dental appliance vs device

dental appliance and device both are nouns.

Word	Noun	Adjective	Verb	Adverb
dental appliance	Yes	No	No	No
device	Yes	No	No	No

As nouns, device is a hypernym of dental appliance; that is, device is a word with a broader meaning than dental appliance:

dental appliance (noun)	device (noun)
a device to repair teeth or replace missing teeth	any clever maneuver
	an instrumentality invented for a particular purpose
	an emblematic design (especially in heraldry)
	any ornamental pattern or design (as in embroidery)
	something in an artistic work designed to achieve a particular effect