Old forms of toothpaste and tooth powder and similar did actually work, to some extent. See the one described above; it’s basically an abrasive. Of course it worked. Toothpaste only _really_ advanced far past that in the 1950s with fluoridation.

Various other things worked to some extent. The key difference is that no-one was really trying to _demonstrate_ that they worked; that really only came with evidence-based medicine in the late 19th century.