In this study, patients with an insufficient height of bone for implant placement in the posterior mandible were treated by repositioning of the inferior alveolar neurovascular bundle (IANVB). These patients were divided into two groups: those in group A ( n = 69) did not require a bone graft and implants were placed at the time of nerve repositioning; those in group B ( n = 9) received bone grafts in conjunction with nerve repositioning and implants were placed upon maturation of the grafts. One hundred and twenty-one nerves were repositioned in 78 patients and 308 implants were placed. Three implants failed within the first 10 months after placement. With a certainty of 95%, an estimated overall mean survival rate better than 97.8% was observed after a mean observation period of 84.5 months. The recovery of sensation was monitored using standardized tests. The recovery of sensation varied from 24 h to 6 months. Five patients reported some residual altered sensation. The technique of repositioning the IANVB provides an effective way of treating the atrophic posterior mandible with acceptable morbidity and a high implant survival rate; however the risk of dysesthesia must be acknowledged and patients properly informed.
The amount of bone available in the posterior mandible for implant placement is limited by the position of the inferior alveolar canal. This may be further compounded by resorption of the alveolar ridge as a result of normal atrophy following tooth loss or a number of other causes. These include an increased rate of resorption due to the use of a soft tissue-supported removable prosthesis and pathologies associated with failing teeth or implants.
The management of these patients is challenging in view of the difficulty in constructing removable tissue-borne partial dentures to provide masticatory function. Alternative treatments to provide fixed implant-supported restorations include the use of short implants, bone augmentation, distraction osteogenesis, and bypassing the inferior alveolar canal.
Repositioning of the inferior alveolar neurovascular bundle (IANVB) is reported as a method of making the entire height of the mandible available. The procedure carries an inherent risk of damage to the IANVB, which has been reported by various authors and is summarized in recent systematic reviews and reports. This must be seen in the context of the inherent risk of working in this region, where high incidences of nerve damage are reported (up to 19% at the 2-year recall).
A distinction is made within the literature for repositioning of the IANVB. Nerve lateralization refers to a technique not involving the mental foramen and consists of moving the neurovascular bundle laterally and returning it to lie against the implants following their insertion. Nerve transpositioning is described as involving the mental foramen, severing the incisive branch and constructing a new foramen in a more distal position. Nerve transpositioning is reported to have a higher incidence of dysesthesia than nerve lateralization.
The aim of this retrospective analysis was to review the recovery of sensation after nerve repositioning, including both lateralization and transpositioning, and to evaluate the survival of the implants placed.
Materials and method
A retrospective analysis of clinical records of patients treated between 1988 and 2013 was performed. All treatment options and associated risks and benefits were discussed with the patient and written consent obtained prior to treatment. All patients treated with IANVB repositioning were included in the analysis. These patients fell into two groups: those who did not require a bone graft (group A) and those who required a bone graft in addition to the nerve repositioning procedure (group B). All patients who required nerve repositioning had edentulous jaws of class IV, V, or VI, as described by Cawood and Howell.
Group A patients did not require a bone graft ( Fig. 1 ; nerve lateralization). With regard to bone volume, patients had a bone height of between 2 mm and 8 mm available above the inferior alveolar canal, and a minimum width of 6 mm was present. However the estimated total height of mandibular bone available after IANVB repositioning was in excess of 10 mm. With regard to soft tissue, the crest of the ridge was above the floor of the mouth, and attached keratinized tissue was present.
Group B patients required a bone graft ( Figs. 2 and 3 ; nerve transpositioning). With regard to bone volume, patients had a bone height of between 0 mm and 6 mm above the inferior alveolar canal and/or an insufficient width (less than 4 mm of width). The estimated effective mandibular bone height after repositioning of the IANVB was also less than 10 mm. With regard to soft tissue, the crest of the ridge was below the floor of the mouth and had little or no attached or keratinized tissue, and consequently there was a risk of long-term maintenance problems.