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.
