periodontics vs periodontia

periodontics and periodontia both are nouns.

Word	Noun	Adjective	Verb	Adverb
periodontics	Yes	No	No	No
periodontia	Yes	No	No	No

As nouns, periodontics and periodontia are synonyms defined as:

periodontics and periodontia: the branch of dentistry dealing with diseases of the gums and other structures around the teeth

periodontics (noun)	periodontia (noun)
the branch of dentistry dealing with diseases of the gums and other structures around the teeth	the branch of dentistry dealing with diseases of the gums and other structures around the teeth