Dental caries caused by oral microbiome dysbiosis with the elevation of acidogenic bacteria is the most prevalent non-communicable disease worldwide. Early prevention and timely fluoride treatment are crucial for caries lesion management. Herein, to address the challenges of in situ sensing and topical drug delivery within the oral cavity, a miniaturized, battery-free, and wearable dental patch system was developed for microenvironment monitoring and controlled fluoride treatment. With the integration of near-field communication, the dental patch realizes wireless energy harvesting and data transmission with mobile terminals like smartphones when attached conformally to the tooth surface. The acidic microenvironment caused by bacterial metabolism are electrochemically detected, while fluorides can be delivered locally from the electric-responsive drug delivery electrode for on-demand treatment. As flexible electronics armed to the teeth, this intraoral theranostic wearable system provides an inspiring platform for point-of-care monitoring and treatment of dental caries and oral diseases.