Abstract
The aim of this study was to evaluate the success and complications following inferior alveolar nerve (IAN) transposition/reposition for dental implant placement in edentulous or partially edentulous mandibles. This was a multicenter retrospective study; patients who had undergone IAN transposition/reposition at four surgical clinics were retrospectively evaluated. Adverse effects, especially neural disturbances, were recorded and followed. Overall, 68 IAN reposition and 11 nerve transposition procedures were performed in 57 patients (only three patients reported on smoking). The residual bone above the IAN was an average 3.88 ± 1.98 mm. A total of 232 dental implants were inserted in the area after transposition/reposition of the nerve. The average follow-up time was 20.62 ± 9.79 months, ranging from 12 to 45 months. One implant loss was observed during the follow-up period. Four patients reported prolonged transient neural disturbances immediately following surgery (5% of the operations). The duration of neural disturbances after the surgery ranged from 1 to 6 months. No permanent neural damage was reported. Thus, within this study’s limitations, it can be concluded that IAN transposition and reposition are useful adjunct techniques for managing severely atrophic edentulous or partially edentulous mandibles with dental implants. The risk of neural dysfunction appears to be low.
Introduction
Tooth loss is one of the common causes of a reduced quality of life in adults. Dental implants have become a widely accepted treatment option for both partially and completely edentulous patients. Rehabilitation of edentulous posterior mandibular regions with severe ridge atrophy using implants is subject to anatomical, surgical, and biological difficulties, and poses a challenge to the dental team. Osseointegrated dental implants are often placed in the posterior mandible, mostly for support of fixed restorative prostheses. In many cases the bone has atrophied such that sufficiently long fixtures cannot be placed without encroaching on the inferior alveolar nerve (IAN). In that situation, restorative options include the use of short fixtures, onlay bone grafting to increase the ridge height, and more complicated and detailed imaging studies to allow positioning of implants alongside and not in the nerve canal during the procedure. Another option is to move the IAN laterally from its canal either by nerve lateralization or nerve transposition.
During nerve lateralization the IAN is exposed and traction is used to deflect it laterally while the implants are placed. The IAN is then left to fall back in place against the fixtures with no interference with the incisive nerve. During nerve transposition a corticotomy is done about the mental foramen and the incisive nerve is transected, such that the mental foramen is repositioned more to a posterior area. The advantages of IAN transposition include the ability to place longer fixtures and to engage two cortices for initial implant stability.
The amount of bone superior to the IAN canal is often insufficient for placement of fixtures of the desirable length, and this, together with the fact that the bone that is present superior to the IAN canal is often of poorer quality than its cortical counterpart, has led to the development of methods of IAN displacement that allow placement of longer dental implants. With these methods, the inferior cortex of the mandible is engaged, which leads to greater initial stability. Apart from longer implants, IAN transposition allows for the use of a greater number of implants, which improves the overall strength of the final prosthesis and might significantly improve quality of life.
The aim of the present study was to evaluate the success and complications following IAN transposition/reposition for dental implant placement in edentulous or partially edentulous mandibles. This was a multicenter retrospective study.
Methods
Study population
Patients who had undergone IAN transposition/reposition at four surgical clinics between 1999 and 2009 were retrospectively evaluated. Patients were selected consecutively from the four centers. Demographics as well as smoking habits, residual bone above the alveolar nerve, and implant parameters were recorded. Adverse effects, especially neural disturbances, were recorded and followed. Patients were examined during follow-up visits that were scheduled following the surgery – once a week for 1 month, then every 2–3 weeks until a full recovery was achieved.
Surgical technique
A crestal incision was performed to allow visualization of the lateral aspect of the mandible. An anterior releasing incision was extended anterior to the projected fixture site and well into the vestibulum, mainly to allow a good exposure of the entire mental foramen. Posteriorly, the incision passed through the retromolar pad to minimize the tension after releasing the IAN ( Figs. 1 and 2 and Table 1 ).
| Alveolar nerve repositioning | Alveolar nerve transpositioning |
|---|---|
| 1. Buccal/lateral bone window | 1. Buccal/lateral bone window |
| 2. Complete osteotomy of the mental foramen | 2. Partial osteotomy of the mental foramen distal portion |
| 3. Micro-dissection of the IAN | 3. Maintaining the integrity of the incisive nerve |
| 4. Incision of the incisive nerve | 4. Gentle buccal traction of the IAN |
| 5. Repositioning of the IAN | 5. Replacement of the IAN on the implant surface (with collagen and PRF protective layer) |
| 6. Incorporation of the IAN into the buccal flap |
Piezosurgical instruments were used to protect the soft tissue while cutting the bone; nevertheless, caution is necessary due to the fact that the working tips of these instruments tend to overheat. During the procedure a vessel loop was wrapped around the IAN bundle in order to protect it and allow manipulation. The bone window design followed the trajectory of the inferior alveolar canal and was positioned 3–5 mm above and beneath the canal. The vertical cuts were positioned according to the prosthetic plan 3–5 mm posterior to the most distal implant. The anterior vertical cut was designed according to the surgical technique that was selected – for transposition, distal to the mental foramen, and for repositioning, medial to the mental foramen. The decision regarding the surgical technique should take into consideration mainly the amount of stretching that is needed to mobilize the IAN. Stretching the nerve by 10–17% of its original length can disrupt the nerve fibers internally. If a repositioning technique is used, the surgeon should consider removing 5–6 mm of bone anterior to the mental foramen in order to expose and dissect the anterior loop of the IAN. The bone window can be removed with fine curved osteotomes. The dissection of the nerve was accomplished with the combined use of microsurgical instruments and fine piezosurgery diamond burrs, and the nerve was then retracted with nerve hooks. At this stage dental implants can be inserted, and due to this surgical design, the fixture will be engaged bicortically giving improved primary stability. The bone defect can be covered by several methods: repositioning the bone window that was removed as a cortical onlay, or crushed and mixed with an allograft or xenograft. A biological barrier in the form of platelet-rich fibrin (PRF) was wrapped around the neurovascular bundle. Closure was achieved with resorbable sutures. Implant exposure was performed 3 months after the surgical procedure.
Testing of nerve function
During the scheduled follow-up visits, nerve function was evaluated using a two-point discrimination test with sharp calipers, as well as the Von Frey test and pin prick with a sharp instrument. The areas of impaired nerve function were mapped and followed during each follow-up appointment. The evaluation of nerve function was performed by four calibrated examiners.
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