Primary and Secondary Stability of Subcrestal Morse-Taper Implants Placed Immediately into Extraction Sockets or into Grafted or Healed Ridges: A Retrospective Cohort Study

Background/Objectives: Immediate implant placement into fresh extraction sockets is often assumed to provide lower primary stability than placement into healed ridges, but comparative data for subcrestal Morse-taper (conical-connection) implants are lacking. This study compared insertion torque value (ITV) and implant stability quotient (ISQ) between two management protocols: immediate placement and delayed placement. Methods: This retrospective single-surgeon cohort included consecutive Argon K3 Pro implants placed in 2019–2022, grouped as immediate (IM), delayed into sites grafted within the preceding 12 months (DG) or delayed into healed ridges (HR). The protocols differed in more than timing (placement depth, grafting, flap design and healing management). ITV, ISQ at placement and ISQ at 3 months were compared with mixed-effects models accounting for multiple implants per patient. ISQ differences were tested against a post hoc ±5-unit equivalence margin; no equivalence test was applied to ITV. Results: Of 178 implants screened, 130 implants in 85 patients (52 women, 33 men) were analyzed: 56 IM, 30 DG and 44 HR. No difference was detected in ITV (delayed minus IM −1.4 Ncm, 95% CI −5.0 to 2.1), placement ISQ (IM 72.3 ± 7.8 vs. delayed 72.5 ± 9.0) or 3-month ISQ (78.8 ± 4.8 vs. 79.4 ± 5.6); in the primary analysis, the 90% confidence intervals of both ISQ differences lay within ±5 units, but the placement ISQ interval did not lie within ±3 units, and equivalence at placement was borderline in a size-adjusted sensitivity analysis. ISQ change was strongly related to starting ISQ (Spearman’s ρ = −0.77), largely through arithmetic coupling and regression to the mean, and baseline-adjusted 3-month ISQ did not differ between protocols (p = 0.46). All 19 immediate implants starting below ISQ 70 reached ISQ ≥ 70 by 3 months under the protocol used. In an exploratory analysis, ITV correlated with placement ISQ in healed ridges (ρ = 0.55) and more weakly in extraction sockets (ρ = 0.25); the difference between these correlations was inconsistent across methods. Conclusions: In this cohort, immediate and delayed protocols showed no detectable difference in insertion torque or ISQ, and ISQ differences were statistically within a post hoc ±5-unit margin. Whether torque is a weaker indicator of stability in extraction sockets is a hypothesis for prospective study.