Monitoring implant stability: the challenges of multicentric reproducibility

The long-term success of implant rehabilitation relies on the kinetics of osseointegration, for which primary and secondary stability constitute the major clinical indicator. While macro-design innovations — such as tapered bodies or micro-threaded collars — aim to optimize this mechanical engagement, most current evidence stems from monocentric or experimental studies, limiting their representativity in daily practice. This multicentric prospective study, conducted across nine Indian institutions, addresses this lack of field data by evaluating the Refirm implant system (Grade 23 titanium) under real-world conditions.

The specific objective was to evaluate longitudinal stability patterns using resonance frequency analysis (RFA) at four key stages: placement, second-stage surgery, impression-taking, and prosthetic try-in. The authors tested a dual null hypothesis: the absence of a statistically significant difference in implant stability quotient (ISQ) values between these different clinical time points, as well as between maxillary and mandibular implant sites. The aim is to determine whether the specific design of this implant ensures predictable and reproducible stability across various clinical configurations.

Experimental protocol and stability evaluation

This multicentre prospective study, conducted in nine university hospitals, evaluates the longitudinal stability patterns of the Refirm implant system (Grade 23 titanium alloy). The cohort included 230 patients for a total of 295 single implants.

The protocol included sites healed for at least 4 months, presenting adequate bone volume (Lekholm and Zarb Classes I-III) without recourse to bone regeneration or sinus lift. The implants, featuring a hybrid conical design and a switched platform, were inserted at the crestal level following a preoperative CBCT assessment.

• Stability measurement: Resonance Frequency Analysis (RFA) via the Penguin® RFA system and MulTipeg™ transducers.
• Temporal evaluation: ISQ readings at placement (primary stability), at the second surgical stage, during impression-taking, and at the prosthetic trial.
• Data collection: Average of vestibulo-lingual and mesio-distal values for each implant.

Statistical analysis utilized non-parametric tests to compare repeated measures and evaluate disparities between maxillary and mandibular sites. The correlation between primary stability and secondary values was analyzed to identify biological healing trends.

Results: Robust primary stability and an implant survival rate of 94.92%

The study involved 230 patients (119 men, 111 women; mean age 47.6 ± 12.3 years) for a total of 295 Refirm implants. In terms of clinical safety, 15 failures were recorded (13 during the osseointegration phase and 2 after prosthetic loading), bringing the cumulative survival rate to 94.92% at the prosthetic trial stage.

Evolution of ISQ values: a significant progression

Resonance frequency analysis (RFA) measurements indicate that ISQ values remained high throughout the follow-up. Although moderate fluctuations were observed, the Friedman test confirms statistically significant differences between the various clinical time points (p < 0.001).

Clinical time	Mean ISQ (± SD)
Implant placement	73.06 ± 11.66
Second-stage surgery	75.44 ± 6.09
Impression taking	74.76 ± 6.35
Prosthetic trial	75.07 ± 8.23

Anatomical comparison: Mandible vs Maxilla

L'analyse montre que les implants mandibulaires présentent une stabilité significativement supérieure à celle des implants maxillaires lors de la pose et de la deuxième étape chirurgicale (p < 0,05). Cependant, cette différence s'estompe lors des phases prothétiques ultérieures, où les valeurs deviennent comparables.

Clinical time	Maxilla (ISQ)	Mandible (ISQ)	Significance (p)
Implant placement	68.10 ± 11.57	73.65 ± 9.33	< 0.05
Second step	70.90 ± 11.96	76.15 ± 6.35	< 0.05
Prosthetic trial	74.33 ± 8.51	75.10 ± 8.10	NS

Stability correlations

The study highlights a positive correlation between the initial ISQ (primary stability) and subsequent measurements. Spearman's correlation coefficient is 0.62 (p < 0.001) between placement and the second stage, confirming that primary stability is a reliable predictive indicator of secondary stability for this system.

Analysis of the results: robust and long-lasting primary stability

This prospective study conducted across nine university centers provides tangible clinical data on the Refirm system. With a cumulative survival rate of 94.92% over 295 implants (15 total failures), the results confirm the device's reliability in real-world conditions. The major finding lies in the stability kinetics: the initial mean ISQ of 73.06 ± 11.66 demonstrates excellent primary stability. This result is particularly notable as the majority of sites presented moderate bone density (D2 and D3), suggesting that the hybrid conical design and cervical micro-threading effectively optimize initial mechanical anchorage.

Maxillary vs mandibular dynamics: the biological catch-up

A crucial clinical point of interest lies in the comparison of the arches. While the mandible displays superior initial stability (ISQ 73.65 versus 68.10 in the maxilla, p < 0.05), this gap progressively narrows to become non-significant at the prosthetic trial stage (75.1 versus 74.33). This phenomenon demonstrates that, despite a lower bone density, the biological remodeling around this implant allows the maxilla to catch up with mandibular standards. The identified positive correlation (r = 0.62 between placement and the second surgical stage) confirms the utility of ISQ as a reliable predictive tool for medium-term implant behavior.

Study limitations

The study is, however, limited to sites healed for at least 4 months, effectively excluding immediate implantation protocols or cases requiring guided bone regeneration (GBR). Although the multicentric nature strengthens external validity, the absence of a control group limits direct comparison with other macro-geometries. These results nevertheless constitute a solid basis for validating the use of the system in conventional single restorations.

This multicentric study involving 295 implants demonstrates robust longitudinal stability with a survival rate of 94.92%. The mean ISQ progresses significantly (p < 0.001) from 73.06 at placement to 75.07 during the prosthetic trial, confirming a positive correlation (r=0.62) between primary mechanical anchorage and secondary biological stability.", "practitioner_takeaways": [ "Anticipate the maxillary/mandibular gap: The mandible shows significantly higher initial stability (73.65 vs 68.10), but this difference fades by the impression stage; remain vigilant during loading protocols in the maxilla.", "Leverage the predictive value of ISQ: High primary stability is a strong statistical predictor of success for subsequent prosthetic phases, validating the hybrid conical design to secure osseointegration.", "Reliability in moderate density bone: The system maintains high ISQ values even in D2 and D3 sites (85% of cases studied), confirming the effectiveness of cervical micro-threads for stress distribution." ], "full_html": "

Summary of results

This multicenter study involving 295 implants demonstrates excellent longitudinal stability of the Refirm system, with a survival rate of 94.92%. The mean ISQ progresses significantly from 73.06 ± 11.66 at placement to 75.07 ± 8.23 during the prosthetic trial phase. The data confirm a robust positive correlation (r = 0.62; p < 0.001) between initial primary stability and secondary stability measured during surgical reopening.

In concrete terms, for the practitioner:

• Manage the arch differential: If the mandible offers superior initial stability (73.65 vs 68.10), this gap levels out during the impression-taking stage. Caution remains necessary in the maxilla during the initial healing phases.
• Predictive reliability: A high ISQ from the moment of implantation is a reliable indicator for securing future prosthetic stages, validating the benefit of the hybrid conical design for immediate mechanical anchorage.
• Performance in D2/D3 type bone: The system maintains high stability levels in moderate bone densities, which were the majority in this study, thanks to the optimization of cervical micro-threads and macro-geometry.

Technical lexicon of the Refirm study

Resonance Frequency Analysis (RFA): A non-invasive and reproducible method for assessing implant stability. It measures the vibration frequency of the implant in the bone, which is then translated into a quantitative value (ISQ) for longitudinal monitoring.

Implant Stability Quotient (ISQ): Numerical indicator of implant stability. In this study, ISQ is used to define the "stability profile" across four clinical stages: placement, second-stage surgery, impression taking, and prosthetic trial.

Grade 23 Titanium Alloy: Material used in the Refirm implant system. It is selected for its superior mechanical strength, fatigue resistance, and anticorrosive properties compared to other titanium grades.

Platform switching: Implant design characteristic aimed at shifting the abutment-implant junction towards the center, with the goal of optimizing stress distribution and promoting the maintenance of cervical bone.

CBCT (Cone-beam computed tomography): Three-dimensional imaging technique used in the study protocol for the preoperative evaluation of bone quality (according to the Lekholm and Zarb classification) and available dimensions.

Primary stability: Initial mechanical engagement between the implant and the surrounding bone during insertion. It is distinguished from secondary stability, which develops via biological bone remodeling during the healing phase.

MulTipeg™ Transducer: Specific hand-tightened component on the implant to allow ISQ measurement via the Penguin® RFA device in buccolingual and mesiodistal directions.

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