Inferior alveolar nerve repositioning: the benefit of the 3D surgical guide

Inferior alveolar nerve repositioning: towards a computer-assisted approach

Inferior alveolar nerve repositioning (IANR) remains a complex surgery in implantology, indicated primarily when severe mandibular atrophy precludes the placement of conventional or short implants. This procedure, aimed at protecting the neurovascular bundle before performing osteotomies, however, exposes the practitioner to risks of sensory complications, the prevalence of which varies according to the technique used: approximately 1.5% for lateralisation and 12% for transposition. Given these challenges, surgical precision is decisive.

This clinical case report highlights the innovative use of a surgical bone-cutting guide, designed by computer-aided design (CAD) based on CBCT data and an intra-oral scan. The precise objective of this study is to evaluate the relevance of a guide supported by both adjacent teeth and the mandibular bone to secure the procedure. By facilitating intra-operative navigation and the exact tracing of osteotomies, this device aims to optimise surgical precision while minimising the risks of nerve injury. Although this approach involves an additional manufacturing cost, it presents itself as a relevant alternative for the practitioner seeking to secure interventions in an atrophic zone without resorting to bone grafts, which are often more time-consuming for the patient.

Methodology of the computer-assisted approach

This study describes the development and clinical use of a surgical guide designed to optimise precision during inferior alveolar nerve repositioning (IANR) procedures. Unlike conventional surgical approaches, this method relies on rigorous pre-operative digital planning.

• Guide design: The device is manufactured in the laboratory by merging DICOM data from a CBCT scan and STL files obtained by intra-oral optical impression. This superimposition allows for the precise localisation of the inferior alveolar nerve path and the mental foramen within the mandible.
• Functionality: The tooth- and bone-supported guide is designed to accurately delineate the necessary bone cuts, thereby facilitating the osteotomy while securing the preservation of the neurovascular bundle.
• Planning objectives: The use of computer-aided design and manufacturing (CAD/CAM) software allows for virtual pre-operative navigation, aiming to anticipate anatomical difficulties, such as the proximity of the apices of adjacent teeth, thus reducing the risks of iatrogenic nerve injuries during the intervention.

Although the protocol highlights increased precision, the authors specify that the use of these guides imposes an additional cost linked to their custom manufacturing. The study underlines the need to report more clinical cases in order to statistically evaluate the real benefits of this guidance technology in complex oral surgeries compared to conventional manual methods.

Clinical results and surgical precision

The use of a tooth- and bone-supported surgical guide, designed by merging DICOM (CBCT) and STL (intra-oral scan) data, allowed for precise planning of the mandibular osteotomy. The guidance window facilitated the exact localisation of the inferior alveolar canal and the mental foramen, thus securing the tracing of the bone cuts performed with a piezotome.

The following table summarises the risks associated with the different inferior alveolar nerve repositioning techniques, as reported in the literature cited by the authors:

Technique	Risk of permanent nerve injury
Lateralisation	~ 1.5%
Transposition	~ 12%

Regarding the reported clinical case, the use of the guide allowed for controlled exposure of the mental nerve and secure management of the bone access. The surgical approach, performed under exclusive local anaesthesia (2.2 ml of lignocaine 1:80,000 in nerve block, supplemented by 4.4 ml of lignocaine in infiltration and 4.4 ml of articaine 1:100,000), allowed the repositioning objective to be achieved without any major intra-operative incident.

The authors highlight that, although this computer-assisted approach improves precision and reduces the risk of nerve trauma, it generates additional costs related to the manufacturing of the guide. To date, no comparative statistical data (p-values) are available to validate the superiority of the guide over the conventional technique, as the report is limited to a single case description.

Repositioning of the inferior alveolar nerve: digital precision at the service of safety

Repositioning of the inferior alveolar nerve (IANR) remains a complex procedure in oral surgery, aimed at protecting the neurovascular bundle during implant or reconstructive interventions in areas of bone atrophy. This clinical case illustrates the use of a surgical guide designed via digital planning to secure the osteotomy.

By using DICOM data from CBCT fused with an intra-oral scan (STL files), the team was able to design a tooth- and bone-supported guide. This approach allows for precise visualization of the path of the mandibular canal and the mental foramen, thereby facilitating the marking of the bone window before the piezosurgery intervention. For the practitioner, the major advantage lies in the reduction of the risk of injury related to virtual surgical navigation that anticipates anatomical difficulties, such as the proximity of adjacent dental apices.

However, this technique has limitations inherent to its development. The manufacturing of this custom-made guide generates an additional cost. Furthermore, although the guide improves precision, it does not exempt the practitioner from rigorous surgical expertise. The literature mentions risks of post-operative sensory sequelae, estimated at approximately 1.5% for lateralization and 12% for transposition, highlighting that despite digital assistance, the neurosensory risk persists. Finally, the need for rigorous patient selection (stable general and dental health, psychological maturity) remains the essential prerequisite for the success of this surgery.

Surgical optimization of inferior alveolar nerve repositioning

This clinical case reports the use of a tooth- and bone-supported surgical guide, designed via CAD/CAM from CBCT data and intra-oral scans, to secure the transposition of the inferior alveolar nerve. This computer-assisted approach aims to increase the precision of the osteotomy and minimize the risks of iatrogenic nerve lesions compared to conventional techniques.

Concretely, for the practitioner:

• Digital planning: The use of a specific guide allows for the precise localization of the mandibular canal and the virtual definition of bone cut limits, thus securing the intervention despite the proximity of dental apices.
• Risk management: Keep in mind that nerve transposition carries a risk of permanent injury of approximately 12%, compared to 1.5% for simple lateralization. Informed consent must imperatively reflect this differential.
• Alternative to grafts: Although repositioning is faster than bone grafts, it remains a complex surgery reserved for mandibles presenting severe atrophy where conventional implantology is impossible.

Specialized surgical technique aimed at exposing and moving the inferior alveolar neurovascular bundle out of its bony canal to prevent any nerve injury during reconstructive or implant procedures. Variant of IANR where the inferior alveolar nerve is identified, excavated, and moved laterally, without sectioning the anterior incisive branch. Technique of IANR consisting of moving the inferior alveolar nerve posteriorly and laterally, involving the sectioning of the anterior incisive branch. Digital data format from cone beam computed tomography (CBCT) used for computer-assisted surgical planning. File format from a digital intra-oral scan, combined with DICOM data to design personalized surgical guides. Surgical guide designed by computer-assisted planning, resting on dental and bone tissues to stabilize and ensure the reliability of bone cuts during osteotomy.

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