# The Effect of Insertion Angles and Depths of Dental Implant on the Initial Stability
## 4 Discussion
[45] contendedthat using only one approach to measure primary stability is not sufficient; therefore, this study used both ISQ and PTV to assess the primary stability of dental implants. Many dental implant fixture manufacturers had launched tilted implant products [17]. [PERSON] et al. analyzed numerous clinical studies on tilted implants before 2014 and discovered that the angles ranged from 11\({}^{\circ}\) to 45\({}^{\circ}\)[17]. In addition, scholars had noted in many clinical studies on maxilla and mandibles [18; 23; 31; 46; 47] that the angle of the tilted implants was less than 45\({}^{\circ}\). Therefore, two angled abutments (17\({}^{\circ}\) and 30\({}^{\circ}\)) were chosen for the experiment in this study. The adopted insertion depth was based on the clinical study of [PERSON] and [PERSON] [22], which mentioned two levels of insertion depth for titled implants, namely the distal subcrestal position and the mesial supracrestal position. Inserting implants at the distal subcrestal position may lead to deep pockets, whereas inserting them at the mesial supracrestal position may cause mucosal recession and exposure of the textured portions of implants. Therefore, the evencrestal position, distal subcrestal position, and mesial supracrestal position were chosen as the insertion depths for the experiment in this study. Investigation of the correlation between the PTV and ISQ of vertical inserted fixtures (Group 1) revealed that PTV and ISQ were highly correlated (\(r=-0.85\), \(p=0.04\)). This also confirmed the results of the experiments by [PERSON] et al. [48] and [PERSON] et al. [44], noting that the PTV and ISQ of inserted fixtures displayed a highly negative correlation (\(r=-0.8\)-\(0.9\) and \(r=-0.97\), respectively). The experimental results demonstrated that ISQ for both tilted implants (17\({}^{\circ}\) and 30\({}^{\circ}\)) and vertical implants measured in each test direction exhibited no significant difference (Table 1). This may be because the tilted implants have had different contact areas with the superior artificial cortical bone at different depths, but their contact areas with the inner artificial cancellous bones were almost the same. Some studies had noted that ISQ was less affected by the superior cortical bone and was more affected by the inner cancellous bone [36]. Therefore, ISQ exhibited no significant differences in each test direction, regardless of the degree of implant tilt. Additionally, in a clinical report from 2014, [PERSON] et al. [49] conducted primary stability tests on tilted implants in patients with edentulism using various directions, and their results also indicated no significant difference between the ISQ of the buccal-lingual and mesial-distal directions. Regarding the PTV measurement results of tilted implants along all directions, the PTV measured from the distal side was significantly smaller than that measured from the mesial side, in both 17\({}^{\circ}\) and 30\({}^{\circ}\) tilted implants (Table 2, Figures 4 and 5). The reason may be that more skin on the mesial side was removed following the dental implant manufacturer's suggestion for pilot holes, resulting in a gap between the platform and the bone. When the dental implant fixture was tapped from the distal direction (from the distal side to the mesial side), it thus fell toward the mesial side. The gap at the mesial side caused a longer rebound time for the fixture, resulting in a greater PTV value, and thus, a less stable result, as indicated by the PTV of the primary stability. Regarding the effect of tilted implants on the PTV, [PERSON] et al. [45] performed 59 vertical implants and 41 fixture placements at 30\({}^{\circ}\) on patients with edentulism and compared the results that indicated that tilted implants yielded a greater PTV than vertical implants. In other words, the stability of tilted implants was inferior to that of vertical implants. However, some studies have noted that tilted implants do not affect stability. [PERSON] et al.