• Comparative Microbial Adherence to Various Implant Dental Restorative Materials

      Alshehri, Malek Rofidi A; Masri, Radi, 1975- (2018)
      The oral cavity contains the most complex microbial community of the body, which has more than 700 bacterial species. These microbial species colonize different habitats in the oral cavity. The biological interaction between dental restorative materials and the encompassing oral microbes is one of the most important factors for their clinical prognosis. Many studies have shown that there are distinctive interactions between the rate of microbial formation and the restoration material itself. Currently, there are several Implant Dental Restorative Materials on the market like poly-methyl methacrylate, feldspathic porcelain, dental zirconia, and dental composite resin. The purpose of this study was to comparatively evaluate initial adherence for C. albicans and S. aureus on five different implant dental restorative materials. Ten samples/group were constructed as 5mm x 5mm x 2.5 mm rectangles and were fabricated as per the manufacturer's instructions for each groups. Five groups were made from different types of materials: Polymethyl methacrylate denture material processed with the compression molding technique (PMMA), computer-aided design and computer-aided manufactured dental acrylic (CAD/CAM PMMA), feldspathic porcelain, dental zirconia, and pink dental composite resin. There was a significant difference between the five groups for C. Albicans (F=891.16, p=.0005). CFUs/ml for the pink dental composite resin were significantly higher than the other four groups. However, The dental zirconia group showed the lowest CFUs/ml for initial adherence between all the groups. For S. aureus, CFUs/ml for the pink dental composite resin was significantly higher than the other four groups. Heat polymerized PMMA and the CAD/CAM PMMA group showed significantly higher CFUs/ml than Feldspathic porcelain and dental zirconia groups. In conclusion, there was a significant difference between the five groups for initial adherence of C. albicans and S. aureus. The dental zirconia group showed the lowest initial adherence and the pink dental composite resin group showed the highest initial adherence for both microbes. Within limitation for this study, understanding what is the best for final dental restorative material from aspect of how much it could harbor microbes is an important factor in the final success of treatment and this study investigated this aspect under control conditions.
    • In Vitro and in Vivo Characterization of Candida albicans and Streptococcus mutans Interactions

      Khoury, Zaid; Jabra-Rizk, Mary Ann; 0000-0001-9596-3560 (2019)
      The oral cavity is a complex environment harboring diverse microbial species that often co-exist within biofilms formed on oral surfaces. Within a biofilm, inter species interactions can be synergistic in that the presence of one organism generates a niche for another enhancing colonization. Among these species are the opportunistic fungal pathogen Candida albicans and the bacterial species Streptococcus mutans, the causative microorganisms strongly linked to the development of oral candidiasis and dental caries, respectively. Recent studies have reported the enhanced prevalence of C. albicans in children with early childhood caries indicating that this fungal-bacterial interaction may have clinical implications. In this study, we aimed to elucidate and characterize this interaction between these diverse species. Specifically, we designed in vitro and in vivo studies to validate the hypothesis that the presence of C. albicans in the oral cavity augments S. mutans colonization, potentially mediating dental caries development. Using various C. albicans mutant strains and a GFP-tagged S. mutans, metabolic viability and fluorescent biofilm assays were performed to assess S. mutans recovery from mixed biofilms and to elucidate the mechanisms of interactions. Additionally, to visualize the architecture of formed biofilms, confocal scanning laser fluorescent and electron scanning microscopy were used. Importantly, a clinically relevant mouse model of oral co-infection was developed to demonstrate C. albicans mediated enhanced S. mutans colonization in a host. The findings demonstrated significantly higher recovery of S. mutans from biofilms with C. albicans in vitro. Images revealed a high bacterial affinity to C. albicans, and secreted fungal cell wall polysaccharides were identified as the key factor mediating biofilm formation, particularly mannans. Importantly, analyses of harvested tissue demonstrated significantly higher S. mutans recovery from teeth of co-infected mice compared to mice infected only with S. mutans. Collectively, the findings strongly indicate that the presence of C. albicans in the oral environment may impact the development of dental caries and should be considered as a factor in evaluating the risk of caries. Results obtained in this thesis will support future studies using animal models of dental caries to further characterize this relationship in a closely related model in our laboratory.