The purpose of this study was to the determine the optimal torques values to tighten the retaining screw. 3-different implant system tested were as follows : Branemark implant system$(3.75mmD{ imes}100mm)$, Steri-Oss implant system$(3.8mmD{ imes}10mm)$. One fixtures of each implant system was mounted into the epoxy resin block and abutment^{erstructure complex was constructed. Eighty dental college students(male : 40, female : 40) of Chosun University were selected and were asked to tighten the retaining screws. Abutment}superstructure complex of each implant system was tightened to the maximum torque by use of hand-held screw driver, and then torque value was measured with torque value was measured with torque driver(Tohnichi torque driver, model 20 FTD, Tohnichi MFG, Co., LTD., Tokyo, Japan). Abutment^{erstructure complex of each implant system was titghtened to each torque of 10 N-cm, 20 N-cm and 30 N-cm, and then the dynamic load(vertical & diagonal load) was applied to the abutment} superstructure complex. The gap between abutment^{erstrure in each implant system was measured with 3-dimensional measuring microscope(model No. 850, Germany). The results were as follow : 1. Torque values according to the individual subjects showed wide range. 2. Torque values according to sex showed statistical significant difference. Those are as follows : in case of male, $9.38{pm}2.93$<} N-cm ; incase of female, $7.80{pm}2.25$ N-cm. 3. Torque values according t implant systems showed statistical significant difference. Those are as follows : in ase of Branemark implant system, $6.54{pm}1.54$ N-cm : in ase of Steri-Oss implant system, $10.1{pm}2.88$ N-cm ; in case of IMZ implant system, $9.18{pm}2.17$ N-cm. 4. The more torque value of tightening screw was increased, the less the gap was after the vertical and diagonal loading. 5. The gap after the diagonal loading was greater than that after the vertical loading. 6. The magnitude of gap between abutment/superstructure in order of IMZ, Steri-Oss, Branemark implant system after the verical and diagonal loading. 7. The gap under the diagonal loading after applying 30 N-cm torque showed no statistical significant difference in cases of the Branemark system and the Steri-Oss implant system but it showed significant different in case of the IMZ implant system.