dentiphone

from The Collaborative International Dictionary of English v.0.48

Dentiphone \Den"ti*phone\ (d[e^]n"t[i^]*f[=o]n), n. [L. dens,
   dentis, tooth + Gr. fwnh` sound.]
   An instrument which, placed against the teeth, conveys sound
   to the auditory nerve; an audiphone. --Knight.
   [1913 Webster]