Graduate Thesis Or Dissertation
 

Bioactive glass filled resin composites : mechanical properties and resistance to secondary tooth decay

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/dv13zw59j

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  • Dental resin composites are widely used in modern dentistry due to their aesthetic appearance. However, resin based restorations have inferior mechanical properties (fracture is the second reason for restorations replacement) in comparison to alloy based composites and their antimicrobial properties still remain poor, leading to secondary tooth decay development on tooth-filling interface (which is the primary reason for restorations failure). In this work the Bioactive glass (BAG) was used as an antimicrobial filler. Experimental composites were prepared with 0-15 wt% BAG filler and 72-57 wt% silane treated silica glass, keeping a total filler content constant at 72 wt%. BAG composite's mechanical properties were examined, using 3-point bending beams for flexural strength measurement, pre-cracked compact-tension samples, C(T), for fracture toughness and fatigue crack growth evaluation. All mechanical properties were tested for different soaking treatments of the samples: 24 hours in DI water (all experiments) 2 months in sterile media (flexural test only) and 2 months in media with Streptococcus mutans bacteria (all experiemtns). All mechanical properties findings were compared to those ones of commercial Heliomolar composite. Main toughening mechanisms for BAG composites were evaluated post-test by SEM. The results showed that all mechanical properties for BAG composites were unaffected by increasing the filler content from 0 to 15 wt%. Moreover, all mechanical properties of BAG composites were significantly superior over Heliomolar composites. BAG composite's flexural strength properties were not affected by any of aging treatments and a slight decrease in fracture toughness and fatigue crack growth resistance was observed after 2 months soaking in media with bacteria. Main toughening mechanisms were related to BAG composite's increased filler, which resulted in more frequent crack deflection, and crack bridging at the crack tip and far away from it. In next phase of the research, a novel bioreactor and new test specimen type were developed, which allowed investigating the synergistic effect of cyclic loading and bacterial exposure on secondary tooth decay. The bioreactor was able to provide environment suitable for bacteria, similar to lab incubators. Teeth samples were machined into the disk shape (3 mm tall, 9 mm diameter), mainly consisting of dentin and the middle of sample was drilled and restored with 0 wt% BAG (0BAG) composite (2 mm deep, 5 mm diameter), introducing semi-circumferential gap between dentin and restoration of 10-30 microns. All samples were initially disinfected with 1% chloramine solution. Streptococcus mutans biofilm was grown over the samples and then they were placed in bioreactors and subjected to 1.5 Hz loading cycling at maximum load of 25% from breaking load and R=0.1 for 2 hours, followed by 4 hours resting at minimal load. The procedure was repeated for total of 2 weeks of an experiment, during which bacteria biofilm was constantly supplied with BHI media, carbon dioxide and 37oC temperature. After 2 weeks test, samples' biofilm viability was evaluated with live/dead staining kit and then, after fixing the biofilm on the samples in 4% gluteraldehyde, all samples were sectioned across the gap and stained with Gram Crysrtal Violet CAT+ dye , followed by fluorescence microscopy to reveal the depth of bacterial penetration down the gap. The depth of bacterial penetration of loaded samples was compared to one of non-loaded samples and results revealed a significantly deeper bacterial penetration for cyclically loaded samples versus non-loaded, thus, it was concluded that cyclic loading and bacterial exposure together aid secondary tooth decay propagation. In the last phase of this project the anti-microbial properties of BAG composites were evaluated. Using the same sample preparation technique and methods from the previous phase (except that now the composite was 15 wt% BAG, a.k.a 15BAG), we found out that bacterial penetration down the gap for 15BAG composite was significantly lower (almost 50% difference) in comparison to 0BAG composite, which made us confident to draw a conclusion that 15BAG composite possesses good antimicrobial properties and can be used for secondary tooth decay prevention.
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