Lateralization of the Inferior Alveolar Nerve in the Rehabilitation of Mandibular Atrophy: Case Report

The edentulous mandibular posterior region with severe bone atrophypresents one of the most challenging areas for implant-prosthetic rehabilitation. After teeth extraction, the resulting bone resorption undergoes two phases: The first is a remodeling process that involves the buccal cortex, while in the second phase, this phenomenon expands to the palatal or lingual cortex.¹

In today's dentistry, clinicians can rely on multiple techniques for prosthetically guided implant placement. In selected cases of severe vertical atrophy, lateralization or transposition of the inferior alveolar nerve (IAN) may be considered for implant-prosthetic rehabilitation.^2-7

The lateralization of the inferior alveolar nerve (LIAN) involves selective osteotomies that allow the transposition of the path of the IAN lateral to its canal. This technique permits the positioning of implants in basal bone using the area of the mandibular canal for the fixture's osseointegration.^8-10

The lateralization procedure offers several advantages: It does not require donor sites and allows the immediate placement of the implant, resulting in reduced morbidity, healing time, and costs. The main risks associated with this type of technique are altered sensory nerve function, weakening of the mandibular body, and, in rare cases, fracture.^11,12

The purpose of this clinical case report is to describe LIAN as an alternative to various regenerative techniques for rehabilitation of a patient with an implant-supported fixed prosthesis.

A 38-year-old female patient presented for an implant-prosthetic consultation about her mandibular left posterior region. Two mandibular left molars (teeth Nos. 18 and 19) and the mandibular left second premolar (tooth No. 20) had been extracted the previous year, thus this area was identified as an edentulous ridge distal to the mandibular left first premolar (tooth No. 21). Furthermore, this tooth was assessed as hopeless (Figure 1 and Figure 2).

Because of the short distance between the mandibular canal and the alveolar ridge (<5 mm) and the minimal interarch distance, a vertical guided bone regeneration (GBR) approach was excluded in treatment planning. A lateralization of the inferior alveolar nerve was planned in order to insert implants in this region. The patient was informed of the specific risks of this procedure, in particular temporary or permanent paresthesia related to LIAN and other surgical procedures in this area.

Surgical Procedure

After preoperative medication (amoxicillin and clavulanic acid 1 gram, one tablet every 12 hours from the day before surgery; 0.2% chlorhexidine mouthrinse every 8 hours from 3 days before surgery) the patient underwent surgery under conscious intravenous sedation. A full-thickness trapezoidal flap was elevated from tooth No. 22 to the mandibular left branch (Figure 3). The lateral osteotomy to the mandibular canal was performed using a piezoelectric device (Piezosurgery^® 3, Mectron, dental.mectron.us) with sterile saline solution. Next, the vestibular bone block was removed using surgical chisels. The IAN was detected and moved laterally using a periosteal curved elevator. During the drilling of the implant site in the molar region, a wide elevator was maintained in order to protect the nerve (Figure 4 and Figure 5). A tissue-level implant, 3.3 mm x 12 mm (Straumann^® Standard Plus [SP], Straumann, straumann.com), was inserted in the area of tooth No. 19 (Figure 6). Hopeless tooth No. 21 was then extracted and an implant, 4.1 mm x 10 mm (Straumann SP), was simultaneously inserted in the No. 21 position.

To avoid direct contact between the implants and the IAN, autogenous bone chips taken from the block of the osteotomy were grafted in among the implant and the nerve.¹⁰ An absorbable membrane was placed to protect the graft, and, finally, the flap was sutured using 4-0 absorbable sutures.

Postoperative Protocol

A postoperative therapy was prescribed to the patient comprising amoxicillin and clavulanic acid 1 gram, one tablet every 12 hours for 5 days; 0.2% chlorexidine mouthrinse every 8 hours starting from the day after the surgery until the suture removal; and anti-inflammatory therapy (nimesulide 100 mg) two to three times per day for at least 3 days. Also recommended to the patient were a topical cryotherapy, to be applied the day of the surgery until the evening of the same day, and a cold and liquid diet for the first 24 hours after the surgery; thereafter, a soft and medium-temperature diet was recommended until the suture removal.

Orthopantomography was performed after surgery to confirm the proper position of the implants (Figure 7). Any postoperative complications were registered. To check for correct nerve function and detect any possible injuries or alterations related to the IAN, only clinical evaluations were performed (two-point discrimination test, nociception test, thermal test); a discriminated distance of 5 mm or less was considered a satisfactory sensory response. Nociceptive sensitivity was judged to be good if the patient had an adequate response to stimulation with increasing intensity. Thermal sensitivity was tested using Crio spray.

The healing phase occurred without symptoms, and 4 months after surgery the final prosthetic rehabilitation was performed with a metal-ceramic framework supported by implants (Figure 8).

After tooth extraction, the residual bone plays a crucial role in implant rehabilitation. In the mandible, the minimum residual bone height for implant placement is 6 mm with a safety distance of 2 mm from the IAN and 6 mm thickness.¹³ In case of atrophy, it is necessary to restore an adequate volume of hard and soft tissues that allows a proper implant insertion. Compared with other regenerative techniques, LIAN allows for a reduction in treatment time because of the prosthetically guided standard implant placement.¹⁴ Another advantage of this technique is that implants may be inserted in the native mandibular bone, which has better quality than any regenerated bone.^15,16

In addition, this technique offers the possibility of guiding the implant placement, thus protecting the nerve-vessel boundary. Presently, LIAN should not be considered a risk-free technique for rehabilitation of the atrophic mandible, as the risk of damage to the IAN ranges between 33% and 87%.¹⁷ Piezoelectric devices allow selective cutting of bone without causing soft-tissue injury, enabling safe and relatively easy lateralization of the IAN.

Although the literature on LIAN and the results of this case presentation are limited, and further research is needed, LIAN may be considered a viable surgical technique. Among its advantages are reduced treatment time and guided prosthetic implant placement. While LIAN has significant risks, including loss of nerve function, no complications were noted in this case report. In the authors' experience, careful planning and the use of piezoelectric devices can significantly reduce neurological sequelae.

The authors report no conflicts of interest related to this study.

Alessandro Luigi Rossi, DDS
Specialist in Oral Surgery, Department of Health Sciences, Unit of Oral Surgery, Santi Paolo and Carlo Hospital, University of Milan, Milan, Italy

Federico Guerri, DDS
Specialist in Oral Surgery, Department of Health Sciences, Unit of Oral Surgery, Santi Paolo and Carlo Hospital, University of Milan, Milan, Italy

Cristina Cattaneo, DDS
Specialist in Oral Surgery, Department of Health Sciences, Unit of Oral Surgery, Santi Paolo and Carlo Hospital, University of Milan, Milan, Italy

Federico Gaspare Pappalardo, DDS
Specialist in Oral Surgery, Department of Health Sciences, Unit of Oral Surgery, Santi Paolo and Carlo Hospital, University of Milan, Milan, Italy

Matteo Arcari, DDS
Resident in Oral Surgery, Department of Health Sciences, Unit of Oral Surgery, Santi Paolo and Carlo Hospital, University of Milan, Milan, Italy

Luigi Tagliatesta, DDS
Specialist in Oral Surgery, Department of Health Sciences, Unit of Oral Surgery, Santi Paolo and Carlo Hospital, University of Milan, Milan, Italy