Scholarly article on topic 'Effect of different surface treatments of luted fiber posts on push out bond strength to root dentin'

Effect of different surface treatments of luted fiber posts on push out bond strength to root dentin Academic research paper on "Materials engineering"

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Tanta Dental Journal
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{"Fiber posts" / "Surface treatments" / Sandblasting / Silane / Chloroform / "Micro push out bond strength"}

Abstract of research paper on Materials engineering, author of scientific article — S.E. Sultan, A.M. Korsiel, M.S. Kamel, W.M. Etman

Abstract Purpose The purpose of this in vitro study was to evaluate the influence of different post surface treatments on the micro push out bond 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 the long axis at the labial cemento-enamel junction. All root canals were instrumented, obturated, the post spaces were prepared to a depth 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 in addition to the application of silane coupling agent (Calibra), Group 4:-surface treatment by sandblasting using 50 μm alumina particles, 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 1/3 of each root were obtained. Micro push out test was performed on a universal testing machine at a cross-head speed of 1.0 mm/min until 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 strength compared with other treatments. There was no significant difference in bond strength between the chloroform group before and after silanization. Conclusions Airborne-particle abrasion in addition to silanization provided the highest increase in bond strength between the fiber post and the resin luting agent evaluated.

Academic research paper on topic "Effect of different surface treatments of luted fiber posts on push out bond strength to root dentin"

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Tanta Dental Journal 10 (2013) 116-122

www.elsevier.com/locate/tdj

Effect of different surface treatments of luted fiber posts on push out

bond 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 out bond 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 the long axis at the labial cemento-enamel junction. All root canals were instrumented, obturated, the post spaces were prepared to a depth 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 in addition to the application of silane coupling agent (Calibra), Group 4:-surface treatment by sandblasting using 50 mm alumina particles, 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 1/3 of each root were obtained. Micro push out test was performed on a universal testing machine at a cross-head speed of 1.0 mm/min until 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 strength compared with other treatments. There was no significant difference in bond strength between the chloroform group before and after silanization.

Conclusions: Airborne-particle abrasion in addition to silanization provided the highest increase in bond strength between the fiber post 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

1. Introduction

* Corresponding author. E-mail address: dr_sherif82@yahoo.com (S.E. Sultan). Peer review under the responsibility of the Faculty of Dentistry, Tanta University

Endodontically treated teeth may be damaged by decay, excessive wear, or previous restorations, resulting in a lack of coronal tooth structure.

The restoration of these teeth may require the placement of a post to ensure adequate retention of a core foundation [1—3]. Cast metal posts and cores have been traditionally used in these situations to provide

1687-8574/$ - see front matter © 2014, Production and Hosting by Elsevier B.V. on behalf of the Faculty of Dentistry, Tanta University. http://dx.doi.org/10.1016/j.tdj.2013.11.003

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

Recently, the use of esthetic (tooth colored) posts such as fiber and zirconia posts in the restoration of endodontically treated teeth has increased in popularity [5,6]. Fiber posts are currently perceived as promising alternatives to cast metal posts, as their elastic moduli are similar to that of dentin, producing a favorable stress distribution [5]. These posts, also, increase the light transmission within the root and overlying gingival tissues, thereby, eliminating or reducing the dark appearance often associated with non-vital teeth and metal posts and cores [7].

A choice must be made between different types of fiber posts based on their light-transmitting capacities, non-translucent posts block light passage, therefore, light-polymerizing luting materials must be substituted with auto polymerizing resin composites, and these materials are typically fluid and have a long polymerization time [8].

Selecting an appropriate adhesive and luting procedure for bonding posts to root dentin is another challenge. Sealing is expected to be strong due to recent improvements in the sealing ability of adhesive resin luting agents [8]. Moreover, various types of bonding systems can be used in combination with different luting resin [8,9]. In a recent investigation, carbon fiber post and core foundations cemented with dentin bonding and resin luting agents showed less microleakage than those luted with glass-ionomer and zinc—phosphate cements [10]. Resin luting agents may be polymerized through a chemical reaction, a light-polymerization process, or a combination of both mechanisms [11]. Most current resin luting agents polymerize using a dual-polymerizing process that requires light exposure to initiate the reaction [11,12].

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

One difficulty with some of the available prefabricated fiber posts is that the polymer matrix between the post material fibers is highly cross-linked and, therefore, less reactive. This makes it difficult for these posts to bond to resin luting agents and tooth structure [2,15].

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

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

2. Materials & methods

Sixty freshly extracted human periodontally involved, single straight rooted upper central incisor teeth with single canal were selected. To standardize the root canal length for this study, the roots were cut (from the coronal end) to a uniform length of 16 mm. The root canals were instrumented to a working length of 1 mm from the apex up to #55 Master apical file. All root canals were instrumented by the same operator using a stepback technique with stainless steel K-files. The canals were obturated with gutta-percha cones (Dentsply-Maillefer, Ballaigues, Switzerland) and sealer (AH-26, Dentsply DeTrey GmbH, Konstanz, Germany) using lateral condensation technique. After complete end-odontic treatment, the cervical root canal openings were filled with an eugenol free provisional restorative material (Orafil G, Prevest Denpro Limited, India). The roots were then fixed in standardized self-cured cylindrical acrylic blocks to facilitate handling of specimens. The temporary restorations were removed and the cavities were cleaned. The post spaces were prepared to a depth of 11 mm with special preparation drills supplied from the manufacturer of the Easy Post systems (Dentsply-Maillefer, Switzerland) using a low speed straight hand piece attached to bench drilling machine.

Number 3 Easy Posts with 1.6 mm diameter at the coronal end and 20 mm length were used. The specimens were randomly classified into five equal groups (n = 12) according to the type of treatment performed to the post surface:- Group I:-No post surface treatments, considered as 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 chloroform impregnated tissue for 1 min.

- Group III:-Post surface treatment as in group II in addition to the application of silane coupling agent using a brush then left undisturbed for 1 min and gently air-dried.

- Group IV:-Post surface treatment by extra oral sandblasting device using 50 mm alumina particles at 2 Mpa air pressure for 10 s with the posts held perpendicular to the incoming particle stream at 20 mm distance. The sandblasted post is then cleaned

5 min in an ultrasound bath to remove any loose particles, cleaned with alcohol and air dried [17]. Group V:-Post surface treatment as in group IV in addition to the application of silane coupling agent using a brush then left undisturbed for 1 min and gently air-dried. After surface treatment of posts, one specimen from each group was examined by scanning electron microscope (JEOL—JSM 5200—LV) to show the effect of surface treatments

on the topography of tested posts. A dual-polymerizing resin luting agent (Calibra esthetic resin cement, Dentsply-Maillefer, Switzerland) was used for cementation of posts according manufacturer instructions. Three segments from the cervical 1/3 of each root were obtained by sectioning the root under water coolant using an isomet saw, the sections were 1 mm in thickness, the coronal surface of each section was marked with an indelible marker, and the thickness of each specimen was measured by using a caliper. For performing micro push out test a specially designed attachment was fabricated and it consists of 3 parts, upper part (Figs. 1 and 2).

Which is carrying 1.3 mm diameter cylindrical plunger that pushes the post segment, the plunger tip was sized and positioned to touch only the post, without stressing the surrounding post space walls, lower part (Fig. 3). In which there is a large cavity that receives the pushed post fragment, and a movable part (Fig. 4).

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

Fig. 2. Upper part.

a 2 mm diameter which is slightly larger than the post space diameter.

The load was applied in an apical-coronal direction on the apical aspect of the root slice. The load pushed the post toward the larger part of the root slice to avoid any limitation to the post movement owing to the post space taper. Loading was performed on a universal testing machine at a cross-head speed of 1.0 mm/min until bond failure occurred. Failure was manifested as a complete extrusion of the post segment. The force (N) required to debond the post from the dentin disc was recorded for all posts. To express the bond strength in MPa, the load (Newton) at failure point was divided by the area of the bonded interface, which was calculated with the following formula:

A = 2prh

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

nJ<W"..................rmmtmmnmtr.t'- ~.....

...............iiiiiiiauiiaLiïïiaiiiTiitiéiÉii^nu^rkfu;:.

******...............üüiiiUi{i..üi;ii'fmht':u:.:............ «

Fig. 1. Specially designed attachment.

Fig. 3. Lower part.

Fig. 4. Movable part.

All data was collected and tabulated to be statistically 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 of the posts after each surface treatment (Figs. 5—9).

4. Discussion

In this study the lowest bond strength values were obtained in the control group (group I) because the post surfaces were not altered by any treatment. Thus, the lower bond strength values may be attributed to poor mechanical interlocking between the smooth surface of the post and the resin cement. The high crosslink density in the epoxy polymer matrix of the Easy post makes it difficult to bond the post to composite resin luting cements. Monomers of the Calibra resin luting cement cannot penetrate into the crosslinked polymer matrix [18]. Therefore, an actual chemical bond between the composite resin and post surface may not be feasible.

Chloroform is a strong organic solvent, which was chosen as a chemical surface treatment for fiber posts in the current study. The chloroform action increased adherence values almost 20%, and the silane had then little further positive effect on these values where group II recorded a mean value of 28.8 Mpa versus group 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 treatments on the push out bond strength of fiber posts. One of these treatments was the chloroform which increased the bond strength by 20%, which was explained by the cleaning action of the chloroform to the posts surfaces from all surface debris creating a well-defined surface pattern with apparent fibers making them more available for micro retention by bonding agent penetration. They also used silane after chloroform and found that it had a little positive effect than chloroform alone.

In addition the results of the current study demonstrated that airborne-particle abrasion treatment of post surfaces (group IV) produced higher post retention than non-treated posts (control). These findings agreed with those obtained by Soares et al., 2008 [19] who studied SEM images of post surfaces after airborne-particle abrasion and observed roughness on their superficial structures. The authors attributed the roughness to fractured glass fibers and partial removal of the epoxy matrix.

In the present study, the highest bond strength was obtained in group V where the posts were sandblasted and then silanated, the overall bond strength was improved by 50% compared to the control group. This might be explained as sandblasting leads to roughening of post surface by removing the resin matrix between the silicon fibers making it more retentive in addition to the chemical reaction of silanes which relies on the formation of Si—O—Si siloxane bonds and conversion of the mineral surface into a less polar surface compatible with organic bonding agent [5,6]. These findings were matching with those obtained by Perdi-gao et al. (2004) [20], which concluded that the silica fiber surfaces need to be freshly exposed preferably by physical abrasion (sandblasting) in order to benefit from silane coupling effects.

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

Table 1

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

Gp I Gp II Gp III GpIV Gp V F (p)

m ± s 23.4 ± 0.39 28.8 ± 0.66 29.4 ± 0.42 28.6 ± 0.48 34.6 ± 0.47 1337 (0.00)a

a Highly significant at 0.05 level.

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 = 0.05.

Fig. 5. SEM micrograph x500 of untreated post surfaces (group 1) showing solid void free surface and evenly distributed parallel oriented fibers.

Fig. 6. SEM micrograph x 500 of surface treatment with chloroform (group 2) showing expansion of the polymer network.

Fig. 8. SEM micrograph x500 of surface treatment with sandblasting (group 4) showing a rough surface creating more spaces for micromechanical retention.

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

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

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

References

Fig. 9. SEM micrographs with of group 5 (surface treatment with sandblasting + silane) showing more retentive surface.

bond strength values of fiber posts to the roots represented in both groups III (surface treatment with chloroform followed by silane) & V (surface treatment with sandblasting followed by silane) compared to the chemical and micromechanical roughening of the fiber posts surfaces alone represented by groups II & IV respectively. Using Pairwise test, a non-significant increase in bond strength was recorded between group II& III. Therefore using silanization after chemical treatment of the post surfaces by chloroform did not significantly enhance the bond strength of the posts.

On the other hand a significant difference between group IV & V was recorded with an increase in the mean values of the push out bond strength of the specimens of group V versus those of group IV which was confirming the results of Cheleux et al., 2007 [17] who found that combination of silanization with sandblasting resulted in significantly better push out bond strength than sandblasting alone. However these results did not confirm those obtained by Perdigao et al., 2006 [21] who studied the effect of silane on the bond strength of three types of fiber posts and concluded that the use of silane coupling agent did not increase the push out bond strength to any of the three posts. This controversy might be due to the idea of using silane alone without any micromechanical or chemical treatments to the post surfaces. Which was not tested currently.

5. Conclusion

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

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