# Impact of Implant Design and Bone Properties on the Primary Stability of Orthodontic Mini-Implants
## 4 Discussion  
This study was focused on the impact of bone quality and the impact of mini-implant design (its length, diameter, and threading) on primary stability. The highest average pull-out force (F\({}_{\text{Mean}}\) = 252.12 N) was found in a Tomas-pin mini-implant with a 1.6 mm-diameter and 6 mm-length at CBTC \(\geq\)0.68 mm, while the lowest average pullout force (F\({}_{\text{Mean}}\) = 113.50 N) was found in a Perfect Anchor mini-implant with a 1.4 mm-diameter and 8 mm-length at CBTC <0.62 mm. Regardless of the type of implant, the average pullout forces were found to be higher for the CBTC between 0.62-0.67 mm on average, compared to the CBTC <0.62 mm, where the measured force averages were found to be lower. A number of other studies also lead to similar conclusions; namely, the success of a mini-implant depends largely on the cortical bone thickness (CBTC) [19; 20]. Experiments performed on animals have shown that a mini-implant's stability is determined by the quality and quantity of the bone into which the implant is inserted [9; 16]. A visual observation made in our study showed that slightly larger differences occurred in averages at the same CBTC with the Perfect Anchor 1.4 mm \(\times\) 8 mm implant. It could be said that the higher pulling force is more inherent to the thicker cortex, and vice versa. However, in cases where the CBTC is \(\geq\)0.68 mm, such regularity (the greater the CBTC, the higher the pulling force) was inherent only to the Tomas-pin 1.6 mm \(\times\) 6 mm implant, while the Perfect Anchor 1.6 mm \(\times\) 8 mm and 1.4 mm \(\times\) 8 mm implants showed no such noticeable regularity. The Perfect Anchor 1.6 mm \(\times\) 8 mm implant had a lower average value at CBTC \(\geq\)0.68 mm compared to CBTC 0.62-0.67 mm and CBTC <0.62 mm, while the Perfect Anchor 1.4 mm \(\times\) 8 mm implant had a higher average value of the pullout force at CBTC \(\geq\)0.68 mm compared to CBTC <0.62 mm, although as a result it had a lower pullout force compared to the CBTC 0.62-0.67 mm. An analysis of the standard deviation values associated with the pullout forces of the three types of mini-implants at different CBTC values (Table 2) showed that variations of the pullout forces were more often present at CBTC \(\geq\)0.68 mm compared to other CBTC values, regardless of the type of mini-implant. Table 3 shows the post-hoc results of the Scheffe test of later comparisons made between the types of mini-implants. A statistically significant difference in the average values of the pullout force was confirmed between the Perfect Anchor 1.4 mm \(\times\) 8 mm implant and the Tomas-pin 1.6 mm \(\times\) 6 mm implant (\(p\) < 0.020), and between the Perfect Anchor 1.6 mm \(\times\) 8 mm implant and the Tomas-pin 1.6 mm \(\times\) 6 mm implant (\(p\) < 0.028), whereas the difference was not found to be statistically significant between the Perfect Anchor 1.4 mm \(\times\) 8 mm implant and the Perfect Anchor 1.6 mm \(\times\) 8 mm implant (\(p\) < 0.991). \begin{table}
\begin{tabular}{c c} \hline \hline
**Factors** & **(\(p\)-Values)** \\ \hline Pitch & 0.015 \\ Depth & 0.015 \\ TSF & 0.015 \\ \hline F—pulling force. & \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Results of the variance analysis for the TSF shape factor, depth, and pitch. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Mini-Implants** & **Depth (mm)** & **Pitch (mm)** & **TSF** \\ \hline Korean Hubit & & & \\ Perfect Anchor 1.6 \(\times\) 8 mm & 0.272 (0.016) & 0.800 (0.004) & 0.340 (0.021) \\ Korean Hubit & & & \\ Perfect Anchor 1.4 \(\times\) 8 mm & 0.303 (0.005) & 0.799 (0.006) & 0.380 (0.006) \\ Dentaurum & & & \\ Tomas 1.6 \(\times\) 6 mm & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Depth, pitch and TSF average values and standard deviations by type of mini-implant.