Screw loosening in dental im plant treatment is one o f the m ajor problem that has been frequently reported by m ultiple authors. There are several factors involved in keeping im plant screws tight. The purpose o f this study was to determine whether various im plant fixture and abutment connection system w ould affect screw looseness. Im plant fixture and abutment o f the four different connection system were connected and tightened w ith 30N Cm and then the loosening torque was measured. T ightening screw removal values were measured 10 times repeatedly under same condition. The results were as follow s. 1. The highest loosening torque value appeared after tightening 3-5 times repeatedly. 2. Morse taper connection system showed statistically significant high loosening torque value. There were no significant difference in loosening torque values w ith other connection system, spline, internal hex, external hex.