Abstract: Abstract: Objective To study the clinical satisfaction and the success rateof a new style improved vacuum formed space maintainer and its influence on periodontal tissue compared with traditional band and loop space maintainer.Methods 40 patients with the need of maintaining space were divided into 2 groups randomly,each wearing one kind of space maintainers.Visual Analogue Scales （VAS）was used to evaluate the degree of comfort wearing different space maintainers after 4 weeks.Plaque indexes,gingival indexes and probe depth of the lower first molar,and the success rate of the space maintainer were recorded after 4 weeks,8 weeks and 12 weeks respectively.All data were subject to ttest and χ2 analysis.Results The degree of comfort when wearing improved vacuum formed space maintainer was obviously higher than that when wearing traditional band and loop space maintainer and the periodontal index was also better （P＜0.05）.The success rates of two groups were not statistically different （P>0.05）.Conclusions Improved vacuum formed space maintainer is more favorable compared with traditional band and loop space maintainer and is more effective in reducing the influence on periodontal health.

Key words: space maintainer, VAS, plaque index, gingival index, probe depth