|Year : 2019 | Volume
| Issue : 4 | Page : 566-572
Shear bond strength and microleakage of novel glass-ionomer cements: An In vitro Study
E Meral, NM Baseren
Department of Restorative Dentistry, School of Dentistry, Hacettepe University, Ankara, Turkey
|Date of Acceptance||03-Jan-2019|
|Date of Web Publication||11-Apr-2019|
Dr. E Meral
Department of Restorative Dentistry, School of Dentistry, Hacettepe University, Ankara 06100
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background: The overall success of dental restorations depends on the materials' ability to bond to dental structures and to eliminate the microleakage. Therefore, the aim of this study was to evaluate the shear bond strength (SBS) and microleakage of novel glass-ionomer restorative materials. Materials and Methods: In this study 62 intact molars were used, of which 30 molars were sectioned buccolingually, embedded in acrylic resin, and polished to obtain flat dentin surfaces. Then, glass-ionomer cylinders were built on the specimens (n = 15) with a high-viscosity glass-ionomer cement (GIC) (EQUIA Fil), a glass-carbomer (Glassfill), a zirconia-reinforced GIC (Zirconomer), or a conventional GIC (RivaSelfCure), and SBS testing was performed. For microleakage test, Class V cavities were prepared on buccal and lingual surfaces of the remaining 32 teeth and divided into four groups (n = 16). Each group was restored with one of four GICs and subjected to microleakage testing. The data were statistically analyzed (P = 0.05). Results: The highest SBS values were observed in Glassfill group (P < 0.05). There were no significant differences on the SBS values of other three materials (P > 0.05). Regarding microleakage evaluations, no significant differences were observed at enamel margins (P > 0.05), whereas at dentin margins, EQUIA Fil and Zirconomer showed less microleakage than Glassfill (P < 0.05). Conclusions: Although the glass-carbomer restorative materials revealed higher SBS, other tested materials might be more reliable in clinical use, as they offer better leakage resistance.
Keywords: Glass-carbomer cement, glass-ionomer cements, microleakage, shear bond strength
|How to cite this article:|
Meral E, Baseren N M. Shear bond strength and microleakage of novel glass-ionomer cements: An In vitro Study. Niger J Clin Pract 2019;22:566-72
| Introduction|| |
Dental cervical lesions are identified with the loss of hard tissue at the cervical region of the tooth and can be caused by incorrect tooth brushing, caries, or traumatic occlusal loads. The restoration of cervical lesions is often challenging, for there is little or no enamel to provide good adhesion at the cervical margin, which leads to increased microleakage., Because microleakage is a major reason for failure in cervical restorations, the marginal sealing ability of materials is an important consideration.,
Glass-ionomer cements (GICs) are recommended materials for Class V restorations because of their ability to chemically bond to dentin and enamel, microleakage resistance, and to release fluoride over time., These materials have a wide range of use from pediatric to geriatric patients, to restore both deciduous and permanent teeth, for being less technique-sensitive, and the only materials that can form a chemical and micromechanical bonds with tooth substance that might be beneficial to increase retention. Despite these advantages, the lack of strength, low resistance to abrasion, and sensitivity to moisture contact during the hardening process are the major drawbacks of GICs. Furthermore, GICs are shown to have high degrees of solubility, which may cause the degradation of the cement and lead to secondary caries caused by the gaps in marginal integrity.
Manufacturers have made various modifications in the composition of glass-ionomer materials to improve the physical and mechanical properties. As a result, high-viscosity glass-ionomer cements (HVGICs) entered the market in the mid-1990s. The moisture sensitivity of these materials is lower while hardness and wear resistance are better than other materials, which makes them the best choice to use in high occlusal stress areas. EQUIA, which is a restorative system combining a HVGIC with a resin-based coating agent entered the market several years ago and the success of the material is proven with clinical trials as it showed similar clinical performance with composite resin.
The need for a more durable material has led to the development of a new material that adds zirconia filler particles to the glass-ionomer composition. Zirconomer, also called “white amalgam,” has combined the durability of amalgam with the biocompatibility and fluoride-releasing characteristics of glass-ionomer materials.
Recently, another glass-ionomer-based reinforced material, glass carbomer, has been introduced with claims of improved physical characteristics. This new material has nanosized hydroxyapatite-fluorapatite particles in powder form. The addition of nanoparticles has improved compressive strength and the wear resistance of cement. Another advantage of glass-carbomer cement is the greatly reduced moisture sensitivity.
Although previous studies evaluated some physical properties of these materials, there has not yet been a study that compared these materials with each other.
Therefore, the aim of this study was to evaluate the microleakage and shear bond strength (SBS) of four different glass-ionomer-based restorative materials.
The null hypotheses tested were:
- There will be no significant difference between the materials in terms of SBS
- There will be no significant difference between the materials in terms of microleakage.
| Materials and Methods|| |
A total of 62 sound human third molars were selected from a pool after obtaining the informed consent from patients under a protocol approved by the local ethics committee (#GO 17/327). The teeth were cleaned with a hand-scaling instrument and professional prophylaxis application, stored in chloramine-T solution for a week, and then stored in distilled water until use. Following surface debridement, the teeth were examined at 20× magnification under a light microscope, and those with any visible structural defects, cracks, or carious lesions were discarded. Materials used in this study are presented in [Table 1].
For SBS testing, 30 teeth were selected. The teeth were divided into two sections mesiodistally, parallel to the long axis of the tooth, and each section was embedded in acrylic blocks with their buccal or lingual surfaces positioned for bonding. After polymerizing the acrylic blocks, the buccal or lingual surfaces were ground flat in a polishing machine (Presi Mecapol P320, Grenoble, France) using 600 grit silicon carbide paper under water cooling until a uniform dentin layer was achieved. The exposed dentin surfaces were evaluated with a stereomicroscope (Olympus SZ61, Olympus Corporation, Japan) to ensure that no enamel remained and no pulp exposure had occurred. All the specimens (n = 15) were then randomly distributed into four groups corresponding to different glass-ionomer-based restorative materials. A bonding jig with a Teflon bonding template was used (inner diameter of 2 mm and height of 2 mm). The bonding template was isolated with petroleum jelly before applying materials.
High viscosity GIC (HVGIC) group
A HVGIC system (EQUIA Fil, GC Co. Tokyo, Japan) was used in this group. The capsule was activated and mixed for 10 s in a mixer and injected into the bonding template attached to dentin surfaces. The material was held under mild pressure using a glass slide allowing excess material to leak out. After setting, the bonding template was removed and the surfaces were coated with EQUIA Fil coat.
Glass-carbomer (GC) group
Glass-carbomer (GCP Glass Fill, GCP Dental, Leiden, Holland) capsule was activated and mixed in a high-frequency mixer (GCP CarboMix, GCP Dental) for 15 s. The material was held under light pressure with a glass slide and light-cured with a high output light device (GCP CarboLED, GCP Dental) for 90 s. After the bonding template was removed, the surfaces were coated with GCP gloss (GCP Dental) and light-cured for 90 s.
Zirconia-reinforced GIC (ZRGIC) group
A powder-to-liquid ratio of 2:1 was used to prepare zirconia-reinforced GIC (Zirconomer, Shofu Dental, Tokyo, Japan) material according to manufacturer's instructions. The material was hand-mixed and used to build on dentin surfaces.
Conventional GIC (CGIC) group
Conventional glass-ionomer (Riva Self Cure, SDI Ltd, VIC, Australia) capsule was activated, mixed in a mixer for 10 s, and bonded to dentin surfaces. After the setting, Riva Coat (SDI Ltd, Victoria, Australia) was applied and light-cured.
All the specimens were stored in distilled water at 37°C for 24 h. A universal testing machine (LRX, Lloyd instruments Ltd, Fareham, England) was used for SBS testing, with a crosshead speed of 0.5 mm/min until debonding was observed at the dentin to GIC interface. The bond strength data were obtained in Newtons, recorded to computer, and converted to megapascals.
After the test, the fractured samples were examined under a stereomicroscope under ×10 magnification for fracture mode analysis. Fracture modes were classified as adhesive (between GIC and dentin), cohesive (within the GIC), or mixed (adhesive and cohesive fractures formed at the same time). The results were presented as percentages.
A total of 64 Class V cavities (width of 4 mm, height of 3 mm, and depth of 2 mm) were prepared on both buccal and lingual surfaces. The gingival margin was placed on dentin, and the occlusal margin was placed on enamel. The depth of the preparations was measured using a periodontal probe. The teeth were randomly divided into four groups, and each group contained 16 preparations. Each of the groups was restored with one of the glass-ionomer-based materials. All the restorations were finished using polishing disks (Optidisc, Kerr, CA, USA) and after the polishing procedure, the surface coating agents were reapplied. For Zirconomer material, petroleum jelly was used as lubricant during the finishing and polishing processes. Following the polishing, all teeth were placed in a thermocycling device (MTE 101 thermocycling machine, Esetron, Ankara, Turkey) alternating between 5°C and 55°C for 5000 cycles with an exposure time of 30 s and a dwelling time of 15 s. The apex of each tooth was sealed with sticky wax, and the entire tooth, except 1 mm beyond the margin of the restoration, was coated with nail varnish to prevent dye penetration from neighboring dentin. The teeth were then immersed in 0.5% basic fuchsin for 24 h. After being removed from the dye solution, the teeth were embedded in acrylic blocks and sectioned two times bucco-lingually with a sectioning machine (Microcut 201, Metkon, Bursa, Turkey) for a total of three sections from each tooth. Sections were examined at 40 magnification with a stereomicroscope, and only the section with the most microleakage from each specimen was used for scoring. The depth of dye penetration was analyzed for both dentin and enamel margins using the scale below:
Score 0: No dye penetration
Score 1: Dye penetration of less than ½ of the cavity wall
Score 2: Dye penetration of more than ½ of the cavity wall
Score 3: Dye penetration up to the axial wall but not involving the axial wall
Score 4: Dye penetration containing the axial wall.
For SBS testing, the data were analyzed using one-way analysis of variance and multiple comparisons by Tukey's test. For microleakage testing, Kruskal–Wallis test was used for enamel and dentin margins, and the comparisons between enamel and dentin margins around the same material were done by Wilcoxon test. All statistical analyses were performed using SPSS 13.0 for Windows (SPSS Inc., Chicago, IL, USA).
| Results|| |
The mean SBS values, and standard deviations for all groups are shown in [Table 2].
According to SBS testing, GC group showed the highest bond strength values to dentin. No significant difference was observed between high-viscosity, conventional, and zirconia-reinforced glass ionomer groups (P > 0.05).
According to failure mode analysis, zirconia-reinforced and conventional GICs showed mostly mixed failure, while GC and HVGIC showed mostly cohesive failure (P < 0.05). The percentages of failure modes for all groups are shown in [Table 3].
|Table 3: Different lower cases within the same column represents significant differences. Different upper cases within the same row represents significat differences|
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Microleakage scores of the four glass-ionomer-based materials for both enamel and dentin margins are shown in [Figure 1] and [Figure 2].
|Figure 1: Distribution of microleakage scores in enamel for all materials|
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|Figure 2: Distribution of microleakage scores in dentin for all materials|
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There was no significant difference between enamel margins for all materials (P < 0.05). In dentin margins, HVGIC and ZRGIC groups showed less microleakage than GC group. Also, in most of the samples, crack lines filled with dye were observed in the GC group.
GC, ZRGIC, and conventional GIC showed no significant difference in microleakage scores between enamel and dentin margins. Dentin margins showed higher microleakage values than enamel margins (P < 0.05) in the HVGIC group only.
| Discussion|| |
An ideal restorative material should have the properties of good marginal seal, chemical adhesion with dental tissues, similar thermal expansion coefficient with the tooth, good color stability, and biocompatibility., The adhesion of restorative materials to dentin is a desirable property because it can prevent the formation of secondary caries, microleakage, marginal discoloration, and subsequent pulpal damage. Therefore, in the current study, SBS and microleakage of novel glass-ionomer-based restorative materials were evaluated.
SBS testing is an easy-to-use procedure that is widely used to evaluate the bonding performance of restorative materials. It is the preferable method, especially for GICs exhibiting low bonding strength, because other bonding tests are very difficult to apply.
There are few studies regarding the SBS of GICs. There is also no data in the literature on the SBS of ZRGIC.
The highest SBS values were observed in the GC group in the current study, whereas other three materials showed no significant differences from each other. Therefore, the first null hypothesis tested was rejected.
In a previous in vitro study, glass-carbomer cement and a HVGIC were compared in terms of SBS for both sound and caries-affected dentin. Glass-carbomer cement showed lesser SBS than HVGIC for both substrates. These results are in contrast with the current study; however, the application of dentin pretreatment before placing the filling materials may explain the higher SBS of HVGIC. Also, bovine teeth were used for the earlier study. In the current study, no dentin pretreatment was applied in order to standardize the conditions for all materials, and human molars were used.
In another clinical study, Gorseta et al. compared the performance of glass-carbomer cement and a resin-based sealant as fissure sealants and reported that the two materials had similar retention rates. Glass-carbomer cement has a similar retention rate to resin-based sealants, which are accepted as the gold standard because of their high retention rate compared to glass-ionomer-based sealants. This supports the results of the present study showing higher bond strength with glass carbomer.
The manufacturer claimed that the wear resistance and compression strength was improved because of the incorporation of nanoparticles in glass carbomer's structure with high output light source. On the contrary, the addition of nanoparticles to GICs (nanohydroxyapatite/nanofluorapatite) improved the mechanical behavior and bond strength to dentin. This may explain the high bond strength of glass-carbomer cement in the current study.
Zirconomer is a zirconia-reinforced glass-ionomer material marketed with the ability to eliminate the esthetic and mechanical disadvantages of conventional glass ionomers. Till now, there is no published data on the bond strength of Zirconomer material. Kishore et al. observed that Zirconomer released higher degrees of fluoride compared to conventional glass ionomers. In another in vitro study, Zirconomer was compared with conventional glass ionomer and amalgam in terms of compressive strength, and Zirconomer and amalgam showed similar compressive strength values, which were both higher than glass ionomer.
In the current study, because of presenting similar SBS values to EQUIA, Zirconomer might be considered as a reliable restorative material in the posterior area of the mouth, especially for patients with high caries activity because it has high fluoride release and durability.
According to the results of the current study; EQUIA and GlassFill showed mostly cohesive fracture whereas, Zirconomer and Riva Self Cure showed mostly mixed fracture. Cohesive and mixed fractures are the most reported failure types in glass ionomer materials.,,,, It was also reported that the presence of cohesive and mixed failures in GICs indicate that the bond strength values may only provide information on the tensile strength of the material, other than the SBS of the adhesive interface., This may imply that the interfacial bond strength is higher that the inherent strength of the material.
One of the primary causes of failure for dental restorations is microleakage. Microleakage allows bacterial invasion at the interface of the tooth and restorative material, providing the basis for secondary caries and pulp inflammation., Therefore, the success of restorative materials depends on their ability to prevent microleakage., For this purpose, the current study also examined the microleakage of different glass-ionomer-based restorative materials placed in Class V cavities using a dye penetration method. Class V cavities were selected due to their complex morphology involving both enamel and dentin margins that allowed the evaluation of microleakage in dentin and enamel at the same time. In this study, we used the most frequent method for microleakage evaluation, which is dye penetration. Thermocycling was used to simulate the temperature changes of an oral environment.
In the current study, no significant differences were observed on microleakage in enamel margins for all materials. However, in dentin margins, EQUIA and Zirconomer showed lower degrees of microleakage than glass carbomer. Hence the second hypothesis tested was also rejected. In addition to higher microleakage, crack lines filled with dye were observed in the glass carbomer restorations. These findings are similar to those in the study by Chen et al., which detected similar crack lines in glass carbomer restorations. The reason for this situation in the current study may be the use of a thermocycling procedure. Glass carbomer's solubility degree might be higher than the other three materials. However, in a previous study, Subramaniam et al. reported that glass carbomer cement showed lower degrees of solubility when compared to conventional glass ionomer; however, the glass ionomer used in that study was Fuji VII which has lower mechanical properties than materials used in the current study. Further studies are required to confirm the degree of solubility of glass-carbomer cement.
An in vitro study by Çehreli et al. evaluated the microleakage of Class I cavities restored by different materials applied with and without surface coating. In that study, the microleakage in enamel margins was evaluated, and similar to the present study, coated glass carbomer and coated glass ionomer showed no significant differences in microleakage values.
An ideal restorative material should provide high bond strength and prevent microleakage. Higher bond strength is generally expected to result in less leakage; however, the relationship between bond strength and microleakage is not fully understood.
Despite showing high SBS, glass carbomer also showed high values of microleakage. The reason for this dilemma may be the use of thermocycling only for microleakage testing and not for SBS testing.
In their in vivo study, Gürgan et al. reported that cavities restored with EQUIA had high survival rates and showed no significant differences from micro-hybrid composite resin restorations. Based on these findings, EQUIA Fil can be accepted as an ideal permanent restorative material. In the current study, Zirconomer and EQUIA materials showed no significant differences for SBS and microleakage values. Hence, based on the limitations of this study, Zirconomer material might also be a convenient material for the posterior area of the mouth.
To the extent of authors' knowledge, there are only a few published studies regarding Zirconomer and glass-carbomer materials, and this study is unique for comparing the four materials used in the study. Therefore, further in vitro and in vivo research is required to examine the performance of the novel glass-ionomer-based materials.
| Conclusions|| |
Based on the limitations of the study, it can be concluded that:
- Besides its advantages, the glass-carbomer material needs improvements regarding its sealing capacity, to be considered as a dependable restorative material
- Zirconia-reinforced, high-viscosity, and conventional glass-ionomer materials may be preferable over glass-carbomer material, as permanent restoratives.
This study was supported by Hacettepe University Research Fund.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
- The moisture isolation in pediatric dentistry is a great challenge, therefore glass ionomers are widely used
- The study may enlighten some questions about the clinical performances of the novel glass ionomers
- The information about these novel glass ionomers may lead the clinicians to the accurate indications of these remineralizing and protective materials which can enhance the oral health and decrease the caries ratio.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]