|Year : 2019 | Volume
| Issue : 3 | Page : 265-270
Comparative evaluation of compressive strength and surface microhardness of EQUIA Forte, resin-modified glass-ionomer cement with conventional glass-ionomer cement
P Poornima, Paromita Koley, Mallikarjuna Kenchappa, NB Nagaveni, Kashetty Panchakshari Bharath, Indavara Eregowda Neena
Department of Pedodontics and Preventive Dentistry, College of Dental Sciences, Davangere, Karnataka, India
|Date of Web Publication||30-Sep-2019|
Dr. P Poornima
Department of Pedodontics and Preventive Dentistry, College of Dental Sciences, Davangere, Karnataka
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Purpose: The study aimed to evaluate and compare the compressive strength and surface microhardness of EQUIA Forte, light cure, and conventional glass-ionomer cement (GIC). Methodology: Fifty-four pellets of G-Coat (GC) Gold Label 2, GC Gold Label light-cured universal restorative material, and EQUIA Forte GIC were prepared of dimensions (6 × 4) mm and were divided into three groups (18) each and were stored at 37°C for 1 h and then immersed in 20 ml of deionized water, artificial saliva, and lactic acid six each, respectively, over 30 days. Samples were subjected to surface microhardness and compressive strength test on the 1st day, 7th day, and 30th day. Results were subjected to ANOVA and Bonferroni post hoc test. Results: Comparing the compressive strength of EQUIA Forte from day 1 to 30 when placed in artificial saliva, there was a significant increase on day 30 (P = 0.007); compared to other groups. The surface microhardness of EQUIA Forte from day 1 to 30 when placed in artificial saliva nonsignificantly decreased comparing to other groups. Conclusion: Surface microhardness and compressive strength of EQUIA Forte were significantly high in comparison to the other groups.
Keywords: Compressive strength, conventional glass-ionomer cement, EQUIA Forte, resin-modified glass-ionomer cement, surface microhardness
|How to cite this article:|
Poornima P, Koley P, Kenchappa M, Nagaveni N B, Bharath KP, Neena IE. Comparative evaluation of compressive strength and surface microhardness of EQUIA Forte, resin-modified glass-ionomer cement with conventional glass-ionomer cement. J Indian Soc Pedod Prev Dent 2019;37:265-70
|How to cite this URL:|
Poornima P, Koley P, Kenchappa M, Nagaveni N B, Bharath KP, Neena IE. Comparative evaluation of compressive strength and surface microhardness of EQUIA Forte, resin-modified glass-ionomer cement with conventional glass-ionomer cement. J Indian Soc Pedod Prev Dent [serial online] 2019 [cited 2020 Apr 1];37:265-70. Available from: http://www.jisppd.com/text.asp?2019/37/3/265/268184
| Introduction|| |
Glass-ionomer cements (GICs) are widely used in restorative dentistry. One of their advantages over other restorative materials is that they can be placed into tooth cavities without an additional bonding agent. They also possess a fiuoride-releasing property and are relatively biocompatible with the pulp. Although GICs are commonly used dental cements, they have some disadvantages. The most intractable problem with the conventional GICs is probably their lack of strength and toughness. In order to improve the mechanical properties of conventional GICs, resin-modified GICs were developed. These resin-modified GICs (RMGICs) provided improved mechanical properties and adhesion, better esthetics, easier application with reduced moisture sensitivity, and immediate light cure after placement.,,,
When selecting a restorative material, one of the main considerations is its mechanical properties. As restorative materials are used to replace missing tooth structure, it needs to be strong enough to withstand the forces associated with mastication. Hardness test and compressive strength test can be used to evaluate these mechanical properties. Although, there are studies available comparing microhardness between GIC and RMGIC, there is lack of research regarding the surface microhardness of the materials containing glass hybrid (EQUIA Forte). The physical properties of tooth-colored restorations are affected by their surrounding chemical environment. Direct tooth-colored restoratives have been shown to leach filler and other constituents when stored in distilled water. As direct tooth-colored restoratives are constantly being surrounded by saliva, findings obtained from storage in distilled water may be of little clinical relevance. The use of artificial saliva allows for better simulation of the way restoratives interact with human saliva. Leaching of restorative constituents has been reported to be higher in artificial salvia when compared to distilled water. Thus, the aim of the present study is to evaluate and compare the compressive strength and surface microhardness of conventional, resin-modified, and EQUIA Forte GIC materials after placing in three liquid media.
| Methodology|| |
Three GIC materials were used in the study, GIC Type II (G-Coat [GC] Gold Label Universal Restorative), GIC Type II (GC Gold Label Light-cured Universal Restorative), and EQUIA Forte Fil with EQUIA Forte Coat.
Preparation of test specimen
A total of 54 cylindrical test specimens of dimensions 4 mm diameter × 6 mm height were prepared from a custom-made Teflon mold using conventional GIC, RMGIC, and EQUIA Forte GIC. Of 54 test specimens, 18 of them were prepared from conventional GIC, which served as the control group; 18 of them were prepared from RMGIC material and EQUIA Forte restorative material, respectively, which served as the experimental groups. A thin layer of petroleum jelly was coated on the lateral walls of the mold to prevent material adhesion. The powder and liquid of the conventional GIC and RMGIC were mixed according to the manufacturer's instructions and placed in the molds. RMGIC samples were cured for 40 s using light-emitting diode (LED) (Coltolux.75) light-cure unit. The EQUIA Forte capsules were mixed in the capsule mixer for 10 s which were removed and placed in the molds with the help of the GC capsule applier. The mixed cement was placed into the custom-made Teflon mold by slightly overfilling them and was placed between the two glass plates with the Mylar strips placed between Teflon mold and the glass plate to prevent the adhesion of GIC to glass plate. The glass plates were held firmly during setting to avoid the presence of air bubble and to obtain a smooth surface. After setting, the pellets were removed from the mold, and the excess was trimmed using a Bard-Parker blade. For EQUIA Forte specimens after removal, a layer of GC was applied with a microbrush on the cement surface and light cured for 20 s with an LED curing light. The specimens were randomly grouped into three groups; six in each group. The specimens were then stored in 20 ml of deionized water, artificial saliva, and lactic acid at temperature of 37°C for 3 h daily for 30 days, and the solutions were changed every week, after which they were tested for compressive strength and surface microhardness on the 1st day, 7th day, and 30th day.
Assessment of compressive strength
Conventional GIC (GC Fuji II gold label) was served as control. The compressive strength of each material was measured using a universal testing machine (Tinius Olsen Co), (AG-50kNG) at cross head of 1 mm/min, and strength was determined after 1 day, 7 days, and 30 days, respectively.
Assessment of surface microhardness
The microhardness measurements were carried out using a microhardness tester (model-MMT-X7A, no-MM5549X, Matsuzawa Co., Ltd., Japan). The indentations were made within 10 s from the loading of 0.25N for all specimens to eliminate the possible plastic deformation of the polymer matrix of resin-modified GICs that would influence the surface microhardness values. For each test specimen, the values were read referring to the size of the greater diagonal. The values were transformed into the Vickers hardness number. Five simultaneous measurements were taken. Surface microhardness was calculated using the following formula: VH = 1.854 × F × 103/d 2 where F is the applied test load (N) and d is the average of the indentation diagonals (mm).
| Results|| |
The results were tabulated and statistically analyzed using the one-way ANOVA and repeated measure ANOVA followed by the Bonferroni post hoc test. P= 0.05 or less was considered statistically significant.
Comparing the compressive strength of EQUIA Forte (Group 1) from day 1 to 30 when placed in artificial saliva as depicted in [Table 1], there was a significant increase in compressive strength on day 30 (P = 0.007). When placed in lactic acid, there was no significant increase in compressive strength comparing the 1st day, 7th day, and 30th day, whereas in deionized water, there was a significant increase in compressive strength from day 1 to day 30 (P = 0.002). Comparing the compressive strength of Type II LC (Group 2) and Type II GIC (Group 3) from day 1 to 30 when placed in artificial saliva, there was nonsignificant increase in compressive strength.
|Table 1: Comparison of compressive strength between different time intervals in each group and subgroup|
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The comparison of surface microhardness at different time intervals in each group and subgroup is depicted in [Table 2]. There was a non-significant decrease in the surface microhardness of EQUIA Forte(Group 1) from day 1 to 30 when placed in artificial saliva. When placed in lactic acid, there was nonsignificant increase in surface microhardness comparing 7th–30th day. The surface microhardness of Type II LC(Group 2) from day 1 to 30 decreased significantly (P < 0.001) when placed both in artificial saliva and lactic acid. Comparing the surface microhardness of Type II GIC (Group 3) from day 1 to 30 when placed in artificial saliva, there was nonsignificant increase from day 1 to day 7 and then slight decrease on day 30.
|Table 2: Comparison of surface microhardness between different time intervals in each group and subgroup|
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| Discussion|| |
Compressive and surface microhardness tests are used in dentistry for laboratory simulation of the stress that may result from forces applied clinically to a restorative material. Compressive stresses contribute to fracture failure through masticatory forces, although an exact critical value is unknown. A British specification established that the minimum value necessary to resist the masticatory forces in the posterior teeth would be 125 MPa, while some authors  believe that this value should be 100 MPa in the primary dentition.
EQUIA (GC, America) is a new glass-ionomer restorative system. It is a combination of a self-adhesive, chemically cured, highly filled GIC (Fuji IX GP Extra, GC), and a self-adhesive, light cured, filled resin surface sealant (GC Plus, GC). The manufacturers of EQUIA claim that the material has increased fracture toughness, flexural strength, and flexural fatigue resistance. The coating agent added to the surface of the glass ionomer of the EQUIA system contains a nano-filled resin that may have contributed significantly to the increased resistance of the material to mechanical forces. This assumption is supported by the results of an in vitro study which tested the influence of a resin coat (GC Plus) spread over the Fuji 9 extra and Ketac Molar Easymix.
The physical properties of tooth-colored restorations are affected by their surrounding chemical environment. Direct tooth-colored restoratives have been shown to leach filler and other constituents when stored in distilled water. Studies have been performed in an attempt to better understand their properties, and compressive strength testing is the most commonly employed method to evaluate the strength of these materials.
In the present study, the surface microhardness of EQUIA Forte decreased when placed in deionized water from day 1 to day 30 but was not statistically significant. Comparing surface microhardness of EQUIA Forte for day 1, it was significantly higher in deionized water in comparison to artificial saliva and lactic acid. Vaid et al., in their study, found that there was no statistically significant difference observed between the clinical performance of EQUIA, RMGIC, and nanohybrid composite. Comparison of EQUIA Forte with other studies is not possible, as previous studies are either clinical based or based on the evaluation of mechanical properties of EQUIA Forte other than surface microhardness.
In the present study, the surface microhardness of RMGIC decreased from day 1 to day 30 when placed in all the three medium; however, the surface microhardness of RMGIC was significantly higher when compared to EQUIA Forte and conventional GIC when placed in artificial saliva as well as lactic acid for day 1. This finding of our study is supported by Bourke et al. who stated that RMGIC reaches their maximum hardness on day 1, after which no significant increase was observed.
Light-cure GIC set by various competing reactions resulting in a complex structure. The polymeric network will contain both ionic and covalent crosslinks. However, these products have a tendency to undergo phase separation and may contain domains of different hydrophobic and hydrophilic phases. It is, hence, expected that the water taken up will migrate preferentially to the hydrophilic sites and will probably provoke the dissolution and leakage of ionic species, which may result in a decrease of the physical properties of these materials. Thus, in an aqueous environment, RMGICs take up great amounts of water, they swell, became plastic, and are mechanically less resistant.
According to Prabhakar et al., the surface hardness of the conventional GICs was found to be higher than those of the resin-modified materials when stored in deionized water for 30 days. In the present study, the surface microhardness of conventional GIC in deionized water gradually decreased in lactic acid, while it increased in artificial saliva when comparing from day 1, day 7 to day 30.
In contrary to our study, with regard to storage time, there was an increase in the microhardness values with the increase in storage time for RMGIC, as shown in the findings of Aliping-McKenzie et al., (2003), Okada et al., (2001), Raggio et al., (2004), Xie et al., (2000), Yao et al., (1990), and Yap et al., (2002). It could be observed that the increase in the microhardness values was more accentuated in the interval between 24 h and 7 days and more uniform in the interval between 7 and 30 days when stored in distilled water.
According to the earlier literature, the compressive strength of conventional and resin-modified GICs has a trend to increase with prolonged water immersion.,,, In the present study, the compressive strength of RMGIC in deionized water, lactic acid, and artificial saliva showed significantly increase from day 1 to day 30, and it was significantly high in deionized water in comparison to artificial saliva and lactic acid. In a study by Williams and Billington  the compressive strength of RMGIC increased in the first 30 days when stored in distilled water which is in alliance with the present study. The compressive strength in acidic media showed less values when compared to neutral solution because in acidic media, various ions such as aluminum, silicon, and phosphorus, like calcium showed increased released with time. This suggests an increase in the proportion of acid-soluble components with time, which, in turn, suggests that the change is a consequence of the maturation processes thus reducing the final structure of the set cement which future effect strength of the cement.
Ideally, core materials whose mechanical properties are comparable to those of dentin should be used. Craig and Peyton found a compressive strength of 297.2 MPa and diametral tensile strength of 41.4 MPa for human dentin. In the present study, the highest determined value for the compressive strength of EQUIA Forte was 259.86 MPa at the 30th day when placed in deionized water which is comparable to that of dentin.
The drawback of the present study is that it only determined the compressive strength and surface microhardness of the study materials. Physical properties such as fracture toughness, shear strength, and elastic modulus of core materials have been reported to correlate the physical as well as handling properties of materials. Nevertheless, future studies which determine all the physical properties of these materials are recommended before drawing any conclusion.
| Conclusion|| |
The physical and handling properties may lead the clinician to favor one material over another. Ultimately, a core build-up must be able to withstand the forces of mastication and parafunction over a period of many years. In this context, compressive strength measures the strength of material, whereas surface microhardness estimates the longevity and surface wear which is measured in this study, and it has been found that EQUIA Forte GIC shows comparatively better mechanical properties than the other groups of the study. Hence, it can be suggested for use as a posterior restorative material.
Further clinical research is required to confirm our findings since few studies can be found in the literature over the mechanical properties of Bulk filled glass hybrid GIC (EQUIA Forte) compared to resin modified and conventional restorative GIC.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2]