@patent {7, title = {Zirconia Toughening of Glass-Ceramic Materials}, volume = {5173331}, year = {1992}, edition = {United States of America}, chapter = {US}, url = {files/clarke/files/us5173331.pdf}, author = {Adams, Richard W. Jr. and David R. Clarke and Sarah H. Knickerbocker and Linda L. Rapp and Bernard Schwartz} }