gingiva vs roof of the mouth

gingiva

noun
  • The gum, consisting of the tissue surrounding the roots of the teeth and covering the jawbone. 

roof of the mouth

noun
  • The upper internal surface of the mouth that separates the oral and nasal cavities, found in people and some mammals. 

How often have the words gingiva and roof of the mouth occurred in a corpus of books? (source: Google Ngram Viewer )