# Optimal Insertion Torque for Orthodontic Anchoring Screw Placement: A Comprehensive Review
## 4 Discussion
### Placement Methods (Self-Drilling or Self-Tapping)  
ITs and success rates of OASs placed in the buccal alveolar and mid-palatal areas are listed in Figures 2-4. However, data from one study [10] were not included because the data for \(\varphi\)1.3 mm and \(\varphi\)1.5 mm OASs in the buccal alveolar area were unified, and separate values were not available. Figure 2: Insertion torques (ITs) and success rates according to OAS features in the maxillary buccal alveolar area. Explanations for each bar graph in the figure were listed in the following order: screw dimensions, screw form, authors, and published year [1; 6; 7; 9; 11; 13; 14; 15]. Figure 4: Insertion torques (ITs) and success rates according to OAS features in the mid-palatal area. Explanations for each bar graph in the figure were listed in the following order: screw dimensions, screw form, authors, and published year [8, 12, 15]. Figure 3: Insertion torques (ITs) and success rates according to OAS features in the mandibular buccal alveolar area. Explanations for each bar graph in the figure were listed in the following order: screw dimensions, screw form, authors, and published year [7, 9, 13, 15]. In self-drilling OASs, the ITs ranged from 6.0 \(\pm\) 3.2 Ncm [9] to 21.1 \(\pm\) 2.2 Ncm [15], while the success rates ranged from 64.3% [6] to 100.0% [10; 15]. Thinner, cylindrical, \(\varphi\)1.5 mm OASs had the lowest ITs [9], whereas the highest ITs were in the mid-palatal area [15]. Thus, IT in self-drilling OASs was affected not only by OAS diameter but also by the placement site. Short 3.0 mm OASs had the lowest success rates [6] (Tables 2 and 3). Therefore, short, self-drilling OASs were found to increase the risk of failure. Regarding self-tapping OASs, [PERSON] et al. [7] used tapered \(\varphi\)1.6 \(\times\) 8.0 mm OASs in the upper and lower buccal alveolar areas. In their study, OASs with a 1.0 mm pilot hole in maxilla (diameter ratio: bone drilling diameter/screw diameter \(\times\) 100 [%] = 62.5%) and a 1.3 or 1.4 mm pilot hole in the mandible (diameter ratio = 81.3-87.5%) showed ITs and success rates of 7.6-8.9 Ncm and 91.8-95.0% in the maxilla and 8.5-8.8 Ncm and 91.9-100.0% in the mandible, respectively (except for the early-loading adolescent group) [7] (Tables 2 and 3, Figures 2 and 3). They also stated that the pilot-hole diameter in the mandible was extended from 1.3 mm to 1.4 mm when IT exceeded 10 Ncm depending on bone stiffness or cortical bone thickness. ITs and pilot-hole diameters are likely to affect the success rates in self-tapping OASs [7]. In the mid-palatal area, tapered \(\varphi\)2.0 \(\times\) 6 mm OASs placed into 1.2 mm (diameter ratio = 60.0%) and 1.5 mm pilot holes (diameter ratio = 75.0%) had success rates of 94.5% (IT = 25.6 \(\pm\) 5.5 Ncm) and 83.0% (IT not available), respectively, with a significant difference [8] (Table 2). Therefore, it is suggested that the IT should be controlled, using different pilot-hole diameters in different placement sites with varying cortical bone thickness, to prevent bone and OAS fracture. [PERSON] et al. [14] compared the two placement methods in the maxillary buccal alveolar area using tapered OASs (\(\varphi\)1.6 \(\times\) 8 mm) and found no significant differences in ITs and success rates between self-tapping (1.0 mm pilot hole) and self-drilling OASs (Table 2). In contrast, [PERSON] and [PERSON] [15] also examined ITs in \(\varphi\)1.5 \(\times\) 8 mm self-drilling (tapered) and self-tapping OASs (cylindrical; 1.1 mm pilot hole) and reported that self-drilling OASs had higher ITs than self-tapping OASs in the maxillary buccal alveolar area [15] (Tables 1 and 2). This contradiction between the results of two studies [14; 15] may be explained by the differences in OAS characteristics. One important difference was the diameter ratio for self-tapping OASs (62.5% in the [PERSON] et al. [14] study). The tightness for tapered OASs could increase the IT and may be considered equivalent to the ITs observed in self-drilling OASs.