Dr Saloni Mistry, Dr Omkar Shete, Dr Shalu Shah, Dr Gauraja Kadam, Dr Ankita Walke
Professor and HOD,
Second year Post Graduate Student,
First year Post Graduate Student.
Y.M.T Dental College and Hospital, Kharghar.
The goals in reconstructing mandibular discontinuity defects are to provide architectural support to restore and preserve lower facial contour and occlusal relationships. Patients with unrestored mandible have cosmetic disfigurement, compromised function, and difficulty in socializing. A wide variety of methods have been reported to reconstruct these defects with osseous grafts harvested from various donor sites like ilium, radius, metatarsal, scapula, and fibula.
However, each of these donor sites has significant limitations related to the length of available bone or the reliability of the associated soft tissue. The advantages of the fibula as a donor site are not limited to the surgical aspect, but with the use of technology as an adjunct to a surgical procedure in the form of a 3D printed stent; the prosthetically driven placement of the fibular graft is now possible. Computer-aided design/computer-aided manufacturing (CAD/CAM) technology has recently opened new frontiers in maxillofacial bone reconstruction.
The crucial role of a Prosthodontist is to guide the fabrication of surgical stents manually or by 3D printing, which helps oral surgeons to contour the fibular grafts for favorable functional and harmonious prosthodontic rehabilitation in terms of occlusion.
This article overviews the metamorphosis of rehabilitation procedures from the conventional free fibular grafts approach to a novel approach of rehabilitating the mandible with pre osseointegrated implants using a 3D printed stent.
Citations : Mistry S, Shete O, Shah S, Kadam G, Walke A.JAW IN A DAY - A Fibular Reconstruction of The Mandible. J Prosthodont Dent Mater 2020;1(1&2): 10-18.
Resection of a part or complete mandible is a treatment modality for many pathological conditions. Patients with unrestored mandible have cosmetic disfigurement, compromised function and difficulty in socializing. The microvascular fibula free flap popularized by Hidalgo has become one of the most significant advances in reconstructing the maxillofacial region. The conventional process of rehabilitation demands time and meticulous sequential procedures to be followed.
However, with the use of technology as an adjunct to a surgical procedure in the form of 3D printed stents and virtual planning, the prosthetically driven placement of the graft and implants makes this approach more accurate, predictable and also considerably decreases the time required.
A] Choice of graft
The ultimate goal in mandibular reconstruction cases is the res¬toration of both form and function. We can achieve this through various surgical tech¬niques, mainly non-vascularized bone grafts (NVBGs) and vascularized grafts.
Direct comparisons of NVBGs and vascularized bone flaps (VBFs) have shown the superiority of the latter in terms of bony union (69% for NVBGs vs. 96% of VBFs) as well as superior functional and aesthetic scores for diet, speech, and midline sym-metry. Superiority of VBGs compared to NVBGs increases significantly in mandibular defects greater than 6 cm or previously irradiated tissue. Vascularized flaps withstand irradiation better. Available options for VBGs are the fibula, radial forearm, scapula, and iliac crest.
B] Why fibula is the choice of graft?
- The use of free vascularized fibula has become the “gold standard” for mandibular reconstruction since its introduction by Hidalgo in 1989,1 due to various advantages over other VBGs.
- It provides the longest bone segment with 20 to 30 cm long, 14 mm wide with a bicortical plate, allowing implant placement and osseointegration.
- A reasonably long vascular pedicle with large diameter vessels, mainly peroneal artery, and the segmental blood supply of the bone permits multiple osteotomies.
- The most reliable septocutaneous perforators are located in the mid¬dle and distal third of the fibula.
- We can harvest Soleus muscles with the fibula if additional bulk is required.
- We can use proximity of the sural nerve for the reconstruction of the inferior alveolar nerve.
- Minimal donor site morbidity and ease of harvesting.
C] Two ways to get there
The complete rehabilitation of the mandible can be carried out in 2 different approaches the conventional and digital namely, depending on the method followed for the reconstruction.
1. Conventional approach: The conventional approach is completely based on the expertise and experience of the clinician. It includes simultaneous resection of the mandibular pathology as well as the harvesting of the fibular graft. This is done based on of manual measurements, making it not 100% accurate. The resection is then followed by the surgical reconstruction of the mandible by harvesting the fibular graft. Before the placement of implants, the patient has to wait for a period of 3-5 months for the graft to get accepted.
After the acceptance and healing of the graft, we can conduct a second surgery to place the implants; followed by another waiting period of 3-6 months for the osseointegration of the implants. The process of fabrication for the prosthesis beings after this, thereby increasing the time frame required for the complete rehabilitation to 9-12 months.
Drawbacks of a conventional approach
- Long waiting period till satisfactory function and aesthetics are achieved.
- Formation of a thick layer of soft tissue post the first surgery hampers the placement of implants; in such cases “Debulking” of the soft tissue is necessary.
- Manual measurements used for resection make it difficult to reach the optimal positioning of implants.
- Each surgical intervention increases the risk of infection.
A study of 56 patients has reported 92% implant success versus only 42.9% prosthetic success. The reasons proposed by the authors are patient’s poor cooperation (30.4%), tumour recurrence (14.3%), and surgery-related factors (10.8%) in which the authors include both implant failure and an unfavorable relationship between the maxilla and the reconstructed mandible. One should consider that a high implant osseointegration rate is not significant if the functional prosthetic result is bad. Thus, from this study, it is inferred that the success of such cases is predicted from the standpoint of final occlusion achieved and duration needed for the complete reconstruction ,which necessitates the use of digital methods.
2. Digital approach
3D printing is a rapidly growing technology in the medical field, which can provide adapted solutions. After resection of malignant tumours, mandibular reconstruction using a free fibular flap and a 3D printed resection guide is considered to be more accurate than conventional reconstruction. Moreover, this technique is expected to contribute to shorter surgical times and overall cost savings.
Working a case from the digital stand point begins with a CT – scan of the mandible with the pathology and a CT-angiography for the fibula. A CT- angiography is done to check for the peroneal artery’s patency, to be harvested along with the graft. These files are provided in DICOM formats.
After the scan, various software e.g.- Geoform, MAGICS etc are used to convert the DICOM file into STL format, which is essential for the virtual planning of the case. The files are uploaded onto the software; the various tools are then used to analyze the extent of the lesion and create a personalized treatment plan. The accessed pathology is virtually resected by keeping safety margins (Figure 1). Following which a resection stent is designed to be used at the time of surgery for the accurate excision of the pathology (Figure 2).
Figure 1 - Virtual Delineation of The Part to Be Resected
Figure 2 - Virtual Image Of Pathology Resection Stent
Simultaneously the fibula is analyzed for the area to be resected depending on the anatomical considerations. Those include using the middle portion of the bone, not including the distal end of the bone to maintain its vascularity. Cases,which include the resection of the anterior section of the mandible are more difficult to rehabilitate as it entails the reconstruction of the anatomical curvature. This can be achieved via virtual planning (Figure 3A,3B).
Figure 3 - Virtual Images f The Fibula Sectioning Using The Fibular Stent
3A - Three Segments Aligned
3B - Three Segments Aligned to Achieve the Anterior Curvature of The Mandible.
The cutting planes for the fibula are decided based on the amount of graft needed for the reconstruction. The angles between these cutting planes act as a guide to achieve the anterior curvature of the mandible. Along with the angles the resected pieces help us gauge the height, width and placement of the implants (Figure 4), thereby guiding us to rehabilitate the occlusal harmony post-surgery. Post the planning two more stents are designed, one for the resection of the fibula and another for the implant placement (Figure 5A, 5B).
Figure 4 - Virtual Image of Resected Pieces Gauging the Height, Width and Placement Of The Implants
The resection stent has a snap-fit onto the bone, thus making the resection accurate and easy. The designed stents are then 3D - printed and sterilized by UV radiation and H2O2 plasma. A 3D printed model of the mandible can also be printed to contour the reconstruction plate (Figure 6).
Figure 6 – Digital Approach, 3D Printed Implant Placement Stent
On the day of the surgery, two surgical teams simultaneously resect the mandible and harvest the fibular graft using the previously printed stents, attach the reconstruction plate to the harvested fibular graft , and attach it to the remnant mandible; implants are placed thereafter using the stent (Figure 7A). Following the implant placement, there is a waiting period of 3-6 months for the graft to get accepted and implants to Osseointegrate simultaneously. A prosthesis is then fabricated (Figure 7B).
JAW IN A DAY :
Introduced by Levine in 2013, this approach proposes the complete reconstruction and rehabilitation of the maxilla and mandible in the same surgical intervention. This technique used digital technology to plan, design, fabricate and deliver a comprehensive reconstruction for an ablative mandibular defect using a fibular free flap that included immediate implant placement and a provisionalized fixed dental prosthesis. As a result, the reconstructive surgeon now has the ability to place dental implants and deliver a temporary fixed prosthesis on the same day as the jaw resection and free flap reconstruction, fully restoring the patient surgically and prosthetically to form and function in a single operation.
Patient Selection - It is crucial to know the pathology and to have a biopsy confirming the diagnosis to plan the resection with adequate margins, comorbidities that could affect the success of a microvascular reconstruction, such as vascular or autoimmune disease. ‘Jaw in a Day’ is limited to using an osseous fibula flap with no significant soft tissue component. To avoid further complications this technique is currently used for non-cancerous benign lesions.
Radiographic assessment – Maxillofacial CT and a CT angiogram of the bilateral lower extremities, with resolution scans with image slice of 1mm or less. These help us to plan the surgery, virtually, allowing us to “work backwards” and have a prosthetically driven approach. Technique – Imaging of dentition with either Digital impression using an intraoral scanner or laser scanning of traditional alginate impression is done, which is merged with Maxillofacial and CT angiogram of lower extremities. These images are imported to the surgical planning software using DICOM format. Using software systems, virtual surgical planning (VSP) is done. Virtual surgery is then performed by a biomedical engineer.
By identifying the pathology on the model, a resection is planned with acceptable margins and resection guide is designed. It has predictable holes correlating to holes for reconstruction plates, which are drilled before resection to ensure their accurate placement of the bony segment using a reconstruction plate as an index. These resection guide can be tooth-borne or bone-borne. Tooth borne being more accurate due to the absence of soft tissue between bone and guide. Following which, the appropriately sized segment of the fibula is chosen ,and the number and position of implants are planned and incorporated into the same fibular resection cum implant placement guide.
This guide has to be secured with a monocortical screw to prevent movement. Then, custom reconstruction plates are designed. The design of the plates and cutting guides are finalized and approved by the surgeon, and the cutting guides and hardware are fabricated and delivered for surgery. The provisional prosthesis can be designed virtually as well and milled prior to surgery. Placing dental implants into fibula bone is similar to placing implants in to dense type 1 mandible. Osteotomies should be slightly overprepared, paying close attention to widening the cortices with the final drill. Following final drill, the osteotomy site is thoroughly irrigated and inspected for soft tissue remains.
The implants are then screwed into the bone and hand-torqued to the appropriate value and primary stability is determined, following which prosthetic abutments with screw retained temporary cylinders are placed and torqued. While still pedicled to the leg, the fibula/reconstruction plate/provisional construct is tried into a pre-prepared stereolithic model of the segmental defect site and checked. Once accurate occlusion is achieved, the prosthesis is luted to provisional cylinders. Then the whole assembly is transferred to the site and maxillomandibular fixation is carried out to ensure satisfactory occlusion prior to osteosynthesis of the osseous fibular flap to the jaw.
D] Choice of prosthesis
- Fixed Prosthesis- might stimulate the bone but can be more difficult to adapt because of anatomical conditions, especially a reduced mouth opening. It also requires a high number of implants, which is not always possible in these patients. It is recommended in case of short grafts (Figure 8).
- Removable Prosthesis - necessitate fewer implants. The rehabilitation, follow up and oral hygiene are easier. The procedure is cheaper. It can also easily compensate for an aesthetic defect, especially in the anterior part of the mandible. However, hyposalivation might lead to mucosal irritations and the significant decrease of blood vessels in the oral mucosa renders soft tissues more susceptible to traumas.
- The main problem with prosthesis remains the unfavorable implant–crown ratio and axis of the implants, which is not always the same as an axis of the prosthesis, leading to torque forces that may endanger implant survival.
- Use of image-guided surgery and surgical guides decreases the risk and minimises the angulation between the prosthetic axis and implant axis and also allows precise planning and accuracy of the rehabilitation.
- When the placement of five implants or more is possible, a fixed ceramic prosthesis can be placed. A fixed hybrid ‘‘Branemark-like’’ prosthesis can be a good alternative for permanent rehabilitation. A bar framework (Figure 9) can also be proposed for patients wearing a removable denture, as well as O-ring retained dentures or telescopic retention.
Merits of Digital Approach –
- “Reverse engineering” helps to achieve accurate and predictable results.
- Occlusal driven planning increases the efficiency of the final prosthesis.
- Decreases time and number of surgeries.
- Decreased trauma to tissues.
- Decreases chances of infection.
Like with almost any other process, there are also drawbacks of 3D printing technology, which should be considered before using this process. These drawbacks include High Energy Consumption, 3D printing technology is not cost-effective, limited materials, chances of harmful emissions, copyright infringements etc.
The advent of 3D printing has opened many avenues to the field of medical science. Further Use of this technology will help us evolve our treatment options in the future. The new emerging ideas to be considered for mandibular rehabilitation includes-
- Prefabricated free fibular grafts – introduced by Rohner21 in 2013, includes the prior osseointegration of the implants in the fibula followed by the resection and reconstruction.
- Titanium frameworks – in cases with extensive resection, an alternative to use of fibular grafts is the use of 3D printed titanium frameworks to hold and give shape to the mandible.
- Tissue engineering approaches utilizing collagen-based scaffolds combined with bone marrow-derived stromal cells and growth factors. Additionally, off-label use of bone morphogenetic protein-2 (rhBMP-2) in a collagen carrier has been described as a new alternative to vari¬ous types of autogenous bone grafting procedures.
Disfigurement of the face, impaired speech and inability to chew are stigmas that are significant in the social world. Rehabilitation of patients with maxillofacial defects poses a challenge to the able clinician. Medical imaging and computer-assisted surgery help in improving these surgical techniques. The digital approach discussed in this article not only overcomes the demerits of the conventional approach but also proves its own merits in numerous ways to achieve harmonious occlusion, function and aesthetics. Precise knowledge and the blend of biological principles and technology is the key to defining success in rehabilitating patients with maxillofacial defects.
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We are very grateful of Dr. Guruprasad Rao (Director, 3D Imaginarium) and his team for their guidance and Dr. Kartik Bhanushali(4 Quadrant Dental Solution.Pvt.Ltd) for his continuous support.