Aim: The aim of this study was to compare Vickers Micro hardness of three conventional glass ionomer cement (Ketac Molar 3M, Photac Fil 3M and Equia System GC) before and after being submitted to an artificial aging and to evaluate the degree of marginal micro leakage.

Materials and Methods: There were made 45 samples, 15 of each material, from a standard matrix. Each sample was submitted to a first Vickers Micro hardness measurement, and then repeated after artificial aging. Using the same glass ionomer cements, 45 Class I restorations were realized in molars, then immersed in blue methylene 2%. They were then sectioned and the results were read with the use of a magnifying glass with 40 times magnification.

Results: The effect and magnitude of aging are dependent on the type of glass ionomer cement. The Micro hardness differs significantly between the Photac and the other two types of glass ionomer cement (p < 0,001). In Micro leakage, there were no relevant statistical differences between the three different materials (p = 0,053).

Conclusion: Equip System was the one with a smaller difference between the initial and final micro hardness values. All materials presented some degree of micro leakage and Photac Fil was the one with less degree.

In the last years there has been a great evolution in restorative materials. Glass ionomer cements have appeared due to the low physical and chemical properties of restorative materials and they have shown good chemical bond to enamel and dentin, fluoride releasing, good Biocompatibility and low toxicity. (Seemann, Flury, Pfefferkorn, Lussi, & Noack, 2014)

Wilson and Kent have introduced glass ionomer cements in the 70s, and since then there has been a great evolution of this material. These materials are considered types and subtypes of the original glass ionomer cement. They are divided as restorative materials in conventional glass ionomer cement, resin modified glass ionomer cement, metal modified glass ionomer cement and a subtype of conventional glass ionomer cement, the high viscosity glass ionomer cement. (Vieira, Louro, Atta, Navarro, & Francisconi, 2006)

The resin modified glass ionomer cement emerged around the 80s, to improve the physical and chemical proprieties of conventional glass ionomer cements. The low initial hardness and the water sensibility of glass ionomer cements were disadvantages, which decreased with the adding of resin to their constitution. This adding also gave glass ionomer cement the ability to have micromechanical adhesion to dentin, besides the chemical bond that was given by the acid base reaction of glass ionomer cement. (Wiegand, Buchalla, Attin, 2007).

On the other hand, a subtype of the original conventional glass ionomer emerged with characteristics that favour the mechanical properties of glass ionomer cements. The high viscosity glass ionomer cement has a higher powder liquid ration and smaller glass particles, which allow having a higher resistance to compression and higher hardness. Recently there has been an association of the high viscosity glass ionomer with a resin coating that promotes the sealing of restorations and maintains the integrity of the teeth-restoration interface. (Gurgan., et al. 2015)

ART (A traumatic Restorative Treatment) has been reported as having excellent outcomes. Specifically in terms of restoration retention, and ability to treat large numbers of children in otherwise inaccessible and isolated areas. The ART treatment has been introduced primarily using traditional glass ionomer materials and after specifically formulated glass ionomers have been developed for this ART technique. These are high powder-to-liquid ratio traditional glass ionomer materials, with enhanced physical properties (high viscosity glass ionomer cements). (Gurgan, Kutuk, Ergin, Oztas, Cakir, 2015)

Micro leakage and Micro hardness are ways to evaluate the clinical performance of the materials. In Micro leakage studies, colour dye penetration is the most commonly technique and the use of methylene blue 2% is the simplest and one of the fastest method. Due to the constant appearance of new restorative materials, it is important to have simple and fast in vitro tests to evaluate the performance of the new restorative materials. (Fabianelli., et al. 2007) In Micro hardness, one of the tests that can be used is the Vickers micro hardness test. It is very used once it allows using a small size of the samples in study, obtaining results in short time with a minimal cost. (Wang., et al. 2003)

The abrasion resistance of a material is a factor that must be taken into account when evaluating the performance of the restoration. One of the in vitro tests that can be used to evaluate abrasion resistance is the Chewing Simulator test. The mechanical and thermal cycles done by the Chewing Simulator can reproduce the physiological function and this allows it to be a useful test to study the behaviour of restorative materials in the oral cavity in an in vivo situation. (Guo., et al. 2014)

Vickers Micro hardness
Samples of the three different materials were made using a metallic mold of 10 mm diameter and 2 mm thickness (ISO 4049: 2009). To achieve a smooth surface, there were placed a glass plate underneath the metal matrix and between the matrix and the restorative materials an acetate sheet. All materials were prepared according to the manufacturer's instructions. They were made 15 samples of each material. It produced a total of 45 disks divided into 3 groups: 15 Ketac Molar disks, 15 Equia System disks and 15 Photac Fil disks. The disks were stored in distilled water at 37 degrees for 24 hours, in the dark and was subsequently initiated the readings of Vickers Micro hardness of all samples. The Vickers indentations were performed on the polished surface of the samples, each indentation for 5 seconds with 29.42N. 5 indentations were performed on each sample to obtain an average of each disk. There were made 225 measurements Vickers.

After the readings of the initial Vickers Micro hardness of each sample, they were submit to artificial aging, using the Chewing Simulator. In the chambers of Chewing Simulator the force applied to each sample was 50N , with a frequency of 1.5 Hz, lowering speed 40 mm/s and lateral movement defined 0.7 mm to 20 mm/s. 240000 cycles, corresponding to one year in vivo. During artificial aging, it was placed in the chambers distilled water at 37 degrees to simulate the temperature of the oral cavity and to remove particles resulting from the wear of the surface of the samples.

To avoid oscillation movements of the samples during the artificial aging, the discs were wrapped in acrylic resin (Vertex). After the complete cycles, all disks were clean and dry with paper towels. Distilled water was removed from the chambers Chewing Simulator.

After artificial aging, all the samples were again submited to a new Vickers Micro hardness reading. Five indentations were performed on each sample to obtain an average of each disk.

Marginal Micro leakage
Class I cavities were performed with cylindrical diamond drill bits in the 45 teeth with standardized dimensions: depth of 3 mm , mesiodistal width of 6mm and buccolingual width of 2mm . They were restored in accordance with the standards of the manufacturer: 15 teeth with Ketac Molar, 15 with Photac Fil and 15 with Equia System GC . The teeth were fully covered with a lacquer layer except the restoration and 1 mm around the interface restoration/tooth .

The teeth were placed in distilled water at room temperature and then immersed for twenty-four hours in a solution of 2% methylene blue. After that, they were removed and washed with running water for 15 minutes. All the teeth were sectioned longitudinally towards Mesio - Distal direction, using a cutting machine. The observation of micro leakage was held in magnifying glass with magnification of 40 times.

The quantification of micro leakage was determined using the following scale:
Grade 0 - No infiltration ;
Grade 1 - With infiltration that only reaches enamel;
Grade 2 - With infiltration reaching enamel and dentin;
Grade 3 - With infiltration reaching enamel, dentin and pulp.

Micro leakage
A descriptive analysis was performed between the three materials and it was carried out a statistical analysis taking into account only the material that had suffered micro leakage and without micro leakage (Table 1).

Equia Fil showed no micro leakage in 7 teeth (Figure 1), 6 teeth showed micro leakage in enamel, and 2 teeth dentin micro leakage

Photac Fil showed no micro leakage in 8 teeth, 5 teeth with micro leakage in enamel (Figure 2) and 2 teeth with dentin micro leakage

Depedent variable	Group (I)	Group (j)	Significance
Initial Microhardness	Ketac	Equia	0,985
		Photac	0,000
	Equia	Ketac	0,985
		Photac	0,000
	Photac	ketac	0,000
		Equia	0,000
Final Microhardness	Ketac	Equia	0,979
		Photac	0,000
	Equia	Ketac	0,979
		Photac	0,000
	Photac	Ketac	0,000
		Equia	0,000

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