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The Influence of Low Insertion Torque on Primary Stability, Implant Survival, and Maintenance of Marginal Bone Levels: A Closed-Cohort Prospective Study.

PURPOSE
The purpose of this study was to evaluate the impact of low insertion torque on primary stability and the short-term clinical outcome of single-tooth implants placed into healed ridges and fresh extraction sockets.


MATERIALS AND METHODS
A cohort of n = 30 implants was self-selected on the basis that their insertion torque measured ≤ 20 Ncm. The cohort was closed with the follow-up set at 1 year. Resonance frequency analysis was evaluated in both mesiodistal (MD) and buccolingual (BL) directions at the time of implant insertion and at the time of restoration. Immediate temporization was determined by the esthetic need and a minimum implant stability quotient (ISQ) reading of 55. Implants were definitively restored after approximately 3 months. Implant survival was recorded along with changes in the level of the marginal bone relative to a fixed reference point, at the 1-year follow-up.


RESULTS
Twenty-two patients with a total of 30 implants were grouped by insertion torques of < 5 Ncm (spinners), > 5 < 10 Ncm, 10 Ncm, 15 Ncm, and 20 Ncm. One implant was excluded because follow-up data were unavailable. Of the remaining 29 implants, the mean ISQ measured 67 (MD) and 65 (BL) at surgery. The values increased to 80 (MD) and 79 (BL) after a period of 3 months. The survival rate at the end of the 1-year period was 96.7%, including the excluded implant, but 100% for the remaining 29 implants. The frequency of implants demonstrating no marginal bone loss was 71.4%, 0.1 to 0.5 mm bone loss was 21.4%, and bone loss > 0.5 mm (max = 2.82 mm) was only 7.2%. No implants were lost during the functional loading period. Data on immediate temporization revealed no significant difference in ISQ or marginal bone loss values for implants in this group.


CONCLUSION
Lower insertion torques yield favorable survival rates with optimal marginal bone levels compared with the accepted norm.