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.