A mouth guard comprises a base member configured to fit inside the mouth of a user, and at least one shock-sensing and indicating device coupled to the base member. In one exemplary embodiment, the shock-sensing and indicating device is a passive shock-sensing and indicating device that detects a shock substantially along a selected axis with respect to the base member. In another exemplary embodiment, the at least one shock-sensing and indicating device detects a shock substantially along a plurality of selected axes with respect to the base member, each selected axis being substantially orthogonal from another selected axis. The shock-sensing and indicating devices can be configured to detect different levels of shock. In one exemplary embodiment, the shock-sensing and indicating device comprises a multi-component chemical-reaction system, such as a chemi-luminescent reaction system.