III Gp IV Gp V

Gp I 37.333 (26.376)a 55.952 (26.376)a 32.714 (26.376)a 84.00 (26.376)a

Gp II 18.619 (26.376) 4.619 (26.376) 46.66 (26.376)a

Gp III 23.238 (26.376) 28.05 (26.376)a

Gp IV 51.28 (26.376)a

a Significantly different groups at a level of significance ¼ 0.05.

Fig. 7. SEMmicrograph�500of surface treatmentwith chloroformþsaline (group 3) showing some fibers interrputed.

Fig. 8. SEM micrograph �500 of surface treatment with sand-

blasting (group 4) showing a rough surface creating more spaces for

micromechanical retention.

120 S.E. Sultan et al. / Tanta Dental Journal 10 (2013) 116e122

Fig. 9. SEM micrographs with of group 5 (surface treatment with

sandblasting þ silane) showing more retentive surface.

121S.E. Sultan et al. / Tanta Dental Journal 10 (2013) 116e122

bond strength values of fiber posts to the roots repre-sented in both groups III (surface treatment with chlo-roform followed by silane) & V (surface treatment withsandblasting followed by silane) compared to thechemical and micromechanical roughening of the fiberposts surfaces alone represented by groups II & IVrespectively. Using Pairwise test, a non-significant in-crease in bond strength was recorded between group II&III. Therefore using silanization after chemical treatmentof the post surfaces by chloroform did not significantlyenhance the bond strength of the posts.

On the other hand a significant difference betweengroup IV & V was recorded with an increase in the meanvalues of the push out bond strength of the specimens ofgroup V versus those of group IV which was confirmingthe results of Cheleux et al., 2007 [17] who found thatcombination of silanization with sandblasting resulted insignificantly better push out bond strength than sand-blasting alone. However these results did not confirmthose obtained by Perdigao et al., 2006 [21] who studiedthe effect of silane on the bond strength of three types offiber posts and concluded that the use of silane couplingagent did not increase the push out bond strength to any ofthe three posts. This controversy might be due to the ideaof using silane alone without any micromechanical orchemical treatments to the post surfaces. Which was nottested currently.

5. Conclusion

Within the limitations of this in vitro study of thebond strength between the post system and luting agenttested, the following conclusions were drawn:

1. The bond strength of the glass fiber-reinforced post(Easy post) luted by resin based luting cement wasinfluenced by different post surface treatments.

2. Silanization increased the bond strength of the mi-cromechanically treated fiber post surfaces, whilethe chemically treated post surfaces were not influ-enced or affected.

3. The increase in bond strength was more remarkablein the sandblasted posts followed by silanization.

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