## 2 Materials and Methods  
This work is a prospective study that shows the in-house digital workflow for the management of complex fractures in atrophic edentulous mandibles. The study was conducted in the period between October 2020 and March 2021 on patients admitted to the Maxillo-Facial Surgery Unit of Federico II University Hospital in Naples. The study met the criteria established by the Declaration of Helsinki and was approved by the Ethics Committee of the Federico II University hospital of Naples with protocol number 373/19. The patients enrolled in the study satisfied the following inclusion criteria:  
* post-traumatic communiuted mandibular fractures verified with a CT scan within 12 h from the trauma
* atrophic edentulous mandible
* unavailability of the patient's personal dental prostheses that could guide the occlusion; written informed consent to undergo the surgical procedure  
Patients who met the following criteria were excluded:  
* previous surgically treated mandibular fractures
* patients who have refused surgical treatment
* partial edentulism
* taking drugs that affect bone resorption  
Among nine patients likely to be enrolled, only four patients satisfied the inclusion criteria and were enrolled in the study; two patients presented partial edentulism but enough to allow a fracture reduction based on the occlusion; one patient had tumour pathologies and took bisphosphonates medications, causing a poor bone quality; one patient refused surgical treatment; one patient previously underwent surgical treatment for mandibular neoplasia. Among the four patients enrolled in the study, a computer-assisted digital workflow was settled to perform the virtual reduction of the fractures and to finalize a patient specific plate (PSP) to fix the mandible. For each patient, the same CAD/CAM based workflow was applied as defined below:  
(1) Digital Imaging and Communications in Medicine (DICOM) to Stereolthyography (STL) files: by using Materialize Mimics Medical 21.0 software (Technologielaan 15,3001 Leuven, Belgium) to perform the virtual reduction. The first step was to upload the DICOM-Files to generate a 3D model of the patient. Then, the segmentation of bone fragments was possible thanks to the New Mask tool. Generally, the range of bone threshold was between 0-1250 HU. Once the first step was completed, a three-dimensional image of the entire splanchonceranium was obtained. The division of each bone fragment was needed to proceed with the simulation of the fracture reduction. Therefore, in the second step, the Split Mask tool allowed to divide of the main mask into single segments for each bony fragment. In this way, each fragment could be repositioned virtually mimicking the fracture reduction, while the optional function Smart Fill was used to fill the bone cavities. The process of identification of the fracture lines was performed by three different maxilla-facial surgeons (VA, UC and ST). The produced images were then converted into \"objects files\". Using the 3-Matic Medical 3D (Materialise, Leuven, BE) it was possible to convert the stumps into a 3D plan and obtain a virtual reduction with the stumps in the correct anatomical position. To avoid any bias, three different maxillofacial surgeons (VA, UC and ST) also performed the procedure. The reduction was obtained by considering the alignment of the condyles in the glenoid fossa. At the end of the procedure, the virtually reduced mandible file was converted into a STL file adapted for the \"Formlab-Form 3B\" 3D printer (Figure 1a,b). (2) In House Rapid prototyping 3D Print--Resin model and 2.4 reconstruction plate modelling: a specific slicing software (PreForm 3D Printing Software--Formlabs 3B+) was used to set the model for 3D printing. It was necessary to use the supports to have the highest possible quality of the model (Figure 1c). A resin Stereo-Lithography Apparatus (SLA) 3D printer (Formlab-Form 3B+, located in Somerville, MA, USA) was used for in-house rapid prototyping.