Rehabilitation of an irradiated marginal mandibulectomy patient using immediately loaded basal implant-supported fixed prostheses and hyperbaric oxygen therapy: A 2-year follow-up

Highlights • Mandibulectomy after oral cancer resection can cause severe facial disfigurement.• The use of adjunctive radiotherapy may compromise the success rate of reconstructive implant therapy.• Hyperbaric oxygen therapy (HBO) can repair tissue damage after radiotherapy.• Basal implants reduces risk of peri-implantitis and osteoradionecrosis.• This report describes HBO and basal implant treatment for marginal mandibulectomy.• HBO and basal implants are successful treatment modalities for these patients.


Introduction
Mandibulectomy following oral cancer resection can result in a severe facial disfigurement with multiple disabilities, such as impaired mastication, phonation, swallowing, and poor salivary and tongue control; these adversely affect patient quality of life [1][2][3][4]. Although surgical eradication is the most commonly used treatment modality for oral cancer, patients with extensive primary and/or late stage cancer may require adjunctive radiotherapy or chemotherapy [3,5]. The majority of patients with head and neck cancer receive between 50 and 70 grays (Gy) as a therapeutic dose [6].
The use of HBO to prevent osteonecrosis was first introduced by Marx et al. [11] in 1985, who recommended 20-40 preoperative dives once or twice per week, for 60 min each, and 10 postoperative dives [11]. A well-known adjunctive protocol of HBO for tooth extraction or implant therapy is the provision of 20-30 sessions before (each session lasting 90 min) and after (each session lasting 10 min) the treatment; these sessions are conducted at an absolute pressure of 100% oxygen, and at a compression of 2.4 atmospheres [6]. This protocol ensures better wound healing in the implant site, especially when the bone in this region has received more than 50 Gy of radiation [1,6].
The prosthetic rehabilitation of patients with mandibular resection is extremely challenging due to the severe loss of both hard and soft tissues, reduced vestibular sulcus, diminished salivary flow following radiation, and the psychological status of the patient [1,2,7]. Edentulous patients who have undergone a marginal mandibulectomy commonly present with a limited remaining bony structure; this may compromise the retention, support, and stability of a removable reconstructive prosthesis [1,7]. Thus, the use of dental implants can significantly improve the functional outcome of the prosthesis [1,2,6,7]. Nevertheless, many risk factors may influence the use of dental implants in patients who have undergone radiotherapy, such as patient age, sex, implant site, total radiation dose, time between end of radiotherapy and implant osteotomy, and type of radiation therapy [6,[12][13][14][15]. Furthermore, the use of endosseous implants may necessitate a bone grafting procedure, which can be further complicated with the induction of radiotherapy [16][17][18]. On the other hand, the use of basal implants in these patients can be successfully attempted to avoid the bone grafting procedure and its associated complications [16][17][18].
Basal implants are designed to utilize the strongest cortical bone available in the jaw [16][17][18]. The basal cortical screw (BCS ® ) implant is a special basal implant design characterized by a (1) minimally invasive crestal insertion approach (flapless technique); (2) smooth surface that eradicates the risk of peri-implantitis and thus eliminates the risk of osteoradionecrosis; and (3) thin guidance tip that ensure the centralization of the implant [16][17][18]. Moreover, the BCS ® implant has a monoblock design, which minimizes the risk of prosthetic failure associated with the implant-abutment interface. Additionally, implants are splinted using a circular metal frame- work that enhances the biomechanical distribution of masticatory forces; this facilitates the use of an immediately loaded prosthesis [16][17][18].
The main cause of implant failure in irradiated bone is the lack of osseointegration and primary stability [7,8,12]. As such, the use of basal implants can be very advantageous in irradiated jaws,  owing to the high primary stability achieved by deeply anchoring the horizontal plates of the implants inside the cortical bone [16][17][18]. Although the successful use of immediately loaded, fixed, basal implant-supported prostheses has been reported [16][17][18], its efficacy in patients who have undergone mandibulectomy and radiotherapy remains unclear. This report is the first to describe the use of HBO and basal implant treatment in a patient with marginal mandibulectomy. This case report complies with the SCARE criteria [19].

Presentation of case
A 46-year-old male was referred to the Department of Prosthodontics after marginal resection of the mandible, owing to squamous cell carcinoma. The patient underwent radiation sessions (with a total dose of 70 Gy) 16 months following mandibular resection. On clinical examination, the patient presented with severely resorbed edentulous jaws, with an anterior marginal mandibular resection (Fig. 1a, b). The vestibular sulcus of the mandible was obliterated anteriorly (Fig. 1b). A radiographic evaluation of the maxillary and mandibular jaws, using the digital panoramic view (Planmeca ProMax, Finland), showed features of hypocellularity. (Fig. 1c).
A multidisciplinary team was formed to formulate a comprehensive treatment plan, which involved the construction of a vestibuloplasty stent, and the provision of 20 HBO sessions (90 min each) before implant treatment, followed by 10 sessions postoperatively to improve the bony foundation [1,6,7]. This was followed by the insertion of BCS ® implants to support the fixed prostheses, and vestibuloplasty to improve the esthetic outcome. The treatment plan was fully discussed with the patient, and informed consent for treatment and publication was obtained. Ethical approval was acquired from the ethical committee of the authors' institute.

Treatment
Both panoramic and cone-beam computed tomography views were captured following the first 20 sessions of HBO (Fig. 1d, e). A mandibular diagnostic impression was obtained using irreversible hydrocolloid to obtain a diagnostic cast, on which a heat-cured acrylic resin vestibuloplasty stent was constructed (Fig. 1a-f).
The surgical procedures were performed under aseptic conditions and antibiotic prophylaxis. Local anesthesia (lidocaine 2% with adrenaline 1:100000) was injected, and 16 BCS ® implants of a suitable length and width were inserted using a flapless technique (Fig. 2).

The definitive fixed basal implant-supported prostheses
Impression copings were secured and the final impression was acquired using silicone impression material (Ivoclar Vivadent AG, Schaan, Liechtenstein) (Fig. 3a). One day later, a metal framework try-in was attempted (Fig. 3b). On the third day, the final acrylic hybrid prostheses were inserted and cemented using Glass Ionomer Luting Cement (Fuji I ® GC Corporation, Japan) (Fig. 3c). Postoperative radiographs were obtained (Fig. 3d). A vestibuloplasty was performed at the anterior region of the mandible, and this was accompanied by stent insertion and suturing. (Fig. 4a, b) The patient was provided with oral hygiene instructions and recalled at 2 weeks, and 3, 6, 9, 12, and every 6 months thereafter. Two weeks after complete soft tissue healing, the vestibuloplasty stent was removed, revealing a highly esthetic outcome (Fig. 5a).
Both clinical and radiographic examinations were performed throughout the follow-up visits (Fig. 5b, c, d,e). No complaints were reported by the patient, who noted improvements in his esthetics, chewing efficiency, speech, overall self-esteem, and social life.

Discussion
Prosthetic rehabilitation of edentulous patients following surgical removal of oral cancer presents with a number of challenging factors [1,2,6,7,12]. Thus, a multidisciplinary treatment plan is necessary to ensure successful outcomes [1].
Although several prosthetic options have been described for mandibular reconstruction, their ability to maintain and provide an optimal foundation for the retention, stability, and support of a removable prosthesis is unclear [1,2,14]. This is especially so in patients presenting with comprehensive post-surgical anatomical alterations and eliminated vestibular sulci. Therefore, in such cases, the use of implants can significantly improve a patient's oral function and self-esteem [1,2,7,13,14].
Basal implants have several advantages in patients with limited bony support [16][17][18]. For example, it eliminates the need for augmentation procedures, and their associated risks. Moreover, these implants reduce the cost of treatment and the time required to provide an immediately functional prosthesis. The smooth surface and small penetrating tip of BCS implants can reduce, or even eliminate the risk of peri-implantitis, thus maximizing implant survival and success rates [16][17][18].
According to the literature, the use of a removable, implantsupported overdenture can improve patient oral hygiene [4,7,13,14]. However, in the present case, the use of a hygienic design ensured the same advantages by providing a space for salivary washing actions, and permitting the use of a small interdental brush for cleaning [4,7]. Moreover, this fixed prosthesis design eliminated the mucosal pain and discomfort that may be associated with mucosal irritation in implant overdentures [4,7,13]. Such irritation may result in frictional ulcers and subsequent infection, particularly in irradiated patients [4,7,13,14]. Pjetursson et al. [20] conducted a systematic review of the survival and complication rates of fixed implant-supported prostheses with a mean observation period of 5 years, and reported that such treatment is both safe and predictable.

Conclusion
HBO, in combination with basal implants, is a highly successful treatment modality for patients with head and neck cancer who have a history of radiation therapy.

Declarations of Competing Interest
None.

Funding
No funding was obtained for this study.

Ethical approval
The research was registered at the research centre of the Khartoum Dental Teaching Hospital, Federal Ministry of Health, Khartoum, Sudan, after the approval of the research ethical committee of Khartoum Dental Teaching Hospital.

Consent
The approval of the patient was obtained for the treatment and publication of this case report.

Author contributions
Awadalkreem F contributed to the conceptualization, manging the patient, writing, editing, finalization and submission of the case.
Khalifa N contributed to the conceptualization, validation, and supervision of the case.
Ahmad A contributed to the conceptualization, validation, manging the patient, and supervision of the case.
Suliman AM was contributed to the conceptualization validation, and supervision of the case.
Osman M contributed to the conceptualization, manging the patient, editing, and finalization of the manuscript.

Registration of research studies
The research was registered at the research centre of the Khartoum Dental Teaching Hospital, Federal Ministry of Health, Khartoum, Sudan, after the approval of the research ethical committee of Khartoum Dental Teaching Hospital, Federal Ministry of Health, Khartoum, Sudan.

Provenance and peer review
Not commissioned, externally peer-reviewed.