This prospective cohort study investigates the types and duration of neurosensory disturbances (NDs) related to mandibular nerve (MN) lateralization for placement of implants. From March 2001 to March 2007, 87 patients underwent implant placement surgery with MN lateralization. All patients had panoramic radiograph and CT scans taken preoperatively. Patients completed questionnaires to report NDs 1 week after surgery, and at the end of each month within the year after surgery. All 87 patients (110 posterior segments, 23 bilateral and 64 unilateral) participated in the study. All patients reported NDs in the first week: anaesthesia in 81 sites, hypoesthesia in nine sites, burning in nine sites, pain in eight sites, pinching in two sites, and tickling in one site. The sites with NDs decreased to 29 sites (26%) at the end of first month, and to three sites (3%) at the end of the sixth month with no changes to the end of the year. 82 patients were satisfied with the result of nerve lateralization after 1 year. The mean time for full recovery of MN was 37 ± 15 days. These findings indicate that concerning NDs, MN lateralization is a useful method for placing implants in the atrophic posterior mandible.
Mandibular nerve (MN) lateralization is one of the options when placing implants in an atrophied mandible, where no sufficiently long fixtures can be placed without encroaching on the MN. Use of short fixtures, onlay bone grafting to increase ridge height, and positioning of implants alongside and not into the nerve canal are other options .
Moving the MN laterally from its canal can be performed using nerve lateralization or nerve transposition techniques. In nerve lateralization the MN is exposed and traction is used to deflect it laterally while the implants are placed. The MN is then left to fall back in against the fixtures. No interference with the incisive nerve occurs. In nerve transposition, a corticotomy is done near the mental foramen and the incisive nerve is transected, such that the mental foramen is repositioned and moved posteriorly .
An advantage of MN lateralization is the ability to place longer fixtures without grafting, and its limiting factor is the risk of nerve damage. This technique is a precise method requiring clinical experience, knowledge of the anatomy, and the ability to treat potential interoperative and/or postoperative complications . Lower degrees of nerve deficiency occur with this method compared with nerve transposition .
The purpose of the present study was to investigate neurosensory function following MN lateralization for implant surgery in the posterior mandible. The specific aims were to investigate the type and duration of neurosensory disturbances (NDs) related to MN lateralization, the mean time to full recovery of nerve function, and the patients’ satisfaction with the results of this method.
Materials and methods
A prospective cohort study was carried out. The study population comprised all patients referred to the Implant Department of Tehran University for implant surgery in the posterior mandible between March 2001 and March 2007. The patients were excluded if they had systemic diseases or a history of previous oral surgery. All aspects of the operation were discussed with the patients and all of them agreed to undergo surgery with the MN lateralization technique.
To precisely localize the MN, all patients had panoramic radiographs and computed tomography (CT) scans taken. The procedures for bilateral cases were performed under general anaesthesia while local anaesthesia was selected for unilateral cases. The same surgeon operated in all cases and the dental implants were placed at the time of nerve lateralization in all cases.
To report NDs, the patients were given a questionnaire before surgery ( Table 1 ). They were instructed to fill in the questionnaire at specific intervals during the first year after surgery. They were requested to record any NDs including hypoesthesia, tickling, burning, painful, pinching and anaesthesia. The time points were 1 week after surgery, and the end of each month during the year after the surgery. All the patients agreed to fill in the questionnaire and returned them in due time.
The procedure is initiated by making the soft tissue incision slightly buccal to the crest of the residual alveolar ridge. The incision begins at the retromolar region and is carried forward to the mesial portion of the cuspid tooth area, where a vertical relaxing incision is made. A full thickness mucoperiosteal flap is reflected to the inferior border of the mandible.
For the purpose of inferior alveolar nerve lateralization, the corticotomy starts usually 3–4 mm distal to the mental foramen. It should be extended distally, 4–5 mm distal to the most distal implant position. A small round bur in a straight hand piece with high torque and copious amount of water irrigation is used to prepare the corticotomy site. To remove the trabecular bone and gain access to the neurovascular bundle, only hand instruments (small curettes) are used. The MN is mobilized from its position. After the nerve is completely released from the canal, and before starting to drill, half a rubber piston from a dental anaesthetic cartridge or a piece of aluminum foil is inserted between the nerve bundle and the bone where the drill is expected to reach ( Figs. 1 and 2 ).
Once the drilling is completed, the implant is inserted while the nerve bundle remains retracted in situ ensuring that the apical ends of the implants are positioned inferior to the canal ( Figs. 3 and 4 ). Once the implants are in position, the nerve is repositioned over the lateral aspect of the implants ( Fig. 5 ).
110 posterior mandibular segments in 87 patients (23 bilateral, 64 unilateral) underwent implant placement after MN lateralization (47 males and 40 females; median age 39.3; range 28–54 years).
The patients (in all sites) reported NDs in the MN in the first week after the operation: anaesthesia in 81 sites, hypoesthesia in nine sites, burning in nine sites, pain in eight sites, pinching in two sites, and tickling in one site ( Table 2 ). At the end of the first month NDs disappeared in 81 sites (74%). Reported NDs at this time were hypoesthesia in 12 sites (all resulted from first-week anaesthetic sites), tickling in eight sites (seven sites resulted from first-week anaesthetic sites), burning in five sites, and pain in four sites (two sites resulted from first-week anaesthetic sites). At the end of the first month, nine sites of hypoesthesia reported in the first week had returned to normal, and 21 sites of anaesthesia had changed to other types of NDs (12 sites changed to hypoesthesia; seven sites changed to tickling; and two sites changed to pain).