A dental device has a U-shaped carrier with at least one channel for embracing an arch of teeth. The carrier has recessed insets in the channel. Discrete inserts carrying a beneficial agent can fit into the insets and release the agent gradually. The device may be used in a therapeutic application and as an athletic mouthguard. Temporary blanks may be initially fitted in the insets while a portion of the mouthguard is softened before an arch of teeth is pressed into the channel to make a custom impression. The inserts possess different physical properties than the carrier and may be positioned and shaped to mechanically buffer teeth of the arch from mechanical shocks as well as release beneficial agents. The inserts may be replaced or refreshed to maintain the beneficial agent. A dental device having a core carrying a beneficial agent inside a liquid-permeable shell functions as an infant's teething device.