Using cumbersome dental X-ray machines to diagnose tooth decay could become a thing of the past, thanks to a simple technique that detects local pH changes. 

When bacteria and carbohydrates interact on the surface of a tooth, acidic molecules that destroy the dental enamel and dentin underneath are generated. A drop in pH, therefore, can indicate bacterial activity, tooth decay, or cavities.

Researchers from the Tokyo Medical and Dental University have now developed a microscopic iridium-based sensor that detects tooth decay through surface pH measurements. The needle-shaped sensor can identify treated and active sites of decay in various pH-dependent states. Specifically, it discriminates the early cavity-free stage of tooth decay from the beginning of a cavity — an impossible feat for X-ray. Combining this quantitative information with visual inspection is expected to provide a more reliable and accurate assessment of tooth decay.