Glass ionomer cements (GICs) were first introduced in 1970 by Kent and Wilson, and are used as restorative material, base and liner, and luting cements.

Restorative GIC can be used in the restoration of small defects of permanent teeth that are not under occlusal forces, as well as temporary restorations in permanent teeth and atraumatic restorative treatment. Besides, due to having a low elastic modulus these materials are used in numerous cases including (i) restoration of class V cavities and abfraction lesions that exist on the root and are under tensile stresses, and (ii) cervical restorations in which esthetic is not a critical issue. These materials are advised specifically for tooth decay in high-risk patients. ¹

Owing to numerous well-known advantages of glass ionomers, they are being used under different commercial names in all dentistry branches. These advantages include fluoride release, ² chemical adhesion to enamel and dentin, biocompatibility, ³ similar thermal expansion to teeth, ⁴ and an acceptable esthetic than to metal restorations. ⁵

For an acceptable clinical application, GIC should have certain properties such as a strong bond in the mouth, high tensile strength, high compressive strength, proper setting time, and adequate, radiopacity. ⁶

The radiopacity of dental materials used in restorations is highly important. A material with adequate radiopacity provides secondary caries detection and distinction of that from restorative material and dental tissue; moreover, distance to pulp tissue, margin, and overhang defects will be well detected. ⁷ It is required that the radiopacity amount of GIC be always higher than the radiopacity of dentin and enamel, otherwise their distinction would not be possible in radiologic images. ⁸ To measure radiopacity by digital radiography, aluminum step wedge and specimen are placed on a film and exposed with digital or conventional apparatus. After scanning images, the radiopacity of the samples is calculated by Adobe Photoshop.

The time required for reaction fulfillment is named setting time. In case the reaction speed is high or the material has a short setting time, the setting might occur before the formation of the mixed materials is done by the operator. On the other hand, in case the reaction speed is too low or better to say setting takes long, much time is required for the reaction fulfillment; therefore, proper setting time is one of the most important properties for restoration materials. ⁹ As the Glass ionomer produced in Iran has significantly lower price, the present article aimed to compare the net setting time and radiopacity of Fuji II glass ionomer (GC, Japan) with the Iranian restorative GIC produced by Ava Tajhiz Dandan.

In this experimental/in vitro study, we studied two types of glass ionomer: One, Fuji II (self-cure restorative glass ionomer, powder batch number: 1608061, liquid batch number: 1608031, GC Corporation, Tokyo, Japan), and two, an Iranian Glass Ionomer produced by Ava Tajhiz Dandan of Qazvin were studied. Both are restorative and self-cure.

To investigate the net setting time in accordance with ISO 9917-1:2007 standard, we used an Aluminum mold with length of 10 mm, width of 8 mm, and height of 5 mm. Using a digital scale (AandD, Japan), we prepared samples of both cement types, each with the powder to liquid ratio of 2.7:1 (according to their manufacturer's instructions) and with accuracy of 0.0001 g. We used a plastic spatula to divide the powder into two equal parts. The first part was completely mixed with liquid in 10 s, and then the second part was added to the mixture; a smooth mixture was produced in 30 s. The mixture was poured into the molds, and 60 s after mixing, the samples were placed into an incubator (Peco, Iran) with a temperature of 37 ± 1°C, and a moisture of minimum 90%. After 90 s from the mixing, an indenter (Gilmore needle) with a weight of 400 ± 5 g and a diameter of 1 ± 0.1 mm was placed vertically on the cement samples and was remained in this condition for 5 s. It was repeated every 30 s, insofar as the circular-shaped effect of the needle end was not observable on the glass ionomer surface.

Eventually, we recorded the setting time as the time lapsed from the end of cement mixing to the time the needle stopped making a circular-shaped effect. This test was done with a chronometer having an accuracy of 0.01 s.

In the test for measuring radiopacity, we prepared samples of both cement types, each with the powder to liquid ratio of 2.7:1 (according to their manufacturer's instructions) and with accuracy of 0.0001 g. We used a plastic spatula to divide the powder into two equal parts. The first part was completely mixed with liquid in 10 s, and then the second part was added to the mixture; a smooth mixture was produced in 30 s. The mixture was poured into the molds with diameters of 15 ± 0.01 mm and thickness of 1 ± 0.1 mm. The molds were compressed between two stainless steel plates to make sure no air is remained. Then, the mixture was placed into water (based on ISO 9917-1:2007 standard) and in incubator (Peco, Iran) with a temperature of 37 ± 1°C for 30 min. The samples then were removed from the mold and their thickness in the central part was measured by digital micrometer and with an accuracy of 0.1 mm. Merely the samples with a thickness of 1 ± 0.1 mm were accepted, then the samples were placed into water in an incubator with a temperature of 37 ± 1°C for 23 ± 1 h.

To measure radiopacity by digital radiography, the samples along with an aluminum step wedge were placed onto the sensor of radiography film of PSP type (step wedge is a device used for densitometry studies and has several aluminum steps with certain and specific thicknesses, each step has a difference of 0.5–1 mm in terms of thickness with the next step. The wedge exposing to X-ray wave, the resulting image includes strips that gradually become more radiopaque). X-ray tube was placed at a distance of 400 mm from the sample and step wedge, and exposure was done with 60 kV, 10 mA; and time duration of 0.32 s by Minary device (Soredex-Finland). Then, using a phosphate plate scanner (Durrdent-Germany) the images were scanned and entered into Scanora software. Eventually, by Adobe Photoshop CS3, the radiopacity of images was calculated from five different areas of each sample. The mean of which was determined as the sample radiopacity. The scanning electron microscope (SEM; VEGA//TESCAN-XMU; Cezch Republic) equipped with EDS SAMX, France device was used for evaluating the mixture and the morphology of powder samples with an accelerating voltage of 15 kV. To increase electrical conductivity and to stop charging, the samples were coated with gold and were prepared for analyzing. Particle size analysis (PSA) was done by Coulter Ls 100 Fluid module particle size analyzer to determine the mean particle size. For preparing this analysis, powder samples were dispersed in alcohol at the temperature of 37°C. Energy Dispersive X-ray spectroscopy (EDS) analysis was done to discover the elemental composition and give an overall mapping of the sample.

After collecting data and inputting it into the SPSS software (version 21, IBM Corp., Armonk, NY, USA), we calculated the descriptive results using mean and standard deviation. We employed an Independent t-test to investigate the relationship between quantitative variables (such as net setting time and radiopacity), and qualitative variables of both glass ionomers. We set the P ≤ 0.05.

The test results for net setting time for 10 samples of both cement types are shown in Table 1and Table 2.{Table 1}{Table 2}

According to Table 1, the mean of setting time in Fuji II glass ionomer was obtained as 4.83 min, and in Iranian glass ionomer, it was obtained as 3.83 min. In Fuji II cement, the minimum setting time was 4.67 min and the maximum of that was 4.98 min. Also in the Iranian cement, the minimum setting time was 3.67 min and the maximum of that was 3.95 min.

Using Kolmogorov–Smirnov test, the normality of data related to net setting time was approved (P > 0.05), then using an independent t-test and P value which was obtained to be ≤0.05, we conclude that between the net setting time of these 2 glass ionomers, there is a significant difference. Considering the mean values are shown in Table 2, the net setting time in Fuji II glass ionomer is higher than the Iranian glass ionomer, as shown in Figure 1. Figure 1

Distribution of the mean of setting time in two groups of Fuji II and Iranian glass ionomer.

According to ISO 9917-1:2007 standard, the minimum net setting time for restorative glass ionomers is considered to be about 1.5 min, and the maximum time is about 6 min. ¹⁰ Our study results indicated that the mean of net setting time of both cements was in the standard range.

Particle size of glass powder is one of the impacting factors on net setting time; smaller particles causes the setting time to be shorter. ¹¹ , ¹² Considering the PSA in Fuji II glass ionomer powder Figure 3, the size of 10% of particles was <1.32 μ, 50% were <4.73 micron, and 90% were <19.51 micron. In the Iranian glass ionomer powder Figure 4, the size of 10% of particles was <1.56 micron, 50% were <7.80 μ and 90% were <26.84 μ Table 5. According to these results, the particle size difference of the two glass ionomers was so slight. In scanning electron microscope (SEM) images which were taken with a magnification of 5.00 kx, the mean of particle size of Iranian glass ionomer powder was a little bigger than Fuji II Figure 5and Figure 6. This slight difference in particle size seems not to have any effect on the faster setting of the Iranian glass ionomer. Figure 5

Electron microscope image of Fuji II Glass inomer.

The results of testing net setting time and radiopacity for Iranian glass ionomer were in the acceptable limit of ISO 9917-1:2007. In cases where all other properties of this glass ionomer are set appropriately in future investigations, this material can be introduced as an alternative for Fuji II glass ionomer.

Financial support and sponsorship

Nil.

Conflicts of interest

The authors of this manuscript declare that they have no conflicts of interest, real or perceived, financial or nonfinancial in this article.