Use of rhBMP-2 to reconstruct a severely atrophic mandible: a modified approach

Abstract

This study reports the case of a patient with a severely resorbed mandible who was treated without a bone graft, using short implants, internal rigid fixation, rhBMP-2 and β-tricalcium phosphate. A 76-year-old woman, with a severely resorbed mandible (less than 3 mm), reported a history of nearly 25 years of complete edentulism and consecutive treatment failures, with total bilateral exposed inferior alveolar nerves and complete bone resorption of the inferior border in some areas. The treatment of choice was the placement of a 2.0 mm thick unilock bone plate (MatrixMandible, Synthes Maxillofacial, Paoli, PA, USA), to reinforce the mandible. Eight short implants with a regular platform (Nobel Biocare, Goteborg, Sweden) were placed: three on the external oblique line on both sides and two on the symphysis. In order to augment mandible height and coat the exposed thread of the anterior implants, rhBMP-2 (Infuse Bone, Meditronic Sofamor Danek, Memphis, TN, USA) and β-tricalcium phosphate (Cerasorb; Curasan, Kleinostheim, Germany) were used. Four 1.3 mm L miniplates were placed to support the graft. 14 months after surgery, the patient was satisfied and had excellent function without complications.

Severe mandibular atrophy (Cawood and Howell Class VI) as a consequence of long-term edentulousness in the lower jaw often results in functional and aesthetic problems. These problems include insufficient retention of the prosthesis, difficulties with speech and eating, loss of soft-tissue support, loss of vertical dimension, an aged face and a reduced range of expression. Such limitations can negatively affect quality of life and daily activities. Ultimately, resorption may also result in pathological fracture of the mandible. The advent of endosseous implants and advances in pre-prosthetic surgery have improved the aesthetic and functional results in these patients.

Described by Urist, bone morphogenetic proteins (BMPs) are a group of osteoinductive, sequentially arranged amino acids and polypeptides that are pleiotropic regulators of bone volume, skeletal organogenesis and bone regeneration. BMPs function as signalling agents that affect cell events, such as proliferation, differentiation and extracellular matrix formation. Capable of stimulating adult mesenchymal stem cells to induce bone formation, BMPs offer the promise of a true osteoinductive bone graft substitute that foregoes the need for a donor site. Initially released onto the market in 2002 as Infuse Bone Graft (Medtronic Sofamor Danek, Memphis, TN, USA), recombinant human bone morphogenetic protein 2 (rhBMP-2) was originally approved by the American Food and Drug Administration for use as an alternative to autografts in lumbar and cervical spine fusions. In 2004, rhBMP-2 was approved for adjuvant use in open tibia fractures and, in March 2007, it was approved ‘as an alternative to autogenous bone graft for sinus augmentations and for localized alveolar ridge defects associated with extraction sockets’.

The purpose of the present study is to report a case of a patient with a severely resorbed mandible who was treated without bone graft, using short implants, internal rigid fixation, rhBMP-2 and β tricalcium phosphate.

Case report

A 76-year-old woman was referred to a private clinic in the city of Recife, Brazil, with a severely resorbed mandible (less than 3 mm). The patient reported a history of nearly 25 years of complete edentulism and consecutive treatment failures. Cone beam tomography was performed and severe atrophy was confirmed, revealing total bilateral exposed inferior alveolar nerves and complete bone resorption of the inferior border in some areas ( Fig. 1 ). There was a high risk of pathological mandible fracture due to very low density in critical areas. The treatment of choice was the placement of a 2.0 mm thick unilock bone plate (Matrix Mandible, Synthes Maxillofacial, Paoli, PA, USA), to reinforce the mandible. A rapid prototype model was made to help precontour the plate, enabling the insertion of the plate through the transoral approach ( Fig. 2 ). Eight short implants with a regular platform (Nobel Biocare, Goteborg, Sweden) were placed: three on the external oblique line (8.5 mm, 7 mm, 7 mm) on both sides and two on the symphysis (7 mm, 7 mm). In order to augment mandible height and coat the exposed thread of the anterior implants, rhBMP-2 (Medtronic Sofamor Danek, Memphis, TN, USA) and β tricalcium phosphate (Cerasorb; Curasan, Kleinostheim, Germany) were used. Four 1.3 mm L miniplates (Synthes Maxillofacial, Paoli, PA, USA) were placed to support the graft ( Fig. 3 ).

Fig. 1
Preoperative cone beam tomography revealing severe level of bone atrophy; yellow arrows show complete bone resorption of inferior border in some areas.

Fig. 2
Rapid prototype model made to help precontour the plate enabling its insertion through a transoral approach.

Fig. 3
(a) Insertion of 3 short implants on external oblique line. (b) Frontal view of 3 short implants on external oblique line on both sides and two on the symphysis (yellow arrows: exposed threads of the implants); insertion of 4 1.3 mm L miniplates to support graft. (c) Insertion of rhBMP-2 plus β tricalcium phosphate. (d) After 6 months, the anterior implants were covered by the new bone (yellow arrow). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

One week after surgery, a Branemark prosthesis protocol was installed in six posterior implants. Space was maintained between the graft and prosthesis to avoid compression during mastication. Six months after surgery, the miniplates were removed and the anterior implants were put into function. 26 months after surgery, the patient was satisfied and had excellent function without complications ( Fig. 4 ).

Jan 24, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Use of rhBMP-2 to reconstruct a severely atrophic mandible: a modified approach
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