Abstract
Objective
This study evaluated the effect of different chemical surface treatments on the adhesion of resin-core materials to methacrylate resin-based glass fiber posts.
Methods
Two types of glass fiber posts (Reblida post; VOCO and RelyX post; 3M ESPE) were divided into eight groups according to the surface treatment used; Gr 1 (control; no surface treatment), Gr 2 (silanization for 60 s), Gr 3 (10% H 2 O 2 for 5 min), Gr 4 (10% H 2 O 2 for 10 min), Gr 5 (30% H 2 O 2 for 5 min), Gr 6 (30% H 2 O 2 for 10 min), Gr 7 (CH 2 Cl 2 for 5 min) and Gr 8 (CH 2 Cl 2 for 10 min). Two resin core materials (Grandio DC; VOCO and Filtek P60; 3M ESPE) were applied to each group for testing the adhesion using micropush-out test. Failure types were examined with stereomicroscope and surface morphology of the posts was characterized after treatment using a scanning electron microscope (SEM). Data were analyzed using ANOVA and Tukey’s test.
Results
The type of post, surface treatment, and core material showed a significant effect on the micropush-out bond strength ( P < 0.001). Groups treated with CH 2 Cl 2 or 30% H 2 O 2 solutions for 5 or 10 min showed the highest adhesion values for both types of posts with the core materials tested. Stereomicroscope showed that most failure modes were adhesive type of failures between post and core material. SEM analysis revealed that the fiber post surfaces were modified after chemical surface treatments.
Significance
Application of CH 2 Cl 2 or 30% H 2 O 2 to the fiber post surfaces enhanced the adhesion to resin cores.
1
Introduction
Endodontically treated teeth that lack coronal tooth structure due to severe damage by decay, previous restorations or excessive wear are exposed to shearing chewing forces and commonly need the placement of a post to provide adequate retention of a core foundation . Fiber posts are currently widely used in the restoration of endodontically treated teeth . The main advantage of fiber post is closer elastic modulus of fiber posts (≈20 GPa) to dentin, producing a favorable stress distribution and high success rates without the occurrence of root fractures .
The durability of a composite resin core restoration relies on the development of a strong bond between the core material and the residual dentin, as well as between the core and post material, allowing the interface to efficiently transfer stresses under functional loading . It has been shown that the establishments of reliable bonds at the root-post-core interfaces are important for the clinical success of a post-retained restoration . Retention of the composite core to the prefabricated post is affected by various factors, including surface treatment of the post , the design of the post head, the post and the composite resin core material .
Surface treatments are commonly used for enhancing the adhesion properties of a material, by allowing chemical and micromechanical retention between different constituents . For post/core restorations, various surface treatments have been proposed in order to improve bonding of composite resin cores to posts . The application of a silane coupling agent as adhesion promoter in fiber post/core units was investigated . The most common silane-coupling agent used in dentistry is 3-methacryloxypropyltrimethoxysilane that is diluted in a solvent mixture consisting of ethanol and water to a pH between 4 and 5 . Its working mechanism is based on enhanced surface wettability with chemical bridge formation between the resin matrix of the adhesive resin or composite core and the glass phase of the post . However, adhesion of composite resin cores to fiber posts was still inferior as compared with the results achieved on dental substrates . This probably due to the polymer between the post material fibers is highly cross-linked and, consequently, less reactive to bond to resin luting agents and tooth structure .
Airborne-particle abrasion with aluminum oxide or silica and hydrofluoric acid etching are techniques used to improve the adhesion between fiber posts and composite resin or resin luting agents . Because these techniques can occasionally damage the glass fibers and affect the integrity of the posts , other chemical treatments have been proposed to improve bonding between fiber posts and composite resin core materials . They included hydrogen peroxide (H 2 O 2 ), potassium permanganate, and sodium ethoxide with varying degree of outcomes . H 2 O 2 at concentrations of 10% and 24% effectively removes the surface layer of the epoxy resin ; however, application periods of 10 or 20 min used in previous studies are clinically impractical . H 2 O 2 is commonly used in dental practice, mostly for dental bleaching, and is easy and safe to utilize .
Methylene chloride (CH 2 Cl 2 ) has been proposed for use to improve the adhesion between acrylic resin denture base materials and acrylic resin repair materials by changing the chemical features and surface morphology of denture base resins and increases their repair strength . Recently, CH 2 Cl 2 has been applied to epoxy resin based fiber post for 5 s in order to improve the adhesion between fiber post and composite resin; however, the results showed that this treatment was not effective . There is no available data on the effect of using CH 2 Cl 2 to enhance the adhesion between methacrylate resin-based fiber post systems and composite resin core build-up materials. Accordingly, the present study aimed to evaluate the effect of fiber post surface treatment with CH 2 Cl 2 and H 2 O 2 on the morphological aspects of the post surface, and the influence of different surface treatments on the micropush-out bond strength of fiber posts to different composite resins for core-build up. The null hypothesis tested was that post-surface treatment and the type of post-core system would not affect the interfacial strength between fiber posts and composite resins core build-up.
2
Materials and methods
Two types of glass fiber reinforced composite posts were used in this study: Rebilda post (RP) and RelyX post (RX). The manufacturers and the compositions of the materials used in this study are presented in Table 1 .
| Material | Product (composition a ) | Code | Lot number | Manufacturer |
|---|---|---|---|---|
| Fiber post | Reblida post (Size # Ø 1.5; 70% glass fiber, 10% filler, 20% UDMA) | RP | 1143115 | VOCO, Cuxhaven, Germany |
| RelyX post (Size # 2; Glass fiber reinforced composite, methacrylate resin) | RX | 173421109 | 3M ESPE, St. Paul, MN, USA | |
| Silanization Ceramic Bond (3-methacryloxypropyltrimethoxysilane in an ethanol/water solution, isopropanol) | – | 1145045 | VOCO, Cuxhaven, Germany | |
| Surface treatment | Hydrogen peroxide 10% and 30% (H 2 O 2 ) | – | – | Liza, Mash Co., Egypt |
| Methylene chloride (CH 2 Cl 2 , formula weight: 84.13 g/mol) | – | M0158111 | El Nasr Pharmaceutical Chemicals Co., Egypt | |
| Grandio Core DC (Matrix: Bis-GMA, UDMA resins. Filler: silica/Ba-glass ceramics (77%, wt). Amines, benzoyl peroxide, BHT) | GR | 1139193 | VOCO, Cuxhaven, Germany | |
| Core build-up material | Filtek P60 (Matrix: Bis-GMA, UDMA, Bis-EMA resins. Filler: zirconia/silica (61%, vol., 83%, wt). Particle size range of 0.01–3.5 μm. Initiators, inorganic pigments) | F60 | N331597 | 3M ESPE, St. Paul, MN, USA |
2.1
Grouping of specimens
The specimens were divided into eight groups ( n = 14/group) according to the method of surface treatment applied, as follows:
-
Group 1: no treatment (control group).
-
Group 2: silanization; a silane coupling agent was applied on the surface of the post with a brush and gently air-dried for 60 s, according to the manufacturer’s instructions.
-
Group 3: the specimens were immersed in 10% H 2 O 2 for 5 min.
-
Group 4: the specimens were immersed in 10% H 2 O 2 for 10 min.
-
Group 5: the specimens were immersed in 30% H 2 O 2 for 5 min.
-
Group 6: the specimens were immersed in 30% H 2 O 2 for 10 min.
-
Group 7: the specimens were immersed in CH 2 Cl 2 for 5 min.
-
Group 8: the specimens were immersed in CH 2 Cl 2 for 10 min.
After the application of H 2 O 2 or CH 2 Cl 2 , all the posts were rinsed with deionized water for 3 min followed by air-drying.
Each group was further equally divided into two subgroups ( n = 7) according to the type of core build-up material used as follows:
-
Subgroup 1: Grandio Core DC (GR; VOCO).
-
Subgroup 2: Filtek P60 (F60; 3M ESPE).
2.2
Core build-up procedure and micropush-out test
Core build-up was performed using a dual cure composite core material (GR) and a composite resin material (F60) ( Table 1 ), using an in vitro technique previously reported by Goracci et al. . Each post was positioned perpendicularly on a glass slab and secured with a drop of sticky wax. A cylindrical plastic matrix (10 mm in diameter) was then placed around the cylindrical portion of the post and an incremental technique was followed to build up the core. Each 2-mm increment of the composite core material was cured for 40 s with a halogen light curing unit (XL2500, 3M ESPE, St. Paul, MN, USA) with an output of 670 mW/cm 2 . The material was polymerized directly from the open upper side of the matrix and through the post. The matrix was subsequently removed after being filled completely with polymerized composite. This resulted in a cylinder of composite resin that was built up around the fiber post. The bottom side of the cylinder that was previously in contact with the glass slab was light cured for an additional 40 s to ensure optimal polymerization of the composite material. There was no aging for the test specimens.
The sectioning and loading of the specimens began on completion of the core build-up procedure, in an attempt to simulate the clinical condition of immediate loading following core build-ups . Each bonded specimen was mounted on the holding device of a low-speed diamond saw (Isomet 1000, Beuhler Ltd., Lake Bluff, IL, USA). The post/composite assembly was sectioned with the diamond saw under water cooling resulting in 5 specimens, each 1 mm thick discs. After measuring the thickness of each disc with a digital caliper (Mitutoyo, Tokyo, Japan) for the push-out test, the specimens were mounted in a universal testing machine (Model TT-B, Instron Corp., Canton, MA, USA). The discs were loaded with a cylindrical plunger, 1 mm in diameter, centered on the disc avoiding contact with the surrounding core surface, with a cross-head speed of 0.05 mm/min. The micropush-out bond strength was expressed in megapascals (MPa) by dividing the load at failure (Newtons) by the bonding area (mm 2 ). The total bonding area for each post was calculated using the following formula :
where r is the post radius, π is the constant 3.14 and h is the thickness of each post section.
Failure modes were analyzed with a stereomicroscope (Olympus SZX-ILLB100-Olympus Optical Co. Ltd., Tokyo, Japan) at 40× magnifications and classified into four categories: Type 1, adhesive failure between the post and the core material; Type 2, cohesive failure within post; Type 3, cohesive failure within the core material; and Type 4, mixed failure. The percentage of failure modes for each group was calculated using the following formula:
where N f is the number of specimens presented for each mode of failure and N t is the total number of specimens in each group.
2.3
SEM
Three additional fiber posts per group were used for the analysis of the morphological aspects of posts after treatment using a scanning electron microscope (SEM) (JEOL; JXA-840A, JEOL, Tokyo, Japan). The specimens were ultrasonically (Bandelin, Sonorex, Germany) cleansed for 3 min using deionized water followed by immersion in 96% ethanol for 2 min and air drying. Each specimen was sputter-coated with gold (Sputter Coater S150A; Japan) and examined with SEM at magnifications of 200×.
2.4
Statistical analysis
A statistical analysis (SPSS 13.0; Chicago, IL, USA) of the micropush-out bond strength values was analyzed using a three-way analysis of variance (ANOVA) considering three factors (type of post, surface treatment, and type of core material) and their interaction. Multiple comparisons were made by Tukey’s test. Statistical significance was set at the 0.05 probability level.
2
Materials and methods
Two types of glass fiber reinforced composite posts were used in this study: Rebilda post (RP) and RelyX post (RX). The manufacturers and the compositions of the materials used in this study are presented in Table 1 .
