orthodontia vs orthodontics

orthodontia and orthodontics both are nouns.

Word	Noun	Adjective	Verb	Adverb
orthodontia	Yes	No	No	No
orthodontics	Yes	No	No	No

As nouns, orthodontia and orthodontics are synonyms defined as:

orthodontia and orthodontics: the branch of dentistry dealing with the prevention or correction of irregularities of the teeth

Other synonyms of orthodontia include dental orthopaedics, dental orthopedics, orthodonture.

orthodontia (noun)	orthodontics (noun)
the branch of dentistry dealing with the prevention or correction of irregularities of the teeth	the branch of dentistry dealing with the prevention or correction of irregularities of the teeth