Additive Manufacturing for Surgical Planning of Mandibular Fracture

Abstract

Currently, imaging techniques such as Computed Tomography with three-dimensional reconstruction (3D) and Magnetic Resonances are being routinely used in pre-surgical planning in all fields of medicine. Nowadays, virtual three-dimensional images, commonly displayed on two-dimensional surfaces, such as the computer screen, can be used to produce rapidly prototyped models, with excellent dimensional accuracy and fine reproduction of anatomical structures, providing professionals with the ability to use the biomodel in planning and simulating medical and dental procedures (oral and maxillofacial surgery, making individualized facial implants and prostheses, measurements and previous adaptations of prefabricated fixation plates), thus contributing to considerable reductions in surgical time and consequently the duration of anesthesia, minimizing infection risks and reducing hospital costs. In this report, we describe a case of surgical planning and treatment of bilateral atrophic mandibular fracture, in which, for surgical planning, authors used Rapid Prototyping as an adjunct tool, considering the advantages already outlined.

INTRODUCTION

The field of dentistry is constantly evolving and changing to best suit patient needs. The progress in medical and dental technology has been made, particularly in imaging technologies. The incorporation of new technology in dentistry has improved the way we serve our patients, and we have just begun to see the impact of advanced modalities such as computed tomography and MRI that have replaced conventional radiographs. These technologies enable to obtain a three-dimensional (3D) view of anatomical regions of surgical interest, as well as provide physicians with important information needed for diagnosis and appropriate therapy of each patient (1-3).

However, 3D images exhibited on 2D displays are not clear enough to provide a thorough understanding of the patient’s anatomy, requiring the professional to mentally reconstruct the 3D geometry generated in the computer (2).

Recently, new technologies such as Rapid Prototyping (RP) have emerged, thus helping professionals in medical-dental field to both plan and perform surgical procedures. RP is a technology increasingly present in dentistry. In this field, 3D human anatomy biomodels are created, in micron-accuracy, from the combination of medical and dental imaging with computers (CAD - CAM) systems. The RP-based biomodels fabrication assumes great importance in Oral and Maxillofacial Surgery and Implantology, by allowing better surgical planning, and shortening surgery time interval (4).

The images captured from computed tomography (CT) or magnetic resonance imaging (MRI) in DICOM format (Digital Imaging and Communications in Medicine) are processed in specific programs, creating a three-dimensional (3D) data set in STL format (Stereolithography) sent to the Rapid Prototyping stations, where the prototypes are built through the CAM system (Computer Aided Manufacturing) (5).

The biomodels are used in measurement of anatomical structures, osteotomies and resection techniques simulation as well as in a thorough planning of oral and maxillofacial surgery (6). Prototyping is frequently used in interventions that require a detailed planning, as in case of severe trauma patients, loss of structure by pathological lesions (7), orthognathic surgery (8) and implantology (9). Its use reduces the procedure time interval, the period of anesthesia and the risk of infection.

The treatment of atrophic edentulous mandible fractures in individuals is a challenge to maxillofacial surgeons. In most cases, these fractures occur to the elderly, in whom the bone regeneration process is physiologically decreased, local vascularization is reduced and poor quality of the jaw bone is often insufficient for proper fixation. Since elderly populations are growing faster than any other age group year by year the professionals’ attention is being required to provide appropriate treatment and reduction of fractures associated with atrophic jaw edges, characterized by low bone mass, in cases that often require surgeons to make use of more rigid mounting material (2).

These facts should be considered: an aging population undergoes structural and functional changes; due to the coexistence of systemic diseases the elderly are predisposed to various types of trauma. In addition, longer longevity and more active lifestyles lead to an increase in head trauma in these individuals, therefore, specialized and more expensive health is required care when compared to younger patients (1, 6).

The increase in the number of edentulous patients with atrophy of the alveolar ridge has become a serious problem for the rehabilitative dentistry.

This particularly relates to the fields of maxillofacial surgery and traumatology so that various therapeutic possibilities are suggested, ranging from the most conservative treatment, such as bloodless approach with the use of gutters, to more invasive procedures such as reduction and bloody fixing, along with bone grafting (10).

When treatment option is open reduction, fixing this kind of fracture is commonly performed with 2.4 mm plate system, since these plates exhibit satisfactory mechanical strength due to their thickness, which makes them more resistant during the modeling process (11).

This article aimed to present a case report of a bilateral mandibular fracture in a geriatric patient due to motorcycle accident, treated by the open reduction and functionally stable fixation method, based on criteria for reduction and fixation of atrophic edentulous mandible fracture, considering the principle of load-bearing. Surgeons decided to use a biomodel for surgical planning, obtained from stereolithographic process, facilitating the pre-modeling of a reconstruction plate system.

CASE REPORT

A seventy-one year-old male patient, motorcycle crash victim, was treated in a public hospital in Campina Grande, Paraíba, Brazil. Physical examination revealed swelling and bruising in the chin region and edentulism along with mandibular asymmetry and bone crackling. A bilateral mandibular fracture in parasymphysis region was observed during imaging analysis (Figure 1, a/b).

Figure 1.

a/b CT scan showing a bilateral mandibular fracture

Three dimensional CT scanning was performed on the patient, using the following parameters: 120KVp, 150mA, matrix 512×512, field of view (FOV) 14 cm × 18 cm, Pitch 1:1, 1.0 mm slice thickness, reconstructed slice increment of 1.0mm, reconstruction algorithm (Bone). All computer tomography images were saved in DICOM format and then, sent to 3D Technologies Laboratory of the Center for Strategic Technologies in Health at the State University of Paraíba. The DICOM series were imported into In Vesalius software (12) where the segmentation of the region of interest was performed. The 3D model was converted into STL format and sent to the 3D Printing System (Objet Connex 350 / Stratasys Ltd.), which used the Objet Verowhite Plus resin to fabricate the biomodel. The machine's printing resolutions were 600 dots per inch (dpi) in both the x and y axes and 1600 dpi in the z axis. The accuracy of the machine is up to 0.1 mm. The construction took about 9 hours to complete.

The previous modeling of the 2.4 mm reconstruction plate allowed far better circumstances for its improved adaptation to the anatomical contours of the region, enabling the reduction of surgical time and a better patient functional recovery (Figure 2, a, b).

Figure 2.

a/b Patient biomodel reproducing the bilateral mandibular fracture and pre-modeling of a 2.4 mm titanium plate

The treatment of fractures was performed through surgery under general anesthesia with orotracheal intubation. Surgeons performed the procedure through extra-oral access, bilateral submandibular, surgical reduction and fixation of the fracture (Figure 3, a).

Figure 3.

a/b Exposure of mandibular fractures and fixation using a 2.4 mm titanium plate and nine cortical screws

It was observed that the prototype reproduced the anatomy of the area to be operated with high precision, since the adaptation of the plate to the patient was extremely accurate and smooth (Figure 3, b).

In the course of tomographic analysis, the postoperative images showed a reduction and fixation with satisfactory alignment of bone fragments and a good adaptation of the reconstruction plate (Figure 4).

Figure 4.

CT scan showing postoperative appearance

DISCUSSION

During the research in which the results of the patients who underwent atrophic edentulous mandible fractures treatment, conducted through an extra-oral approach (open reduction) with internal fixation were analyzed, it was observed that this approach enabled immediate masticatory rehabilitation, reaching good results and a low percentage of complications (13-15)

In the present case report, surgeons decided to perform open reduction with internal fixation under general anesthesia with the purpose to improve patient functional capacity and promote better outcomes

Considering the costs related to functional, aesthetic and social rehabilitation of patients with facial deformities, due to factors such as long hospital stay, number of required reconstructive surgery and time of surgical teams (16) as well as considering the risks regarding general anesthesia, the surgeons chose a procedure that could mitigate these factors. The use of a mandibular biomodel, upon which the reconstruction plate was modeled, has shortened surgical time for about an hour.

Rapid prototyping biomodels manufacturing is a recent technology, with great importance in oral and maxillofacial surgery. However, some complexity is involved in this process, mainly because it requires intense interaction between biomedical and engineering sciences (4, 17).

The good quality of the tomographic image and its appropriate handling by the In Vesalius software facilitated printing a prototype reliably in this case, allowing a more accurate diagnosis and, consequently, a better surgical planning. Furthermore, the printing technology used in this case was PolyJet. Data from a survey aimed at analyzing the accuracy of selective laser sintering, three-dimensional printing and PolyJet technologies in the production of biomodels, showed that the accuracy of the PolyJet was higher when compared to the others, providing greater detail of anatomical structures and precision (18).

A recent systematic review analyzed 158 articles published between 2005 and 2015, focused on 3D printing applications in surgery and they confirmed the fact that the main advantages of this technology are the possibilities of preoperative planning (48.7%), the accuracy of the process used (33.5%), and the saving operating time (32.9%). The surgeons who performed surgery described in this paper were familiar with these advantages (19). Finally, the authors understand that the use of rapid prototyping is still restricted in some parts of the world, such as Brazil, because it is a costly diagnostic tool which requires the use of a sophisticated and complex technology chain, from image acquisition up to the final shape of biomodel itself. However, the use of this therapeutic approach can improve surgical planning in order to improve treatment quality, patient comfort and professional safety by reducing hospital costs and risks during and after surgery.