Journal of Interdisciplinary Dentistry

ORIGINAL ARTICLE
Year
: 2017  |  Volume : 7  |  Issue : 2  |  Page : 47--52

Evaluation of interfacial adhesion of two fiber post systems to composite core material following different surface chemical treatments – An In vitro study


Zacharia Mareeza, Ravichandran Rajagopal, Harshakumar Karunakaran, Vishwambharan Prasanth 
 Department of Prosthodontics, Government Dental College, Thiruvananthapuram, Kerala, India

Correspondence Address:
Zacharia Mareeza
Department of Prosthodontics, Government Dental College, Thiruvananthapuram, Kerala
India

Abstract

Aim: The aim of the study was to evaluate and compare the effect of various surface chemical treatments on the interfacial adhesion of glass and quartz fiber posts to composite core material by assessing the microtensile bond strength. Materials and Methods: A total of 40 glass fiber posts (Group I) and 40 quartz fiber posts (Group II) were selected. Posts in each group were divided into four subgroups based on the surface chemical treatment employed such as A (10% hydrogen peroxide), B (4% hydrofluoric acid), C (37% phosphoric acid), and D (control silanization alone). After prescribed surface treatment protocol for respective subgroups, a core was built around each post using a dual-cure core buildup composite material. Each bonded specimen was sectioned to obtain 'microtensile' specimen which was subjected to tensile load at a crosshead speed of 1 mm/min until failure, in a Universal Testing Machine. The changes in the post surface characteristics after surface treatments were evaluated using scanning electron microscope. Results: Mean bond strength was higher in quartz fiber posts when compared to glass fiber post. Surface treatment with hydrogen peroxide had the greatest impact on post surface in both glass and quartz fiber post groups. Conclusion: Surface chemical treatments of fiber posts significantly increased the interfacial bond strength by enhancing the chemical and micromechanical interaction between the fiber posts and composite core.



How to cite this article:
Mareeza Z, Rajagopal R, Karunakaran H, Prasanth V. Evaluation of interfacial adhesion of two fiber post systems to composite core material following different surface chemical treatments – An In vitro study.J Interdiscip Dentistry 2017;7:47-52


How to cite this URL:
Mareeza Z, Rajagopal R, Karunakaran H, Prasanth V. Evaluation of interfacial adhesion of two fiber post systems to composite core material following different surface chemical treatments – An In vitro study. J Interdiscip Dentistry [serial online] 2017 [cited 2017 Dec 13 ];7:47-52
Available from: http://www.jidonline.com/text.asp?2017/7/2/47/212604


Full Text

 Clinical Relevance to Interdisciplinary Dentistry



Restoration of endodontically treated teeth is a challenge in our day-to-day dental practiceFiber-reinforced composite post is widely used nowadays as it is safer, aesthetic, conserve tooth structure and provides improved fracture resistance to those compromised teeth. However, achievement of adequate bond strength between fiber post and composite core is very critical for a successful restoration.

 Introduction



Endodontically treated teeth are more prone to fracture due to a variety of factors such as loss of extensive tooth structure, moisture content as well as a decrease in resistance due to endodontic access. Consequently, complete coverage crown is the ideal restoration to aid in better resistance to external forces.[1] Hence, the restoration of endodontically treated teeth with inadequate coronal tooth structure often requires placement of a post to ensure sufficient retention of the core foundation.[2] Metallic prefabricated and cast posts have been traditionally used in such situation. The major disadvantages associated with these systems are stress concentration leading to root fractures, corrosion, necessity of the removal of extensive root structure, and loss of retention.[3],[4]

As an alternative to these metallic posts, Duret has introduced a nonmetallic material for the fabrication of posts based on the carbon-fiber reinforcement principle.[5] The major advantage of fiber post is its similar elastic modulus to dentine, producing a stress field similar to that of natural teeth, whereas the metal post exhibits high-stress concentration at the post dentin interface.[6] Bonding of fiber post to composite core relies mainly on the interaction between the post surface and the resin material used for building up the core.[7] In an attempt to maximize resin bonding to fibre posts, many chemical and mechanical surface treatment procedures have been proposed recently.[8] Studies have proven that mechanical techniques are too aggressive in nature and can decrease the fit of fiber posts in the root canal. Chemical treatments can roughen the post surface and can enhance the mechanical interlock with a composite resin core.[9],[10] The aim of the present study was to evaluate and compare the effect of different chemical surface treatment methods on the interfacial adhesion between two fiber post systems and dual-cure composite core buildup material. Moreover, the changes in the surface characteristics of the post following different pretreatments were evaluated using scanning electron microscopic (SEM).

 Materials and Methods



Two fiber-based post systems, glass fiber post (Prosthetic Over Post, Over Fibers Italy), and quartz fiber posts (D.T Light Post Illusion XRO, RTD France) having a maximum diameter of 1.8 mm were used in this study. Prosthetic over posts are reinforced composite which is made up of high strength “S” type glass fiber in an epoxy resin matrix. DT LIGHT Posts are made of unidirectional pretensed quartz fibers embedded in an epoxy resin matrix.

Group I consists of 40 glass fiber posts (Prosthetic Over Posts) and Group II includes 40 quartz fiber posts (DT Light post illusionXRO) which were divided into four subgroups A, B, C, and D based on the surface chemical treatments. Four different surface chemical treatments were tested for their efficacy on etching the resin phase of the fiber post surface for both the groups (sample size n = 10 in each group). Fiber posts in Subgroup A were immersed in 10% hydrogen peroxide for 20 min at room temperature and then rinsed with distilled water. In Subgroup B, etching was done by immersing the posts in 4% hydrofluoric acid for 60 s followed by rinsing with distilled water. Whereas in the Subgroup C, the posts were immersed in 37% phosphoric acid for 15 s at room temperature and rinsing with distilled water. After the application of chemical agents, all posts were rinsed with distilled water and air dried. The silane coupling agent (Monobond S) was applied in a single layer with a brush on the post surface of each experimental and Subgroup D (control group) and was left to air dry.

Core buildup procedure and microtensile bond strength evaluation

A transparent rectangular plexiglass mold having was used as a matrix for core buildup. The base of the mold was having a central indentation similar to post diameter which enabled accurate positioning of the post [Figure 1]. Each post was positioned exactly in the the mold ensuring the centralization. Core buildup was performed using dual-cure composite core material (MultiCore Flow, Ivoclar Vivadent, Liechtenstein). An incremental technique was followed to build up the core. Each 2 mm increment of composite was cured for 40 s with a light curing unit with an output of 500 mW/cm2. The composite was directly polymerized from the upper end of the mold and was subsequently removed after being filled completely with polymerized composite. The bottom side of the specimen was light cured for additional 20 sec to ensure complete polymerization. Thus, a rectangular slab of composite core with fiber post in the center was obtained [Figure 2]. All the posts were bonded in the same manner, and the specimens were then stored in distilled water for 24 h.{Figure 1}{Figure 2}

Each bonded specimen was mounted on an acrylic block and sectioned using slow speed diamond saw (Leica1600, Buehler, Lake Bluff, USA). Transverse sectioning of the specimen was done to obtain “microtensile stick” having 1 mm thickness. Thus, the microtensile specimen was obtained with a post in the center which was surrounded by core buildup. Each specimen was secured to metal jig of the universal testing machine and subjected to a tensile load at a crosshead speed of 1 mm/min until failure. The tensile bond strength of each sample was calculated by dividing the maximum load at failure (N) with bonded cross-sectional area (mm2) and was expressed in megapascal.

Scanning electron microscopic evaluation

To evaluate the post surface at the interface after different surface chemical treatments, additional eight specimens (one from each subgroup) were prepared in the same manner as mentioned above. The prepared specimens were washed in deionized water for 5 min, followed by immersion in 95% ethanol, and were gently air-dried. Each specimen was sputter coated with gold palladium and was examined using scanning electron microscopic (SEM).

 Results



Data were expressed in its mean and standard deviation. Statistical analysis was done using independent sample t-test and one-way ANOVA with post hoc comparison by Bonferonni test. The mean and standard deviation of microtensile bond strength of the groups tested were given in [Table 1]. Subgroup A (H2O2) showed maximum bond strength value, whereas Subgroup D (control) showed the minimum in both Group I and Group II. Mean bond strength was higher in quartz fiber group when compared to glass fiber post [Graph 1]. Multiple comparisons in glass (Group I) with one-way ANOVA and post hoc comparison by Bonferonni test revealed a significant difference between all (P < 0.05) except H2O2 and H3 PO4. Multiple comparisons in quartz (Group II) with one-way ANOVA and post hoc comparison by Bonferonni test revealed a significant difference between all the subgroups (P < 0.001).{Table 1}[INLINE:1]

SEM was done to evaluate the changes on the post surface which revealed that there was a modification of the post surface morphology with dissolution of epoxy resin matrix, and thus exposing glass and quartz fibers. Specimens which received surface treatment with 10% hydrogen peroxide [Figure 3] showed the maximum surface modification with exposure of fibers followed by those with phosphoric acid and hydrofluoric acid [Figure 4] and [Figure 5]. SEM image of both glass and quartz fiber posts treated with silane alone showed the minimal surface modification [Figure 6].{Figure 3}{Figure 4}{Figure 5}{Figure 6}

 Discussion



It has been proven that the attainment of reliable bonds at the root-post-core interfaces is critical for the clinical success of a post retained restoration. If bonding at these interfaces is weak, debonding or fracture of the post and core will occur.[11] There are many factors which can affect the interfacial bond strength like surface treatment methods, type of posts as well as composite core material employed.[12] In this experimental in vitro study, the interfacial adhesion of glass and quartz fiber posts to dual-cure composite core buildup material after various surface chemical treatments was investigated. The use of hydrogen peroxide, hydrofluoric acid, and phosphoric acid pretreatment enhanced the interfacial bond strength with dual-cure core material in both glass and quartz fiber posts. On the other hand, surface conditioning only with silane (control group) showed least microtensile bond strength value in both glass and quartz fiber posts types.

Studies by Mannocci et al. and Monticelli et al. suggested that the etching of fiber posts with hydrogen peroxide acts by dissolving and removing partially the superficial epoxy resin matrix, exposing a great number of intact fibers inside the post without damage, and making the fibers available to react with silane coupling agents (chemical optimization), thus these surface treatments would promote micromechanical retention of the composite resin with the post.[6],[7],[8],[9]

The present study revealed that etching with 10% hydrogen peroxide for 20 min improved the interfacial bond strength for both glass and quartz fiber posts. Interfacial bond strength assessed using microtensile testing showed a mean value of 17.41 MPa for glass fiber post (Group I) and 20.98 MPa was observed with quartz fiber post (Group II) which was the maximum in both groups. The bond strength achieved was significantly higher than the other subgroups in Group II (P < 0.05). A significant difference was observed with all other surface treatments except phosphoric acid in Group I. SEM observation depicted that the post surface at the interface between the cores was modified with the application of hydrogen peroxide [Figure 3]. There was partial dissolution of the epoxy resin matrix, thus exposing glass and quartz fibers enabling better silanization. Hence, the present study is also in agreement with the previous studies proving that application of 10% hydrogen peroxide for 20 min produces post surface modifications, and hence improving the adhesion between fiber posts and composite core.

Phosphoric acid has been used for etching the tooth surfaces in concentrations ranging from 30 to 50%. Thirty-seven percent phosphoric acid is used for acid etching the tooth surface for creating micropores on enamel thus aid in micromechanical retention of the resin.[13] Based on the same principle, 37% phosphoric acid for 15 s were used as post surface conditioning agent in this study. The interfacial bond strength achieved stood next to hydrogen peroxide. Furthermore, SEM evaluation showed significant changes in the post surface with the removal of epoxy resin matrix, thus exposing more glass and quartz fibers. However, the amount of fiber exposure was less than the exposure seen with hydrogen peroxide [Figure 4].

Hydrofluoric acid has been used to etch porcelain to improve the bond strength of resin cement to silicate-based ceramics.[6] For hydrofluoric acid, a higher diversity between protocols was observed with concentrations varying from 4% to 10% and diverse application time. In the study, a concentration of 4% hydrofluoric acid was applied onto the posts surface for 60 s. This was the etching protocol commonly employed for ceramics. The amount of interfacial bond strength achieved was less comparing with hydrogen peroxide and phosphoric acid groups. However, there was considerable improvement in bond strength compared to post group which received only silanization. SEM evaluation revealed the amount of dissolution of resin matrix was less as compared to hydrogen peroxide and phosphoric acid [Figure 5].

The use of silane coupling agents has been proposed to promote adhesion between inorganic surfaces and polymeric molecules. Organosilanes have three alkoxide group, and the chemical reaction begins with hydrolysis of the alkoxide groups (R) into silanols (SiOH) that may condense forming siloxane bonds.[14] In the present study, Monobond-S was used which is prehydrolyzed single-component silanizing agent and contains 1wt% of 3-methacryloxypropyl trimethoxysilane in an ethanol/water-based solvent. The silane was applied in a single layer as per the manufacturer's instructions. Debnath et al. stated that the formation of a multilayer structure may result in a reduction of the effectiveness of silane coupling since the number of free methacrylate groups is reduced and cohesive failure within the silane coating may occur.[15]

The method utilized for bond strength testing was the microtensile bond test that has been reported to be suitable for the evaluation of interfacial bond strengths on very small specimens.[16] The small size of the specimens is the condition for a more uniform distribution of the stress on loading which limits the chance of cohesive failures, and thus enabling for an accurate assessment of the interfacial bond strength. The nontrimming variant of the technique was chosen as there are indications in the literature that it is less aggressive than the variant which involves trimming the specimen to an hourglass shape at the bonded surface.[6],[16] There are few limitations for the study. Only a few clinical reports are available for correlating the in vitro observations with the in vivo clinical surface treatments. Another drawback of this study was that the sectioning of the specimens was done after 24 h. This could not simulate the clinical situation of immediate loading following core buildups. Moreover, it is better to compare different composite materials in clinical use and evaluate whether they have any influence in interfacial bond strength after the surface treatments.

 Conclusion



Thus, the present study revealed that the interfacial adhesion between fiber post and composite core can be significantly improved by post surface conditioning using chemical agents. In this study, 10% hydrogen peroxide showed maximum influence on post surface with a significant increase in interfacial bond strength. Post surface treated with 37% phosphoric acid was having the next highest bond strength showing that this is also an acceptable method for improving interfacial adhesion. These conditioning techniques are easy, inexpensive and can be employed as chairside procedure. Hence, these chemical surface treatments of fiber-reinforced composite post provide a significant improvement in the interfacial adhesion between post surface and composite resin core, thus increasing the longevity and success of the restoration.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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