Atrophic mandibular fracture treatment : prototyping as a tool in surgical planning

Introduction: Atrophic mandibular fractures are injuries found in old age due to facial trauma. Its treatment is a challenge, even for experienced surgeons, due to the different approaches that can be taken from clinical decisions. Taking into consideration the limitations that the age presented by most of the affected patients brigs, there are devices that stand out by seeking benefits in terms of predictability and time gain in the intraoperative period. The additive manufacturing is a valuable resource in the surgical planning and rehabilitation of these patients. Objective: To expose a clinical case that demonstrates the success in the use of surgical planning through a prototype printed in 3D technology. Clinical case: Elderly woman, 75 years old, victim of a fall from her own height who had a bilateral atrophic mandible fracture due to facial trauma. The surgical procedure was planned using a prototype printed in 3D technology providing predictability and reduced surgical time. The patient evolved in the postoperative period without complaints, with function immediately restores and without signs of infection or plate exposure. Conclusions: Atrophic mandible fractures are still related to a challenging treatment, therefore, adequate surgical planning and the use of auxiliary strategies such as 3D prototyping provide greater predictability of results, as well as time gain during the intraoperative.


Introduction
The edentulous mandible is more vulnerable to the occurrence of bone fractures, through trauma, due to the decrease in volume resulting from a series of biological mechanisms that cause the loss of the alveolar process. This phenomenon causes a progressive atrophy in this bone, weakening it (Wittwer et al., 2006;Brucoli et al., 2019; Maloney & Rutner, 2019).
The treatment of atrophic mandible fracture is considered challenging due to a number of characteristics, among which, those stand out: the age of the patient, who is often elderly, Development, v. 9, n. 9, e796997986, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i9.7986 4 with comorbidities associated with increased operative risks, compromised bone quality, reduced osteogenesis and fragments with reduced contact area that hinder the healing process (Wittwer et al., 2006;Shuker, 2015).
The open reduction of the fractures and the internal fixation are considered the gold standard of treatment and the most predictable method of managing atrophic mandibular fractures due to the benefits of recovering function immediately (Wittwer et al., 2006;Melo et al., 2011). Usually this type of fracture is fixed with a 2.4 system plate that exhibits an adequate mechanic resistance due to its thickness, this fact requires more time during the modeling process (Mardones, 2011).
The incorporation of health technology through image exams, such as computed tomography and magnetic resonance, allows the acquisition of images in three dimensions that provide a view of anatomical regions, contributing to the correct diagnosis and appropriate therapy for each patient (Liu et al., 2006;Rosa et al., 2004).
In recent years, Rapid Prototyping has demonstrated promise in helping medical and dental professionals to plan and execute surgical procedures. This technology is characterized by biomodels of human anatomy in 3D, created from the combination of the images obtained and computer systems, Computer Aided Design (CAD) and Computer Aided Manufacturing (CAM). Taking into account the area of actuation of Maxillofacial Surgery and Traumatology, the Rapid Prototyping provides benefits for preoperative planning and shortening surgery time (Safira et al., 2010).
The aging of the population turns the occurrence of this type of fracture an increasingly common event, consequently, it is necessary that the surgeons are prepared to make agile and satisfactory therapeutic decisions for the management of these patients. Thus, a clinical case is presented, in which the use of health technology through obtaining 3D prototyping was part of the planning process for the treatment of the atrophic mandible fracture through pre-modeling the plate that was used for a stable fixation of the fractured segments.

Methodology
This paper is characterized as descriptive observational case report. In the literature, scientific articles were searched, taking into consideration the theme addressed for review and support of the clinical case performed, through the Medline database, using PubMed and LILACS as search devices. Research, Society and Development, v. 9, n. 9, e796997986, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i9.7986
A study carried out in Russia (Pankratov & Melkumova, 2000) demonstrated that the occurrence of fractures in the elderly population occurs about 1.5 times more in edentulous patients than in those with toothed segments, being directly related to the fragility that affects the mandible in the process of physiological resorption of the alveolar ridge.
The most common etiology of mandibular fractures in elderly people was a fall in several studies in the literature (Nishiike et al., 2002;Brucoli et al., 2019;Melo et al., 2011), as well as how occurred with the patient of this case. Studies indicate that with adequate preparation and management, open surgical techniques regain function and bring immediate benefits to patients (Marciani, 2001;Wittwer et al., 2006;Melo et al., 2011). These characteristics are in common with the patient in the case described.
In the study conducted by Melo et al. (2011), 41,17% of the patients had bilateral mandible fracture. The most affected region was the mandibular body, followed by the parasymphysis region. Corroborating the described tomographic findings.
In Luhr class III jaws (where the thickness of the bone is less than 10 mm), the prominence of the chin, together with the dramatically thinner body and parasympathetic regions, determine a change in the biomechanics of mandibular fractures: in this case, the body and the parasymphysis become the most frequent regions of fractures (Brucoli et al., 2019). This information brought from the literature corroborates with the profile of the fractures that occurred with the treated patient, the thickness of the atrophic mandible was 8 mm, being characterized as a Luhr class III.
The extraoral approach during the surgical approach avoids the complete periosteal removal of the mandible, thus reducing risks related to infection or exposure of plates (Hachleitner et al., 2014;Brucoli et al., 2020). Still, in Luhr class III, the inferior alveolar nerve is found in the most superior part of the alveolar crest, hindering an intraoral approach (Brucoli et al., 2020). The risk of damage to the facial nerve is a negative factor mentioned in the literature, as a consequence of the extraoral approach (Aziz & Najjar, 2009), however, there was no damage to it during the extraoral approach.
The AO principles in the treatment of atrophic mandible fracture recommend the reduction of the fracture and the immediate restoration of function, indicating that they should