Primary Stability of Implants Inserted Using Different Osseodensification Systems in Low-Density Bone: An In Vitro Study

Background/Objectives: It remains unclear which drilling strategy is most effective for maximizing mechanical stability in low-density bone and whether high insertion torque is determinative. The aim of this in vitro study was to compare the primary stability of implants placed using different drilling protocols—conventional (CV), undersized (US), and osseodensification (OD). Three osseodensification systems—Versah burs (V), Bone Reamer Drills (WF), and Master Conical Densifiers (DSP)—were also compared. Methods: A set of 11 blocks was used for the drilling protocol comparison (CV, US, OD) and a separate set of 11 blocks was used for the osseodensification system comparison (V, WF, DSP). External-hexagon implants were inserted epicrestally. Insertion torque was measured using a torque meter, and implant stability quotients (ISQs) were assessed through resonance frequency analysis. Results: ISQ for OD was significantly higher than that for CV but statistically similar to that for US, whereas insertion torque for OD was significantly higher than that for both US and CV. A weak correlation was found between variables for CV and US, and a moderate one was observed for OD. Both WF and DSP showed significantly higher ISQ values than V. Insertion torque for DSP was significantly higher than that for both WF and V. A moderate correlation was found between variables for DSP and V, and a weak one for WF. Conclusions: In this invitro study, the OD protocol performed better than CV in terms of ISQ and better than both CV and US in terms of insertion torque. WF and DSP outperformed V in ISQ, whereas DSP yielded the highest insertion torque. Weak-to-moderate correlations between variables in both analyses indicated that higher insertion torque did not necessarily translate into greater stability.