|Year : 2021 | Volume
| Issue : 2 | Page : 62-68
Evaluation of surface roughness and push-out bond strength of glass fiber post with and without surface pretreatments: A scanning electron microscopy study
Rathna Piriyanga Subramani1, Rajasekaran Meenakshisundaram2, Anilkumar Ramachandran2, Karumaran Chellaswamy Savarimalai2
1 Department of Conservative Dentistry and Endodontics, CSI College of Dental Sciences and Research, Madurai, Tamil Nadu, India
2 Department of Conservative Dentistry and Endodontics, Ragas Dental College and Hospital, Chennai, Tamil Nadu, India
|Date of Submission||18-Oct-2020|
|Date of Decision||23-Jan-2021|
|Date of Acceptance||12-Mar-2021|
|Date of Web Publication||11-Jun-2021|
Dr. Rathna Piriyanga Subramani
Department of Conservative Dentistry and Endodontics, CSI College of Dental Sciences and Research, East Veli Street, Madurai - 625 003, Tamil Nadu
Source of Support: None, Conflict of Interest: None
Objective: The aim is to evaluate and compare the surface roughness and push-out bond strength of glass fiber post with and without surface pretreatments using scanning electron microscopy.
Materials and Method: A total of 40 extracted human maxillary central incisors selected were decoronated at 15 mm coronally from the root apex. The teeth were subjected to root canal treatment and the postspace preparation was done with Peeso reamers size 1, 2, and 3, leaving a minimum 4 mm apical seal and created a standard postspace of 10 mm. Forty glass fiber posts (Easy Post, Dentsply) were divided into four groups based on surface treatment of the post with 10 in each. Group I: Without Pretreatment (Control Group) (10 Nos), Group II: 9.6% hydrofluoric acid (10 Nos), Group III: Sandblasting with 110 μm aluminum oxide particles (10 Nos), and Group IV: erbium: yttrium-aluminum-garnet (Er: YAG) Laser (10 Nos). The surface roughness analysis with and without pretreatment was performed under Scanning Electron Microscope and measured in Mountains map premium 7.4 software. The posts were luted with Self-adhesive resin cement (RelyX U200) and light cured for 40s. Push-out bond strength was evaluated using the universal testing machine; the values were recorded, tabulated, and statistically analyzed.
Results: The push-out bond strength of the post is significantly increased when the postsurface is treated with 9.6% hydrofluoric acid at all three levels.
Conclusions: Acid etching of post with 9.6% hydrofluoric acid increased push-out bond strength significantly without changing the structural integrity of the post whereas Er:YAG can be used as alternative to sandblasting.
Keywords: Bond strength, erbium, glass fiber post, hydrofluoric acid, scanning electron microscopy
|How to cite this article:|
Subramani RP, Meenakshisundaram R, Ramachandran A, Savarimalai KC. Evaluation of surface roughness and push-out bond strength of glass fiber post with and without surface pretreatments: A scanning electron microscopy study. Endodontology 2021;33:62-8
|How to cite this URL:|
Subramani RP, Meenakshisundaram R, Ramachandran A, Savarimalai KC. Evaluation of surface roughness and push-out bond strength of glass fiber post with and without surface pretreatments: A scanning electron microscopy study. Endodontology [serial online] 2021 [cited 2021 Oct 18];33:62-8. Available from: https://www.endodontologyonweb.org/text.asp?2021/33/2/62/318126
| Introduction|| |
Endodontic treatment is broadly performed on teeth affected by caries, multiple repeat restorations and/or fracture. The fundamental rationale of an endodontic post is to retain the coronal restoration in a root canal-treated tooth that has endured an extensive loss of crown structure because of decay, excessive wear, or old restoration.
In 1990, the fiber posts were introduced with the modulus of elasticity approaching that of the root canal dentin that effectively transmits and distributes the stress uniformly throughout the dentinal walls. These fiber posts can be adhesively luted to the root canal dentine using polymerizable resin cement. The inherent chemical homogeneity between the fiber post and the resin cement enables them to function together as a homogeneous biomechanical unit, known as tertiary monoblock that mechanically replaces the lost dentin.
To achieve micromechanical retention between the resin cement and root dentin few bonding strategies are usually employed. The crucial part of the adhesive procedure for fiber post cementation is that two interfaces are involved namely, resin cement and root dentin interface and resin cement and fiber postinterface. The adhesion in both interfaces is vital for long-term success of postendodontic restoration.
Regarding dentin and resin cement interface, a wide range of investigation was done using surface treatment of root canal dentin to remove the smear layer and increase surface energy followed by cementation with conventional and self-adhesive cement. To improve the adhesion between fiber post and resin cement interface, pretreatment on the postsurface has been proposed.
Glass fiber posts are composed of various types of glass fibers such as SiO2, CaO, B2O3, Al2O3, inorganic filler, and polymer matrix, commonly an epoxy resin or other resin polymers. Thus, to enhance the interaction, postsurface treatments are recommended to remove the superficial epoxy resin matrix and expose the internal glass fibers. Various surface treatments, such as silanization, hydrofluoric acid etching, hydrogen peroxide, airborne-particle abrasion, methylene chloride, and laser irradiation have been applied for conditioning of the postsurface.
Laser innovation is probably the most recent advancement that was found to affect the change of the material surface for improving surface roughness and bond quality. Among the various laser types employed in dentistry, the neodymium:yttrium-aluminum-garnet laser and erbium: yttrium-aluminum-garnet (Er:YAG) laser were the most highly recommended to carry out roughening of materials, due to their high power.,
Therefore, the purpose of this in vitro study was to evaluate the surface roughness and push-out bond strength of glass fiber post after various surface treatments, including sandblasting, HF acid, and Er: YAG laser treatments.
The null hypothesis was that there is no change in surface roughness and bond strength after pretreatments with 9.6% hydrofluoric acid, sandblasting, and Er: YAG laser.
| Materials and Method|| |
The present study protocol was reviewed and approved by the Institutional Review Board, Ragas Dental College and Hospital, Chennai, India. Forty single-rooted human maxillary central incisors extracted due to periodontal problems were selected. After extraction, the teeth were cleaned and stored in 0.1% thymol solution at 4°C. Each tooth was examined radiographically to have a single root canal, a closed apex and no evidence of a caries lesion or restoration. The coronal portion of each tooth was sectioned 15 mm coronally from the root apex using diamond disc under copious water cooling.
All the teeth were embedded in a tooth-colored self-curing acrylic resin, using a putty index made out of addition silicone impression material. Access cavities were prepared and the working length was established by placing a size 20 K-file (Dentsply) into the canal with 1 mm short of apex. The biomechanical preparation is done with hand instruments up to ISO size 50 (Dentsply/Malliefer, Switzerland), using a series of stainless steel k files to the working length of each tooth by step-back technique. All teeth were obturated by cold lateral condensation technique using 0.02% taper gutta-percha cones of size 45–15 and AH Plus root canal sealer. The decoronated and filled roots were stored for 7 days in normal saline at 37°C.
The gutta-percha was removed with peeso reamers size 1, 2, and 3, leaving a minimum 4 mm apical seal and creating a standard postspace of 10 mm from the coronal surface corresponding to the tapered Radix Easy post size #1. Following the preparation, the postspaces were rinsed with 3% sodium hypochlorite. Final irrigation was accomplished with distilled water, and then, the postspaces were dried with paper points.
In the present study, light-transmitting Easy glass fiber post (Dentsply/Malliefer, Switzerland) was employed because the use of light-transmitting posts has been suggested to enhance resin cure at all root levels. This post has a uniform taper in the radicular portion and radiopaque. The post size 1 with 0.8 mm apical diameter and 1.47 mm coronal diameter was selected. This post incorporates linear tapering which facilitates better adaptation of the post to the root dentin with minimal dentin removal. The material used with composition is listed in [Table 1].
A total of 40 glass fiber posts were randomly divided into four groups according to the surface treatment of the post with 10 in each
- Group I: Without Pre-treatment (Control Group) (10 Nos)
- Group II: Pretreatment with 9.6% hydrofluoric acid (10 Nos)
- Group III: Sandblasting with 110 μm aluminum oxide particles (10 Nos)
- Group IV: Pretreatment with Er: YAG Laser (10 Nos).
Scanning electron microscopy analysis
The surface of the posts was analyzed using Scanning electron microscope (S3400 N, HITACHI, Japan) under ×20, ×500, and ×1000. The samples underwent gold sputtering in the gold sputtering machine for about 15 s to make the samples more electro-conductive underneath the Scanning Electron Microscope (SEM) [Figure 1]a, [Figure 1]b, [Figure 1]c, [Figure 1]d.
|Figure 1: SEM image of postsurface (a) before pretreatment, (b) after 9.6% HF pretreatment, (c) after sand blasting pretreatment, (d) after laser pretreatment|
Click here to view
Surface roughness analysis
The surface roughness of the posts was measured with and without pretreatments. By using Mountains maps software, the two-dimensional (2D) SEM images taken at various resolutions were reconstructed into three-dimensional (3D) analytical models and the surface profiles were measured. The measurements were taken more than one time to obtain the mean surface roughness value (Ra) for all the groups.
Surface treatments of specimens
This group served as the control group, so no treatment was applied to the post surfaces in it.
Sandblasting with aluminum oxide particles
The surface of the post specimens were sandblasted with 110 μm Al2O3 particles for 10s. The air pressure for sandblasting was maintained at 2 bars at a distance of approximately, 10 mm between the surface of the specimen and the blasting tip in the sandblasting unit. After rinsing, the samples under running water, they were dried with oil-free compressed air to remove the remnants for 10s.
Etching with 9.6% hydrofluoric acid
The posts surfaces were etched with 9.6% hydrofluoric acid gel (Porcelian etch, Ultradent) for 20 s, rinsed with water for 30 s and air dried.
Irradiation with erbium: yttrium-aluminum-garnet laser
Surfaces of the postspecimens were irradiated with an Er: YAG laser (Fidelis Plus III, Fotona, Germany). Laser energy was delivered in pulse mode by a 2 mm diameter laser optical fiber for 20s with the repetition rate of 10 Hz, energy of 150 mJ, output power of 1.5W, and pulse duration of 400 μs under cooling.
Luting of post with self-adhesive resin cement
The posts were luted with RelyX U200 (3M ESPE, Germany), a self-adhesive resin cement according to the manufacturer's instructions. The specimens were stored in water bath under room temperature.
Preparation of samples for analysis of push-out bond strength
Forty samples luted with glass fiber post were transversely sectioned perpendicular to the post starting at 6 mm from the apex of the specimen using a hard-tissue microtome (Isomet 1000; Buehler, USA), along with continuous water irrigation to prevent overheating. In this manner, 3 slices of 1.0 ± 0.2 mm were created pertaining to the cervical, middle, and apical region of each root specimen resulting in 30 slices/group.
Push-out bond strength assessment
The push-out bond strength (MPa) was determined using the universal testing machine (INSTRON 3369). A custom-made stainless steel platform was fabricated with a punch hole in the center of the platform. The specimens were positioned on the jig in an apicocoronal direction to avoid interferences due to root canal taper. The post segments were loaded with a cylindrical plunger of 1 mm in diameter centered on the post segment; without contacting the surrounding dentin surface. Loading was performed on a universal testing machine at a crosshead speed of 0.5 mm/min until the post got completely extruded from the specimen. The peak force of postextrusion was considered as bond failure and recorded in Newton (N) and converted into megapascals by dividing the load applied by the bonded area (A), in which, area was calculated by the formula:
A = π (r + R) × h2 + (R − r)2
where R and r were the largest and the smallest radius, respectively, of the cross-sectioned tapered post, and h is the thickness of the section.
All the values were tabulated and statistical analysis was performed using Software SPSS, Version 20.0 (IBM Corp. Released 2011. IBM SPSS Statistics for Windows, Version 20.0. Armonk, NY: IBM Corp). To compare the difference in surface roughness in between groups were analyzed using One-way analysis of variance (ANOVA) test as it had more than one group.
Push-out bond strength was calculated at cervical, middle, and apical third for all the four groups and the values were tabulated in megapascals. One-way ANOVA was used to study the overall variance in between groups. As it is not possible to identify the difference between groups with the help of the P value obtained from ANOVA, a specific statistical test was used. The Post-hoc Tukey test was designed to perform a pairwise comparison of the means to identify the specific inter groups in which significant difference expression occurs.
| Results|| |
Surface roughness analysis
The mean and standard deviation of the surface roughness values are presented in [Table 2]. The statistical analysis of the data revealed significant differences among the groups (P value < 0.0001). The results obtained from the evaluation of surface roughness clearly demonstrate that postsurface treatments with 9.6% hydrofluoric acid, sandblasting, irradiation with Er: YAG laser significantly created surface roughness and increased the bonding surface area. Furthermore, the surface roughness of Group III was significantly higher than other groups.
|Table 2: Mean and standard deviation comparison of surface roughness of four groups using analysis of variance|
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Push-out bond strength analysis
[Table 3] presents the mean and standard deviation of the bond strength values in megapascals (MPa) achieved upon dislodging the various surface-treated posts at different levels. The statistical analysis of the experimental group with the control group shows high push-out bond strength has been achieved in Group II.
|Table 3: Mean and standard deviation of push-out bond strength (mega pascals) obtained between the groups and different levels|
Click here to view
| Discussion|| |
Surface treatments are frequently used methods for enhancing the general adhesion properties of a material by facilitating chemical and micromechanical retention between the different constituents. In adhesive dentistry, surface conditioning techniques have been developed for enamel, dentine, and restorative materials. The concept of conditioning artificial substrates to improve bond strength is exemplified by the etching of Maryland bridges and feldspathic porcelain restorations. Based on the same precept, exceptional conditioning strategies, to start with proposed for ceramics, have additionally been tested for fiber posts., Surface treatments of glass fiber posts have been shown to increase the surface area by exposing the glass fibers and filler particles that can be reached by the resin-luting cements to improve the bond strength.,
Usually, the surface analysis was performed using profilometer, but nowadays, due to recent advances in imaging technology, the 2D images captured under the microscope are reconstructed and deviation in the surface is being analyzed using various imaging software. Imaging software uses amplitude parameters to quantify the height deviations of the measured surface. 2D parameters are calculated from a single profile, whereas 3D parameters are calculated from the overall surface measured which provides a more balanced description of the surface. This permits stable results to be obtained.
The SEM images of the posts which showed the surface changes at different resolutions more precisely and distinguishable were analyzed with software (Mountains Map Premium 6; Digital Surf). A mean roughness profile was achieved from each image, and the parameters were determined for Ra mean.,,
The outcomes acquired in this investigation plainly exhibit that postsurface treatments including, HF acid etching, sandblasting, and Er:YAG laser light essentially influenced the malleable bond quality of glass fiber presents on the resin cement. Therefore, the null hypothesis was rejected.
Although, sandblasted and Er:YAG laser-irradiated posts had the most elevated mean surface roughness esteem, they did not provide noteworthy higher tractable bond strength incentive than that of the control group esteem.
Interestingly, etching with 9.6% hydrofluoric acid provided a significant increase in surface roughness as well as bond strength of post to the root dentine. One possible clarification for these outcomes could be that hydrofluoric acid specifically breaks down the glass part of the fiber post, creating unusual patterns of microspaces on the postsurface. This may expand the surface area and encourage the infiltration of the self-adhesive cement, which enhances the microretention of the treated post surface., The effect of the acid has been proved to be time dependent and influenced by the postcomposition.
It was accounted for that glass fiber presents submitted on sandblasting was harsher and seemed to give an increase surface area, which could propose improvement in mechanical interlocking for the resin cement. Being so, in this examination, it did not expand bond quality estimations of the posts. Pretreatment with sandblasting indicated reduction in the push-out bond quality of the post when compared with that of the hydrofluoric acid group at all levels can be because of the expanded measure of material expulsion from the post regardless of improved surface roughness.
The results of the present study showed a significant reduction of push-out bond strength of Group III, that is, surface treated with sandblasting compared to that of Group II at all the levels. Lack of selectivity in terms of this technique can be a reason for the decrease in bond strength, which means the alumina particles affect both resin and silica composition of the glass fiber post.
The aftereffects of the current investigation did not affirm the proposal of Soares et al., where he expresses, the treatment of fiber post surfaces with sand particles upgrades surface hardness and made monoblock interlocking., The other studies reported that this treatment was considered too aggressive for fiber posts, because of the risk of significantly modifying their shape and fit within the root canals.,
The impact of Er:YAG lasers has been demonstrated to be fundamentally more viable than the control group. Push-out bond strength was diminished in correlation with acid etching and sandblasting at the cervical third and there was no critical distinction among sandblasting and laser at the apical third. This outcome was in concurrence with the result of Sipahi et al.'s investigation.
The important effect of laser energy is the conversion of light energy into heat, and the most important interplay among the laser and substrate is the absorption of the laser energy by the substrate. The pigmentation of the surface and its water content together with different surface traits decide the amount of energy that is absorbed by way of the irradiated surface. Along with that many factors such as the post composition and laser parameters used can eventually play role in creating surface roughness., Such factors during the laser irradiation with contact on the fiber postsurface produce a carbonization area, which significantly interferes with the cement.
Er:YAG lasers use a water irrigation system wherein water is directly applied to the surface, thus forming a film of water on the irradiated area. Since the energy of erbium lasers is well absorbed by water, the water pellicle formed on the ablated surface of the glass fiber post during irradiation with Er; YAG laser may have consumed energy and influence the bond strength.
Despite the pretreatment method applied, there is linear decline in push-out bond strength within the Group in the order of cervical followed by the middle and apical third. This can be attributed to the better penetration of the resin tags into coronal dentinal tubules which were considerably higher in number and greater in size than the middle and apical third.
It could also be due to the smear layer formed during biomechanical preparation and postspace preparation, which are deposited on the root canal walls. This interferes with the effective penetration of self-adhesive resin cements to the underlying dentin which in turn impair its bond strength.,
This result is consistent with Monteceli et al. and contradicted with other previous studies Albashaireh et al. where they suggested that increased cement thickness in the cervical region negatively affected the bond strength.,
Therefore, future investigations could focus on fracture strength of fiber posts after irradiation and various parameters of wavelength, frequency, and irradiation time.
| Conclusions|| |
Within the limitations of the present study, it was concluded that:
All the surface pretreatments had significantly
- Increased the surface roughness and push-out bond strength compared to that of the control group without pretreatment. Surface roughness created by pretreatments was higher in the order of sandblasting followed by 9.6% hydrofluoric acid and then by laser
- Pretreatment with 9.6% hydrofluoric acid for 20 s recorded the highest Push-out bond strength in the cervical third of the root dentin followed by middle third and exhibited slightly lesser values in apical third among all the groups, thus favoring uniform stress distribution along the root dentin-luting cement-post interface
- Pretreatment with Er: YAG laser showed better push-out bond strength which was comparable to the results of sandblasting, so that it can be used as an alternative to sandblasting in the clinical situation.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3]