Microenvironmental characterization and manipulation to prevent secondary caries

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A common reason cited for dental composite replacement is the recurrence of caries around existing restorations due to microbial activity. Treatment typically involves the removal of decayed tooth structure and placement of a new restoration. Since the microbial environment remains the same, the new tooth-restoration complex may also be susceptible to failure. Thus, the problem is not adequately addressed in current dental treatment approaches. More innovative materials are required that can purposefully bias the microbial environment toward improved health. Our preliminary data demonstrate that Mg2+ or Zn2+ released from bioactive glass (BAG)-containing resin composites can support a healthy microbial environment, thus directly addressing the root of the caries problem. Here we propose a new strategy involving Mg2+-and Zn2+-releasing dental composites that can favorably alter the microbiome on and around dental restorations such that the local pH >5.5. AIM 1: Optimize Mg2+- and Zn2+-releasing bioactive glass (BAG)-containing dental composites for long-term support of a healthy oral microbiome. Scanning electrochemical microscopy (SECM) will be used to optimize pH dependent Mg2+ and Zn2+ release kinetics from different Mg- and Zn-BAG formulations. Later, dental plaque derived multi species biofilm growth rate, volume, species composition and pH at the BAG surface will be quantified and optimized such that local pH > 5.5. AIM 2: Test the effectiveness of new Mg-BAG and Zn-BAG composites in an in vitro secondary caries model. Placement of a restoration has the inherent challenge of gap formation between the dental material and the tooth structure. Currently, little information is available on how bacteria behave in microgaps. For example, microbial colonization, diffusion rates, and organic acid metabolites may be very different within gaps as compared to exposed surfaces in the oral cavity, potentially leading to enhanced tooth decay at the interface. Here we will develop an in vitro microgap model using the electrochemical sensors techniques to measure the biological activity and the effect on the microbial population in these microenvironments such that local pH > 5.5. AIM 3: In vivo evaluation of Mg-BAG and Zn-BAG composites with intraoral appliances. The cytotoxicity of Mg-BAG and Zn-BAG will be tested using undifferentiated dental pulp cells compared to standard dental composites. The in vitro optimized Mg-BAG and Zn-BAG composites that are shown to have equal or lower cytotoxicity than typical composite will be placed in intraoral appliances to be tested in volunteers. This real-life scenario will evaluate the effectiveness of the composites when all biologically relevant parameters are present that potentially interfere with the performance of Mg-BAG and Zn-BAG composites. This will also provide a direct comparison between the in vitro model and the clinical situation. Our proposal will lay the foundation for further metal ions driven research on biofilm growth and behavior, as well as for the development of a more realistic in vitro secondary caries model that includes chemical microenvironments created by differential biofilm metabolic activities within microscopic gaps.