# Optimal Insertion Torque for Orthodontic Anchoring Screw Placement: A Comprehensive Review
## 4 Discussion
### Shapes and Dimensions of OASs
#### 4.2.2 OAS Dimensions  
The smallest OAS diameter in the selected studies was 1.3 mm, used in the buccal alveolar area in [PERSON] et al. [10]. They reported success rates of 87.5% and 72.7% for maxilla and mandible, respectively (Tables 2 and 3, Figures 2 and 3).  
An in vitro study by [PERSON] et al. [21] examined the mechanical properties of \(\varphi\)1.3 \(\times\) 7 mm OASs (self-drilling) using artificial bone with densities of 20, 30, and 40 pcf, and reported ITs of 3.9, 5.2, and 10.0 Ncm, respectively.  
An in vivo study by [PERSON] et al. [22] used \(\varphi\)1.3 mm OASs of different lengths (5.0, 6.0, and 7.0 mm) considering root proximity, and evaluated the ITs and success rates. They divided the OASs into three groups on the basis of ITs (\(<\)5 Ncm, 5.1-10 Ncm, and \(>\)10.1 Ncm) and reported the success rates of 100.0%, 80.0%, and 50.0% for 5.0 mm OASs; 96.3%, 88.9%, and 66.7% for 6.0 mm OASs and 96.2%, 100.0%, and 83.3% for 7.0 mm OASs, respectively, in the maxillary buccal alveolar area [22]. The values for the mandibular buccal alveolar area were 64.3%, 25.0%, and 50.0% for 5.0 mm OASs, 100.0%, 77.8%, and 40.0% for 6.0 mm OASs, and 100.0%, 75.0%, and 62.5% for 7.0 mm OASs, [22]. The smaller \(\varphi\)1.3 mm OASs tended to have higher success rates, and resultantly lower ITs in the maxilla and mandible.  
Large \(\varphi\)2.0 \(\times\) 6 mm OASs used in one study in the mid-palatal suture area had a success rate of 94.5% and the highest ITs (25.6 \(\pm\) 5.5 Ncm) [8] (Figure 4). An in vitro study by [PERSON] et al. [23] evaluated \(\varphi\)2.0 \(\times\) 9 mm OASs using pig pelvic bone and reported that the ITs for insertion depths of 4 mm, 5 mm, and 6 mm were 15.4 \(\pm\) 7.0 Ncm, \(26.2\)\(\pm\) 10.4 Ncm, and 27.2 \(\pm\) 14.1 Ncm, respectively. Considering these results [23], thehigh ITs of \(\varphi\)2.0 \(\times\) 6 mm OASs [8] may be appropriate for regions with high-density bone, such as the mid-palatal suture area.  
Another study used large OASs (\(\varphi\)2.0 \(\times\) 12 mm) at the infrazygomatic crest and the buccal shelf area and reported ITs and success rates of 10.1 Ncm and 91.7% for the infrazygomatic crest, and 10.3 Ncm and 100.0% for the buccal shelf area, respectively [10]. An in vitro study by [PERSON] et al. [24] measured the ITs of OASs (\(\varphi\)2.0 \(\times\) 12 mm) placed into artificial bone, assuming the placement in the infrazygomatic area, and reported that the IT for cylindrical OASs was 10.9 Ncm. These results were similar to [PERSON] et al. [10]. Nevertheless, further in vivo studies are required to determine the optimal IT for longer OASs.  
[PERSON] et al. [6] evaluated the shorter \(\varphi\)1.7 \(\times\) 3 mm OASs placed in two maxillary buccal alveolar areas (between the canine and the first bicuspid, and between the second premolar and the first molar) and reported ITs of 7.4 \(\pm\) 1.9 Ncm and 7.8 \(\pm\) 1.2 Ncm and success rates of 64.3% and 70.0%, respectively (Table 2, Figure 2). In an in vitro study, [PERSON] et al. [25] compared \(\varphi\)1.75 mm OASs of different lengths (3.0 mm and 6.0 mm) in synthetic bone and reported that longer OASs (6.0 mm) had significantly higher ITs than shorter OASs (3.0 mm). They also reported that as the cortical thickness or the bone density increased, this tendency also increased [25]. Thus, shorter OASs of 3.0 mm in length seemed to have lower ITs. Lower success rates (64.3-70.0%) of these OASs (3.0 mm) reported by [PERSON] et al. [6] (Table 2, Figure 2) might also be explained in this way. The authors would, therefore, like to recommend the use of OASs with a 3.0 mm length as a second option in anatomically difficult areas, such as small inter-root distances.