Maxillofacial Prosthetics and the Radiation Oncology Patient

Given that the treatment of head and neck neoplasms often involves radiation therapy alone or in combination with surgical ablation or chemotherapy, it is useful for the maxillofacial prosthodontist to become involved in patient care during the diagnostic phase of any proposed intervention. Because the risk for osteoradionecrosis is increased when a poor dentition is allowed to remain within irradiated maxillary or mandibular alveolar bone, a thorough evaluation of the dentition and periodontium is extremely useful in establishing dental prognoses before the initiation of radiation therapy. Additionally, because the xerostomia induced by a majority of head and neck radiation fields requires an increased diligence respecting home care and follow-up during and after radiation therapy, the maxillofacial prosthodontist’s early consultation can help prevent dental disease that could later contribute to added debility, possibly including osteoradionecrosis.

Because many head and neck cancers are treated by surgical ablation followed by radiation therapy, the maxillofacial prosthodontist’s diagnostic efforts should be performed preoperatively so that any necessary oral surgical interventions can be accomplished in conjunction with the otolaryngologist’s surgical encounter. This allows a sufficient amount of time for mucosal and alveolar bone healing before the initiation of radiation therapy, which usually occurs 6 weeks later. Patients whose dentoalveolar evaluations are accomplished after ablative surgeries are sometimes fast approaching a juncture in their care when radiation therapy should expeditiously commence in the interest of controlling local and regional oncologic disease, and delays associated with healing oral surgical wounds may be unacceptable. Likewise, the maxillofacial prosthodontist must consider similar delays in the initiation of radiation therapy when treatment plans call for primary radiation therapy or radiation therapy to be delivered concurrently with chemotherapy in the absence of an ablative surgical encounter.

Dental Diagnoses and Oral Surgical Management Preceding Radiation Therapy

Any dentoalveolar evaluation in preparation for radiation therapy should include a thorough assessment of the periodontium, as well as the dentition, and should be done with the intent of establishing lifelong prognoses for those teeth likely to be included in radiation therapy fields anticipated to receive doses in excess of 5000 cGy.

Extractions are indicated for teeth with poor prognoses meeting the criteria listed in Box 98-1.^1–13 Although the assessment is accomplished in the interest of preventing osteoradionecrosis, it is also done considering the potential for any prosthetic rehabilitation that may become necessary. Because this assessment requires consideration of primary tumor size and location, as well as regional lymph node status, diagnostic information gleaned through participation in multidisciplinary head and neck tumor board conferences supplements decisions made in the dental clinical setting where medical imaging is limited and endoscopy is not typically available.

In addition to an evaluation of the dentoalveolar structures, the maxillofacial prosthetic assessment includes intraoral and extraoral palpation and visualization of hard and soft head and neck tissues, panoramic radiography, and intraoral radiography of those teeth thought to be sound enough to retain vis-à-vis imminent radiation therapy. Although the intraoral radiography generally includes routine bitewing and periapical exposures, occlusal radiographs are sometimes helpful for primary tumor staging by affirming bony erosion associated with oral cavity lesions affecting gingivae, buccal or palatal mucosa, or the floor of mouth.

With respect to the periodontium, teeth with periodontal sulci equal to or greater than 5 mm in depth may be assigned poor prognoses and should be considered candidates for extraction before radiation therapy. Likewise, teeth with mucogingival defects or furcation involvement should be given similar prognoses and should be considered for extraction. Although prior successful endodontic treatment should not necessarily condemn a tooth for extraction, the unpredictability of endodontically treating active periapical or pulpal pathoses in the usually limited time available before radiation therapy should give rise to enough caution that the extraction of endodontically involved teeth should be strongly considered. Although gingival recession is not in itself a definite indication for exodontia in the absence of deep periodontal sulci, consideration must be given to the maintenance of radicular surfaces exposed to the xerostomic oral environment as a result of recession, because cementum is more prone to the development of inoperable carious lesions than is the more mineralized coronal enamel.

With regard to the dentition, mobile primary teeth should be extracted from alveolar bone to be irradiated, as should any unrestorable teeth. If no plan is or can be made to restore the occlusion of unopposed posterior teeth that will be irradiated, consideration should be given to their extraction, because subsequent supraeruption can contribute to expansive gingival embrasures that are difficult to maintain free of plaque and food debris, possibly resulting in localized periodontitis or radicular carious lesions that are difficult or even impossible to repair. Although extracting impacted teeth from alveolar bone soon to be irradiated is meritorious, consideration should be given to the length of healing time often required of associated surgical sites. This is particularly true of impacted third molars that carry an increased risk for developing acute alveolar osteitis. When deciding whether an impacted tooth should be extracted before radiation therapy, the impacted tooth’s likelihood of erupting enough to gain exposure to the oral environment should be considered. If a bony impacted tooth is unlikely to erupt permucosally, the relative risk of it contributing to a future osteoradionecrosis should be judged low and the tooth should be allowed to remain in situ, unless of course there is a pathosis associated with the tooth that overrides a conservative approach. Conversely, an impacted tooth within a proposed radiation field whose anatomic position suggests a potential for intraoral eruption should be deemed a candidate for extraction before radiation therapy.

The presenting or oftentimes soon to be rendered edentulous or partially edentulous condition of many newly diagnosed head and neck cancer patients also demands evaluation of maxillary or mandibular exostoses, tori, and tuberosities primarily in preparation for removable, but sometimes fixed, prosthodontic rehabilitation after the completion of oncologic care. Preprosthetic surgery to include the removal of tori and exostoses and the reduction of tuberosities that could prove obtrusive relative to future prosthetic considerations should coincide with any necessary exodontia as far in advance of radiation therapy as possible. The reduction of these anatomic structures can improve prosthetic-bearing areas and reduce the risk of prosthetic-induced mucosal violations that could contribute to the development of osteoradionecrosis. Although the completion of such preprosthetic surgery before radiation therapy is paramount for those structures lying within proposed radiation fields, the extended mucogingival flaps required for removing bony prominences require consideration for the removal of such prominences even if their juxtaposition to the primary field does not lend to an anticipated dose exceeding 5000 cGy.

Patients using removable prostheses should be advised to minimize prosthetic use during and immediately after radiation therapy to diminish the risk of exacerbating mucositis underlying intaglio prosthetic surfaces, particularly when prostheses are ill fitting and radiation therapy fields directly encompass the oral cavity. Even small prosthesis-related mucosal ulcerations could result in the exposure of alveolar bone and the initiation of osteoradionecrosis. When oral cavity mucositis is anticipated, restorative dental care of high priority should be expeditiously undertaken considering the fact that compromised patient comfort will make restorative dental care difficult or impossible after as little as 1000 to 2000 cGy of radiation. Routine dental prophylaxes should also be sought before head and neck radiation therapy because the relative attenuation of plaque and calculus could diminish the severity of gingival mucositis induced by direct oral cavity irradiation and could decrease the potential for cariogenic dental colonization associated with xerostomia. Additionally, a hiatus in orthodontic care could be considered for those whose radiation therapy coincides with orthodontia because the removal of bands, brackets, and wires could lend to a diminution of trauma to inflamed mucosal surfaces.

For patients retaining a full or partial natural dentition whose head and neck radiation therapy will induce xerostomia, it is important to institute a daily and lifelong regimen of topical fluoride gel use to concur with the initiation of radiation therapy.¹–⁷,⁹,¹²,¹⁴–¹⁸ This is true for patients whose retained dentition is or is not encompassed by radiation therapy fields. Dental casts generated from clinical impressions recorded before radiation therapy but subsequent to any oral surgical procedures in preparation for radiation therapy should be used to fashion thermoplastic vinyl fluoride gel carriers (Fig. 98-1) into which topical fluoride gel can be applied. After routine brushing and flossing, patients should be instructed to place pharmacy-prescribed 1.1% neutral sodium fluoride or 0.4% stannous fluoride gel into the dental aspects of the fluoride gel carriers for 5 to 10 minutes every day indefinitely before applying them to their dentition. The topical fluoride gel application should be followed by expectoration of excess gel and a period of 30 minutes during which the patient is encouraged not to rinse, eat, or drink.

Figure 98-1. Thermoplastic vinyl fluoride gel carriers and the models on which the gel carriers are made.

Prosthodontic Support of the Radiation Oncologist

The maxillofacial prosthodontist may be called on to lend support to the radiation oncology team in their efforts to manage dosimetry by way of patient posturing,^19–22 anatomic displacement or shielding,^3,6,19,23,24 fabrication of brachytherapy appliances,^3,25 or construction of devices capable of mimicking normal tissues.^3,19,24 Although the devices should be constructed following any oral surgical procedures that are done in preparation for radiation therapy, they must be manufactured before radiation therapy simulation appointments in that they must be positioned at the time of simulation.

The undulating topography of head and neck cutaneous structures makes the uniform delivery of radiation difficult at best without the use of boluses constructed of materials considered more or less to be tissue equivalent in terms of their relative resistance to photon or electron penetrance. Consequently, the radiation oncologist may call on the maxillofacial prosthodontic team to assist with facial moulage recording and bolus fabrication when evaluating the physics associated with treating malignant head and neck skin lesions. A facial moulage cast with a gypseous dental stone can aid the radiation oncology team’s delineation of a proposed treatment field and prescription of an appropriate bolus thickness before a bolus is constructed of dental baseplate wax or polymethylmethacrylate. Boluses can be particularly useful for providing more even dose distributions for nasal (Fig. 98-2) or orbital malignancies.

Figure 98-2. A, Basal cell carcinoma of the nasal bulb to be treated with external electron beam radiation therapy. B, Facial moulage being recorded. C, Facial moulage prepared for casting. D, Model on which the wax bolus was fabricated. E, Frontal view of the bolus. F, Lateral view of the bolus. G, Intaglio surface view of the bolus.

Although Aquaplast masks are routinely used to immobilize patients throughout the course of head and neck radiation therapy,¹⁹ customized intraoral devices can be used to provide a stable maxillomandibular relationship when attempts are made to precisely localize an external photon or electron beam relative to oral cavity anatomy. The use of intraoral positioning devices is particularly useful when there is a desire to shield all or part of the maxilla or the mandible from radiation when the opposing jaw is to be included in an external beam field. By positioning the mandible in a prescribed open position with the use of a polymethylmethacrylate appliance that prevents deviation from an arranged spatial relationship to the maxilla, the radiation oncology team can make shielding possible by way of replicable daily positioning of patients from the time of simulation to the completion of radiation therapy. This strategy is helpful when mandibular structures are to be spared from sinonasal or maxillary radiation or when maxillary structures are to be excluded from fields involving the floor of mouth, oral tongue, or other sites encompassing the mandible. In addition to stabilizing the maxillomandibular relationship, the incorporation of radiopaque materials such as orthodontic wire, ball bearings, or gutta percha into such devices can lend support to the radiation oncology team’s efforts to identify structures for inclusion in proposed radiation fields at the time of simulation (Fig. 98-3).

Figure 98-3. A, Panoramic radiograph of a patient’s status after segmental mandibulectomy, total glossectomy, floor of mouth resection, and microvascular fibula free flap reconstruction for a squamous cell carcinoma. B, Models of the maxillary and neomandibular structures articulated in relation to one another. C, Wax pattern of the proposed positioning device before its completion. The wax pattern covers the microvascular free flap tissues in the area of the floor of mouth once occupied by the oral tongue. Bilateral pillars engage the maxillary model to maintain a consistent maxillomandibular relationship during each radiation therapy fraction. D, Clinical view of the anterior aspect of the polymethylmethacrylate positioning device. A segment of orthodontic wire placed within the midsagittal plane of the positioning device identifies the dorsum of the microvascular free flap structures during radiation oncology simulation and ensures its inclusion in proposed radiation therapy fields. E, Simulation radiograph exposed with the positioning device positioned intraorally.

Furthermore, intraoral polymethylmethacrylate appliances can be constructed that harbor Lipowitz’s alloy.^19,21,26 Being the same metal used by radiation oncology teams to create the portals and shields suspended from frames situated between patients and linear accelerator collimators that fashion conventional three-dimensional (3D) conformal radiation therapy fields, Lipowitz’s alloy, a low-fusing combination of lead, bismuth, tin, and cadmium, can suitably shield intraoral anatomy when electron beam therapy is indicated. These devices typically serve the dual purposes of shielding and maxillomandibular positioning because their interocclusal construction also stabilizes the maxillomandibular relationship. These alloy-containing intraoral appliances are often fabricated for lip (Fig. 98-4) and ipsilateral parotid gland (Fig. 98-5) fields. The protective intent of these appliances is supplemented when they are constructed in such a fashion as to physically displace soft tissues away from the source of an electron beam. When parotid gland shielding devices are used, patients are instructed to position the tongue anteriorly during treatment. Doing this while occluding on the interocclusal appliance forces the bulk of the tongue into a contralateral position where less radiation is encountered. When parotid gland malignancies are treated with a combination of photons and electrons, radiation oncologists sometimes find it helpful to use two appliances, one with Lipowitz’s alloy and one lacking metal. The use of the appliance devoid of alloy during the delivery of photons offers the advantages of consistent day-to-day maxillomandibular positioning and soft tissue displacement without the electron backscatter potentially associated with an appliance that harbors a large volume of metal.

Figure 98-4. A, Clinical frontal view of a Lipowitz alloy-containing shielding device used during external electron beam radiation therapy for a squamous cell carcinoma of the lower lip. The device was held in its interocclusal position during fractionation and served not only to shield normal anatomy but also to anteriorly displace the labial tissues being treated from posterior structures to be spared of radiation. B, Clinical frontal view of a Lipowitz alloy-containing shielding device with the patient’s lips retracted. C, Extraoral view of the shielding device.

Figure 98-5. A, Shielding device positioned on the articulated models on which it was constructed. The device was fashioned for use during radiation therapy for a left parotid gland adenoid cystic carcinoma. The device extends as far into the oropharynx as the patient will allow without gagging. Lateral view demonstrates that portion of the polymethylmethacrylate intended to displace buccal tissues in an ipsilateral direction to further separate tissues to be treated from those that should not be treated. B, Clinical verification of the fit of the device before it is filled with Lipowitz’s alloy. C, The device is hollowed from the medial side before being loaded with Lipowitz’s alloy.

The radiation oncologist’s desire for tissue equivalence is not limited to the application of surface boluses because postoperative tissue voids can give rise to an uneven distribution of radiation resulting in suboptimal dosing or overdosing of tissue peripheral to cavernous surgical defects such as those resulting from a maxillectomy. Unfortunately, however, the rigidity of wax and polymethylmethacrylate does not solely allow the dependable use of these materials as intracavitary tissue mimicking materials by virtue of soft tissue and bony undercuts usually associated with these defects. Consequently, filling an intracavitary void with tissue-equivalent material in the interest of improving radiation therapy dose distribution often requires the use of pliable materials that assist daily insertion and removal without unduly traumatizing surrounding tissue. The combination of an inflexible customized intraoral device that stabilizes the maxillomandibular relationship with a pliable material that fills an intracavitary void can, however, overcome the limitations posed by the complex nature of a maxillectomy defect. This combination can be achieved by constructing an intraoral positioning device that incorporates a shelf of polymethylmethacrylate immediately inferior to the maxillectomy defect. The device is capable of supporting a balloon that can be inflated with a tissue-equivalent mixture of radiopaque liquid and water before radiation therapy simulation and each fraction (Fig. 98-6).

Figure 98-6. A, Anterior view of articulated maxillary and mandibular models and the wax pattern used to generate an intraoral device that serves to repetitively position the mandible and oral tongue and support a diaphragm to be filled with water during radiation fractionation. The water-containing diaphragm thus occludes maxillectomy defects and serves as a tissue-equivalent material. B, Inferior view of the wax pattern demonstrating an axial shelf to inferiorly confine and exclude the oral tongue from the radiation fields. C, Anterior view of the finished intraoral device. D, Anterior view of the positioned intraoral device demonstrating the diaphragm-supporting shelf situated immediately inferior to the maxillectomy defect.

Although the maxillofacial prosthodontist is not likely to lend assistance in the clinical application of interstitial brachytherapy, the management of intracavitary brachytherapy often requires the combined efforts of the radiation oncology and maxillofacial prosthetic teams. The orbit and nasopharynx comprise the most common intracavitary head and neck brachytherapy sites, and the stents used for these sites are typically constructed of polymethylmethacrylate that surrounds catheters into which radioisotopic seeds are inserted. The radiation oncologist or physicist, in accord with an intended dose distribution specific for the radioisotope proposed for use, prescribes the catheter positions in consultation with the maxillofacial prosthodontic team after the generation of a master cast from an impression of the site to be treated. When the stents are positioned, they are retained for the duration of treatment by anatomic soft tissue undercuts (Fig. 98-7) or dentoalveolar structures.

Figure 98-7. A, Orbital exenteration site for a patient whose positive melanoma margins necessitated postoperative brachytherapy. B, Brachytherapy device in position demonstrating accessibility to catheters for radioisotopic seeding and treatment.

Dental Management during Radiation Therapy

Recalling patients every 2 to 3 weeks during radiation therapy is beneficial from the standpoint of identifying dental, periodontal, and mucosal pathoses that may coincidentally appear or arise secondary to radiation therapy. Such a follow-up interval is also meritorious for reinforcing the import of increased hygiene vigilance and the use of topical fluoride gel. It is not uncommon for patients with newly diagnosed life-threatening neoplasms to forget virtually everything that was discussed during an initial maxillofacial prosthodontic evaluation that may have coincided with appointments in otolaryngology, radiation oncology, diagnostic radiology, nuclear medicine, medical oncology, anesthesia, internal medicine, and oral surgery. The overwhelming nature of patients’ initial oncologic experience lends to a necessary redundancy with respect to patient communication and education.

Although restorative dental care can be accomplished during radiation therapy, procedures that potentially exacerbate mucositis should be avoided. However, particularly in cases involving oral cavity radiation, patients may reach a point—usually after 2 to 3 weeks of fractionation—where mucositis is severe enough that they do not want to be subject to dental restorative procedures. Regardless of the need for restorative dental care, a readily concocted mouthrinse to obtund mucositis consists of mixing 1 teaspoon of baking soda and 1 teaspoon of salt in a quart of water that is warmed before use. Alternatively, a compounded solution of tetracycline, diphenhydramine, nystatin, and hydrocortisone termed “magic mouthwash” can be obtained from a pharmacy. Two teaspoons of magic mouthwash swished and gargled thrice daily before swallowing serves to mollify radiation-induced stomatitis and pharyngitis.

Dental Management after Radiation Therapy

Follow-up examinations should be arranged every 4 to 8 weeks after the completion of radiation therapy with patients returning to a standard interval thereafter as long as they comply with hygiene and daily topical fluoride gel regimens. Patients can be considered routine patients in terms of their candidacy for restorative dental care after head and neck radiation therapy; however, they must understand that they should not undertake bone-exposing oral surgery within anatomic areas that received more than 5000 cGy of radiation. Such exposures could prompt the development of osteoradionecrosis that could precipitate a pathologic fracture or necessitate a bony resection.^{2,6,7,9,12,27–34} Therefore when patients complete their radiation therapy, they should be asked to inform the maxillofacial prosthodontist of any future oral treatment proposal to include a tooth extraction, the surgical placement of an endosseous titanium implant, or periodontal or endodontic flap surgery in advance so that an estimation of dosimetry can be provided to the surgeon. When these estimates indicate that a bone-exposing violation of mucosa could occur in an area that received more than 5000 cGy of radiation, the Marx hyperbaric oxygen protocol should be considered as an adjunct to the surgical procedure.^{3,6,7,9,12,27,28,32} Marx’s hyperbaric oxygen regimen involves 90-minute dives at a barometric pressure of 2.4 atmospheres while breathing 100% oxygen. Twenty dives are undertaken preoperatively, and 10 dives are completed postoperatively in the interest of stimulating an angioneogenesis that partially and irreversibly³² counteracts the hypovascularity caused by radiation therapy that is responsible for the increased risk of osteoradionecrosis.