| Abstract|| |
Objective: Roughening of the aged composite resin core (CRC) surface seems essential for durable adhesion. The aim of this study was to investigate the influence of various surface treatments and different resin cements on microtensile bond strength (µ TBS) between two aged core build-up composites (CBCs) and feldspathic ceramic.
Materials and Methods: A total of 16 composite blocks made of two CBCs, Core.it and Build-it were randomly assigned to four surface treatment groups after water storage and thermocycling (2 weeks and 500 cycles). Experimental groups included surface roughening with air abrasion (AA), hydrofluoric acid, pumice, and laser and then were bonded to computer-aided design/computer-aided manufacturing feldspathic ceramic blocks using two resin cements, Panavia F2 (PF), and Duo-link (DL). The µ TBS was tested, and the fracture mode was assessed. The data were analyzed with multiple analysis of variance to estimate the contribution of different surface treatments, resin cements, and two aged CRCs on µ TBS. Statistical significance level was set at α < 0.05.
Results: Surface treatment and cement type significantly affected bond strength (P < 0.001) but the type of CRC did not (P = 0.468). Between roughening methods, the highest and the lowest values of µ TBS were sequentially obtained in AA and Er.YAG laser groups. The highest bond strength was in AA group cemented with PF (31.83 MPa). The most common failure mode was cohesive fracture in the cement.
Conclusion: Different surface treatments had different effects on µ TBS of aged CRCs to feldspathic ceramics. PF was significantly better than DL.
Keywords: Aged composite resin core, feldspathic ceramic, resin cement, surface treatment
|How to cite this article:|
Esmaeili B, Alaghehmand H, Shakerian M. Effect of different surface treatments on microtensile bond strength of two resin cements to aged simulated composite core materials. Indian J Dent Res 2015;26:309-14
Reconstruction of a tooth with excessive loss of structure using a composite resin core (CRC), and crown has an important role in providing esthetic, function, preservation of remaining structure, and reinforcement of weakened tooth., Improvements in adhesive dentistry have extensively led to the application of CRC restorations. They are available in auto-cure, dual-cure, and light-cure types, and as they set quickly core preparation can be completed immediately.
|How to cite this URL:|
Esmaeili B, Alaghehmand H, Shakerian M. Effect of different surface treatments on microtensile bond strength of two resin cements to aged simulated composite core materials. Indian J Dent Res [serial online] 2015 [cited 2020 Apr 1];26:309-14. Available from: http://www.ijdr.in/text.asp?2015/26/3/309/162871
In recent years, all ceramic restorations have gained popularity because of their excellent esthetic quality, chemical stability, biocompatibility, low plaque accumulation, and high compressive strength. Despite these advantages, brittle nature of ceramics is their drawback, therefore the success of all ceramic restorations depends on a reliable bond that could integrate all parts of the system, including CRC, luting cement, and ceramic. To achieve a desirable bond between these components, a number of mechanical and chemical ceramic surface treatments have been developed.
Moreover, achieving a reliable bond between CRCs and luting cement is a concern. In restorative dentistry, it is often inevitable to bond ceramic restorations to CRCs that have been exposed in the oral environment for some time and subsequently have a decreased number of available free methacrylate groups for cross-polymerization with the resin cement. Also, in the oral environment, CRC absorbs water by diffusion through the resin phase, and this is likely to affect the ability of the cement for adhesion., Studies on bonding of composite to aged composite with different surface treatment are abundant. These treatments compose of air abrasion (AA), surface roughening with diamond bur, etching with hydrofluoric acid (HF), laser, application of silane, and/or bonding agent. But there is no consensus on the results obtained with the different procedures and further studies are required about bonding of feldspathic ceramics to aged CRCs.
The purpose of the present study was to comparatively assess bond strength of feldspathic ceramic blocks and two types of dual-cure resin cements to aged simulated CRCs with various surface treatments. The tested null hypothesis was that different surface treatments would influence the bond strength of resin cement to aged simulated CRC but different dual-cure resin cements and core build-up materials would not lead to any significant difference.
| Materials and Methods|| |
Two types of dual cure core build-up composites (CBCs) Core.it (Spident, Gojan-Dong Namdon, Korea), and Build-it (Pentron, Wallingford Center, USA) were used for this study. Eight specimens from each composite were prepared using polyethylene mold (14 mm × 12 mm in width and 7 mm in depth). CBCs were inserted in a single increment into the mold (according to the manufacturer's instruction), and a polyester strip was placed over them to obtain a flat surface after curing. Then specimens were light-cured for a total of 40 s, 20 s from the top surface and 20 s after removal of the composite specimens from the mold on the other side to ensure optimal polymerization, with a light emitted diode (LED), light curing unit (Valo, Ultradent, South Jordan, USA). The light intensity was calibrated at 800 mW/cm2 with a radiometer (Demetron LED Radiometer, Kerr, USA). One end of each specimen was wet-ground by hand on 600 grit silicon carbide paper (Starcke Matador, Germany) for 30 s, to be prepared for surface treatment. The CBCs then were stored in distilled water at room temperature for 2 weeks followed by thermocycling for 500 cycles. Each cycle was consisted of 30 s in 5°C cold bath and 30 s in 55°C hot bath with a dwell time of 10 s (aging process).
Specimens in each group of CBC blocks were randomly divided into four subgroups and treated as followed:
- Abrasion for 30 s using pumice in a rubber cup, washing with water for 10 s and air drying (control)
- Laser irradiation with Er.YAG (Doctor Smile, Lambda SPA, Italy) based on manufacturer instruction with 2.94 µ wavelength at 133 mJ, 10 Hz repetition rate (low setting) and pulse mode with 0.5 mm distance from the surface. Water irrigation was used during the lasing of the samples. Laser sapphire tip was held by hand perpendicular to the surface for 30 s
- AA with 50 µ aluminum oxide particles (AeroEtcher Intraoral Blaster, Parkell, USA) from a distance of approximately 10 mm at a pressure of 2.5 bar for 30 s followed by rinsing with water for 10 s and air drying
- 9.6% HF application (Pulpdent, Watertown, USA) for 60 s followed by rinsing with water for 10 s and air drying. Before cementation, one coat of silane coupling agent (Pulpdent, Watertown, USA) was applied on CBC surface.
Sixteen feldspathic computer-aided design/computer-aided manufacturing Ceramic Blocks (Vita Mark II, Vident, USA), 12 × 14 in width, were wet ground with 600 grid silicon carbide paper on one side and then were etched with 9.6% HF for 1 min, carefully washed for 10 s and dried with compressed air. A layer of silane was applied on the surface of ceramic blocks and allowed 2 min to elapse for silane reaction. Before cementation of each specimen, one coat of porcelain bonding resin (Bisco, Schaumburg, USA) was applied on the surface of ceramic blocks. The materials chemical compositions are shown in [Table 1].
In each subgroup, 2 types of dual cure resin cements, panavia F2 (PF), (Kuraray, Chiyoda, Tokyo, Japan) and Duo-link (DL) Universal Cement (Bisco, Schaumburg, USA) were used for cementation of treated CBCs and ceramic blocks to each other (according to the manufacturers instruction). For bonding with PF, equal amounts of ED Primer II liquid A and B were mixed and applied on the surface of pretreated CBC specimens, after that equal amounts of A paste and B paste were dispensed on a pad and mixed for 20 s. For bonding with DL, equal amounts of All Bond 3 part A and B (Bisco, USA) were mixed and applied on CBC specimens, then auto-mixing tip was used for mixing of DL cement. The cements were applied on the surface of ceramic blocks and were bonded to the prepared surface of CBCs. Excess luting cement was removed using minibrush. The bonding assembly was kept under a static load of 5 Nand light-cured from four side surfaces each for 20 s with the LED unit (800 mW/cm2). The intensity was monitored before curing of each specimen. Then the specimens were kept in distilled water at room temperature (28°C) for 48 h and thermocycled for 500 cycles at 5 and 55°C.
For preparation of microbars, each cemented block was mounted in an auto-polymerized acrylic resin (Acropars, Marlic, Tehran, Iran) using stainless steel mold and was then fixed to a metal base in a cutting machine (CNC, Nemo, Mashhad, Iran). Cutting was done under wet condition. 1 mm of sectioned block from each side was discarded. From each block, 15 bars of 1 mm × 1 mm in thickness were obtained (totally 240 microbars). The cross-sectional area of the bond interface of each beam was measured using a digital caliper.
Two ends of each microbar were stocked to universal testing machine microtensile bond tester (Bisco, Schaumburg, USA) with cyanoacrylate glue (Mitreaple, Istanbul, Turkey). Specimens were loaded in tension to fail at a crosshead speed of 0.5 mm/min. Microtensile bond strength (µ TBS) values were recorded for each specimen in MPa using the formula:
α = L/A, where L is the load at failure (N) and A is the bonded area (1 mm × 1 mm).
The mode of fracture was determined with a stereo-microscope (EMZ, MEIJI TECHNO Co, Japan) for each specimen at a magnification of ×40. Failure modes were categorized as:
- Adhesive failure at the interface of ceramic and resin cement
- Adhesive failure at the interface of composite and resin cement
- Cohesive failure in the resin cement
- Cohesive failure in the composite
- A combination of adhesive and cohesive failure of resin cement.
Statistical analysis was conducted using the by using SPSS statistical software (version 18, SPSS Inc., Chicago, IL). Normal data distribution was confirmed by the Kolmogorov–Smirnov test and homogeneity of variance was tested according to the Levene's test. A multiple analysis of variance was used to analyze the contribution of surface treatment, resin cement type and CBC type and interaction of these factors to µ TBS. The Scheffe's test was run to make post-hoc multiple comparisons. The statistical significance was set at α =0.05. Fracture mode was described in percentage.
| Results|| |
The mean values of the µ TBS testing (MPa) are outlined in [Table 2]. Multiple variance analysis showed that surface treatment and cement type significantly affected bond strength of aged CRCs to feldspathic ceramics (P < 0.001) but the type of CBC was not statistically effective. Surface treatment with AA was the best method, followed by treatment with HF. The mean µ TBS differences between four surface treatment groups were statistically significant.
As shown in [Table 2], between four roughening methods, the highest and the lowest values of µ TBS were sequentially obtained in AA and Er.YAG laser groups. In comparison of two CBCs, the most and the least µ TBS values, both were obtained in Core.it CBC. There were no statistically significant differences between two composites with different treatments and different cements.
Between two cements, PF showed significantly better results than DL. In the case of Core.it, between two cements, there were statistically significant differences in laser and HF groups; in the case of Build-it, between two cements, there was statistically significant difference only in pumice group [Figure 1].
|Figure 1: Mean microtensile bond strength values of different groups and comparison of two cements. Significant differences among groups are showed by asterisks (P = 0.05)|
Click here to view
[Table 3] shows the failure mode distribution. The main failure type was cohesive fracture in the cement in all tested groups except in Core.it CBC treated with AA and cemented with PF, which mostly failed in mixed pattern. The lowest percentage of fracture was observed as adhesive fracture between ceramic and cement. There was no cohesive fracture within composite. In groups treated with AA, there was no adhesive fracture between composite and cement.
|Table 3: Percentage distribution (%) of failure mode in experimental groups|
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| Discussion|| |
A strong bond between aged composite core, resin cement, and ceramic relies on the establishment of micromechanical interlocking and chemical bonding of these components which requires adequate cleaning and roughening for surface activation. Common treatment options for CRCs are AA, roughening with diamond rotary instrument, pumice cleaning, acid etching, and treatment with laser.
This study was intended to examine the effect of different surface treatments and two resin cements on the µ TBS of composite cores to feldspathic ceramics. In view of statistical differences between the bond strength of different treated groups, thefirst part of our null hypothesis was confirmed. The highest bond strength values were obtained in groups treated with AA [Table 2]. This result agreed with the previous study by Cho et al. that concluded AA with 50 µ aluminum oxide provided the highest shear bond strength (SBS) in repaired composites. In a study by Eslamian et al. and in another case by Bayram et al., AA was a suitable method for bonding of ceramic brackets to aged composite restorations., AA with aluminum oxide particles in composite resin causes nonselective degradation (specially removing matrix and exposing filler particles) and creates a roughened surface with microretentive areas so increases surface area and promotes a strong mechanical bond of adhesive resin to sandblasted composite for bonding. Air abraded area improves the wetting behavior of adhesive cements and chemically activates adherend surface by removing organic contaminants.,,,
Er.YAG laser resulted in lowest bond strength among four treatment approaches (lower than control group). This result was in agreement with Cho et al. finding. In a previous study by Caneppele et al., they found that laser surface treatment reduced bond strength of indirect resin composite to resin cement. On the other hand, Burnett et al. found that TBS of one adhesive system to Er.YAG surface treated indirect composite was better than HF or AA. In studies of evaluation of resin cement bond to zirconia and feldespatic ceramics also laser treatment results were inconsistent., Several theories have been started in explanation of decreased bond strength with laser treatment; laser irradiations can form melted composite surface instead of creating retentive areas and some debris might adhere to the melted surface and be responsible for decreased bond strength. In the SEM micrographs of laser treated composite surface, microcracks were observed that are weak and might be responsible for poor bond strength.,,,
In the present study, after AA treatment with HF resulted in better bond strength than laser and pumice groups [Table 2]. This finding was not in agreement with Eslamian et al. finding which showed SBS of ceramic brackets to aged resin composite surface was not good with HF. Bayram et al. concluded HF application could result in adequate SBS values. HF acts by dissolving the glass particles of the filler, leaving gaps or pores that allow proper surface roughness and micromechanical retention.,,
Dual activated resin-based cements are material of choice for bonding between composite and ceramic. They have extended working time and ensure a high degree of polymerization., Our null hypothesis about influence of cement type on µ TBS was rejected. PF was statistically better than DL [Figure 1]. PF consists of 10-methacryloxyloxydecyle dihydrogen phosphate (10-MDP) functional monomers that have the capacity to interact with the surface and improve adhesion. The use of an MDP-based coupling agent after AA has been shown to result in higher bond strength because the 10-MDP may chemically bond better to aluminum oxides. An MDP containing resin cement like PF provides superior and long-term durable resin bond between air-abraded CBC and ceramic materials.,,
The most commonly seen fracture mode was cohesive fracture within cement followed by the combination of adhesive and cohesive fracture of cement [Table 3]. As cement was the weakest component of the system, this result was predictable. In AA group, there was no adhesive fracture in cement-composite interface (fracture type 2) that points to high bond strength between composite core and resin cement.
Application of a silane coupling agent to the pretreated CBC surface provides chemical bonds and seems to be a major factor for ideal resin bond. Silane has functional groups for reaction with inorganic fillers and methacrylate groups in the composite resin. It can promote a covalent bond between composite core and resin cement. Silanization also increases wettability of the CBC surface. It has been shown to improve bond strength after AA and HF etching due to exposure of the filler particles.,, In the current study, after AA, silane was not applied but the air abraded surfaces showed the highest bond strength. This result is supported by the findings of Cho et al. that found silanization did not significantly improved repair bond strength of air abraded composite surface. In contrast, Jafarzadeh et al. concluded that use of a silane before application of the adhesive and after mechanical grinding produced the best repair bond strength of aged composite but it seems that more researches is needed about relationship between silane application and bond strength of resin cement to composite core. Therefore, we recommend further studies about influence of silane on bond strength between aged CBC materials and resin cements.
| Conclusion|| |
Based on the current results, it can be concluded that various surface treatments had different influence on µ TBS of aged composite cores to feldspathic ceramics. Treatment with AA was the most effective method for preparing the aged CBC surface for bonding to resin cement and application of Er.YAG laser decreased bond strength. PF generally gave higher bond strength values than the DL resin cement did. There was no statistically significant difference between Core.it and Build-it.
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Department of Operative Dentistry, Dental School, Rafsanjan University of Medical Science, Rafsanjan
Source of Support: Nil, Conflict of Interest: None
[Table 1], [Table 2], [Table 3]