How to explain the best answer for my 7yr daughter. she wants to know what is tartar & where it comes from?

Not brushing: Tartar is simply hardened bacterial build up on the teeth. This build up occurs due to lack of adequate teeth cleaning when brushing. The build-up is initially soft but the longer it remains on the teeth the more minerals it absorbs from your saliva and the harder it gets. Only a professional teeth cleaning can remove the tartar once it is hardened on the teeth.