The objectives of this study were to evaluate the survival after 5 years of implants placed using inferior alveolar nerve (IAN) lateralization in cases of mandibular atrophy and to determine the incidence of complications. Twenty-seven patients received 74 implants by means of the IAN lateralization technique. Implant survival after 5 years of loading was 98.6%. Eighteen months after surgery, the recovery of sensitivity was complete in 26 cases. Implant placement with IAN lateralization was seen to be a satisfactory and predictable technique. IAN lateralization requires a high level of technical skill, and strict criteria should be applied when prescribing this treatment.
For many years, osseointegrated implant placement in the posterior region of the mandible was hindered by the presence of the inferior alveolar nerve (IAN). This area also suffers from bone resorption, depending on the length of time passed since the loss of teeth, which means that in many cases there is insufficient bone width and height to allow implant placement. Today, these restrictions can be overcome due to recent developments such as bone grafting, distraction osteogenesis, and IAN mobilization techniques.
IAN mobilization was first described in 1977, applied in cases of extreme bone atrophy in which the alveolar nerve was in a submucosal position over the alveolar crest. However, it was not until 1987 that the first case of nerve mobilization combined with implant placement was published. This surgical procedure can be performed using two different techniques: lateralization and transposition. With lateralization, the bone situated posterior to the mental nerve is removed to allow mobilization of the IAN, while with the transposition technique, the nerve is released from the supporting bone at the point where it exits the mental foramen, sectioning the incisor branch to allow mobilization of the alveolar and mental nerves.
IAN mobilization is subject to some controversy in the literature regarding the selection of suitable patients, implant success, and the complications that can arise. Studies involving a sufficiently long duration of follow-up are too scarce to establish whether or not this technique can be considered predictable and recommendable.
For this reason, the aims of the present study were to evaluate the survival of implants placed in combination with IAN lateralization after 5 years of loading and to register any complications arising from this procedure.
Materials and methods
This prospective study followed the STROBE guidelines (Strengthening the Reporting of Observational Studies in Epidemiology).
A total of 27 consecutive patients attending the buccal surgery and implant dentistry service of the study hospital in Madrid, Spain between 2005 and 2009, for implant-based rehabilitation of the posterior mandibular region using the IAN lateralization technique, were selected ( Fig. 1 ).
Inclusion criteria were established: (1) American Society of Anesthesiologists (ASA) I and II patients who, having been given full information about the study design and objectives and the possible risks of treatment, gave their informed consent to take part. (2) Patients presenting edentulous posterior mandibular regions with a distance between the bone crest and the roof of the alveolar nerve canal of less than 5 mm. (3) Patients who completed all pre-established clinical and radiology monitoring during the full 5 years of the study.
All patients were examined and diagnosed using panoramic radiographs and helical scans, to establish surgical indications and for planning.
Surgery was carried out under general anaesthesia by a single surgeon. First, a crestal vertical releasing incision was made level with the bone crest in the retromolar area. A mucoperiosteal flap was raised and sub-periosteal dissection of the mental foramen region was performed carefully. With the aim of releasing the IAN from the supporting bone at the point of emergence from the mental foramen, a circumferential window osteotomy was performed around the foramen by means of Piezosurgery, following the line of the inferior nerve canal.
Remaining spongy bone was removed with a curette until the inferior alveolar vascular nerve package was exposed; this was then tractioned using a vessel-loop ( Fig. 2 ). When the nerve had been lateralized and placed in a safe position, the implant beds were prepared to receive Phibo TSA implants (of previously planned diameters and lengths) following the usual procedure ( Fig. 3 ).
When the implants had been inserted and primary stability checked using an Osstell (Ostell ISQ, Göteborg, Sweden) implant stability quotient (ISQ) meter, bovine xenografts (Bio-Oss; Geistlich Pharma AG, Wolhusen, Switzerland) were placed in the defect zone left after the window osteotomy and covered with a resorbable collagen membrane (Bio-Gide; Geistlich Pharma AG, Wolhusen, Switzerland) ( Fig. 4 ). After this, the flap was repositioned and sutured using 4–0 monofilament silk; sutures were removed after 15 days.
Postoperative measures consisted of the administration of antibiotics for 7 days after surgery (750 mg amoxicillin every 8 h, or 300 mg clindamycin every 8 h for patients with an allergy to penicillin), anti-inflammatories for 4 days following surgery (50 mg diclofenac sodium every 12 h), and chlorhexidine gluconate 0.2% mouthwash for 7 days.
Clinical and radiographic evaluations
The definition of implant success was based on the clinical and radiological criteria proposed by Albrektsson et al. : absence of clinically detectable implant mobility, no evidence of peri-implant radiolucency, radiographic vertical bone loss of less than 0.2 mm per annum, and absence of pain, infections, and ongoing pathological processes. The total implant survival rate was determined applying the same criteria.
Each patient underwent weekly postoperative check-ups for the first month after surgery in order to monitor tissue healing and register any possible postoperative complications. Thereafter, a single practitioner performed radiological check-ups by examining panoramic and peri-apical radiographs captured using the paralleling technique at the following time points: 3, 12, 24, 36, 48, and 60 months ( Figs 5–8 ). At each check-up, marginal bone loss was evaluated as the distance from the bone level at the time of implant placement to the present bone level. Measurements were taken both mesially and distally to each implant thread and expressed in millimetres; a measuring magnifying glass with 8× magnification and a ruler calibrated in millimetres were used for this purpose.
Both intraoperative complications and those arising during the postoperative follow-up were registered, paying particular attention to any alterations in sensitivity.
The recovery of sensitivity was monitored by means of the two-point discrimination test at 1 week, 3 months, 6 months, 12 months, and 18 month after surgery. The test was performed according to the procedure proposed by Nishioka et al. : discrimination of less than 14 mm was considered normal sensitivity, 14–20 mm was regarded as reduced sensitivity, and over 20 mm was regarded as the absence of sensitivity.
The statistical analysis was performed using IBM SPSS Statistics for Windows, version 22.0 software (IBM Corp., Armonk, NY, USA). Descriptive statistics were generated, obtaining mean and standard deviation (SD) values, as well as frequencies and category percentages.
A total of 27 IAN lateralization procedures were performed, none of which were bilateral. Interventions were more common on the right side (16 patients). Of the 27 patients in the sample, 17 were women and 10 were men. These patients ranged in age from 30 to 70 years (mean age 57.74 years).
A total of 74 implants were placed, with an average of 2.7 implants per patient. Implant lengths ranged from 10 mm to 13 mm, and the implant diameter was 3.75 mm or 4.75 mm ( Table 1 ). All implants presented primary stability with ISQ values over 62 (mean 68).