## 4 Discussion
The distance between the mandible and concrete block was less when the pitch angle was \(10^{\circ}\) compared with \(20^{\circ}\), indicating higher stress was obtained with a pitch angle of \(10^{\circ}\). The condylar process and upper region of the mandibular angle of the impacted side were the most common sites of mandibular fractures. A previous study reported higher stress at impact on the alveolar and mandibular body, which are common fracture sites, after frontal impact on the mandible [21]. These phenomena were related to direct and indirect forces. When direct forces are applied to the front side of the mandible, the mandibular body is fractured. During contact, indirect forces are applied backward to the alveolar region. The present study demonstrated that even after a lateral impact, direct and indirect forces are involved in fractures. These forces were mainly applied to areas surrounding the upper region of the mandibular angle, leading to a subsequent fracture at this site. Generally, the third molar is present at this site, and this might contribute to the increased vulnerability of the mandible because the mandible loses some of its bony structure by the third molar [12; 22]. [PERSON] et al. [23] reported that fractures of the mandibles of monkeys with a third molar required less force compared with those without a third molar (60% of the required forces). Therefore, fractures of the upper part of the mandibular angle occur frequently after a direct lateral impact. At impact, the attackedside of the lateral body of the mandible is deflected to the opposite side, and higher indirect stress occurs at the condylar. The present study is the first to clarify the biomechanical mechanisms related to the common fracture site in the mandible after a lateral fall, using a sophisticated whole-body FE model. The results obtained herein may be useful when managing patients. According to the patients' and witnesses' testimonies, if the patient falls laterally and the face makes contact with a protruding object, medical professionals can predict fractures of the upper part of the mandibular angle and the condyle of the affected side. Furthermore, this information may be useful for paramedics in that they may predict the site of mandible fractures and transport patients to appropriate medical institutions with maxillofacial surgeons. The present study reconstructed the mandibular fractures in older adults that were caused by falling laterally. Once a mandibular fracture occurs, a long hospital stay with surgery is required. According to an analysis of cyclists and motorcyclists with oral and maxillofacial injuries, the number of fractured lines and intermaximillary fixation were independent factors for long-term hospitalization [6]. Another study on patients with oral and maxillofacial injuries by falling or falls from a height suggested that the number of injured teeth and intermaximillary fixation were significant factors affecting the duration of treatment [7]. Therefore, if an individual falls laterally and the face is affected, long hospitalization is necessary. Long hospitalization by the elderly may result in frailty, such as a decline in muscle and cognitive function. Therefore, strategies to avoid falling, such as using a stick and daily exercise to prevent frailty, are recommended. Furthermore, in older adults who frequently fall, the use of a facial guard is recommended. Based on the present results, effective preventive measures need to be established in order to maintain the quality of life of older adults. This study had some limitations. First, lateral falls were modeled from a height of 1.0 m. This height was chosen to represent a situation where an older person fell laterally from a standing position. However, there may be a variety of initial positions, such as a semi-standing position. Therefore, in the future, similar simulations should vary the initial falling height or initial body position. Second, a concrete block of a certain size was modeled.