Abstract: Objective　To study the effects of expansion fashion and expansion quantity on retention of cement-expanded com- positionscrew post(CECSP).Methods　Ninety simulated tooth roots made of polymethylmethacrylate were divided into ten groups, each fashion induded five groups. The expanded plastic sheath of tricuspid valvewasmadewiththe special separated valve device and cemented and tightened up into root with the screw post at the same time by ZPC. Then the root and screw post-core system was tested by the speed of 10 mm/min on the INSTRON 4302 and the retention force was recorded.Results　It appeared that the difference between different expansion fashion and different expansion quantity were significantly(P<0.05). The reten- tion of expansion fashion one was significantly greater than those of fashion two. The retention was best when expansion quantity was within 10%.Conclusion　During clinic operation, we should apply definite fashion and control the expansion quantitywithin 10%, and the screw post should tighten up to the bottom of prepared root.

Key words: expansion fashion, expansion quantity, cement-expanded composite screw post, retention