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Browsing by Subject "A. actinomycetemcomitans"

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  • Hiltunen, Anna (2015)
    Periodontitis is a globally significant disease which destroys the attachment tissues and alveolar bone of teeth, eventually leading to tooth loss. Biofilms, the most intrinsic lifestyle of bacteria, play a pivotal role in the occurrence of this disease. Periodontal biofilms can be treated with topically administered chlorhexidine and strain-specific antibiotics. However, these antimicrobials do not offer solutions for periodontal attachment tissue and alveolar bone loss. Some therapeutical alternatives for these conventional treatments have been investigated. In numerous studies, periodontitis is treated successfully (increased attachment and/or alveolar bone levels) with topically and systemically administered bisphosphonates. Furthermore, a topically administered bone graft substitute (bioactive glass) has shown to improve periodontal parameters. In addition, bioactive glass has known antimicrobial and anti-biofilm effects. Moreover, a few bisphosphonates have shown antimicrobial activity against some bacterial strains. Hence, both bisphosphonates and bioactive glass are promising materials for dental applications, also raising interest in their combination. Indeed, it could be hypothesized that this combination product could simultaneously treat both the underlying cause (biofilms) and consequences (alveolar bone and attachment tissue loss) of periodontitis. Open research questions remain for the combination product. Is the anti-biofilm effect enhanced when bioactive glass is combined with bisphosphonates? Moreover, do bisphosphonates have intrinsic anti-biofilm properties? These questions are investigated in this thesis, which is a continuation of a recent doctoral dissertation. In this dissertation, a clodronate-bioactive glass combination product was studied by applying it into periodontal pockets. However, anti-biofilm effects were not assessed. In this thesis, a close examination is carried out on these effects, utilizing relevant biofilm models. The aims of this work were to investigate anti-biofilm effects of bisphosphonates (alendronate, clodronate, etidronate, risedronate and zoledronate) (i) alone, administered as solutions and (ii) combined with bioactive glass S53P4. Optimization of the used assay methods (96-well plate assay, Static Biofilm method) was performed. The anti-biofilm effects of bisphosphonate solutions were screened in the 96-well plate assay using a model organism Staphylococcus aureus Newman and a periodontopathogen Aggregatibacter actinomycetemcomitans ATCC 33384. After this, experiments were conducted with bisphosphonate-bioactive glass combinations. The experiments were performed with a single-specie (A. actinomycetemcomitans ATCC 33384) dental biofilm model based on the Static Biofilm method. The model mimics conditions encountered by periodontal bacteria in the oral cavity. In this part, bisphosphonate particle sizes were measured to determine a suitable control material. In addition to bacterial experiments, pH measurements were carried out to gain an insight to a possible anti-biofilm mechanism. Bisphosphonates administered as stand-alone compounds did not have an effect on either the Gram-positive model organism (S. aureus Newman) or the Gram-negative periodontopathogen (A. actinomycetemcomitans ATCC 33384). In contrast, most combinations of bisphosphonate-bioactive glass revealed a statistically significant increase in anti-biofilm effect on A. actinomycetemcomitans ATCC 33384. The combinations were compared to a control composed of inert glass and bioactive glass. In these assay conditions, the risedronate-bioactive glass-combination was the most effective (significant statistical difference, p < 0.05). Other combinations also reduced biofilms (significant statistical differences, p < 0.05), with the exception of clodronate-bioactive glass, where the change was not statistically significant. The most effective combinations (containing risedronate and etidronate) subjected the biofilms to a period of low pH. Conversely, the least effective combination (clodronate-bioactive glass) rapidly became alkaline, similarly to the control compounds (inert glass and bioactive glass). Thus, anti-biofilm efficacy could be connected to lowered pH. This observation is supported by recent literature where A. actinomycetemcomitans has been deemed highly sensitive to acidity. However, establishing the anti-biofilm rank order of bisphosphonate-bioactive glass combinations would benefit from experiments with equal bisphosphonate particle sizes.