| Abstract|| |
Context: Newer glass ionomer cements with improved properties are constantly being developed. One such material is the novel Hybrid Glass-Ionomer cement (HGIC) with properties yet to be studied. Aims: The aim of this study was to compare the flexural strength, shear bond strength, wear resistance and fluoride release of Hybrid Glass Ionomer restorative with Conventional Glass Ionomer Cement (CGIC) and Resin modified Glass Ionomer Cement (RMGIC). Settings and Design: This was an in vitro study. Methods and Material: A total of 300 samples were tested in this study, with 100 samples per group and each group was further subdivided into 5 sub-groups with 20 samples each. Flexural and Shear bond strength values were determined by subjecting the specimens to a universal testing machine. For wear resistance, the specimens were assessed using a pin on the disc tribometer. For fluoride release, the test specimen suspended in 10 mL deionised water was tested at 24 h and 1 week. Statistical Analysis Used: One-way ANOVA. Results: RMGIC had the highest flexural and shear bond strength values followed by HGIC and CGIC. HGIC had the least wear rate followed by RMGIC and CGIC. At 24 h and 1 week, HGIC had the highest fluoride release among the study groups. Conclusions: HGIC exhibited the highest wear resistance and fluoride release among the cements studied. However, flexural and Shear bond strength values, of RMGIC, was comparatively higher.
Keywords: Flexural strength, fluoride release, glass ionomer, shear bond strength, wear resistance
|How to cite this article:|
Sainath Reddy T H, Venkatesh K V, Mani R. Comparative evaluation of three different glass ionomer cements. Indian J Dent Res 2021;32:485-8
|How to cite this URL:|
Sainath Reddy T H, Venkatesh K V, Mani R. Comparative evaluation of three different glass ionomer cements. Indian J Dent Res [serial online] 2021 [cited 2022 Jun 29];32:485-8. Available from: https://www.ijdr.in/text.asp?2021/32/4/485/345427
| Introduction|| |
Conventional Glass Ionomer Cement (CGIC) is a clinically proven restorative material, consisting of calcium-fluoroaluminosilicate glass powder mixed with an aqueous solution of acrylic acid with copolymers. CGIC has desirable properties like fluoride release, adhesion to base metals and moist tooth structure, lower cytotoxicity, and biocompatibility. However, CGIC cannot be used in high-stress areas because of its low mechanical properties.
RMGIC was introduced as an alternative to CGIC in order to overcome the drawbacks of sensitivity to moisture and low initial mechanical properties. RMGIC contains CGIC components like acid degradable glass and aqueous solutions of polyacrylic acid along with an added monomer 2-hydroxyethyl methacrylate; available as self and light cure variants.
The novel HGIC is a recently introduced cement which is a hand-mixed, self-adhesive restorative material. It is enhanced with advanced Glass Hybrid Technology which is a combination of two types of fluoroaluminosilicate glass and polyacrylic acid. Manufacturers claim that HGIC has superior physical and mechanical properties compared to CGIC and RMGIC. Literature review suggests that there are only limited studies pertaining to the properties of this novel cement. Therefore, the purpose of this study was to compare flexural strength, shear bond strength, wear resistance, and fluoride release of HGIC with CGIC and RMGIC.
| Materials and Methods|| |
This study was approved by the Institutional Research Ethics Committee (ECR/2055/IEC/2020) of SRM Kattankulathur University, Tamil Nadu, India and was conducted in accordance with the Helsinki Declaration of 1975, as revised in 2000.
A total of 300 samples were tested with 100 samples per group and each group is subdivided into 5 sub-groups with 20 samples each [Table 1].
To assess the flexural strength, 60 specimens of 2 mm (width) × 2 mm (height) × 25 mm (length) were prepared according to ISO 4049.,,,, Specimens were made using stainless steel mould with restorative material after mixing, covered with polyester film and then pressed between glass plates on both sides to remove the excess material. Resin modified Glass Ionomers specimens were light cured through the glass plates for 20 seconds. The excess flash was removed using abrasive paper. Specimens were kept in deionised water at 37°C for 24 hrs. After 24 hrs, specimen dimensions were measured at the centre with micrometre to a precision of 0.001 mm. Universal testing machine was used for flexural strength testing at crosshead speed of 0.75 millimetres per minute until fracture.
Shear bond strength
Sixty maxillary third molars with similar mesiodistal dimensions were utilised for assessing the shear bond strength. The samples were cleared of calculus and debris by ultrasonic scaling, placed in deionised water for 24 h, and later embedded in chemical- polymerising acrylic resin., The occlusal surfaces of the teeth were wet ground with No, 320, 600, 800 silicon carbide sheets to expose dentin and to obtain a homogenous surface. The samples were split into three groups. Teflon moulds having a diameter of 3 mm and a height of 4 mm were made to form the glass ionomer cylinders. The dentin surfaces were conditioned using dentin conditioner for 30 seconds, rinsed with water, and dried using blotting paper for retaining the moisture. The cements were mixed according to manufacturer's instructions. Teflon moulds were placed over the tooth surfaces and the experimental cements were packed into the mould using a condenser and a polyethylene strip was placed over the packed cements and allowed to set. RMGIC specimens were light cured through polyethylene strip for 20 s. After the cement has set, the teflon moulds were removed and the samples were kept in deionised water at a temperature of 37°C at 100% humidity for 24 h. Samples were subjected to the steel wedge-shaped blade of the universal testing machine at crosshead speed 0.5 mm per minute.],,, Shear bond strength values were measured in units of MPa.
Twenty specimens, for each group, were prepared using teflon mould having a 10 mm diameter and 4 mm height. Specimens were kept in deionised water at a temperature of 37°C for a period of 24 h. The wear testing was done using Pin on disc tribometer., The specimens were mounted on fixture pin and tested according to ASTM G99 protocol using a 95% alumina disc as an antagonist with a normal load of 15N at 150 rpm at a sliding distance of 60 mm for 10000 cycles at a room temperature of 23°C.
To assess the fluoride release, twenty disc-shaped samples, for each group, with the dimension of 10 mm diameter and 2 mm height were fabricated using teflon mould. In sealed containers, samples were individually suspended in 10 ml deionised water by a nylon thread and kept at 37°C., The fluoride released into water was measured at 24 h and 7 days. At the end of 24 h, each disk was removed from water and fluoride concentration was measured. Then the discs were dried on filter paper, and immediately submerged in fresh deionised water for further calculation at the end of 7 days. UV Spectro photometer was used for the measurement of fluoride concentration in the water samples at room temperature and expressed in units of mg/l.
Statistical analyses were carried out in IBM SPSS 21 Software. The results were analysed using One-way ANOVA
| Results|| |
Results showed that RMGIC had higher flexural strength and shear bond strengths followed by HGIC and CGIC. HGIC had the least wear rate followed along by RMGIC and CGIC. HGIC had the highest fluoride release at 24 hours and 1 week, followed by CGIC and RMGIC. The results are presented in [Table 2] and [Table 3].
|Table 2: Means and Standard Deviations of Three groups for Flexural Strength, Shear Bond Strength, and Wear Resistance|
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|Table 3: Means and Standard Deviations of Three groups for Fluoride Release at 24 hrs and 1 week|
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| Discussion|| |
Glass ionomer cement possesses certain desirable properties as a restorative material which includes fluoride release, low coefficient of thermal expansion identical to tooth, chemical bonding to enamel and dentine. Glass ionomer cements exhibit long-term stable bond to dentin which does not diminish over time. However, they are brittle and show less wear resistance. These shortcomings have confined their use to areas of low masticatory stresses. Due to the brittleness, low tensile strength and low fracture toughness of glass ionomers, efforts are being made continuously to enhance its mechanical properties.
To increase strength and radiopacity in 1977 alloy powder of amalgam was added to CGIC powder to form metal-reinforced glass ionomer cement. A new material called Ketac Silver was made by sintering silver particles to the glass particles to form Cermet.
In 1991, RMGICs were introduced by addition of monomers, usually 2-hydroxyethyl methacrylate, to the aqueous solutions of polyacrylic acid and the powder is similar to CGIC. WHO in 1996 introduced highly viscous glass ionomer, with a higher powder/liquid ratio which is condensable and recommended for 'Atraumatic restorative treatment'. These are indicated for restoring small class I, class V cavities, core build-ups, deciduous teeth, in sandwich technique and as long-term temporaries.
In the present study, flexural strength, shear bond strength, wear resistance and fluoride release of CGIC, RMGIC and new HGIC were analysed. Flexure testing involves both tensile and compressive components and is considered a more clinically relevant property. The average flexural strength of CGIC was 24.5 MPa and RMGIC was 61.5 MPa, which is contiguous with previous in vitro studies. HGIC had a value of around 48.49 MPa.
RMGIC had higher shear bond strength values to dentin than CGIC and HGIC with a mean of 13.85 MPa. RMGIC bonds to the tooth structure through both micromechanical and chemical bonding. Although micromechanical bonding is achieved through the penetration of resin component of RMGIC, the main bond strength is achieved through chemical bonding. CGIC had a mean shear bond strength value of 4.5MPa, being self-adhesive restorative materials that bond chemically to the tooth structure. The shear bond strength values of CGIC and RMGIC are consistent with those of the previous studies. HGIC had a mean shear bond strength value of 6.5 MPa which was statistically better than the CGIC.
HGIC had the least wear rate compared to the other two glass ionomer cements. This may be due of the addition of two types of fluoroaluminosilicate glass and two different types of polyacrylic acid. CGIC had higher wear rate compared to RMGIC as expected.
HGIC had fluoride release of 10 mg/l at 24 hrs and the cumulative fluoride release at 1-week interval was 70 mg/l which was statistically higher than CGIC and RMGIC.
Moberg et al., compared the properties of four different CGICs with that of four different RMGICs and concluded that RMGICs had improved the physical properties like fracture toughness, flexural strength and Knoop hardness than CGIC.
Lohbauer et al., did a similar study comparing high viscous glass ionomer cement with CGIC, RMGIC and composite resin and concluded that highly viscous glass ionomers had comparatively higher mechanical and physical properties than CGIC and RMGIC but lower than that of composite resin.
HGIC does not require layering, its non-sticky, packable and adapts well to the cavity walls. It bonds well to young and sclerotic dentin and is moisture tolerant with good wettability. There is no shrinkage stress when used as a bulk fill material. It has more voluminous glass fillers that strengthen the restoration. According to the manufacturer, a multifunctional monomer is incorporated where it increases surface hardness by 35% and wear resistance by 40%. Higher amount of fluoride is present in the formulation and a unique water-gel matrix that allows ions to move freely through it. It has improved high viscosity owing to the addition of highly reactive fluoroaluminosilicate glass filler particles. The micron-sized fillers (4 μm) release more metal ions which improve the cross-linking of polyacrylic acid matrix. It has two types of polyacrylic acid with different molecular weights and the higher molecular weight polyacrylic acid combines with ions released from the highly reactive glass fillers to build a strong matrix and the lower molecular weight polyacrylic acid assists adhesion and helps ensure good cavity adaptation and a strong durable bond minimising the risk of hypersensitivity. The strong matrix further improves chemical stability, acid resistance and physical properties in the set cement. The finer particles are able to occupy areas in between the larger particles increasing matrix density thereby improving both strength and wear resistance. HGIC has a better consistency which in turn improves the manipulation and handling characteristics of the restorative material.
The limitations of this study include lack of in-vivo clinical trials, long-term fluoride release was not tested and the sample size was limited. The formulation of HGIC is unavailable.
Further studies need to be done by comparing HGIC with different types of resin composites with a comparison of physical and mechanical properties.
| Conclusion|| |
With the limitations of the current study, it can be concluded that HGICs exhibit higher wear resistance and fluoride release compared to CGIC and RMGIC. Flexural Strength and Shear bond strength values of HGIC was higher than that of CGIC. Therefore, this study supports the use of this novel material, HGIC, as better alternative to CGICs.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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Dr. T Hari Sainath Reddy
Department of Conservative Dentistry and Endodontics, SRM Kattankulathur Dental College and Hospital, Chennai - 603 203, Tamil Nadu
Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2], [Table 3]