Implant-Supported Prosthetic Rehabilitation of a Patient With Squamous Cell Carcinoma: A Case Report

Oral squamous cell carcinoma (SCC) is the most common head and neck cancer. Human papillomavirus can cause SCC. Drinking alcohol and cigarette smoking may also cause SCC in patients negative for human papillomavirus.¹  Treatment methods for head and neck cancers include radiotherapy, chemotherapy, surgical resection, or a combination of these techniques.²  Surgical resection can lead to a connection between the nasal and oral cavities and the maxillary sinus depending on the location and type of the tumor, resulting in a maxillary defect. The maxillary defect causes ambiguous speech because of the inability of air to be trapped, food and drink escaping into the nostrils, swallowing and chewing difficulties, and consequently malnutrition, respiratory diseases, and impaired facial esthetics.^3,4 

Reconstruction of a maxillary defect can be accomplished by surgically creating microvascular flaps or by using a prosthetic obturator. Microvascular flaps are recommended for large defects, whereas small defects can be treated with obturators.⁵  If surgical reconstruction is not possible because of the duration of treatment, general status, medical risk of operation, risk of complications, length of hospital stay, or patient's request, the only remaining treatment option is the obturator.^4–6  Prosthetic rehabilitation of the maxillary defect with obturator is a common treatment option because of the low cost, ease of modification of the prosthesis, and immediate provision of oral function and facial esthetics. In addition, because the site is easily visible, in the event of cancer recurrence, a second surgical operation is not necessary; thus, a decreased length of hospital stay can be counted among the advantages of the obturator.^7,8 

Support, retention, and stability of the obturator depend on the size of the defect site, the number and position of healthy support teeth, the remaining residual alveolar ridge, and the hard palate. In addition, insufficient retention of the obturator may be caused by xerostomia that develops as a result of radiation and/or absence of saliva secretion properties of free tissue flaps. In complete edentulous patients, the obturator generally lacks stability and retention.^2,4,5,7,8 

Retention and support for the obturator can be provided with residual alveolar ridge, surgical defect, or implants placed in the zygomatic bone.²  In previous studies, different attachments such as ball, bar, and telescopic attachments have been defined to provide retention of the obturator.^6,9–11  This case report describes implant-supported prosthetic rehabilitation of a patient undergoing maxillary resection as a result of SCC.

Following a diagnosis of SCC (pT4aN0M0), a 53-year-old male patient underwent a partial maxillectomy at the Department of Oral and Maxillofacial Surgery in 2018. Before surgical resection, an impression was made from the patient with hydrocolloid impression material (Blueprint, Dentsply, Rome, Italy), and casts were obtained from type IV dental stone (Ultrarock, Kalabhai, Mumbai, India). Considering the resection planned by the surgeon, a surgical obturator was prepared from clear heat-polymerized acrylic resin (Rodex, Willmann & Pein GmbH, Barmstedt, Germany). Following maxillectomy surgery under general anesthesia, the surgical obturator was adjusted using soft lining material (Mollosil, Detax GmbH & Co.) in the patient's mouth. After 1 week, the surgical obturator was removed, and until the surgical field was completely healed, an interim obturator to the maxilla and a removable partial denture to the mandible were prepared by the conventional method to improve the patient's function, speech, swallowing, and esthetics. The interim obturator was rechecked 3 times, and corrections were made if necessary. When the patient was kept an appointment for the construction of a definitive obturator 3 months after the operation, he stated that he was not satisfied with his current obturator because of insufficient retention and stability and chewing difficulties. The obturator that received support from undercuts in the defect area also caused pain. Computerized tomography was made to evaluate the patient's zygomatic and remaining maxillary bone anatomy, and a decision was made to construct an implant-supported maxillofacial prosthesis for the maxillary arch to improve the patient's current condition.

After evaluating the local and systemic status of the patient, 2 zygomatic implants (Implance, AGS Medical, Trabzon, Turkey), one on the right side (4.3 × 35 mm) and one on the left side (4.3 × 37.5 mm), were placed under general anesthesia in accordance with the occlusal plane. In addition, 2 conventional implants were placed in both the right (4.8 × 12 mm) and left (4.8 × 8 and 4.8 × 10 mm) maxillary posterior regions (Figure 1). Because of the insufficient interocclusal distance in the posterior region, it was decided to extract tooth number #17 and reconstruct the existing removable partial denture in the mandibular arch. Implants to the maxillary left posterior region were performed in a single-stage surgery. Implants placed in the maxillary right posterior region were expected to heal in the submerged position. A second-stage surgery was performed 4 months later. After the soft tissue healing was completed, the patient's prosthetic rehabilitation was started (Figure 2).

To perform a screw-retained prosthetic rehabilitation, multiunit abutments were placed in conventional implants. To prevent the impression material from escaping to undesired places in the defect area and to easily move it away from the existing undercut areas, sponges were placed in specific places. A single-stage impression was made with vinylpolysiloxane impression material (Elite HD+, Zhermack, Badia Polesine, Italy) using a splinted open tray impression technique¹²  for the maxillary arch. In the mandibular arch, the definitive impression was made with hydrocolloid impression material using the individual impression tray, and casts were obtained with type IV dental stone.

Based on the casts, a light-polymerized acrylic resin base plate was prepared on the maxillary arch, and a metal framework was prepared on the mandibular arch. After the compatibility of the framework and base plate was checked in the patient's mouth, vertical and horizontal records were made, and the maxillo-mandibular relationship was transferred to the articulator (Artex CR, Amanngirrbach, Pforzheim, Germany) with a facebow (Artex Facebow, Amanngirrbach, Pforzheim, Germany). Next, bilateral cast Hader bars (VSP-GS, Bredent GmbH, Senden, Germany) were prepared from cobalt-chromium alloy (Wirobond SG, Bego, Bremen, Germany). The cross-sectional shape of the bar is round, and its cross-sectional area is 5 mm². Because of the insufficient interocclusal distance at the posterior region, a bar extending over the most distal implants was prepared in the form of a molar tooth (Figure 3). The passive fit of the bar was checked by a Sheffield test and the implant/multiunit/bar connection was checked by panoramic radiography (Figure 4). For retention, 2 joint snap-in matrices (Vario-Soft-VSP-GS, Bredent GmbH) and 1 friction matrice (Vario Soft 3, Bredent GmbH) were used both on the right and left side (Figure 5).

After tooth alignment, the positions of the teeth, esthetics, and occlusion were checked in the patient's mouth. The midline and occlusal plane were corrected, and removable prostheses were finished with the conventional method and delivered to the patient (Figure 6a and b). The patient was informed about how to achieve optimum oral hygiene and was recommended to use dental floss and an interdental brush in addition to a toothbrush.

Rehabilitation of an edentulous patient whose maxillary was resected as a result of a tumor is very difficult. Although the treatment of patients varies depending on the location and size of the defect site, the key decision is whether the defect site is best rehabilitated surgically or prosthetically. In a systematic review study, Brandão et al⁷  stated that well-designed clinical studies are needed to determine whether obturator prostheses or free tissue transfer is better in terms of quality of life of patients. However, they stated that obturator prostheses may be a better option because of a shortened treatment period and the immediate return of the patient's oral function. They also suggested that the patient's age may be considered as a criterion in determining the treatment option. Different surgical reconstructive options can be reliable for almost any size defect; however, the treatment of small defects with the obturator is a valuable option, especially for patients whose general health condition does not allow for surgery.⁵ 

Obturators often lack stability and retention. If the patient's defect area is large, stability and retention will be further reduced. In such cases, the use of dental implants placed in the residual alveolar ridge and/or zygomatic bone will increase stability and retention. The main indication for zygomatic implants is rehabilitation of the edentulous atrophic maxilla and the defect site after maxillary resection.^11,13  Studies have indicated that zygomatic implants can be used successfully in specific cases.^14–17  Zygomatic implants can be applied to a single implant (unilateral), 1 implant to each maxillary process (bilateral), or 2 implants to each maxillary process (quad). Because bilateral zygomatic implants cannot supply sufficient resistance against occlusal loads, it is recommended to provide support anteriorly with short implants or to use quad zygomatic implants.¹⁷  de Sousa and Mattos¹⁸  stated that retention will be limited if conventional implants are made unilaterally and that the implant survival rate will decrease by causing unwanted stresses in the implants because of acting as a cantilever of the obturator on the contralateral side. Miyamoto et al¹³  stated that making 1 or 2 implants to the zygomatic bone on the defect side and 2 or 3 implants to the residual alveolar bone on the unaffected side would provide an ideal distribution according to their finite element analysis. In the present case, if only conventional implants were made to the posterior maxilla, in the anterior-posterior direction, it would result in an obturator cantilever in the anterior as if the unilateral implants were made. Bilateral zygomatic implants were made and splinted with posterior maxillary residual bone implants to prevent this cantilever movement, reduce stress in the implants, and support the obturator in the anterior. The aim was to ensure that the occlusal loads were delivered to both zygomatic implants and conventional implants at a minimum level by achieving an ideal distribution. In addition, the fact that the opposite occlusion was a removable partial denture resulted in less of an occlusal load.

The difference between the zygomatic bone and the alveolar bone is that, after tooth loss, resorption may be seen in the alveolar bone, whereas there is no such resorption in the zygomatic bone. Although implants are made to the zygomatic bone in cases where there is no residual alveolar bone, it is generally not appropriate to place implants on the zygomatic bone because the zygomatic bone contains various amounts of trabecular bone.¹⁷  Zygomatic implants are somewhat difficult to perform in a hospital setting under general anesthesia, the use of relatively long implants, and difficulties in determining the position of the implants because of the anatomy of the zygomatic bone are issues. In addition to conventional implant complications, issues such as perforation of the orbital floor, intracranial placement of the implant, paresthesia in the infraorbital nerve, and subperiosteal and sinus infections may occur.^17,19  Despite all these disadvantages, zygomatic implants, which are ideally planned before the operation and made by an experienced surgeon, provide retention, stability, and support to the obturator that will be fabricated after maxillary resection and enable much better functions such as chewing, speaking, swallowing, and improvement in patients' quality of life.

Implant-supported overdentures can be attached to implants with different prosthetic retention systems such as ball, magnet, locator, or bar. Hygienic maintenance of the surroundings of the bars is more difficult than other single-unit attachment systems. In research reports, values indicating the state of peri-implant health such as pocket depth, plaque index, bleeding index, and gingival index were found to be higher for bar attachments compared with single-unit attachments.^20,21  Thus, sufficient space should be left between the inferior surface of the bar and the underneath soft tissue to allow the entrance of dental floss and/or interdental brushes, and the inferior surface should be made convex when designing the bars.²  The patient should be informed in detail about cleaning of the implants, prosthetic attachments, soft tissues, and prosthesis. In addition, professional cleaning should be done at regular intervals with follow-up appointments.

Misfit between implants and prosthetic components can lead to biological and mechanical complications. Conventional cast bars have a risk of misfit. The tilted implants, implants on different vertical levels, and long-span bars increase this risk.²²  For implant-supported framework fabrication, cobalt-chromium alloys are a suitable alternative to precious metal alloys because of their low cost and corrosion resistance. Compared with the passive fit and the stresses transmitted to the implants from cast frameworks prepared by using different materials, commercially pure titanium showed better results than cobalt-chromium alloy.^23,24  The use of computer-aided design and computer-aided manufacturing technologies such as milling or laser welding would further improve the precision of the compatibility between implants and prosthetic components.^22,25  However, a specific numerical threshold value to identify passive fit is not supported by scientific evidence. In addition, there is no scientific report identifying how much misfit between implants and prosthetic components is clinically acceptable without causing any complications. In the present case, the treatment applied to the patient was costly. Because of the economic condition of the patient, the bar was prepared from cast cobalt-chromium alloy to avoid increasing the cost. Moreover, cobalt-chromium alloy has high mechanical strength.²⁶  Therefore, its use is advantageous in patients with limited interarch distance.

Implant-supported maxillofacial prostheses are a valuable treatment option to improve quality of life, function, esthetics, speech, and swallowing after maxillary resection. Optimal interdisciplinary communication is essential to provide satisfactory prosthetic results.

Abbreviations

SCC:

oral squamous cell carcinoma

This work was presented at the 24th International Scientific Congress of Turkish Prosthodontics and Implantology Association, Muğla, Turkey, November 2019. The authors thank CDT Ismail Karabulut and ByDental Karabulut Laboratory for design of the bar and fabrication of the dental prosthesis.

The authors declare no conflicts of interest.