الفهرس 
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Abstract
This research aimed at investigating mesoporous fillers as dental composite resin fillers in an attempt to obtain mechanical interlocking between the fillers and the resin matrix. Various approaches were also tried to increase the fillers loading thus improving the composite resin properties. Such approaches included combining nonporous spherical fillers with mesoporous fillers. Another attempt was using methacrylate modified mesoporous silica fillers. Silanation of mesoporous fillers was another trial used in this research.
Composites were made using five different types of fillers (and combinations of them) at various filler loadings. The five fillers used were irregular mesoporous silica fillers, silane treated irregular mesoporous silica fillers ,hybrid(organic modified mesoporous fillers),commercially available nonporous 500 nm silica spheres and silane treated commercially available nonporous 500 nm silica spheres. Such combinations gave rise to nine experimental composite resins, which were compared to a commercial packable composite (solitaire2)
The following properties were tested: compressive strength, flexural strength, flexural modulus, fracture toughness and post gel shrinkage strain (PGSS).Similar specimens were made for each group , water stored for 3 months and tested for all the previous mechanical properties.
Compressive strength was tested by subjecting cylindrical specimens to compressive loading using the universal testing machine till fracture. As for the flexural strength, flexural modulus and fracture toughness they were obtained by subjecting barshaped specimens to a 3-point loading .The PGSS was measured via using strain gages whose leads are connected to the strain monitoring device.
On investigating the compressive and flexural strength results , group 8 (sil. mesoporous+sil.nonporous) showed compressive strength mean value most similar to group 1(solitaire 2). Silanation of both mesoporous fillers and nonporous fillers didn’t significantly affect the compressive strength values of the experimental composite groups. However silanation of nonporous fillers significantly increased the flexural strength. Using hybrid mesoporous fillers also showed no effect on both strength properties.
Regarding the flexural modulus values, groups 8 and 7(non sil. mesoporous+sil.nonporous) showed the highest flexural modulus values exceeding that of group1. Groups 3(non sil. mesoporous) , 4(hybrid mesoporous) and 9 (hybrid mesoporous +non sil. nonporous) on the other hand showed the lowest flexural modulus values. Silanation of mesoporous fillers and nonporous fillers significantly improved the flexural modulus of the composite resin groups. However using hybrid mesoporous fillers significantly reduced the flexural modulus.
Fracture toughness results showed that groups 1, 2(sil. nonporous) and 3 showed the highest values, while groups 6 (non sil. mesoporous+non sil. nonporous), 9 and 4 showed the lowest fracture toughness values. Silanation of nonporous fillers was found mandatory to improve fracture toughness. However silanation of mesoporous fillers decreased the fracture toughness when used alone (group5) and had no effect on it when used in combination with nonporous fillers. Hybrid mesoporous fillers also decreased the fracture toughness when used alone (group 4), however it had no effect when used with the nonporous silica fillers.
Groups 4 and 5 showed the highest PGSS values. Silanation of mesoporous fillers increased the PGSS when used alone, however it had no effect when used in combination with nonporous fillers. As for the hybrid mesoporous fillers when used alone or in combination with nonporous fillers, they reduced the PGSS.
On investigating the water storage results, it was found that 3 months water storage caused a reduction in all the previously measured mechanical properties. It was also noted that the percentages DROP in the properties of all groups were very near to each other. Only few groups (groups 1,3 and 5) showed significant differences than the rest. Water induced degradation of the composite resin groups was well detected via SEM. The surfaces of the water stored specimens appeared rougher when compared to those of specimens without water storage due to the degradation of the resin matrix and the plucking out of the fillers .Groups 1, 3 and 5 showed the least percentage change (drop) in compressive strength, flexural strength, flexural modulus and fracture toughness.
CONCLUSIONS
Within the limitations of this study the following could be concluded:
1-Using silanated or hybrid mesoporous fillers instead of untreated mesoporous silica isn’t an effective procedure in improving the compressive and flexural strength of a dental composite resin, whether these fillers are used alone or in combination with nonporous fillers.
2-Whether used alone or in combination with nonporous fillers, silanation of mesoporous fillers is mandatory to enhance the flexural modulus of the composite resin, however using hybrid mesoporous fillers should be avoided if an increase in the flexural modulus is indicated.
3-When mesoporous fillers are used alone in a composite resin, silane treatment of such fillers or using hybrid mesoporous fillers isn’t recommended to formulate a high fracture toughness composite resin.
4-Post gel shrinkage strain (PGSS) can be reduced by avoiding silanation of mesoporous fillers when used alone or by using hybrid mesoporous fillers instead of inorganic mesoporous fillers, when used alone or in combination with nonporous fillers.
5-An experimental composite resin formulated with a combination of silanated mesoporous and nonporous silica fillers had mechanical properties somehow comparable to a commercial packable composite, with higher flexural modulus and lower fracture toughness values.
6- Using mesoporous silica fillers whether silanated or not might be a successful method in reducing the hydrolytic degradation of the dental composite resins.