The Deaf Hear Through the Teeth

I was skimming through some very old vintage advertising materials from the 1880′s and came across the Dentaphone, a device that “by it’s use, the deaf are enabled to hear all ordinary conversations, lectures, concerts…” according to the advertising copy, the device is “a thin, flexible folding diaphragm of a peculiar composition, chiefly vulcanite, which possesses the property of gathering up on it’s delicate surface the sound vibratons that sensitute spoken language, music, etc., and conveying them to the teeth of the person using it.” Supposing the $10 or deluxe $15 vulcanite device fails to work for the user, not all was lost, because according to the advertising copy, when unfolded, it could also be used as an [expensive!] hand-fan.