In order to promote the optional subjects' function in perfecting knowledge construction and developing the character of the students,through analyses of the results of 670 classmates’selection of optional subjects,we know in detail what kind of optional subjects students like and need.Therefore based on how to organize teaching and manage optional subjects we bring up the suggestions for enhancing the optional subjects ' development and management:setting students as the center and increasing optional subjects,establishing the leading teacher's system,reforming teaching method,enriching teaching means,and strengthening the management of the examination of optional subjects.

ety, reduce the risk of infection and improve the efficiency of nursing service.

Objective:To analyse the causes of early implantation failure and the therapeutic measures with re-implantation after the failures.Methods:6 cases of implantation failure including early infections,loosening and non-osteointegration were reviewed and trea-ted by re-implantation therapy,and the causes of failure were discussed and the effects of re-treatment were evaluated.Results:2 cases were found to be with infection of adjacent teeth after implantation and were treated by removal of the implant,socket curettage,root ca-nal therapy(RCT)and antibiotics followed by reimplantation.Implant loosening and non-osteointegration were observed in 4 cases, which were treated by the similar methods for the implant socket.Reimplantation was successful in all 6 cases followed-up for 1 -3 years.Conclusion:Preventive measure for implantation failure should include indication selection,control of infections in adjacent teeth and periodontosis,use of GBR technic and so on.Re-implantation following proper treatment of adjacent teeth and the socket of implant is effective for the treatment of implantation failure.