الفهرس 
Glass ionomer cementsOnly 14 pages are availabe for public view
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Abstract
Two different RMGICS that are frequently used in proximal posterior cavities were used. Inability to place light curing tip in direct contact with the restoration and the need to place the materiel in more than 2mm thickness was expected. This investigation was done to study the effect of increment thickness and light curing distance on the material mechanical as well as biological properties. The materials were mechanically tested using miniflexure and microhardness tests while the cytotoxicity test was used to study biological behavior. Three increment thicknesses were used to pack the materials (b1:2mm, b2:4mm, and b3:2mm x2mm). The materials were polymerized using a LED curing device at two different curing distances (c1:0mm & c3:10mm from specimens top).
A total of two hundred and forty specimens were prepared for miniflexure testing. The specimens were divided into 2 main groups according to the type of RMGI used; the main groups were divided into three groups according to increment thickness. The groups were divided into subgroups according to light curing distance (n=20). Specimen dimensions were 12mm length x 2mm width. The thickness of the specimens differed according to different incremental thicknesses. Specimens were tested using Universal testing machine. Data was collected and statistically analyzed.
For the microhardness test, sixty cylindrical samples of 4mm diameter were done. The specimen were divided into 2 main
Summary and Conclusions
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groups according to type of RMGI used, the main groups were divided into three groups according to increment thickness. The groups were divided into subgroups according to light curing distance (n=5). Five readings were taken for the top surface and another 5 for the bottom surface. Group relative microhardness was calculated by dividing the mean of bottom reading by the mean of top readings. Importance of microhardness was to determine the depth of cure and compare it with the cytotoxicity test findings.
Cell cultivation was done using Chines Hamster Ovary (CHO) cell line. For the Cytotoxicity test, thirty six specimens were prepared under aseptic conditions with 6 mm diameter and different thicknesses and curing distances. Specimens were placed in the culture medium for 24 hours to leach components. The cells were cultured with the prepared culture medium. Percent of cell death was calculated after 24 hours using Sulpho-rhodamine B (SRB) colorimetric assay.
Data was collected and correlated together using Three Way ANOVA followed by One Way Analysis of Variance (ANOVA) followed by Turkey Post-Hoc test were used to determine the effect of increment thickness on each of performed tests. Independent t-test was used to determine the effect of material and light curing distance on the tests performed.
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The Three-Way ANOVA results for increment thickness and material type had a statistically significant effect on miniflexure, contrary to the light curing distance which had no effect. The interaction between all tested variables had significant effect on miniflexure test results.
Relative microhardness results showed that, material and increment thickness had a significant effect contrary to the light curing distance that had no effect on relative microhardness. The interaction between material and thickness was the only variable that showed statistical significant effect on relative microhardness.
The cytotoxicity behavior showed that; the type of material, increment thickness and light curing distance had significant effect on cell cytotoxicity. All the interactions between the tested variables showed a significant effect on cell cytotoxicity except for the interaction between material and light curing distance.
Conclusions:
Under the limitations of this study, the following conclusions can be drawn:
1. Light curing distance should not be considered as an effective factor on flexure strength and microhardness.
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2. Light curing distance affects the cytotoxicity of both RMGICs.
3. Both tested materials should be placed in increments not exceeding 2mm thickness when flexure strength and microhardness are considered.
4. Incremental packing 2mm x 2mm has a detrimental effect on Fuji II LC flexure strength and Photac Fil Quick Aplicap microhardness.
5. Incremental packing 2mm x 2mm increases the cytotoxicy especially with Photac Fil Quick Aplicap.
Recommendation:
More research work is needed to further identify elutes produced from the tested materials and qualify their cytotoxic behavior.