Abstract: Objective To research the variation of Actinomycetes viscous （A.v） of two kinds of high biocompatibility crown materials in different periods before and after restoration among the elderlg. Methods A total of 60 clinic patients, who needed restoration treatment of the mandibular first molar were collected, and randomly divided into zirconium dioxide all-ceramic crown group and sliver-palladium alloy porclain group. The self control study was used, the one before tooth preparation was set as control group, the one after restoration in six months and twelve months as experimental group. And the subgingival plaque on the edge of the crown was collected, fluorescent quantitative polymerase chain reaction was adopted to have relative quantitative analysis of A.v of samples. Results Compared with those before restoration, the quantity of A.v in six and twelve months after restoration in the zirconium dioxide all-ceramic crown group had no statistital difference（P＞0.05）; the quantity of A.v in six and twelve months after restoration in the sliver-palladium alloy porclain crown group had statistical difference（P＜0.05). Conclusion The zirconium dioxide all-ceramic crown can better reduce the risk of dental caries.

Key words: Elderly, Actinomyces viscosus, Poly-merace Chain Reaction