# Optimal Insertion Torque for Orthodontic Anchoring Screw Placement: A Comprehensive Review
## 4 Discussion
### Placement Location
#### 4.3.2 Mid-Palatal Area  
OAS placement in the mid-palatal area is used for various purposes, such as the retraction of anterior teeth and intrusion, distalization, and protraction of molars in the maxillary arch [28]. OAS placement in this area is also considered anatomically more favorable than the interproximal area [29]. However, as reported by [PERSON] et al. [30], the sutured depth of mid-palatal suture should be considered using adequate imaging, such as cone-beam computed tomography, before OAS placement because there could be incomplete suture closure even in adults. Concerning this matter, they concluded that the OAS placement in mid-palatal sutures should be avoided regardless of age to prevent the insertion into unsuutured areas.  
The mid-palatal area has a thicker cortex, especially close to the median suture, which often requires pre-drilling before OAS placement for IT control [8; 15]. [PERSON] and [PERSON] [15] used both cylindrical and tapered OASs (\(\varphi\)1.5 mm) in this area and reported lower ITs for the former. Cylindrical OASs had ITs and success rates of 14.5 \(\pm\) 1.6 Ncm and 100.0%, respectively. For tapered OASs, [PERSON] and [PERSON] [15] and [PERSON] et al. [8] reported ITs and success rates of 21.1 \(\pm\) 2.2 Ncm and 100.0% (\(\varphi\)1.5 mm OASs), and 25.6 \(\pm\) 5.5 Ncm and 94.5% (\(\varphi\)2.0 mm OAS), respectively. Thus, a greater IT is indicated, even for OASs with smaller diameters, such as 1.5 mm, in this area (Table 2, Figure 4).  
In an in vitro study, [PERSON] et al. [26] reported that the maximum torques at the time of fracture for \(\varphi\)1.5 mm and \(\varphi\)2.0 mm OASs were 20.1 \(\pm\) 3.8 Ncm and 49.2 \(\pm\) 7.5 Ncm, respectively. In an in vitro study by [PERSON] et al. [27], the yield torque to fracture for \(\varphi\)1.5 mm OASs was 16.3 \(\pm\) 1.6 Ncm. Based on these studies, the ITs of 21.1 \(\pm\) 2.2 Ncm for \(\varphi\)1.5 mm OASs reported by Suzuki and Suzuki [15] exceeded the yield torque. Therefore, the use of \(\varphi\)2.0 mm tapered OASs with ITs of 20-25 Ncm is thought to be suitable in the mid-palatal suture area.  
In the paramedian area, [PERSON] et al. [12] reported ITs and success rates of 16.0 \(\pm\) 5.2 Ncm to 18.1 \(\pm\) 5.6 Ncm and 98.8%, respectively, for tapered OASs (\(\varphi\)1.7 \(\times\) 8 mm) (Table 2, Figure 4). [PERSON] et al. [31] also assessed the stability of OASs (\(\varphi\)2.0 \(\times\) 9 mm) and reported ITs of 14.1 \(\pm\) 4.6 Ncm in the paramedian area. IT values in this area were likely to be lower than in the mid-palatal area. [PERSON] et al. [32] also investigated the total and cortical bone thickness in the palate and demonstrated that the thickness tended to decrease laterally from the mid-palatal suture. Due to differences in the cortical thickness, ITs appeared to be lower in the paramedian area compared to the mid-palatal suture area. Further, [PERSON] et al. [27] reported that the yield torque to fracture for \(\varphi\)1.7 mm OASs was approximately 20 Ncm. Consequently, ITs of 12-18 Ncm were considered to be appropriate for \(\varphi\)1.7 mm tapered OASs in the paramedian area.