The present disclosure is directed to methods and apparatus for monitoring bone characteristics for various conditions such as osteoporosis and/or periodontitis. In various embodiments, a dental hygiene appliance (100) may include: a handle (102) adapted to be held by a user; a tool (106) secured to the handle to perform a dental hygiene-related task; emitter(s) (114A, 116, 360A) mounted on the dental hygiene appliance to emit wave(s) (252, 362) towards a mandible (250, 350) of the user; sensor(s) (114B, 116, 360B) mounted on the dental hygiene appliance to detect wave(s) (254, 364) propagating away from the mandible, wherein the detected wave(s) originate from or are caused by the emitted wave(s); and a controller (108) communicatively coupled with the emitter(s) and the sensor(s). The controller may: receive, from the sensor(s), signal(s) indicative of the detected waves; and determine, based on the signal(s), bone characteristic(s) of the user.