2 Ablative and reconstructive surgery of the mandible
2.1 Access osteotomies in the mandible in tumor surgery and osteosynthesis
The provision of optimal surgical access is a fundamental requirement in head and neck surgery. Mandibular access osteotomies facilitate the management of many head and neck tumors and various types of mandibulotomies are described. The procedure should have minimal morbidity and a minimal effect on appearance and function, including speech and swallowing. The choice of a mandibular access procedure is dictated by the clinical and imaging findings, and the degree of access required to successfully ablate the tumor.
2 Indications and contraindications for mandibulotomy
Mandibular access procedure are used:
In the treatment of tumors of the oral cavity, oral tongue and tongue base, oropharynx and hypopharynx.
With modification, the technique can be used to gain access to tumors of the parapharyngeal space and infratemporal fossa.
As a route to gain access to an anterior approach to the cervical spine.
In conjunction with marginal mandibulectomies if indicated.
With the advent of transoral laser resection (TOLR) for oropharyngeal tumors, and the current vogue to treat oropharyngeal squamous cell carcinoma with chemoradiotherapy, the requirement for mandibulotomy has diminished.
Where there is involvement of the more distal mandibular bone by tumor, a segmental resection is recommended.
Previously irradiated patients and patients who have received high-dose antiresorptive medication (bisphosphonates, RANK-ligands) are seen as a relative contraindication.
3 Preoperative imaging
As part of the preoperative evaluation, in addition to the full imaging workup for the head and neck tumor, the following is required:
A full preoperative dental evaluation, including dental x-rays where necessary. It is important to identify and if necessary eliminate any dental pathology and identify any teeth that have a poor prognosis which could potentially complicate the access procedure.
Panoramic digital radiographs of the mandible orthopantomography to rule out the existence of synchronous pathology of the mandible and to identify root shape and position.
High-resolution computed tomography (CT), cone beam CT, or magnetic resonance imaging scan of the mandible to rule out any involvement of the mandible by tumor, especially if the tumor lies in direct proximity to the mandible.
4 Anatomical considerations
4.1 Lip splitting /associated incisions
A mandibular osteotomy may be used alone or in conjunction with a complete or partial lip-splitting technique. A partial lip-splitting technique can still provide adequate surgical access. In this technique, the soft tissues around the chin point are divided through but the division stops at the base of the labiomental fold, thus preserving the orbicularis function and maintaining oral continence. The lip-splitting incisions in common use are illustrated in Fig 2.1-1 .
Mandibulotomy can also be successfully performed without a lip- or chin-splitting procedure, however access is then more limited.
To provide optimal exposure of the tumor site, the mandibular access procedure will invariably be combined with either a unilateral or bilateral lingual soft-tissue release procedure ( Fig 2.1-2 ).
Most mandibular access procedures will be associated with a neck dissection procedure or a direct transcervical approach. This provides access for complete vascular control of the major vessels in the neck.
Mental and inferior alveolar nerves
The osteotomy and subsequent osteosynthesis must not injure the mental or inferior alveolar nerves. The mental foramen is most frequently located in line with the longitudinal access of the second premolar root. The next most common position is between the roots of the first and second premolar but the location can vary from canine to first molar position.
The muscle attachments that need to be considered when planning a mandibular access procedure include the following:
The paired anterior bellies of the digastric muscles arise from a depression on the lower lingual border of the mandible, near the midline.
The paired mylohyoid muscles form the muscular diaphragm of the floor of mouth, which are attached along the complete length of the mylohyoid line of the mandible with the posterior fibers being inserted into the body of the hyoid bone.
The genioglossus and geniohyoid muscles are attached to the genial tubercles on the lingual aspect of the mandible in the midline and are located in the lower half of the basal bone in the dentate mandible. The medial pterygoid muscle is attached as a strong tendinous sheet into the medial and posteromedial mandibular ramus below the level of the lingula.
The bone in the symphyseal and parasymphyseal region of the mandible is vascular and receives its blood supply via the attached musculature; terminal branches of the lingual artery may penetrate the bone directly.
4.2 Surgical approach
Following completion of a neck dissection procedure, or following cervical flap elevation as an access procedure, the lower border of the mandible in the submental area is isolated and exposed. A mandibulotomy procedure alone without any form of lip splitting can provide a significant improvement in access without incurring the additional morbidity of the soft-tissue division of the lip and its associated functional and esthetic effects. However, even though lip splitting provides direct access to the osteotomy site, the surgical approach to the mandibulotomy is essentially the same. The soft-tissue attachments of the chin point are all stripped by subperiosteal dissection, exposing approximately 3–4 cm of the mandible at the approximate site of the mandibulotomy. The mental nerve site is clearly identified and protected.
Intraorally, the labial and lingual sulcus at the site of the osteotomy is infiltrated with local anesthesia. Using a scalpel a gingival crevicular incision is made on both lingual and buccal aspects of the mandible. The attached mucosa is elevated using a Freer elevator so that a subperiosteal communication can be produced from the oral cavity to the chin. After soft-tissue dissection, the mandibulotomy is performed (see next section). Before wound closure, the mucosa in the labial sulcus is divided and a releasing incision is made into the labial sulcus at least 1 cm away from the mandibulotomy site so as to avoid closure of the wound directly over the osteotomy cut.
Depending on the location of the tumor, choices exist regarding the extent of the lingual release. In the dentate mandible, a gingival crevicular incision is preferred and this incision extends from the area of the osteotomy to the retromolar region ( Fig 2.1-2 ).
In the edentulous mandible, the incision is taken along the crest of the ridge. The use of a crevicular and crestal incision is preferred over a sulcular incision for two main reasons:
Ease of closure
Reduces the risk of leakage and fistulation by locating the incision away from the buccal and lingual sulcus
The mobile segments of the mandible are then separated and the mylohyoid muscle is divided along its complete length adjacent to the mandible. When dealing with posterior tongue, oropharyngeal, or parapharyngeal tumors access can be improved by a release incision that extends posteriorly into the anterior pillar and if necessary into the soft palate ( Fig 2.1-3 ).
Lateral rotation of the mandible exposes the lingual nerve coursing medially and dependent on the individual tumor and the access required, resection or division of the lingual nerve may be necessary. Increased access by further rotation of the mandible can be provided by stripping the attachment of the medial pterygoid from the medial surface of the mandible.
5 Types of access osteotomies and osteosynthesis
5.1 Osteosynthesis in mandibular access osteotomies
In this type of access surgery the planned bone cuts are usually marked on the bone and the plates adapted and prelocalized onto the bone with screws before the osteotomy is undertaken. The plate and screws are then removed and can then be carefully stored in the sterile field until the tumor ablation procedure is completed.
Depending on the biomechanical and biological situation, the choice of hardware can range from load-sharing miniplates to rigid load-bearing plates. In certain situations the lag screw technique can also be used. The weaker and more compromised the bone is, the stronger the fixation should be.
5.2 Midline and paramedian mandibulotomies
These osteotomies provide good exposure with acceptable morbidity. A vertical osteotomy cut is marked onto the bone below and in between the roots of the teeth. The osteotomy cut is initially scored using a fine saw blade in a reciprocating saw or a piezotome. At this stage, the titanium plates, which will be used for the final fixation, are prelocalized onto the mandible and temporarily screwed into place. The plates are removed and safely stored. The mandibulotomy cut is then completed using the fine saw blade with a fine spatula osteotome utilized to complete the cut between the dental roots. The lingual periosteum is elevated and protected during this process. The mental nerve is preserved but separation of the genial muscles invariably occurs. During wound closure, muscle repair should be performed to avoid a drooping chin. The site, however, is favorable as it is likely to lie in the periphery of planned radiotherapy ( Fig 2.1-4 and Fig 2.1-5 ).
5.3 Symphyseal or parasymphyseal stepped mandibulotomy
In a stepped osteotomy the upper cut is taken down and below root level and is then completed as a stepped osteotomy to the lower border of the mandible anterior to the mental nerve. The lower limb of the step can be taken anteriorly if a lip split is being used or posteriorly if a non-lipsplitting technique is used. The stepped osteotomy can be fixated with plates as described. The fixation tends to be more stable as the stepped cut limits horizontal and vertical movements of the bone. And there is broader surface of contact between the edges of the bone. With this technique, the attachments of the genial and digastric muscles are preserved, as is the inferior alveolar nerve ( Fig 2.1-6 ).
This approach involves an osteotomy through the body or angle of the mandible. This procedure is rarely indicated as it involves transsection or extended neurolysis of the inferior alveolar nerve without much added benefit.
Chin point osteotomy
This technique is used in conjunction with the lingual release technique and can be used for tongue base and pharyngeal tumors. The complete chin point of the mandible is osteotomized by a horizontal subapical bone cut linked to the lower border of the mandible by bilateral divergent bony cuts which pass anterior to the mental foramen. The horizontal cut passes above the level of the genial tubercles and the chin point is pedicled on the anterior bellies of the digastric and geniohyoid and genioglossus muscles. Miniplate and lag screw fixation can be done in a variable pattern ( Fig 2.1-7 ).
6 Complications and pitfalls
Published complication rates in different series vary between 10.5% and 47.6% with approximately 50% of those patients experiencing minor complications and 50% major complications [Dai et al, 2003; Nam et al, 2006].
Complications associated with mandibulotomy are many and varied, and include:
Bone exposure/plate exposure
Lingual nerve and inferior alveolar nerve injury
Paramedian stepped osteotomies and those osteotomies fixed rigidly with monocortical and bicortical screws and plates are associated with fewer complications [Shinghal et al, 2013].
Radiation therapy was a major factor causing complications (range, 11–30%) [Dziegielewski et al, 2009; Sharan et al, 2008]. Anterior mandibulotomy located at the periphery of the radiotherapy portal carries a decreased risk of osteoradionecrosis, therefore close cooperation with the radiation oncologist in the preoperative planning phase is recommended.
Infection is also reported as a common complication. This needs to be actively managed in the perioperative phase using antibiotics.
7 References and suggested reading
Baek CH, Lee SW, Jeong HS. New modification of the mandibulotomy approach without lip splitting. Head Neck. 2006 Jul;28(7):580–586. Biedlingmaier JF, Ord R. Modified double mandibular osteotomy for tumours of the parapharyngeal space. J Oral Maxillofac Surg. 1994 Apr;52(4):348–352. Boyle JO, Reid V. Complications of surgery of the oral cavity. In: Eisele DW, Smith, RV, eds. Complications in Head and Neck Surgery. 2nd ed. Philadelphia: Elsevier; 2009:257–266. Brown JS, Lowe D, Kalavrezos N, et al. Patterns of invasion and routes of tumor entry into the mandible by oral squamous cell carcinoma. Head Neck. 2002 Apr;24(4):370–383. Chatni SS, Sharan R, Patel D, et al. Transmandibular approach for excision of maxillary sinus tumours extending to pterygopalatine and infratemporal fossae. Oral Oncol. 2009 Aug;45(8):720–726. Collin J, McLennan A. Oblique paramedian mandibulotomy with fixation by lag screws. Br J Oral Maxillofac Surg. 2009 Oct;47(7):560–561. Dai TS, Hao SP, Chang KP, et al. Complications of mandibulotomy: midline versus paramidline. Otolaryngol Head Neck Surg. 2003 Jan;128(1):137–141. Devine JC, Rogers SN, McNally D, et al. A comparison of aesthetic, functional and patient subjective outcomes following lip split mandibulotomy and mandibular lingual releasing access procedures. Int J Oral Maxillofac Surg. 2001 Jun;30(3):199–204. Dziegielewski PT, Mlynarek AM, Dimitry J, et al. The mandibulotomy; friend or foe? Safety outcomes and a literature review. Laryngoscope. 2009 Dec;119(12):2369–2375. Engroff SL, Blanchaert RH, von Fraunhofer JA. Mandibulotomy fixation: a laboratory analysis. J Oral Maxillofac Surg. 2003 Nov;61(11):1297–1301. Gallet P, Gangloff P, Mastronicola R, et al. Combined transoral and suprahyoid approach for oropharyngeal cancers: an alternative to mandibulotomy. Rev Laryngol Otol Rhinol (Bord). 2011;132(2):95–102. Judson BL, Adam SI, Lowlicht R, et al. Transcervical double mandibular osteotomy approach to the infratemporal fossa. World Neuro Surg. 2012 Dec;78(6):715. Kolokythas A, Eisele DW, El-Sayed I, et al. Mandibular osteotomies for access to select parapharyngeal space neoplasms. Head Neck. 2009 Jan;31(1):102–110. Lazaridis N, Antoniades K . Condylotomy or vertical subsigmoid osteotomy with a mandibulotomy anterior to the mental foramen for improved access to parapharyngeal space tumours. J Oral Maxillofac Surg. 2008 Mar;66(3):597–606. Mehanna P, Devine J, McMahon J. Lip split and mandibulotomy modifications. Br J Oral Maxillofac Surg. 2010 June;48(4):314–315. Merrick GD, Morrison RW, Gallagher JR, et al. Pedicled genial osteotomy modification of the mandibular release access operation for access to the back of the tongue. Br J Oral Maxillofac Surg. 2007 Sept;45(6):490–492. Moore EJ, Olsen KD. Complications of surgery of the parapharyngeal space. In: Eisele DW, Smith RV, eds. Complications in Head and Neck Surgery. 2nd ed. Philadelphia: Elsevier; 2009:241–250. Na HY, Choi EJ, Choi EC, et al. Modified mandibulotomy technique to reduce posteroperative complications: 5 year results. Yonsei Med J. 2013 Sept 1;54(5):1248–1252. Nabil S, Samman N. Risk factors for osteoradionecrosis after head and neck radiation: a systematic review. Oral Surg Oral Med Oral Path Oral Radiol. 2012 Jan;113(1):54–69. Nam W, Kim HJ, Choi EC, et al. Contributing factors to mandibulotomy complications: a retrospective study. Oral Surg Oral Med Oral Path Oral Radiol Endod. 2006 Mar;101(3):65–70. Sharan R1, Iyer S, Chatni SS, et al. Increased plate and osteosynthesis related complications associated with postoperative concurrent chemoradiotherapy in oral cancer. Head Neck. 2008 Nov;30(11):1422–1430. Shinghal T, Bissada E, Chan HB, et al. Medial mandibulotomies: is there sufficient space in the midline to allow a mandibulotomy without compromising the dentition? J Otolaryngol Head Neck Surg. 2013 May 2;42:32. Smith GI, Brennan P, Ilankovan V. Vertical ramus osteotomy combined with parasymphyseal mandibulotomy for improved access to the parapharyngeal space. Head Neck. 2003;25:1000–1003.
2.2 Mandible resections without loss of continuity (rim resections)
Malignant tumors may be located in proximity, adjacent to, or involve the mandible. Until the latter part of the 20th century, segmental resection was considered state of the art when a tumor was close to the mandible or when an actual infiltration of the bone occurred. Loss of continuity of the mandible frequently results in esthetic and functional impairment and/or reduction in quality of life for the patient. If rim resection is performed when oncologically sound, no significant statistical difference in survival and recurrence rates are observed between this approach and mandibular continuity resections. Quality of life is also better for patients with rim resections than for those who undergo segmental resections. Therefore, whenever possible, a marginal rim mandibulectomy should be performed.
A rim resection is indicated if the carcinoma is only clinically adjacent or superficially infiltrating the mandible and if no signs of deep bone infiltration are visible in fine-cut computed tomographic (CT) scans or scintigraphy.
2.1 Conventional x-rays
Typically tumors are detected by clinical examination. Panoramic x-ray can give a general picture of whether the mandible is invaded by tumor. Early states of tumor infiltration into the mandible are not easily detected by conventional x-ray because at least 30% demineralization has to occur to permit detection by conventional x-rays. There is 82% accuracy in diagnosing bony invasion with panoramic xrays. The rate of false-negative (2–46%) exceeds the rate of false-positive (0–16%) findings [Brown et al, 1994]. Periodontal diseases, apical and marginal inflammations, and overlay of the spinal column complicate the interpretation. Conventional x-rays should be taken in the second plane for the mandible in a posteroanterior view as described by Clementschitsch .
2.2 3-D imaging
When a malignant lesion is suspected or confirmed by biopsy, an axial and coronal CT scan of the midface and mandible is taken routinely. The images can be reconstructed in multiplanar or in 3-D format. The multi-detector row computed tomography (MDCT) with slices as thin as 0.5 mm have improved sensitivity and specificity. Artifacts from dental restorations can cause false-positive findings; their rate is lower than that of false-negative findings. Tsue et al  believe a CT scan is accurate in exclusion of bone infiltration.
Cone beam CT (CBCT) may also be used to detect bone destruction adjacent to tumor spread. It is not likely to be disturbed by metal artefacts compared to CT, but does not allow differentiation of tumor tissues from other soft tissues.
The neck, thorax, and abdomen are also examined by CT scan to screen for metastasis. When the soft-tissue relation of the tumor to the bone cannot be verified by a conventional contrast-enhanced CT scan, magnetic resonance imaging (MRI) may be used. The high-signal intensity of fatty tissue in T1 images makes MRI ideal to judge bone marrow infiltration. In a study of 22 patients treated with mandibular resection, Chung et al  found a high sensitivity with no false-negative MRI results for tumor invasion. Magnetic resonance imaging has been shown to be prone to false-positive results (range, 73–77%) because lesions from tooth extractions, infectious odontogenic diseases, and osteoradionecrosis cannot be differentiated from tumor invasion. For Bolzoni et al  and Vidiri et al  MRI scans are helpful to differentiate between tumor and fibrosis in irradiated patients. In an MRI case-series of 15 patients, Bolzoni et al  found sensitivity, specificity, and an accuracy of 93% each. The negative predictive value was 96% and the positive predictive value was 87.5%. An MRI study virtually excludes cortical or bone marrow invasion. In contrast to the previous data, Vidiri et al  compared MRI to MDCT in a more recent study in 36 patients and found no statistical difference in sensitivity, specificity, and accuracy (MRI: 93%, 82%, and 86%; MDCT: 79%, 82%, and 81%), respectively. The negative predictive value was 73% for MRI and 86% for MDCT. The positive predictive value was 76% for MRI and 95% for MDCT. The MRI results depend on the researchers and their technique. An MRI also determines tumor volume more accurately.
2.3 Bone scintigraphy and single-photon emission CT
Bone scintigraphy and single-photon emission CT (SPECT) have been used to help screening for metastasis and bone infiltration but the results are disappointing. Isotope imaging is not specific for bone invasion. There is a higher rate of false positive (26–35%) than of false-negative results (0–7%). This means that a negative scanning result makes an extensive bony infiltration unlikely [Brown, 2003; Brown et al, 1994; Shaha, 1991; Zupi et al, 1996] but cannot guarantee for a mandible free of tumor.
3 Anatomical considerations and planning
The decision for a mandibular resection with or without loss of continuity depends on the infiltration mode of the carcinoma which can be estimated by the described imaging methods.
In dentate patients, carcinomas may reach the mandibular bone at the point of contact of the fixed gingiva and Sharpey fibers. The histological image of bone invasion consists of osteoclasts in front of the actual tumor frontier. Direct contact between tumor cells and bone does not exist until later stages of the disease. There are two types of tumor invasion into the mandible. In the first form, “the irregular invasive diffuse infiltration” breaks through the cortical bone and often quickly infiltrates the canal of the inferior alveolar nerve followed by wide horizontal spreading into the mandible’s marrow space. Large tumor masses invading the mandibular body can disseminate perineurally. Perineural spread demands a continuity resection when either the inferior alveolar nerve or the mandibular foramen is reached.
The second form of bony invasion was described by Müller et al  as “erosive and expansive.” It shows a compact broad tumor front which erodes the bone from its area of contact. This form is considered less aggressive than irregular invasion. The thorough study by Brown and Browne  supports the presumption that the erosive infiltration pattern occurs at the lesion’s periphery and later during progression transforms into the irregular invasive one.
Alveolar and retromolar tumors arising from the alveolar crest more often enter the bone via periodontal spaces, while tumors of the floor of the mouth and the tongue enter into the bone directly at the point of contact. In some cases the foramina of the mandible are entry points for squamous cell carcinomas. Invasion into the radiated mandible varies from case to case and is generally characterized by multiple foci. This makes it difficult to predict the mode of infiltration and justifies an extensive continuity resection.
Histological examinations of oral cavity tumors involving the mandible reveal an infiltration rate ranging from 22–48%. Barttelbort et al  found histological bone infiltration in 3 of 21 patients who underwent rim mandibulectomy. Ord et al  described an infiltration rate of 65% in segmental and 7.6% in marginal bony resections of the mandible. The grade of tumor differentiation does not correlate with the invasion rate. The invasive type is found more often with increasing depth of the bony invasion. On average the invasive type infiltrates 12 mm wider than the erosive type. Even though carcinoma invasion of bone occurs in both edentulous and dentate regions of the mandible, extent and depth of bony invasion were greater in dentate regions.
An adequate preoperative assessment of possible bone infiltration helps to decide whether to perform a rim or a segmental mandibulectomy. Using clinical and radiological examination, infiltration can be determined with an accuracy of 82–88%.
Small and shallow carcinomas in proximity to the mandible but without cortical infiltration should be removed with a rim resection. This should include a bone block including the cortex underlying the tumor.
Following the assumption that carcinomas reach the mandible via the attached mucosa, it is important to plan enough bone resection to achieve adequate margins. A caudal rim with height of at least 1 cm should be preserved. Brown et al  introduced a guide to mandibular resection based on the Cawood and Howell classification of the mandible . It helps to judge whether a rim or segmental resection is necessary ( Table 2.2-1 ). Clear margins with at least > 5 mm of normal tissue between the tumor front and the edge of the resection should be achieved because tumor-free margins are essential for survival and local tumor control.
4 Types of rim resections and techniques
Barttelbort et al  postulate three basic requirements for the optimum technique: (1) It must adequately remove the primary tumor as well as those tissues that are also at risk for tumor infiltration. (2) It should be technically simple, biomechanically sound, and have a low complication rate. (3) It should preserve or permit reconstruction of the mandibular arch particularly in anterior lesions to restore normal function and facial appearance.
The access of choice for most of the rim resections is a transoral approach. If needed, it can be combined with an extraoral submandibular approach.
Mandible continuity can be preserved with vertical, horizontal, or oblique rim resection.
The vertical (sagittal) mandibulectomy ( Fig 2.2-1a–b ), including the removal of the lingual plate is technically demanding, and a fracture of the mandible may occur. To prevent a fracture, it is crucial to outline the osteotomy at the mandible’s base with a burr, a saw, or a piezosurgery device. In dentate regions the teeth should be extracted before a sagittal resection is carried out.
The horizontal rim resection is indicated for tumors on the alveolar crest ( Fig 2.2-1c–d ). It permits selective removal of all the tissues at risk based on sound pathological evidence. It is easy to perform, has few complications, and permits maximal form and function for the patient. Osteotomies with sharp edges should be avoided because they function as points of stress concentration and increase the risk of a fracture. Smooth curved osteotomies are biomechanically superior. The length of the osteotomy depends on clinical necessity. Technically, the osteotomy can include the anterior part of the ascending ramus and the coronoid process. Brown et al  favor an oblique saw-cut from cranialvestibular to caudal-lingual ( Fig 2.2-1e–f ).
A rim resection procedure is performed with the patient under general anesthesia in nasal intubation. The patient is placed in the supine position. The mouth and neck are properly washed and disinfected. In addition to the usual head and neck instruments, an oscillating saw, a Lindemann drill, round burrs, various osteotomes, a piezosurgery unit, and a headlamp should be available. Preoperative antibiotics are administered. The mouth is inspected and palpated. Mucosal incisions are outlined with a sterile pen and should have 1–1.5 cm distance to the boundary of the tumor. Local anesthetic with vasoconstrictor is injected into the planned soft-tissue incision line. Biopsies for frozen section histopathology are taken from the whole circumference of the soft tissues surrounding the resected specimen. In case of a positive result the area is resected further. This helps to obtain tumor-free soft-tissue margins during surgery. The planned osteotomy can be outlined with a small round burr and carried out with a saw or piezotome. The amount of bone resection depends on the proximity of tumor tissue to the bone ( Fig 2.2-2 ). If the resection has to be performed in dentate areas, the teeth including their roots and periodontal spaces should be removed en bloc together with the specimen. The aim of a rim resection procedure is to protect the mental and the inferior alveolar nerve if they do not have to be removed for oncological reasons. Piezosurgery may be helpful to protect softtissue structures, such as nerves.
Approximately 1 cm in height should be preserved of the mandible’s base. Saw-cuts should be tapered, as right-angled osteotomies should be avoided ( Fig 2.2-3 ).
The extension of the resection depends on the location and the size of the tumor. Intraoperative palpation helps to assess this issue. Functions of speech and swallowing are better if some attachment of the tongue to the residual mandible can be preserved or reestablished. If the lingual nerve is involved or within the resection margin of the carcinoma, it should be resected. After completing the resection, the specimen is marked with sutures ( Fig 2.2-4 ) and biopsies for frozen section are harvested from the deep margins.
Finally, hemostasis is obtained. Intraoperative markings of the resection margins with titanium vessel clips allow generating a virtual model of tumor margins from postoperative CT data. If the pathologist localizes problem areas with uncertain margins, the oncologist can plan with this data a focused delivery of radiation to the remaining tissues. Finally, the edges of the remaining bone should be smoothed by a round burr to obtain a boat-shaped defect ( Fig 2.2-5 ).
For reconstruction of smaller mucosal defects, a collagen membrane or split skin graft can be used ( Figs 2.2-6 – 2.2-10 ). The preoperative and postoperative panoramic radiographs is shown in Fig 2.2-11 . Local mucosa flaps work well when tension-free closure can be obtained. Regional or free tissue transfers are typically used to cover larger soft-tissue defects.
If a graft or flap is used, a nasogastric feeding tube is inserted at the end of surgery. Oral diet should not be allowed until postoperative day 7 to 10 to prevent dehiscence and infection.
Further reconstruction aims at improving masticatory function and speech. Bone grafting is performed as a secondary procedure when there is sound histological evidence of tumor control ( Figs 2.2-12 – 2.2-18 ). In selected cases distraction osteogenesis may be considered. Dental implant insertion usually requires vestibuloplasty and mobilization of the tongue. This can be done for instance with split skin grafts.
5 Protection plate concept
In cases when the remaining mandibular bone stock is less than 1 cm in height after rim resection, a “protection plate” can be used to stabilize the residual bone. Bone grafting may be done when appropriate to strengthen the residual mandible. In treatment of benign lesions, like cysts or giant cell granulomas, extensive cortical thinning and bone loss can occur by curettage or partial resection. If a weak mandibular strut is suspected or if a fracture of the mandible occurs during resective surgery, a load-bearing conventional or locking reconstruction plate may be used ( Figs 2.2-19 – 2.2-21 ). Depending on the case the locking plate has to be applied via an extraoral approach. If the necessity of a reconstruction plate is likely, the plate should be contoured and provisionally attached to the mandible before the actual resection takes place ( Fig 2.2-20 ). After positioning the plate, it is secured to the mandible by the plate holding forceps. The holes are drilled and the screw length is measured with a depth gauge, and the screw is inserted. Anatomically preformed reconstruction plates, like the MATRIX mandible preformed reconstruction plates, save application time and prevent plate failure following weakening caused by the plate bending process. Depending on the lesion, the plate is removed before tumor resection. Rim resections of the lower border of the mandible may be indicated to treat tumor invasion from submandibular gland tumors or lymph nodes ( Fig 2.2-22 ).
6 Complications and pitfalls
Marginal rim resection may be complicated by a fracture, which can occur intraoperatively or postoperatively under functional loads. To prevent this, it is important to smoothen and to round the edges at the anterior and posterior osteotomy sites.
Depending on the tumor location, patients should expect some degree of inferior alveolar nerve hypesthesia/anesthesia due to traction and proximity to the tumor resection. If the continuity of the nerve is intact, this should resolve within 6–12 months.
Unfavorable soft-tissue situations or previous radiation can cause an increase in complication rates. These problems begin with a decreased accuracy of tumor imaging, impaired wound healing, impaired wound vascularity, wound dehiscence, fractures of the residual bone, and a higher rate of reconstructive failures. A tension-free soft-tissue closure is crucial to prevent wound dehiscence, which typically occurs between postoperative day 4 and 10. When reconstruction of the floor of the mouth is performed, it is often a problem to avoid dehiscence followed by infection due to tongue movements. A vascularized tissue flap helps to achieve abundant soft tissues and good coverage in movable areas.
Only superficially located invasive bony lesions should be treated with a rim resection. In the case that the hard tissue histology turns out to have tumor involved bony margins, it is necessary in a second surgery to extend the resection, which necessitates a complete segmental resection.
Extractions of teeth in contact to a carcinoma should not be done before resective surgery because tumor tissue could be translocated into the extraction sockets. Removal of teeth should take place at the actual tumor surgery. So far there is no correlation between histological evidence of bone infiltration and the risk of local recurrence. It is more frequent in the soft tissues than in bone.
It is difficult to compare survival and recurrence rates in the literature because case numbers are often low. Another reason is the pre-selection of patients for rim or continuity resection depending on the tumor size and location. Smaller tumors are often treated with rim resections. Deeply invading tumors require mostly a segmental resection. Wolff et al  did not find a significantly different 5-year survival rate of 135 patients with marginal (70%) vs segmental (57%) resection. Also local relapses, metastases and second primary tumors did not show significant differences. Pathak et al  compared patients with vestibular cancer to patients with a tumor in the floor of the mouth. All 179 patients were treated with marginal rim mandibulectomy. The 5-year survival rate was significantly better for patients with buccal cancer. Patients with cancer of the floor of the mouth had a lower survival rate.
In summary, rim resection of the mandible is a sound technique for appropriately selected patients with oral cavity carcinomas. Careful attention to the geometry and details of the bone resection, preservation of the inferior alveolar nerve, and soft-tissue closure optimize results.
7 References and suggested reading
Abler A, Roser M, Weingart D. [On the indications for and morbidity of segmental resection of the mandible for squamous cell carcinoma in the lower oral cavity]. Mund Kiefer Gesichtschir. 2005 May;9(3):137–142. German. Ahuja RB, Soutar DS, Moule B, et al. Comparative study of technetium-99m bone scans and orthopantomography in determining mandible invasion in intraoral squamous cell carcinoma. Head Neck. 1990 May–Jun;12(3):237–243. Barttelbort SW, Ariyan S. Mandible preservation with oral cavity carcinoma: rim mandibulectomy versus sagittal mandibulectomy. Am J Surg. 1993 Oct;166(4):411–415. Barttelbort SW, Bahn SL, Ariyan SA. Rim mandibulectomy for cancer of the oral cavity. Am J Surg. 1987 Oct;154(4):423–428. Bittermann G, Scheifele C, Prokic V, et al. Description of a method: computer generated virtual model for accurate localisation of tumour margins, standardised resection, and planning of radiation treatment in head & neck cancer surgery. J Craniomaxillofac Surg. 2013 Jun;41(4):279–281. Bolzoni A, Cappiello J, Piazza C, et al. Diagnostic accuracy of magnetic resonance imaging in the assessment of mandibular involvement in oral-oropharyngeal squamous cell carcinoma: a prospective study. Arch Otolaryngol Head Neck Surg. 2004 Jul;130(7):837–843. Brown J. Mechanisms of cancer invasion of the mandible. Curr Opin Otolaryngol Head Neck Surg. 2003 Apr;11(2):96–102. Brown J, Chatterjee R, Lowe D, et al. A new guide to mandibular resection for oral squamous cell carcinoma based on the Cawood and Howell classification of the mandible. Int J Oral Maxillofac Surg. 2005 Dec;34(8):834–839. Brown JS, Browne RM. Factors influencing the patterns of invasion of the mandible by oral squamous cell carcinoma. Int J Oral Maxillofac Surg. 1995 Dec;24(6):417–426. Brown JS, Griffith JF, Phelps PD, et al. A comparison of different imaging modalities and direct inspection after periosteal stripping in predicting the invasion of the mandible by oral squamous cell carcinoma. Br J Oral Maxillofac Surg. 1994 Dec;32(6):347–359. Brown JS, Lowe D, Kalavrezos N, et al. Patterns of invasion and routes of tumor entry into the mandible by oral squamous cell carcinoma. Head Neck. 2002 Apr;24(4):370–383. Carter RL, Tanner NS, Clifford P, et al. Direct bone invasion in squamous carcinomas of the head and neck: pathological and clinical implications. Clin Otolaryngol Allied Sci. 1980 Apr;5(2):107–116. Cawood JI, Howell RA . Reconstructive preprosthetic surgery. I. Anatomical considerations. Int J Oral Maxillofac Surg. 1991 Apr;20(2):75–82. Chung TS, Yousem DM, Seigerman HM, et al. MR of mandibular invasion in patients with oral and oropharyngeal malignant neoplasms. AJNR Am J Neuroradiol. 1994 Nov;15(10):1949–1955. Clementschitsch F. [Roentgenography in disease and injuries of the jaws]. Dtsch Zahnarztl Z. 1955 Mar;10(5):380–396. German. Dubner S, Heller KS. Local control of squamous cell carcinoma following marginal and segmental mandibulectomy. Head Neck. 1993 Jan–Feb;15(1):29–32. Eley KA, Watt-Smith SR, Golding SJ. Magnetic resonance imaging-based tumor volume measurements predict outcome in patients with squamous cell carcinoma of the mandible. Oral Surg Oral Med Oral Pathol Oral Radiol. 2013 Feb;115(2):255–262. Gilbert S, Tzadik A, Leonard G. Mandibular involvement by oral squamous cell carcinoma. Laryngoscope. 1986 Jan;96(1):96–101. Hirsch DL, Dierks EJ. Use of a transbuccal technique for marginal mandibulectomy: a novel approach. J Oral Maxillofac Surg. 2007 Sep;65(9):1849–1851. Klotch DW, Prein J. Mandibular reconstruction using AO plates. Am J Surg. 1987 Oct;154(4):384–388. Kondoh T, Hamada Y, Kamei K, et al. Transport distraction osteogenesis following marginal resection of the mandible. Int J Oral Maxillofac Surg. 2002 Dec;31(6):675–676. Lydiatt DD. Mandibular resection. Head Neck. 1995 May–Jun;17(3):247–251. Mazzarella LA Jr, Friedlander AA. Sagittal ostectomy of the mandible for floor of mouth cancer. Arch Otolaryngol. 1981 Apr;107(4):245–248. McGregor AD, MacDonald DG. Patterns of spread of squamous cell carcinoma to the ramus of the mandible. Head Neck. 1993 Sep – Oct;15(5):440–444. Müller H, Slootweg PJ. Mandibular invasion by oral squamous cell carcinoma. Clinical aspects. J Craniomaxillofac Surg. 1990 Feb;18(2):80–84. O’Brien CJ, Carter RL, Soo KC, et al. Invasion of the mandible by squamous carcinomas of the oral cavity and oropharynx. Head Neck Surg. 1986 Mar– Apr;8(4):247–256. O’Sullivan GJ, Carty FL, Cronin CG. Imaging of bone metastasis: an update. World J Radio. 2015, Aug 28;7(8):202–211. Ord RA, Sarmadi M, Papadimitrou J. A comparison of segmental and marginal bony resection for oral squamous cell carcinoma involving the mandible. J Oral Maxillofac Surg. 1997 May;55(5):470–477; discussion 477–478. Pathak KA, Shah BC. Marginal mandibulectomy: 11 years of institutional experience. J Oral Maxillofac Surg. 2009 May;67(5):962–967. Prein J, Kellman RM. Rigid internal fixation of mandibular fractures—basics of AO technique. Otolaryngol Clin North Am. 1987 Aug;20(3):441–456. Probst FA, Mast G, Ermer M, et al. MatrixMANDIBLE preformed reconstruction plates—a two-year two-institution experience in 71 patients. J Oral Maxillofac Surg. 2012 Nov;70(11):e657–666. Rogers SN, Devine J, Lowe D, et al. Longitudinal health-related quality of life after mandibular resection for oral cancer: a comparison between rim and segment. Head Neck. 2004 Jan;26(1):54–62. Sader R, Noror B, Horch HH, eds. [Lehrbuch der Ultraschalldiagnostik im Kopf-HalsBereich]. Reinbeck, Germany: EinhornPresse Verlag; 2001. German. Sauerbier S, Gutwald R, Wiedmann-Al-Ahmad M, et al. Clinical application of tissue-engineered transplants. Part I: mucosa. Clin Oral Implants Res. 2006 Dec;17(6):625–632. Schmelzeisen R, Hausamen JE, Neukam FW, et al. Combination of microsurgical tissue reconstruction with osteointegrated dental implants. Presentation of a technique. Int J Oral Maxillofac Surg. 1990;19(4):209–211. Schmelzeisen R, Rahn BA, Brennwald J. Fixation of vascularized bone grafts. J Craniomaxillofac Surg. 1993 Apr; 21(3):113–119. Shaha AR. Preoperative evaluation of the mandible in patients with carcinoma of the floor of mouth. Head Neck. 1991 Sep – Oct;13(5):398–402. Shaha AR. Marginal mandibulectomy for carcinoma of the floor of the mouth. J Surg Oncol. 1992 Feb;49(2):116–119. Slootweg PJ, Müller H. Mandibular invasion by oral squamous cell carcinoma. J Craniomaxillofac Surg. 1989 Feb;17(2):69–74. Söderholm AL, Lindqvist C, Hietanen J, et al. Bone scanning for evaluating mandibular bone extension of oral squamous cell carcinoma. J Oral Maxillofac Surg. 1990 Mar;48(3):252–257. Totsuka Y, Usui Y, Tei K, et al. Results of surgical treatment for squamous carcinoma of the lower alveolus: segmental vs marginal resection. Head Neck. 1991 Mar–Apr;13(2):114–120. Tsue TT, McCulloch TM, Girod DA, et al. Predictors of carcinomatous invasion of the mandible. Head Neck. 1994 Mar– Apr;16(2):116–126. van den Brekel MW, Castelijns JA, Snow GB. The role of modern imaging studies in staging and therapy of head and neck neoplasms. Semin Oncol. 1994 Jun;21(3):340–348. Vidiri A, Guerrisi A, Pellini R, et al. Multi-detector row computed tomography (MDCT) and magnetic resonance imaging (MRI) in the evaluation of the mandibular invasion by squamous cell carcinomas (SCC) of the oral cavity. Correlation with pathological data. J Exp Clin Cancer Res. 2010;29:73. Wolff D, Hassfeld S, Hofele C. Influence of marginal and segmental mandibular resection on the survival rate in patients with squamous cell carcinoma of the inferior parts of the oral cavity. J Craniomaxillofac Surg. 2004 Oct;32(5):318–323. Wolff KD, Hoelzle F. Raising of Microvascular Flaps. Berlin Heidelberg: Springer-Verlag; 2011. Zupi A, Califano L, Maremonti P, et al. Accuracy in the diagnosis of mandibular involvement by oral cancer. J Craniomaxillofac Surg. 1996 Oct;24(5):281–284.
2.3 Benign noncontinuity intraosseous lesions
Benign noncontinuity intraosseous mandibular and maxillary lesions are likely to be treated by curettage and/or enucleation. They include odontogenic cysts (ie, dentigerous cysts), non-odontogenic cysts (ie, aneurismal cysts, solitary bone cysts), benign osteolytic neoplasms (ie, keratocysts, unicystic ameloblastoma, giant cell granuloma), and some fibroosseous lesions (ie, ossifying fibroma, fibrous dysplasia). These pathologies have the common attribute that they usually can be adequately treated without segmental resection of the mandible or maxilla.
These lesions have a distinct potential to grow to a considerable size producing thinning and sometimes erosion of both the inner or outer mandibular or maxillary cortex. Nerve function is usually intact.
A pathological fracture of the structurally weakened bone may occur either before treatment, at the time of tumor removal, or any time after surgery, especially if the mass extends to the inferior mandibular border.
2 Clinical diagnosis and imaging
The pathologies discussed in this chapter typically grow without symptoms until they are either randomly detected by a routine x-ray or have grown to such a size that contour changes are detectable.
Necessary imaging usually includes an orthopantomogram for smaller lesions ( Fig 2.3-1 ). For larger lesions and those in proximity to specific anatomical structures like the inferior alveolar nerves, maxillary sinuses, or condyles, a computed tomography (CT) or cone beam CT is indicated ( Fig 2.3-2 ). A magnetic resonance imaging scan may be complementary for vascular lesions.
3 Treatment considerations
While smaller lesions can be removed in a 1-stage procedure, it is recommended to take biopsies of larger lesions to establish a diagnosis as part of treatment planning. The reason for this is that some lesions like keratocysts or unicystic ameloblastoma require a locally more aggressive treatment.
Removal of the lesion from the bony cavity by enucleation of the cystic membranes and/or curettage is the treatment of choice for most of the lesions with the exception of keratocysts or unicystic ameloblastoma.
A transoral vestibular approach is indicated for lesions arising in the tooth-bearing area and is best accomplished by using an extended broad-based full-thickness mucoperiosteal flap to expose the lateral cortex overlying the lesions. A transcutaneous approach is indicated for mandibular lesions when much of the ramus and the condyle are involved by the pathological process.
Keratocysts or unicystic ameloblastomas, require a thorough curettage complemented by removing a thin layer of bone adjacent to the pathology with a burr. In addition, the modified Carnoy solution may be used to better facilitate removal of those pathologies and avoid recurrences.
There should also be wide access to the mass, which frequently needs a large lateral decortication so that all the pathology can be directly visualized and totally removed.
In most mandibular cases, preservation of the inferior alveolar nerve is possible because the pathological process displaces the neurovascular bundle and the mandibular canal rather than invading the nerve. Nerve function is usually intact before treatment.
3.3 Autogenous or alloplastic bone replacement
Large residual cavities are best grafted primarily with autogenous bone. This remains the gold standard in the treatment of large bone defects. Immediate grafting with autogenous cancellous bone chips will provide bone to improve strength and add bone stock for insertion of dental implants and dental rehabilitation. Autogenous bone provides a good osteoconductive, osteoinductive, and osteogenic substrate able to induce new bone formation at the recipient sites.
The iliac crest and the proximal tibia are possible donor sites, which can be selected according to the expected volume of bone required [Engelstad et al, 2010].
To minimize the amount of graft required to fill large cavities, a mixture of autogenous cancellous bone chips and alloplastic materials like hydroxylapatite (HA) or β-tricalcium phosphate can be used.
3.4 Protection plating
For large mandibular defects, autogenous cancellous bone grafting does not provide immediate stability for the weakened mandible. Although the mandibular bony walls are preserved they are usually thinned, and there is loss of internal resistance and capacity to sustain forces and strains, which act on the mandibular body during mastication.
Postoperative mandibulomaxillary fixation (MMF) may be a preventive measure. Immobilization may be necessary for about 4 weeks to prevent a fracture. On the other hand, MMF has adverse effects, which imply that it is a procedure not as benign as commonly thought [Ellis et al, 1989].
Inserting and fixing a load-bearing reconstruction plate to protect the weakened area of the mandible can avoid a pathological fracture during or after the procedure instead of MMF. The plate must be applied in the same manner as for a comminuted or defect fracture. An angulated or preformed plate can be selected for large lesions. This process is called “protection plating”.
The length of the plate depends on the radiographic and clinical extension of the disease, but a minimum of three screws should be used in each segment on either side of the lesion. Adapting the plate to the mandibular contour before the removal of the lesion is preferred. In case an expansive pathology has changed the original contour of the mandible, an initial adaptation of the protection plate is not recommended. In those scenarios the lesion needs to be removed first, then a reconstruction plate is placed secondarily, usually with the patient in MMF. An alternative is manufacturing of an individual patient-specific protection plate following a CAD/CAM planning and manufacturing process (see chapter 5.3.10).
After complete removal of the pathology, larger defects are filled with autogenous bone, a mixture of autogenous bone and alloplastic material, or alloplastic material alone depending on the biomechanical situation and surgeons and patients preferences ( Fig 2.3-3 ).
If a transoral vestibular approach was chosen, suturing of the mucosal flaps must create a tight seal to minimize contamination from the oral flora.
A therapeutic course of antibiotics is preferred after surgery. The patient is instructed to maintain good oral hygiene, which can be supplemented using chlorhexidine solution.
If a transcutaneous approach has been used, a suction drain helps to avoid the formation of a dead space or a hematoma. The closure is done in layers with resorbable and nonresorbable suture material depending on the surgeon’s preference. A short course of prophylactic antibiotic therapy (maximum 48 hours) is adequate only if any intraoral contamination by the saliva can be excluded. If not, a 10-day therapeutic course of antibiotics should be considered. Protection plating to reinforce a curetted and grafted mandibular defect is functionally stable, thus a soft diet is not necessary in the postoperative period.
3.5 Plate removal
The reconstruction plate can be left in place permanently in adults but patients may request its removal for personal or cosmetic reasons. If screws interfere with the insertion of dental implants, this could also be a reason for screw or plate removal. In any event, the plate should not be removed for a minimum of 6 months after the original surgery.
3.6 Dental implants
In case of tooth loss in the area of the pathology, placement of dental implants in grafted bone may be considered after a 3-month period of initial bone healing ( Fig 2.3-4 ).
4 Complications and pitfalls
If a plate has not been adapted before the removal of the lesion and there is an incidental fracture during the curettage procedure, the patient must be placed in temporary MMF before adaptation and fixation of the reconstruction plate. The procedure is comparable with an osteosynthesis of a fracture in bone of reduced quality.
Early intraoral exposure of cancellous bone chips or alloplastic material because of wound dehiscence should be treated by superficial curettage, revision of the wound, and secondary closure.
Contamination of the graft can lead to infection with swelling and drainage. Management consists of reopening the original wound, taking samples for bacteriology, debridement of the wound, and removal of all sequestra. A therapeutic course of antibiotics is prescribed and if necessary modified according to the results of the bacterial cultures.
The plate should not be removed if it is stable with no loose screws.
5 References and suggested reading
Adamopoulos O, Papadopoulos T. Nanostructured bioceramics for maxillofacial applications. J Mater Sci Mater Med. 2007 Aug;18(8):1587–1597. Ellis E 3rd, Carlson DS. The effects of mandibular immobilization on the masticatory system: a review. Clin Plast Surg. 1989 Jan;16(1):133–146. Engelstad ME, Morse T. Anterior iliac crest, posterior iliac crest, and proximal tibia donor sites: a comparison of cancellous bone volumes in fresh cadavers. J Oral Maxillofac Surg. 2010;68:3015–3021.
2.4 Segmental defects, defect bridging, reconstruction with free nonvascularized bone grafts
1 Introduction—segmental resection of mandibular tumors
If a tumor extends close to the inferior border of the mandible, a discontinuity will be created with resection of the tumor. It will therefore be necessary to bridge the defect with a load-bearing reconstruction bone plate, bone graft or bone flap to maintain the position of the residual mandibular fragments and the mandible [Alpert et al, 2012]. The following points will affect the way that surgery is performed:
When a continuity defect is created, the muscles of mastication attached to the residual mandibular fragments will distract the fragments in different directions unless efforts are made to stabilize the remaining mandible in its normal position at the time of partial resection. Maintaining relationships with the remaining mandible fragments after resection of portions of the mandible is a key principle of mandibular reconstruction. This is important for occlusal and temporomandibular joint positioning. When the residual fragments are left to drift, significant facial distortions can occur from deviation of the residual mandibular fragments. Reconstruction (load-bearing) bone plates inserted at the time of resection are useful for controlling the position of the mandibular fragments [Alpert et al, 2012]. These plates are of sufficient strength to obviate the need for mandibulomaxillary fixation, permitting active use of the mandible in the immediate postoperative period. When the mandibular symphysis has been removed, the tongue can be sutured to the plate, maintaining its forward position to prevent airway obstruction. The bone plate can be left in place when the mandible is secondarily reconstructed with bone grafts, permitting mobility of the mandible during the healing phase of the bone graft. If the condyle requires removal with the surgical specimen and delayed bone reconstruction is chosen, the reconstruction bone plate may need to have a prosthetic condylar process attached until bony reconstruction is performed (see chapter 2.5).
If the resection requires intraoral exposure of the site, delayed bone reconstruction is usually chosen because of the high-infection risk of an immediate nonvascularized bone graft from oral contamination. Alternatively, microvascular bone flaps are an option.
The position of the mandible must be reestablished after the resection procedure to maintain proper occlusion of the remaining teeth. Pre-plating is the best option when possible (see Case 3). If pre-plating is not possible and when adequate teeth are present on each side of the resection defect, arch bars applied to the upper and lower teeth or intermaxillary fixation screws can maintain the occlusion after resection, with the patient in mandibulomaxillary fixation, when the reconstruction bone plate is being adapted. If the patient has inadequate teeth present on one or both sides of the resection defect, pre-plating (if possible) or plates spanning between the maxilla and mandible in areas away from the resection can be applied before resection and reapplied afterward to maintain the proper position of the mandible while the reconstruction bone plate is applied. Alternatively, a fix-bridge temporary plating system can be applied from one side to the other to maintain the position of the fragments until a reconstruction plate is adapted. The fix-bridge is then removed.
If the tumor has not expanded the buccal cortex of the mandible, in situ adaptation of the reconstruction bone plate can be performed before resection (pre-plating), especially if the tumor is benign and the outer cortex intact. This provides perfect positioning of the mandibular fragments so the occlusion should not be affected.
If the tumor has expanded or destroyed the buccal cortex, preadaptation of a bone plate can be performed by making a stereolithographic model of the affected mandible, burring down the involved area, and adapting a reconstruction bone plate to the model. The plate is sterilized and used during surgery, saving time intraoperatively. CAD/CAM technology is another option (see chapter 5.3.12).
2 Principles of defect bridging
When a discontinuity of the mandible is created, a reconstruction bone plate will be required to maintain the position of the residual mandibular fragments and the position of the mandible in space. These plates are strong (load-bearing) and can function for months until bone can be successfully transplanted to obtain osseous reconstruction across the defect. When applying reconstruction bone plates to a mandibular discontinuity, several factors are important:
A reconstruction bone plate 2.4 or similar is recommended because it has sufficient strength to transfer all forces of mastication across to the opposite side, ie, it is load-bearing [Alpert et al, 2012].
A minimum of three screws on each side of the defect are necessary for defect bridging. It is always better to have more ( Fig 2.4-1 ).
Reconstruction bone plates using locking screws are preferable because the chance of a screw loosening with resultant inflammation and (potentially) infection is minimized [Herford et al, 1988]. Loss of fixation is less likely than when nonlocking screws are used because attaching screws to the plate increases the rigidity of the fixation across the defect.
For purposes of this chapter, it is assumed that the tumors that are being removed are benign tumors requiring segmental resection because of involvement of both the alveolar process as well as encroachment on the inferior border. It is further assumed that stable internal fixation of the mandible will occur with a reconstruction bone plate primarily and osseous reconstruction will occur secondarily using nonvascularized bone.
Case 1: Segmental resection of an ameloblastoma in the posterior mandibular region where condyle can be maintained and there is expansion of buccal cortex: pre-plating is not possible ( Fig 2.4-2 ).
Expansion of the buccal cortex precludes pre-plating. Segmental resection of an expanding benign tumor in the posterior mandible/ramus region of the mandible is performed in one of three ways. The following steps highlight these procedures:
Exposure of the site is performed via a transoral approach. The soft-tissue incisions around the resection will vary depending on tumor involvement and location of previous biopsy site. All mucosa surrounding the biopsy must be excised with the specimen ( Fig 2.4-3 ).
For dentate patients, arch bars or intermaxillary fixation screws are placed.
If there will be ample bone remaining in the mandibular ramus after tumor resection, a condylepositioning plate spanning between the zygoma and the mandibular ramus can be applied ( Fig 2.4-5 ).
The resection is performed with burrs, saws, piezoelectric devices, etc ( Fig 2.4-4 ).
The occlusion is reestablished by maxillomandibular fixation (MMF). Wire ligatures are used in the clinical case ( Fig 2.4-5 ). Some surgeons prefer MMF via arch bars as shown in the drawings.
If a condyle positioning plate was adapted, it is now replaced to maintain the preoperative position of the mandibular ramus.
A reconstruction bone plate is adapted and secured across the defect. The MMF is released and the occlusion verified ( Fig 2.4-6 ).
The soft tissues are closed.
Alternatively, a stereolithographic model can be made prior to surgery and the expanded buccal cortex shaved down to mirror the opposite side. A reconstruction bone plate can be preadapted on the model, sterilized and used during surgery ( Fig 2.4-7 ).
Case 2: Segmental resection of an ameloblastoma in the posterior mandible/ramus region of the mandible that necessitates removal of the mandibular condyle requires that a reconstruction bone plate with a prosthetic condyle be available ( Fig 2.4-8 ).
The following steps highlight this procedure:
Exposure of the site is performed via a transoral approach. The soft-tissue incisions around the resection will vary depending on tumor involvement. An extraoral approach may be used simultaneously to facilitate resection and application of the reconstruction bone plate.
For dentate patients, arch bars or intermaxillary fixation screws are placed. For non-dentate patients, bone plates spanning between the maxilla and mandible are applied before resection and replaced after resection but before adaptation of the reconstruction bone plate. To increase the efficiency during surgery, a stereolithographic model that includes the temporal component of the temporomandibular joint can be made before surgery and the anticipated resection performed so that the reconstruction bone plate/condyle unit can be preadapted.
The anterior margin osteotomy is performed with burrs, saws, piezoelectric devices, etc. The dissection includes the entire ramus into the articular capsule. The inferior alveolar vessels require ligation at the mandibular foramen. The specimen is removed with the condyle attached and the articular disc is left in situ.
The MMF is reestablished.
A reconstruction bone plate that contains a prosthetic condyle is positioned into the glenoid fossa and adapted to the residual mandible. It is attached with a minimum of three screws ( Fig 2.4-9 ).
The MMF is released and the occlusion verified.
The soft tissues are closed. A drain may be needed.
Once the mucosa has healed (approximately 8 weeks), bony reconstruction can proceed.
Because the mandibular condyle has been removed, a costochondral bone graft with approximately 3–4 mm of cartilage can be used to reconstruct the missing condyle ( Fig 2.4-10 ). The occlusion is re-established and secured by MMF, and a transfacial approach to the posterior mandibular body and ramus is used to access the defect. After dissection of the bone plate and the creation of a surgical pocket for the bone graft, the condylar portion of the reconstruction bone plate is removed by cutting through the plate with a burr. The costochondral graft is slotted with a fissure burr to allow it to slide around the vertical portion of the bone plate, taking care to assure firm seating into the mandibular fossa ( Fig 2.4-11 ). Bone screws through the rib graft are used to secure the graft to the bone plate. The mandibular ramus and posterior body are then reconstructed by first securing a solid piece of corticocancellous iliac bone to the bone plate, angling the superior portion of the graft toward the lingual side to provide space for reconstruction of the basal bone and alveolus using particulate bone. The particulate bone is packed tightly to provide good bone density and the soft tissues are closed ( Fig 2.4-12 and Fig 2.4-13 ).
Because the rib graft has thin bony cortices, MMF is maintained for 6 weeks to allow the bone grafts to solidify.
Case 3: Segmental resection of a nonexpanding ameloblastoma in the body and symphysis region of the mandible is perhaps the most routine and uncomplicated of all resection procedures ( Fig 2.4-14 ).
The following steps highlight this procedure:
Exposure of the site is performed via a transoral approach ( Fig 2.4-15 ). The soft-tissue incisions in the area of resection will vary depending on tumor involvement. An extraoral approach can be used simultaneously if needed to facilitate resection and application of the reconstruction bone plate.
The mandible is preplated. The plate can either be removed or left attached during the resection depending on access ( Fig 2.4-16 ).
The resection is performed with burrs, saws, piezoelectric devices, etc.
If the symphysis has been removed, the tongue musculature is sutured to the bone plate to prevent glossoptosis ( Fig 2.4-19 ).
The soft tissues are closed.