Objective To observe the changes of root surface and analyze the mineral contents in cementum after local application of CPP-ACP,and to evaluate the effects of CPP-ACP paste on the cementum.Methods Cementum slices were obtained from healthy molars,then the slices were coated with GC Tooth Mousse(comtaining 10% CPP-ACP)for 21,14 and 7 days,respectivel.Control groups were set up.After the treatments,the surfaces were observed under field emission-scanning electron microscopy(FE-SEM).The SEM observations revealed different morphological features brought about by CPP-ACP,and the energy spectrometry analysis was used to measure the mineral contents in cenentum(Ca,P).Results There were obvious morphological differences between each group: a layer of membrane could be seen on the surface of cementum in the slices that were coated with GC Tooth Mousse for 14 and 21 days.The mineral contents of each groups were similar to that of control groups.Conclusion Local application of GC Tooth Mousse on healthy cementum after 14 days,a layer of member can been seen on the surface,and this member have protective effect on cementum.