Solving The Enigma In Fibular Reconstruction Of The Mandible – A Prosthodontic Eye
by : Dr. Saloni Mistry , Dr. Omkar Shete, Dr. Gauraja Kada, Dr. Shalu Shah

INTRODUCTION

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 Hidalgo¹, has become one of the greatest advances in reconstruction of the maxillofacial region. The conventional process of rehabilitation demands time and meticulous sequential procedures need to be followed.

However, with the use of technology as an adjunct to surgical procedure in 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.

REHABILITATION GOALS

A] CHOICE OF GRAFT

The ultimate goal in these cases is res­toration of both form and function. This can be achieved through a variety of surgical tech­niques, mainly non-vascularized bone grafts(NVBGs)and vascularized bone grafts(VBGs). Direct comparisons of NVBGs and vascularized bone flaps (VBFs) have shown superiority of the latter in terms of bony union (69% for NVBGs vs. 96% of VBFs)² as well as superior functional and aesthetic scores for diet, speech, and midline sym­metry ³ . Superiority of VBGs compared to NVBGs increases significantly in case of mandibular defects greater than 6 cm or previously irradiated tissue² . Vascularized flaps withstand irradiation better. Available options for VBGs are the fibula, radial forearm, scapula, and iliac crest ^4-7 .

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 segment of bone with 20 to 30 cm long,14 cm wide with 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 ⁸.

• The most reliable septocutaneous perforators are located in the mid­dle and distal third of the fibula ⁹.

• Soleus muscles may be raised with the fibula if additional bulk is required.
• The proximity of the sural nerve can be used for 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 on the basis 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 (image 3). Before the placement of implants the patient is asked to wait for a period of 3-5 months for the graft to get accepted.

After the acceptance and healing of the graft, a second surgery is conducted 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 conventional approach

• Long waiting period till satisfying function and esthetics 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 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 unfavourable 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 bad¹⁰.

Thus from this study it is inferred that the success of such cases is predicted from the stand point 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 tumors, 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 patency of the peroneal artery to be harvested along with the graft. These files are provided in DICOM formats.

After the scan various softwares for eg.- 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 then uploaded onto the software; the various tools are then used to analyse the extent of the lesion and create a treatment plan. The accessed pathology is virtually resected by keeping safety margins¹¹.

Following which a resection stent is designed to be used at the time of surgery for the accurate excision of the pathology.

Simultaneously the fibula is analysed 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 reconstruction of the anatomical curvature. This can be achieved via virtual planning.

The cutting planes for the fibula are decided on the basis of 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

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

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 precontour the reconstruction plate¹².

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 then attach it to the remnant mandible; implants are placed there after using the stent. 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.

D] CHOICE OF PROSTHESIS

• Fixed Prosthesis– might stimulate the bone but can be more difficult to adapt because of anatomical conditions and 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 grafts¹³

FIXED IMPLANT SUPPORTED PROSTHESIS WITH MULTIPLE IMPLANTS

• 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 mandible¹⁴

REMOVABLE IMPLANT SUPPORTED PROSTHESIS

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 unfavourable implant–crown ratio and axis of the implants, which is not always the same as the axis of the prosthesis, leading to torque forces that may endanger implant survival.
• The use of image-guided surgery and surgical guides decreases the risk and minimises the angulation between prosthetic axis and implant axis and also allows precise planning and accuracy of the rehabilitation^15,16.
• When 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

DENTAL PROSTHETIC REHABILITATION OF A CLASS III DEFECT WITH ORAL IMPLANTS IN THE FIBULA AND SUPRACONSTRUCTION USING A BAR-SUPPORTED DENTURE

can also be proposed for patients wearing a removable denture, as well as O-ring retained dentures or telescopic retention¹⁷.

Merits of Digital Approach 

• “Reverse engineering” helps the 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.
• Deceases chances of infection.

Future scope.

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-

• Pre- fabricated free fibular grafts – introduced by Rohner¹⁸ in 2013, includes the prior osseointegration of the implants in the fibula followed by the resection and reconstruction.
• Jaw in a day¹⁹ – introduced by Levine, proposes the complete reconstruction and rehabilitation of the mandible in the same surgical intervention.
• 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, an off-label use of bone morphogenetic protein-2 (rhBMP-2) in a collagen carrier has been described as a new alternative to vari­ous types of autogenous bone grafting procedures ²⁰ .

Conclusion

Disfigurement of 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 helps 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 merit in numerous ways to achieve harmonious occlusion, function and esthetics. Precise knowledge and the blend of biological principles and technology is the key to defining success in rehabilitating patients with maxillofacial defects.

REFERENCES –

1. Hidalgo DA: Fibula free flap: A new method of mandible reconstruction. Plast Reconstr Surg 84:71, 1989.
2. Foster RD, Anthony JP, Sharma A, et al. Vascularized bone flaps versus nonvascularized bone grafts for mandibular re­construction: an outcome analysis of primary bony union and endosseous implant success. Head Neck 1999;21:66-71.
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ACKNOWLEDGMENT

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.

Conflict of intrest – The authors of this articles declare no conflict of interest.

Authors-

Dr. Saloni Mistry (M.D.S), Professor and Head of Dept. of Prosthodontics at Y.M.T Dental College and Hospital, Kharghar is a well known clinician and academician for the last 20 years with numerous national and international publications to her name. She is the EC member of the IPS and has been a keynote speaker for various conferences and PG conventions. She specialises in creating esthetic realism in prosthodontic rehabilitation.

Dr. Omkar Shete (M.D.S) is currently working as an Associate Professor of Dept of Prosthodontics at Y.M.T. Dental College and Hospital and is an avid academician.

Dr. Shalu Shah (Second year Post Graduate) at Dept of Prosthodontics at Y.M.T Dental College and Hospital, Kharghar.

      Dr. Gauraja Kadam (Second year Post Graduate) at Dept of Prosthodontics at Y.M.T Dental College and Hospital, Kharghar.

Correspondence address –
Dr. Saloni Mistry (M.D.S)
Professor and Head of Dept. of Prosthodontics,
Y.M.T Dental College and Hospital,
Sector – 4, Kharghar
Navi Mumbai-410210, India
E- mail – [email protected]
salshal [email protected]