الفهرس 
Glass ionomer cementsOnly 14 pages are availabe for public view
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Abstract
In this study the effect of incorporation of zirconia nanoparticles on properties of conventional glass ionomer restorative material was studied.
The study aimed to assess the mini flexural strength, compressive strength, micro hardness, as well as water sorption and solubility of conventional glass ionomer with and without addition of zirconium dioxide nanoparticles.
Zirconia nanoparticles were added to the powder of conventional glass ionomer cements with three different concentrations 3, 5 and 7 wt%.
This resulted in creation of three groups from the modified materials, in addition to the unmodified conventional glass ionomer to be considered as a control group.
Specimens were prepared in Teflon molds constructed for each test.
The universal testing machine was used for measuring both the mini-flexural strength and compressive strength.
Vickers microhardness tester was used to measure the surface microhardness.
Electronic balance was used to measure the water sorption and solubility.
Mini-flexural strength:
Ten specimens of each group (12mm length, 2mm width, 2mm thickness) were used for evaluating the mini-flexural strength.
Mini-flexural strength was quantified by a three-point loading test using the Lloyd universal testing machine. The mini-flexural strength was obtained by measuring the load fracture and calculated in Mpa with following equation:
MFS = 3 F X L / 2 W X Th2
Compressive strength:
Ten specimens of each group (4 mm in diameter and 6 mm in height) were used to evaluating the compressive strength. Each specimen was compressed in the Lloyd universal testing machine until fracture occurs.
The compressive strength was calculated from the equation:
CS = 4Pf / πD2
Surface microhardness:
Ten specimens for each group (5 mm in diameter and 2.5 in thickness) were used to determine surface microhardness. Vickers microhardness tester was used. A load of 100 g was applied to the surface of the specimens for 15s to create three indentations on the surface of specimens which were equally placed over a circle and not closer than 0.5mm to the adjacent indentations. The diagonal length of the indentation was measured by built in scaled microscope and Vickers microhardness values were obtained by the machine.
Water sorption:
Ten specimens for each group (20mm diameter and 1.5mm height) were used to determine water sorption. The specimens were stored in desiccator at 37±1 °C being weighted dialy in electronic balance until a constant weight (M1) was obtained. After this the specimens were stored in distilled water for 3 at 37 °C for 3 months . After this period, specimens were removed, washed with water, dried withabsorbent paper, waved in air for 15 s and weighed 1minute after removal from water, this weight was considered (M2).
The water sorption (ws) was calculated using the following equation:
WS= (M2-M1)/ V.
Solubility:
Specimens preparation was done as previously mentioned for water sorption testing. After taking the M2 measure, the specimens were subjected to the conditioning cycle for drying until the weight loss was less than 0.001g. The specimens were then weighed for a final time (M3).
In μg/mm³, solubility value of each specimen will be calculated using the following equation:
Solubility = (m1 – m3)/V
The results of this study showed that:
Adding ZrO2 nanoparticles to glass ionomer restorative material in the percentage of 3%wt or 5%wt enhanced of its mini-flexural strength, compressive strength and microhardness.
Adding ZrO2 nanoparticles to glass ionomer restorative material in the percentage of 3%wt or 5%wt decreased its water sorption and solubility.
Glass ionomer modified with 7%wt ZrO2 nanoparticles to 7%wt showed non significant difference in mini-flexural strength, compressive strength as well as microhardness compared to unmodified conventional glass ionomer.
Glass ionomer modified with 7%wt ZrO2 nanoparticles to 7%wt showed non significant difference in both water sorption and solubility compared to the unmodified conventional glass ionomer.
Conclusions:
Adding ZrO2 nanoparticles to glass ionomer restorative material in the percentage of 3%wt or 5%wt can enhance several mechanical and physical properties including mini-flexural strength, compressive strength, microhardness, water sorption and solubility.
Increasing the concentration of ZrO2 nanoparticles to 7%wt did not offer any improvement compared to the conventional glass ionomer, concerning the tested properties.
Recommendations:
1.GI-containing either 3%wt ZrO2 nanoparticles or 5%wt ZrO2NP are promising restorative dental materials with improved mechanical and physical properties. It is clear that this novel experimental GI may be potentially used for higher stress-bearing site restorations such as Class I and II. Further researches on these materials are recommended.
2. Further investigation could be done concerning the following parameters:
A- Influence of incorporation of zirconia nanoparticles on other properties of glass ionomer, such as fracture toughness, porosity, radiopacity and color change.
B- Increasing the bond between glass ionomer particles and those of zirconia nanparticles and its influence on the properties of this composite material.
C- Trying other concentrations of ZrO2 and assessement of the obtained material.