Fig.1.
Total annual number of publications listed in the United States National Library of Medicine (https://www.ncbi.nlm.nih.gov/pubmed/, 12-3-2018) for years 1900 through 2018 and containing the keyword “hydroxyapatite”. Search was performed at https://www.ncbi.nlm.nih.gov/pubmed/ on December 3, 2018.