Riggs' disease vs periodontitis

Riggs' disease and periodontitis both are nouns.

Word	Noun	Adjective	Verb	Adverb
Riggs' disease	Yes	No	No	No
periodontitis	Yes	No	No	No

As nouns, periodontitis is a hypernym of Riggs' disease; that is, periodontitis is a word with a broader meaning than Riggs' disease:

Riggs' disease: chronic periodontitis; purulent inflammation of the teeth sockets
periodontitis: a disease that attacks the gum and bone and around the teeth

Other hypernyms of Riggs' disease include periodontal disease.

Riggs' disease (noun)	periodontitis (noun)
chronic periodontitis; purulent inflammation of the teeth sockets	a disease that attacks the gum and bone and around the teeth