Increases or decreases of ISQ values are explained as follows: The inserted dental implant body is supported by mechanical interdigitating force after surgery, but this interdigitating force will be reduced time-dependently by the effects of osteoclasts activation at the initial stage of the bone remodeling process, then osseointegration will be completed by an increasing contact area between the bone and dental implant body at the bone regeneration step [38]. The period switch from ISQ decreasing to increasing was considered as the most unstable but important period during the healing period [24].

The average ISQ in this study was 68.0 ± 13.7 after surgery then increased to 71.8 ± 8.3 at 4 weeks and 78.0 ± 5.7 at 12 weeks after surgery; all inserted implants showed ISQ > 60 after 6 weeks (Fig. 3). In addition, the average ISQ decreasing was not observed during the experimental period. According to the publication about the relationship with ISQ value and intraosseous stability of the implant body inserted in the soft bone quality by Held et al., the ISQ value was not decreasing and tended to increase [39]. As per we evaluated implant treatment at the soft bone in this study, migration of the ISQ value in this study showed similarity with the abovementioned document.

The relationship between IT and ISQ remains unclear. Some articles have reported positive correlations between IT and ISQ [15, 17], but others have found no correlation [18,19,20].

While no significant relationship was found between IT and ISQ in this study, the migration pattern of ISQ differed between the low IT group and medium/high IT group. ISQ in the low IT group was initially low, increasing over time. A significant difference was observed between 0 and ≥ 8 weeks (Fig. 5). The ISQ did not change significantly during the experimental period in the medium or high IT groups, but the percentage of high ISQ (≥ 73) specimens was significantly higher at 4 to 6 weeks compared to other time periods in both groups (Figs. 5 and 6). The results in this study suggest that if the implant insertion has been performed with low insertion torque, progress of peri-implant bone maturation (transfer from mechanical interdigitation to osseointegration) slowly stabilizing at 8 weeks after surgery, or if the insertion torque value was moderate or higher, peri-implant bone will maturate following a safe healing period and show stabilization at 6 weeks after surgery.