ISQ at placement: useful stability indicator, but not a predictor of long-term survival

Resonance frequency analysis (RFA) has become a standard tool in implant dentistry for assessing implant stability, yet its actual prognostic value remains contested. This systematic review and meta-analysis set out to define, with quantitative precision, the relationship between the Implant Stability Quotient (ISQ) — the numerical output of RFA — and three clinically relevant parameters: insertion torque (IT), marginal bone loss (MBL), and implant survival or success rates.

Following PRISMA guidelines, the authors searched MEDLINE, Scopus, and Web of Science, framing the inquiry around a PIO question focused on systemically healthy patients undergoing implant placement. Forty-eight studies met inclusion criteria, of which 20 provided sufficient data for meta-analytic pooling of the ISQ–IT correlation. Risk of bias was evaluated using design-appropriate methodological tools.

The central quantitative finding is a moderate, statistically significant correlation between ISQ and IT (pooled r = 0.44; 95% CI: 0.32–0.55; p < 0.001). This means that higher insertion torque — reflecting greater bone density and cortical engagement at placement — does tend to correspond with higher ISQ values, confirming that both metrics capture overlapping but not identical aspects of primary stability. However, the association explains less than 20% of the shared variance, which limits its predictive power in individual cases. Heterogeneity across studies was substantial, reflecting differences in implant systems, bone quality classification, surgical protocols, and RFA device calibration.

Regarding MBL and implant survival, the evidence was insufficient to support baseline ISQ as an independent predictor of either outcome. Studies examining these relationships were too heterogeneous in design and follow-up duration to yield reliable pooled estimates, and the overall certainty of evidence remains low.

For the practicing implantologist, the clinical take-home is nuanced. ISQ is a legitimate and useful indicator of primary stability at the time of placement — it adds information, particularly when correlated with IT, and may help guide loading protocols. But it should not be used in isolation to predict long-term bone maintenance or survival. A high ISQ at baseline does not guarantee osseointegration success, nor does a lower-than-expected value necessarily indicate future failure. The measurement is one data point among several, not a standalone prognostic test.

The review also highlights a methodological gap in the literature: the absence of standardized ISQ threshold values and inconsistent reporting practices make cross-study comparison unreliable. Future research should prioritize prospective designs with harmonized protocols, clearly defined success criteria, and longer follow-up periods to properly establish whether RFA carries independent predictive value beyond the surgical moment.