Determination ofHydroxyapatite Crystallite SizeinHuman Dental EnamelbyDark-Field Electron Microscopy

Ion-thinned longitudinal sections of athird molarwereobserved bybright- anddarkfield electron microscopy. Inbright field, thehydroxyapatite crystallites inenamel appeared aslongrods, but, whenobserved indarkfield, thecrystallites wererectangular, withameanlength of321A. Manyexperimental studies havebeenconducted todetermine thesizeandshape of hydroxyapatite crystallites inhumanenamel. Thesestudies haveusedeither X-raydiffraction or electron microscopy forthe morphological determinations, buttheyhave ledconsistently to different conclusions aboutthesizeandshape ofthecrystallites. Theaveragecrystallite sizeobtained by X-raydiffraction hasgenerally beensmaller thanthesizeestimated bybright-field electronmicroscopy. Withelectron microscopy, Little' de