Tightening and Loosening of the Abutment Screw Negatively Affects Implant Osseointegration in the Early Healing Stage in Rat Tibiae

Purpose: To examine the effect of tightening and loosening the dental implant screw on implant osseointegration in an elderly rat model. Materials and Methods: Titanium dental implants were inserted in the bilateral tibiae of 34 elderly Wistar rats (1 year and 3 months old). Rats were randomly divided into five groups: control (no loading); immediate loading (IL) (vertical load [3 Hz for 15 minutes/day] immediately after implantation); early loading (EL) (load started on postoperative day 7); five times abutment removal (R5) (tightening and loosening of the abutment screw once per day for 5 days each week); and two times abutment screw removal (R2) (tightening and loosening of the abutment screw once per day for 2 days each week). After 4 weeks, the rats were euthanized, and the bone structure surrounding the dental implants was evaluated using microcomputed tomography analysis. Results: Osseointegration failed more frequently in the EL, R2, and R5 groups than in the control and IL groups (P =. 06). The EL, R2, and R5 groups also tended to have lower relative gray values than the control and IL groups. Conclusion: Tightening and loosening the abutment screw might negatively affect dental implant osseointegration in the early healing stage in older adults.