Detecting Inaccurate Insertion Feed Rate through Axial force and Its Effect on Primary Stability of Dental Implants

Primary stability, defined as the initial contact between bone and implant, is essential for the success of implantation. Surgical technique, which involves drilling and insertion, affects primary stability. Keeping a feed rate appropriate for the rotational speed is crucial for achieving optimal insertion and adequate primary stability. Insertion of self-tapping dental implants requires the application of axial force, as well as insertion torque. This study aimed at detecting inaccurate insertion feed rates by evaluating the axial force exerted during insertion and determining its effect on maximum insertion torque (MIT) and implant stability quotient (ISQ), as two indicators of the primary stability of dental implants. Twelve identical implants were inserted into low-density (0.2 $\mathrm{g} / \mathrm{cc}$) polyurethane foam at 25 rpm, divided into three groups based on feed rate: accelerated insertion (AI) at $0.8 \mathrm{~mm} / \mathrm{s}$, perfect insertion (PI) at $0.66 \mathrm{~mm} / \mathrm{s}$, and decelerated insertion (DI) at $0.54 \mathrm{~mm} / \mathrm{s}$. Then, the applied MIT and axial force during insertion were measured using a custom-made device. MIT and ISQ were used to assess primary stability. The results of this study showed that MIT and ISQ did not differ significantly among the three groups ($p=0.138$ and $p=0.551$, respectively). Nonetheless, the axial force differed significantly among the three groups ($\mathbf{p}\lt 0.01$), with the mean maximum axial force for perfect insertion being $1.1 \mathbf{N}$ and for accelerated and decelerated insertions, 14 and -14.1 N, respectively. These findings imply that inaccurate insertion feed rate, although affecting the axial force, does not significantly affect MIT and ISQ in low-density bone. However, monitoring axial force during insertion can serve as an early indicator of inaccurate insertion feed rate, as MIT and ISQ alone may not detect inaccuracies. Other measurements, such as evaluating the extent of damage produced in each group, may shed more light on the insertion process.