Mandibular Reconstruction

Classification of Mandibular Defects

The classification of mandibular defects provides a standardised communication tool and guides the therapeutic algorithm for the reconstruction. There are several classification systems, but Jewer-Boyd is the most widely accepted in clinical practice¹

Jewer-Boyd Mandibular Classification (H-C-L)

In 1989, Jewer and Boyd described the HCL classification for hemimandibular (H), central (C), and lateral (L) defects of the mandible. Boyd modified this classification to include mucous (M) and/or skin (S) involvement.

• Hemimandibular: lateral and horizontal segments including the condyle of any length and not significantly crossing the midline.
• Central: segment between the incisive foramen (2 canines and 4 incisors)
• Lateral: segment not including the condyles  

This HCL mandible classification is seen in the image below.

The length of the defect is not included in this mandibular classification. In reality, many mandibular defects are a combination—for example, LCL.

Other Mandibular Classifications

• CRBS by Urken² assessed the bone  (condyle, ramus, body, and symphysis), soft tissue (lip, buccal, soft palate, floor of the mouth, tongue, and skin) and nerve (inferior alveolar, lingual, hypoglossal nerve, and facial nerve).
• Schultz³ assesses a defect's dentate nature of alveolus and ramus, unilateral or bilateral, laterality of the donor's vessels, and condylar involvement.
• Brown⁴ defines four classes of segmental mandibulectomy: lateral, hemimandibulectomy, anterior, and extensive ± condylectomy.

There is no "perfect" mandibular classification system, and its complexities can make it challenging to apply in routine practice.

Pathophysiology of Mandibular Invasion

Mechanisms

Generally speaking, mone invasion occurs via:

1. Soft tissues: infiltrative spread
2. Lymphatic: embolic spread
3. Nerves: permeative spread
4. Occlusal surfaces: direct after tooth extraction

Role of Teeth

The mechanism of tumour invasion is different for dentate and edentulous mandibles.

• Dentate mandible: invasion occurs via tooth sockets  
• Edentulous mandible: invasion via occlusal surface and alveolar bone resorption provide a shorter route.

Types of Mandibular Resections

Mandibular resections can be classified into 3 different types of mandibulectomies based on their width and length of resection: marginal (rim), segmental and hemi-mandible. Their relative indications are determined by physical examination and radiographic imaging after discussion at a multidisciplinary meeting.

Factors to Consider

The management options for mandibular resection should take into consideration the following variables:

• Tumour: location in relation to the mandible
• Mandible: dentate or edentulous, atrophy, radiotherapy
• Patient: comorbidities and outcome expectations.

Marginal (Rim)

A marginal rim resection of the alveolus ± lingual plate with body and inferior alveolar nerve preservation. It can be considered in the following patients after discussion at a multidisciplinary meeting.

• Mandibular adjacent
• Mandibular periosteum invasion only with no involvement inferior dental canal.
• Dentition adjacent with no periodontal ligament involvement.

This is not suitable for:

• Edentulous mandibles have alveolar bone resorption as the remaining bone is weakened and at high risk of fracture.
• Irradiated bone because the patterns of tumour spread are less predictable.

Segmental mandibulectomy

Segmental mandibulectomy is a full-thickness resection of a mandibular segmental. It can be considered in the following patients after discussion at a multidisciplinary meeting.

• Mandibular invasion regardless of patient dentition.
• Mandibular fixation in an edentulous patient.
• Mandibular hypoplasia restricts a safe rim resection.
• Carious dentition adjacent with periodontal ligament involvement.
• After radiation (radiotherapy disrupts periosteal resistance to tumour spread)

If there is invasion of the inferior dental canal, there is an assumption that there is involvement of the inferior alveolar nerve. This requires resection lateral to the lingula to medial the mental foramen.  

Types of Mandibular Reconstruction

Overview

The type of mandibular reconstruction is primarily determined by the location and size of the mandibular defect, soft tissue loss and goals for dental rehabilitation.

Options for mandible reconstruction include no reconstruction, plates, non-vascularised bone grafts, and vascularised bone flaps.

The goals of the reconstruction should be to provide:

• Stability
• Function: opening, mastication, swallow
• Structure: dental occlusion, articulation
• Aesthetic: lower facial height and contour  

No Mandible Reconstruction

No mandible reconstruction can be considered in a select number of patients. For example:

• Indications: posterior defects with intact anterior segment, ascending ramus or lateral defects, condylar head resected from the TMJ, patient not suitable for extended operation, poor prognosis
• Advantages: quicker operation, can usually maintain speech and swallowing
• Disadvantages: crossbite and malocclusion

These patients can receive soft tissue reconstruction with similar aesthetic and functional outcomes. The goal is to provide vascularized tissue bulk, obliterate dead space, and coverage of essential structures. For example, major pectoralis flap, anterolateral thigh flap, and radial artery forearm flap.

Reconstruction Plates

The operation is faster than other reconstructive options with no donor site morbidities. Mandibular plates can be considered in patients:

• Not suitable for prolonged operation
• Have a poor prognosis
• Good soft tissue coverage
• Not receiving radiotherapy.  

This option is often complicated in the long term by:

• Plate Fracture: increased risk with radiotherapy
• Plate Extrusion: increased risk with anterior mandible and radiotherapy
• Stress shielding: leads to load bearing, bony resorption and osteopenia.  
• Secondary procedures to manage plate complications  
• Dental reconstruction is not possible.
• Loosening of screws

Potential benefits include:

• Less technical
• Shorter operation
• No donor morbidity.

Non-Vascularised Bone Grafts

This technique requires a healthy vascularized wound bed. The graft can be taken from the rib, iliac crest or an allograft.

Non-vascularised bone grafts can be considered for mandibular reconstruction in more minor defects (<6cm) and:

• No radiotherapy
• Not an anterior mandible defect

This reconstructive option has reduced survival with scarring, irradiation and infection. It can be technically challenging due to inadequate skin or mucosal cover.

There is evidence to suggest this is best performed in a delayed fashion⁶

Vascularised Bone Flaps

Vascularised bone flaps are generally considered the gold standard in mandible reconstruction.

• Indications: Large defects (>6cm) or irradiated defects
• Advantages: more strength and stiffness, higher arthrodesis and superior functional outcomes compared to other reconstruction options, allows osseointegration.
• Disadvantages: more extended operation, donor site morbidities.

Reconstruction options include

• Free fibula flap
• DCIA flap: osteotomy possible leaving periosteum and iliacus intact, AIIS to ASIS can be used for ramus. Good vessel calibre, length and bone height. Limited by bulkiness.
• Scapular osteocutaenous flap: low donor site morbidity, versatile as skin and bone have separate pedicles, thin bone for orbit and hard palate. Limited by the volume of bone available and positioning.
• Radial forearm with radius: long pedicle, technically easier, thin skin can conform to any defect. Limited by quality of bone, fracture risk and donor site problems at the wrist. More suitable for orbital reconstruction.  
• MUCH less commonly used a pedicled bone flaps, such as pectoralis major with 5th and 6th ribs or lateral sternum; trapezius with clavicle.

Free fibula reconstruction is improved with pre-operative mandible computer-animated drawing and modelling. Osseointegration can be planned at the same time with ProPlan 3D software - ossteintegration scews are inserted prior to elevation.

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