Rehabilitation of Severely Atrophic Mandible: A 3-Year Follow-Up Protocol

Full-arch implant-supported prostheses have been considered a predictable alternative for optimization of the rehabilitation of severely atrophic mandibles (Cawood and Howell class VI) by providing retention,¹  stability, esthetics, and quality of life to patients.²  However, the severity of bone atrophy often does not allow for the placement of implants without previous reconstructive procedures for lack of bone availability.³  On the other hand, the risk of mandibular fracture before, during, and after the placement of implants in extremely resorbed edentulous mandible is a factor to be taken into account during treatment planning.⁴  Therefore, the placement of a reconstruction plate in association with mandibular reconstruction performed prior or simultaneously to the placement of the implants is one of the clinically viable approaches to increase the longevity of the treatment of severely atrophic mandibles, thus decreasing the risks during the rehabilitation process in these patients.^5,6 

The literature describes some techniques for the reconstruction of severely atrophic mandible, including the use of autogenous grafts and growth factors.^7,8  Although autogenous grafts are considered a gold standard treatment,⁷  they have some drawbacks, such as the need for a larger donor area in cases of severe bone defects, which increases morbidity and costs of the procedure. Nevertheless, growth factors, such as the recombinant human bone morphogenetic protein–2 (rhBMP-2), have been used for 3-dimensional bone augmentation defects and are thus an alternative to autogenous grafts for severe defects.^8,9  Therefore, the combined use of rhBMP-2 and osteoconductive biomaterial allows for a decrease in the amount of growth factors^9,10  while providing better stability for placement of the implants following the period of replacement and remodeling of the bone grafts.^11,12  On the other hand, the use of a shaped titanium mesh maintains the stability of the bone graft and the space for cell proliferation and differentiation during bone reconstruction.^9,10 

Rehabilitation treatments of severely atrophic mandibles with osseointegrated implants have been little explored in the literature. This case report describes the treatment of an elderly female patient whose mandible was severely atrophic by fixing a reconstruction plate with an intraoral approach in combination with a vertical bone reconstruction procedure performed simultaneously with the implant placement.

A 72-year-old healthy woman, who was edentulous for more than 50 years, sought treatment because of esthetic and functional discomfort caused by the maxilla and mandible complete denture, mainly regarding the mandibular one. In the facial analysis without the prostheses, it was observed that her face had an aged appearance with reduced vertical dimension. Clinically, a severely resorbed mandible (Figure 1) and moderate resorption of the upper alveolar ridge were also observed. Cone-beam computerized tomography (CBCT) showed an anterior mandibular height of less than 3 mm and bilateral exposure of the inferior alveolar nerves (Figure 2). Treatment options were discussed with the patient, and a full-arch implant-supported prostheses and a maxilla complete denture was chosen.

Initially, fixation of the mandible was planned using a 2.4-mm reconstruction plate of 2.4 mm (Toride) to be adapted to the base of the mandible to prevent possible fractures due to the limited availability of bone tissue. Next, a prototype of the mandible was made based on CBCT slices to allow adaptation and modeling of the plate before the surgical procedure and its subsequent fixation using an intraoral approach.⁸  Prototyping was also used to create a surgical guide for placement of the implants.

The patient was hospitalized for surgery under general anesthesia. Before surgery, intra- and extraoral antisepsis were performed and appropriate medications were administered (antibiotic cephalexin 500 mg and antiinflammatory dexamethasone 8 mg). After intravenous sedation, intraoral anesthesia was performed at the retromolar region close to the inferior alveolar nerve and complemented with infiltrative anesthesia in the entire mandibular ridge with 4% articaine with epinephrine at 1:200,000 (Nova DFL, Rio de Janeiro, Brazil). A linear incision was carefully made in the ridge, followed by total displacement of the flap until the alveolar bone and bilateral mental nerves were completely exposed.

A 2.4-mm reconstruction plate (Toride) was fixed on the base of the mandible with 10 screws. Two extra-short implants of 4.1 × 4.0 mm (Standard Plus Short SLActive, Roxolid, Straumann, Basel, Switzerland) were placed bilaterally in the posterior region, whereas 3 implants of 4.1 × 8.0 mm (Standard Plus Short SLActive, Roxolid, Straumann) were placed in the anterior mandibular region, that is, between the mental foramina in the remaining bone (Figure 3). Next, a simultaneous 3-dimensional bone augmentation was performed, covering 6 mm of the exposed threads of the implants by using a shaped titanium mesh (5 × 51 mm, 0.2 t, Jeil Medical, Seoul, Korea) in association with rhBMP-2 (INFUSE, Medtronic Sofamor Danek) and deproteinized bovine bone mineral (Bio-Oss, Geistlich; Figure 4). The tissues were sutured in planes using absorbable thread (5-0 Vycril, Ethicon, Johnson & Johnson, São Jose dos Campos, São Paulo, Brazil), interrupted suture in the deep plane, and continuous stitches in the outermost plane to keep the flap passive and completely free of tension.

After the surgery, the medications prescribed were antibiotics (875 mg of amoxicillin + 125 mg of clavulanate every 12 hours for 7days) and anti-inflammatories (400 mg of ibuprofen every 6 hours for 3 days), and a soft diet was recommended. The patient continued using the old prostheses properly adjusted and internally relieved until the complete healing process.

Eight months after the surgery, a small exposure of the titanium mesh was clinically observed but with no infection (Figure 5a). Next, the flap was displaced for surgical removal of the titanium mesh, healing caps were placed, and an extensive new bone formation was observed (Figure 5b). Bone augmentation height (6–7 mm) and thickness (5–6 mm) was shown on CBCT (Figure 6a) and panoramic radiograph (Figure 6b) around all the implants in the anterior region of the mandible.

After 1 month, abutments were placed onto the implants and a transfer impression was performed. Next, record bases with occlusion rims were made and adjusted according to esthetic and functional principles. A centric relation interocclusal record was obtained, and the casts were mounted on a semiadjustable articulator (4000 S, BioArt). Artificial teeth (Trilux) were arranged and evaluated in the mouth to verify the esthetics, lip support, occlusal vertical dimension, maximum intercuspation, and phonetics. Then, the implant position cast was used to fabricate and evaluate the fit of the prosthetic framework, which was cast in cobalt-chromium alloy (Biosil F; Dentsply) with the lost wax technique. Finally, full-arch implant-supported prostheses and the maxilla complete denture were installed (Figure 7). Both maxillary and mandibular prostheses were made with heat-polymerized acrylic resin (Classico; Classico Dental Products), and the bilateral balanced occlusion was adjusted.

The patient had no technical or biological complication during the 3-year follow-up period and reported both esthetic and functional satisfaction with the prosthetic rehabilitation. The CBCT showed maintenance of the bone volume around all implants in the region of the simultaneous 3-dimensional bone augmentation (Figure 8).

Full-arch implant-supported prostheses for severely atrophic mandibles present predictable results when simultaneous 3-dimensional reconstruction is adequately performed by using a combination of techniques, which in this clinical case was through the use of rhBMP-2 in association with particulate xenogeneic bone substitute and titanium mesh. This approach avoided the collection of autogenous bone (intra- and/or extraoral), thus significantly reducing postoperative morbidity and surgery time.¹³ 

Guided bone regeneration (GBR) is a surgical technique that can be used for vertical bone augmentation,¹⁴  and it has provided better results compared with autogenous bone block.¹⁵  Implants placed in areas of simultaneous GBR have achieved high survival rates (98.5%) and low complication rates (12.1%).¹⁵  These results are in accordance with the clinical findings of this case report, as there were no complications during the healing process, no loss of implants, and no bone resorption in the GBR area after 3 years of follow-up.

However, full-arch implant-supported prostheses for severely atrophic mandibles present some limitations, including difficulty in placing the intraoral reconstruction plate, difficulty in achieving the correct fixation of the reconstruction plate, risk of injuring the nerve during placement of the reconstruction plate (thus causing permanent or temporary paresthesia in the patient), risk of mandible fracture during implant placement, risk of perforation of the inferior bone cortex, possibility of sublingual edema, and exposure of the reconstruction plate and titanium mesh. Therefore, it is important to release the flap and perform a passive suture.¹⁴  In addition, the patient must take the necessary precautions to obtain a comfortable postoperative period without temporary prosthesis. Therefore, this surgical technique is highly dependent on the clinician's skills and biological knowledge.

The predictability of the technique observed in the present case report occurred because the 4 main biological principles (PASS) of GBR were followed.¹⁴  Initially, the primary wound closure¹⁴  was achieved from strain-free flaps, passive sutures, and adequate amounts of keratinized mucosa, avoiding the main problem of GBR, which is the exposure of titanium membranes and bone grafts.^15,16  This characteristic creates an environment that is unaltered by outside bacterial or mechanical insult. Angiogenesis occurred because of the initial process of vascularization caused by rhBMP-2 and stabilization of the fibrin network in the osteoconductive biomaterial. The fundamental principle of GBR is based on the maintenance of membrane space to allow proliferation of cells from bone tissue during the bone replacement process and also the exclusion of the connective tissue cells. In the present case, the titanium mesh was used as a barrier because of the extension of the bone reconstruction and the need for dimensional stability.^14–16  Finally, wound stability is important for initial clot adhesion and subsequent repair of bone tissue. This characteristic was achieved by the stability of the titanium mesh protecting the simultaneous GBR.

To generate an osteoinductive cellular response, rhBMP-2 was used due to the extension and severity of the defect, which was also poorly vascularized. Previous research indicated that the combination of rhBMP-2 and osteoconductive biomaterials associated with titanium mesh was associated with sufficient bone augmentation for implant placement, comparable with that of autogenous bone grafts.¹⁷ 

Therefore, the combination of techniques using an intraoral approach has allowed for implant-supported rehabilitation of a severely atrophic mandible, showing favorable results without technical or biological complications during 3 years of follow-up. It is important to emphasize that this surgical technique highly depends on the skills of the clinician.

Abbreviations

CBCT:

cone-beam computerized tomography

GBR:

guided bone regeneration

rhBMP-2:

recombinant human bone morphogenetic protein–2