Objective:To compare the effects on periodontal health of the abutment between concealed denture(flexible denture)and two traditional removable partial dentrue(RPD)-one with flexible retainers,the other with wire clasps and casting clasps,and observe whether the concealed denture can damage the abutment teeth.Methods:255 cases of the patients losing one of the first molar were collected,and divided into three groups,using one of three kinds of RPD and then repaired with the concealed denture,traditional plastic denture and casting frame denture respectively to one group.The indices of periodontal health of the abutment teeth were examined after 1 month and 1year.Results:Among three groups,the plaque index(PLI),gingival index(GI),probing depth(PD),teeth mobility and alveolar bone height of the abutment teeth were similar.Conclusion:Compared with two traditional RPD designs,there are no negative effects on periodontal health of the abutment teeth with the concealed denture long-term.