Although the torque and ISQ values of 06S were greater compared with those of 06D, only the former were statistically significant. These results suggest that although the difference between 06D and 06S in primary stability was small, the risk of slackening was significantly greater for 06D compared with that of 06S. Further, the discrepancy between the statistical significance of the torque and ISQ values may be partly explained by the lower sensitivity of ISQ compared with that of torque. The ISQ values of 06D and 06S compared with that of 12S were 5% and 8% higher, respectively, which were much lower than those of increased torque values. Sakoh et al., who evaluated the primary stability of a conical implant and a hybrid cylindrical screw-type implant according to torque and ISQ values, found that only torque values but not ISQ were significantly different. Resonance frequency analysis (RFA) using the Osstell System and Periotest is commonly used. However, neither system optimally measures stability nor defines a successful implant upon implant placement; and measuring IT prevails over the ISQ and Periotest.

The IT values reported here ranging from 13 to 22 N cm were much lower than the clinically recommended torque value of 35 N cm. The lower torque values can be explained by our use of artificial bone, mimicking type-4 bone, and a cylindrical non-self-tapping design limiting the interface between thread and bone. Moreover, the IT and RT values of 12S were consistent with those of the standard implant (Straumann) measured in our previous study.