The Chairside Delivery of Focused Microwave Energy for Caries Therapy

Dental caries remains one of the most widespread oral diseases disproportionately affecting low income children, the working poor and elderly. Despite advances in non-invasive management, traditional surgical approaches by dentists continue to be practiced as the predominant method of treatment at great economic and biological cost. Objective: To develop a non-invasive method of caries management using the chairside delivery of highly-focused microwave energy, the goal being to rapidly and non-invasively kill microflora inherent to caries. Methods: For development of a self-contained compact microwave unit, theoretical simulations and practical measurements were performed at various frequencies to determine optimal microwave absorption and thermal conduction characteristics of teeth and bacteria. These simulations further provided guidance for the computerized design and construction of a compact unit and antenna for dental application. To assess efficacy, S. mutans in media was both directly and indirectly (via embedment in an extracted tooth) exposed to the microwave energy at specific frequencies and at intervals of 10s, up to 90s. Colony forming ability was determined at each time. The tooth’s surface temperature increase was measured using an infrared thermal imager. Results: A small, portable microwave apparatus having a flexible antenna was developed to emit focused microwave energy. Direct exposure of bacteria at specific microwave frequencies produced kill rates approaching 100% at 20s compared to the untreated control.  Kill rates of the tooth-embedded S. Mutans were consistently over 99%, starting at 15s exposures when using a focused antenna. Colonies in control groups again showed near 100% viability. Using an air coolant, the average surface temperature of prepared teeth increased (from ambient temperature) to 37.2 ^oC (SD=2.6) and to 38.9 ^oC (SD=1.4) for intact teeth. Conclusion: Focused microwave energy may constitute a non-invasive means of controlling active bacteria in caries.