inverted hat vs palatal hook

inverted hat

noun
  • = breve 

  • A háček. 

palatal hook

noun
  • = háček (when it takes the form of a prime) 

  • A hamiform diacritic (̡) formerly used to mark consonantal palatalisation; superseded by the superscript jay: (ʲ). 

  • A small hook for attaching elastic bands on the internal side of braces fixed to the upper teeth. 

How often have the words inverted hat and palatal hook occurred in a corpus of books? (source: Google Ngram Viewer )