An in vitro study evaluating the efficacy of a novel mount with torque control designed to tighten Osstell® transducers

Abstract Objectives To evaluate the efficacy of a novel mount with torque control for tightening of Osstell® transducers and to determine the reliability of recorded ISQ measurements from implants placed in various bone densities. Material and Methods Fifty‐six implants, comprising seven different implant types, were placed in eight polyurethane blocks representing D1, D2, D3, and D4 bone densities. Resonance frequency analysis (RFA) transducers were attached to each implant in four different ways: (a) hand tightening, (b) hand tightening with a SmartPeg Mount™, (c) hand tightening using the novel mount with torque control (SafeMount) and (d) tightening to 6 Ncm with a calibrated torque device. ISQ measurements were taken and a second operator repeated the measurements. Intraclass correlation coefficient (ICC) was calculated to assess the reliability of the measurements and linear mixed effects regression was employed to determine the effect explanatory variables had on ISQ values. Results There was a statistically significant difference in ISQ values obtained by hand tightening transducers compared to the calibrated torque device p < .001, 95%(−2.89, −1.21) but not between any other tightening methods. There was excellent agreement between the two RFA devices (ICC 0.986) and between buccal and mesial measurements (ICC 0.977). For all transducer tightening methods there was excellent inter‐operator agreement in D1 and D2 (ICC > 0.8) but very poor agreement in D4 (ICC < 0.24). Bone density accounted for 36% of the variation in ISQ values, the implant for 11% and the operator for 6%. Conclusions SafeMount, did not significantly improve the reliability of the RFA measurements when compared to the standard mount, but calibrated torque devices seem to have benefits when compared to tightening the transducers by hand. Results also indicate that the ISQ values should be interpreted with caution when measuring implant stability in poor quality bone regardless of the implant geometry.

implant stability corresponds to a higher ISQ value and several factors can affect these readings. Bone density and the macro-and micro-geometries of the implant have all been shown to have an effect (Comuzzi et al., 2021;Gehrke et al., 2015;Marquezan et al., 2012;Merheb et al., 2018;Novellino et al., 2017). The influence of SmartPeg tightening has only been scantly assessed to date.
An intimate fit of a SmartPeg would theoretically give the most accurate ISQ value of an implant by fully allowing for measurement of the vibration of the implant itself. A SmartPeg not sufficiently tightened would move somewhat independent of the implant and an overtightened SmartPeg may damage the connection with the implant, also resulting in inaccurate readings. Osstell ® recommends a SmartPeg to be "finger tight." A study by Geckili et al. recommended SmartPegs to be tightened to 5-8 Ncm (Geckili et al., 2015) but a similar study by Kästel et al. reported that there is no need for standardization of tightening forces as all their investigated values, (2-11 Ncm) resulted in accurate ISQ readings (Kästel et al., 2019). Salatti et al. in agreement with Geckili et al. reported that there was a need for standardization of tightening forces, but recommended tightening the Smart Pegs™ to 10-17 Ncm of torque (Salatti et al., 2019).
At present, there is disagreement as to the optimal torque value that should be applied to SmartPegs and they are either tightened by hand or by using a plastic mount supplied by Osstell ® . In a bid to introduce a degree of torque control, Osstell ® developed a novel plastic mount termed "SafeMount." Once a certain amount of torque is applied with this mount, a tactile and audible click is emitted.
Osstell ® reports this to be happening at 4-4.5 Ncm.
The aim of the current study was to evaluate the effect that different transducer tightening protocols might have on the accuracy of ISQ values of implants placed in artificial bone blocks. An effort was also made to determine the reliability of recorded ISQ measurements from implants with varying macro and microgeometries placed in various bone densities.

| Implant insertion
Seven types of implants were used in this study ( Figure 1): 7. Ankylos™ C/X 3.5 × 11 mm (Dentsply ® Sirona) Eight resin polyurethane bone blocks (BoneModels™) were used in this study. Each block was of uniform density and represented either D1, D2, D3, or D4 bone densities. Two blocks of each density were used. One of each implant type was inserted into each block with uniform spacing. In total, 7 implants were placed per block resulting in 56 implants ( Figure 2). All implants were placed according to the implant manufactures' protocols. Implant osteotomies in D1 bone blocks were completed with a bone tap. Implant osteotomies in D4 bone blocks were undersized to achieve stability.
F I G U R E 1 The seven types of implant used.

| Bench top set up and measurements
Osstell ® SmartPeg transducers were paired to implants as per Osstell's recommendation for each implant and all measurements were taken in a buccal and mesial direction.
Transducers were attached to each implant in four different ways: • Group 1: Hand tightened by using gauze (handtighten).
• Group 2: Hand tightened with the standard plastic mount supplied with SmartPegs (plastic mount).
Bone blocks were secured to a bench top with a vice. A SmartPeg™ was attached to each implant in a randomized order by means of an online randomizer in each of the four ways. Two Osstell ® devices were used throughout to record ISQ values (Osstell IDx and Osstell ISQ). All initial measurements were repeated by the second Osstell ® device. All measurements were taken with the probe tip approximately 2 mm and 90°to the SmartPeg in a buccal and mesial direction. ISQ values were recorded onto an Excel (Microsoft Excel v16.55) spreadsheet. A second operator then repeated the above described bench top set up and measurements.

| Statistical analysis
Descriptive statistics were used to express mean ISQ values by torquing method. Medians of ISQ values by implant type were compared using a Kruskal-Wallis test as values were not normally distributed (Kolmogorov-Smirnov test) when all bone densities were included and also when D4 was omitted. Dunn's multiple comparisons post hoc test was used when p < .05. Different implant systems were only compared for one of the four mounting groups (group 4) as this is generally considered the optimal tightening force. An average measures intraclass correlation coefficient (ICC) was also calculated to determine how well the measurements from the two Osstell devices, the two investigators and the two directions, resembled each other. ICC results were classified according to Koo and Li guidelines (Koo & Li, 2016). These statistical analyses were performed with IBM SPSS software v27.
Linear mixed effects regression was employed to determine the effect that explanatory variables had on ISQ readings. Model complexity was determined by examining change in deviance and information criterion-Akaike's Information Criterion and Bayesian information criterion. The final model selected followed the principle of parsimony. Models were developed using Statistical Software: R (version 4.1.2) (Team RC, 2021) and R Studio (Team R, 2021). Models were further developed using packages lme4 (Bates et al., 2015) and lmerTest (Kuznetsova et al., 2017). p values displayed for the model are based Satterthwaite's method of approximation. Model diagnostics were checked using a simulation-based approach on scaled residuals from the R package DHARMa (Hartig, 2021). Package emmeans was used for post hoc comparisons (Lent et al., 2021).
Model diagnostics were performed on simulated residuals. Results from the outlier test and the Kolmogorov-Smirnov test was nonsignificant (p > .5). A QQ-plot of the standardized residuals illustrated a linear pattern thus indicating that residuals satisfied assumptions are satisfied ( Figure 4).

| RESULTS
Overall, 1792 ISQ measurements were performed. The mean ISQ values and the spread of ISQ values were similar for each of the four tightening groups when all bone densities were included (Table 1).
As expected, a large difference in ISQ values could be seen based on bone density when all four tightening groups were included differences were observed between implants 2 versus 3, 2 versus 6 (p < .001) and 5 versus 6 (p < .001).
Furthermore, ICC values were calculated between operators for each SmartPeg tightening method in each type of bone density.
There was excellent agreement when measuring in D1 and D2 bone between examiners. In D3, agreement was good but it became very poor in D4 bone (Table 2).
Mixed linear effects regression analysis showed a statistically significant difference between ISQ values in the hand tightening group (p < .001) and the values in the control group. No statistically significant differences were detected between the ISQ values from the other two groups and the control. Additionally, the differences between the ISQ values measured in D3 (p = .006) and D4 (p < .001) bone were statistically significant to the ones measured in D1 (Table 3).
Examination of random effects indicate that approximately 10.36% of the total variation of random effects is due to the nested F I G U R E 4 QQ plot and residual diagnostics for the hierarchical (multilevel/mixed) regression model. Approximately 36.34% of the total random variation was due to the implant within each bone density. The effect for Implant alone accounts for approximately 11.23% of the total variation of random effects and the effect of operator alone accounts for 6.06% (Table 4).  (Geckili et al., 2015;Salatti et al., 2019).

| DISCUSSION
There are only a handful of studies assessing the influence of the tightening torque of SmartPegs on ISQ. One study concluded that all their investigated torque values of 2-11 Ncm were appropriate (Kästel et al., 2019). Whereas, the other two study groups recommended specific values of 5-8 Ncm (Geckili et al., 2015) and 10-17 Ncm (Salatti et al., 2019). They reported that too low a torque value reduced the ISQ value. Osstell ® recommends SmartPegs to be tightened to 4-5 Ncm which they report to be "finger tight." This present study used 6 Ncm as the control value. This value allowed for agreement with both the Kästel et al. and Geckili et al. studies There may also be a role for their use with users who are inexperienced with Osstell ® SmartPegs, to ensure they have applied a sufficient amount of force when tightening the SmartPeg. In clinical practice, there may also be a change in operators between the implant surgery and restoration and nonaccurate measurements might falsely alarm the operator regarding possible bone loss.
A limitation of this study is that the statistical power did not allow for a meaningful comparison between the different individual designs of implants. There were no similar previous studies to base a priori power calculation on and post-hoc power calculations are often reported to be conceptually flawed with misleading results (Gelman, 2019;Senn, 2002