## 4 Discussion
The American Society for Testing and Materials F-1839-08 \"Standard Specification for rigid Polyurethane Foam for Use as a Standard material for testing Orthopaedic devices and instruments\" states that \"the uniformity and consistent properties of rigid polyurethane foam make it an ideal material for comparative testing of bone screws and other medical devices and instruments\" [23]. In addition, [PERSON] et al. [24] suggested that artificial bones can replace fresh frozen cadaver bones in research evaluating jaw biomechanics [25]. Most research employing artificial bones to examine fixation techniques in sagittal split ramus osteotomy have used artificial semimandibular bone models, such as in the studies by [PERSON] et al. [17], [PERSON] et al. [25], [PERSON] et al. [16], [PERSON] et al. [21], [PERSON] et al. [18], [PERSON] et al. [26], and [PERSON] et al. [20]. [PERSON] et al. [10] and [PERSON] et al. [19] are among the few using complete mandibular models to conduct in vitro mechanical tests. [PERSON] et al. [10] divided mandibular models into five groups, apart from the control group, with all other models categorized into four groups according to screw and plate fixation techniques applied on them. Subsequently, they performed a BSSRO to advance the mandible by 7 mm and conducted a mechanical test by applying force on the incisal and molar regions. The same study revealed that, regardless of whether in the incisal or molar region, the four experimental groups were all significantly different from the control group regarding their yield loading performance. Among the four experimental groups, only the group with the inverted L-type bicortical screw fixation met the clinical demand for occlusal loading. Furthermore, the force applied in the incisal region exerted a larger influence on the screws and plates at the bone cut site than the force applied in the molar region did. Accordingly, the present study applied force in the incisal region to compare the performance of the three fixation techniques. According to previous studies using either complete mandibular models for tests [10] or models of only one side of the mandible [16], the resistance facilitated by the straight plate fixation approach was lower than that facilitated by the inverted L-type three-bicortical screw fixation approach. In the present study, the results for Groups 1 and 3 were consistent with those in these studies. The resistance force of Group 2 differed non-significantly from that of Group 3 in displacing the mandibular incisal region by 1, 3, and 5 mm. The two groups yielded significantly different data at a displacement of 10 mm, and both groups had a resistance force of more than 100 N. In clinical practice, the muscles at the surgical site are temporarily shortened, and are in a traumatized state during the initial postoperative phase after orthognathic surgery; hence, the occlusal force in this phase is considerably lower than that before surgery. Such a temporary change in occlusal force facilitates natural protection against osteosynthesis segment displacement for overall stability in patients in the postoperative recovery phase after orthognathic surgery. Orthognathic surgery is an elective operation and surgeons should always be alert enough to avoid the risk of unnecessary complications, such as the neurosensory disturbance of lingual nerves. The rates of lingual nerve injury varies; 9%-19% according to literature by [PERSON] et al. [27] and [PERSON] et al. [28]. The placement of excessively long bicortical screws on the superior border of mandibular angle might damage lingual nerve, however, the use of monocorical plate and screw fixation prevents this complication. There are always pros and cons regarding all surgical techniques or procedures. Regardless of fixation protocols, either rigid or non-rigid; with or without positioning devices, the displacement of mandibular condy during ramus osteotomies is inevitable and must be kept as minimal as possible to prevent TMJ arthropathy, thereby leading to immediate or delayed relapse.