Abstract
Screw tightening of the superstructure of osseointegrated implants often produces unsuitable strain on the prosthesis and surrounding bone． The purpose of this study was to investigate the effects of screw tightening on surrounding bone in several conditions．
Three Steri-oss® implants were placed in an acrylic resin experimental model， and a three-unit framework was fabricated on the implants． The fit of the framework was judged excellent by laboratory microscopy． Ten strain gauges were attached on the experimental model surface around the implants． The strain was measured after every screw was tightened by a custom-designed torque controller． Static and dynamic strain was recorded． Each test was repeated five times under the same conditions．
The results were as follows：
1．The order of screw tightening affected stress distribution． The distribution was unequal and asymmetrical to the implants．
2．Staged tightening of the screws decreased the sum of all strains．
3．Tightening torque does not affect stress distribution．
4．Misfit of the abutment／superstructure joint increased the sum of all strains．
5．Strain induced by tightening of the second or third implant was greater than that by tightening the first one．
