Expanding the Surgeon's Armamentarium: Use of the Tubing Technique to Preserve the Inferior Alveolar Nerve During Transposition Procedure

Placement of dental implants at posterior regions in edentulous and atrophied mandibles remains a surgical challenge.^1,2  Over the years, clinicians developed various methods to deal with atrophied mandibles, such as short implants, guided bone regeneration, and autogenous bone grafts. First introduced in 1987, Jensen and Nock²  used the inferior alveolar nerve transposition (IANT) technique in conjunction with dental implant placement in severely atrophied mandibles. In recent years, clinicians have widely used these techniques, and reports have shown that they result in satisfactory functional outcomes, a high implant survival rate, and low morbidity.^3–5  Repositioning of the IAN is performed by either lateralization or transposition of the nerve. During inferior alveolar nerve lateralization (IANL), the IAN is exposed within the canal without involving the mental foramen. The exposure is followed by lateral retraction of the nerve, while implants are placed superiorly. The IAN is then repositioned laterally to the inserted implants, and the buccal fat pad is used to cover the canal opening. With this procedure, there is no interference with the incisive nerve. In the IANT technique, the mental foramen is included in the osteotomy to enable incisive branch transection and placement of the IAN and mental foramen in a distal position.⁶  While both procedures are considered technique sensitive with a substantial risk for postoperative sensory impairment, published data imply a higher incidence of neurosensory disturbances following IANT as compared to IANL,⁷  possibly due to the invasive nature of IANT. Damage to the nerve may occur at different stages during IANT surgery and can include mandibular and mental foramen osteotomy, mobilization of the nerve from the canal, or direct trauma to the exposed IAN due to nerve retraction, implant drilling, or removal of debris using suction.

Several surgical appliances have been used in the past to protect the IAN during the retraction process. These include elastic bands, vessel loops, wide gauze bands, aluminum foil, suture covers, and rubber pistons from anesthetic cartridges.^8–10  All the methods require some degree of retraction or include the application of force on the nerve.

The current work describes our cumulative experience with IANT on edentulous patients using the tubing technique, a practical, feasible, and reproducible method to protect the exposed IAN.

This retrospective study (NHR 0085-19) was approved by the Institutional Review Board and the Helsinki committee of the Galilee Medical Center, complied with the public health regulations and provisions of the current harmonized international guidelines for good clinical practice, and aligned with the Helsinki principles. Medical files of 31 patients admitted to our institution between January 2015 and January 2020 were reviewed. All patients in the current work presented with posterior partial edentulism and insufficient residual vertical bone height (<5 mm available for dental implant placement). Depending on the severity of examined mandibles, patients underwent a unilateral (single-site treatment; n = 16) or a bilateral (double-site treatment; n = 15) IANT procedure, followed by immediate placement of dental implants. In all cases, the tubing technique developed in our department was used. Inclusion criteria included age over 18, an atrophic lower jaw that could not be treated without nerve transposition, and no previous sensory disturbances in the IAN dermatome. Data extracted from the medical records included age, gender, date and time of operation, number of implants, and sensory disorder related to sensory changes. Files lacking any of the information mentioned above or containing insufficient data concerning treatment follow-up were excluded. Patients with a history of neurosensory disorders related to previous trauma, surgery, radiotherapy, or the use of analgesic drugs to treat neuropathic or chronic pain were excluded. Patients with background neuropathic pain disorders, such as fibromyalgia, multiple sclerosis, or unbalanced diabetes-related neuropathic conditions, were also excluded. In addition, patients who had undergone IANL were not included in the study.

Following a local infiltration of Lidocaine hydrochloride 2% and Epinephrine 1:100 000 (Novocol Pharmaceutical of Canada, Cambridge, Canada), a full-thickness flap at the edentulous ridge was obtained by crestal-, anterior-, and posterior-releasing incisions, enabling visualization of the entire mental foramen and the lateral aspect of the mandible. The inferior alveolar canal was accessed by removing a 3–4-mm rectangular segment from the buccal cortical bone using a FG extra-long diamond bur (Strauss & Co, Ra'anana) with constant saline irrigation. Cone-beam computed tomography (CBCT) was utilized to evaluate the relationship between the osteotomy and the inferior alveolar canal (Figure 1). The osteotomy of the mental foramen was performed, and the mental nerve was released, followed by dissection of the incisive nerve 4–5 mm anterior to the mental foramen (Figure 2). The IAN was exposed by delicate carving of the cortex and cancellous bone around the lateral wall of the nerve using a round-edge oral spatula (Figure 3). After completing nerve exposure and its subsequent mobilization from the inferior alveolar canal, the length of the deflected nerve was measured (Figure 4). A sterile suction catheter with dimensions corresponding to the exposed IAN was prepared (12/14/16 Charriere or 4.0/4.7/5.3 outer diameter) (Mülly, Unomedical, Deeside, Flintshire, UK) (Figure 5), and a longitudinal slit was made to create a protective sleeve (Figure 6). The sleeve was carefully wrapped around the exposed nerve to cover the deflected IAN (Figure 7). This facilitated protection of the nerve throughout the surgery with implant placement under direct visualization. No additional retraction was necessary, rendering the technique entirely passive. A 3-0 silk suture (Mersilk, Ethicon, Raritan, NJ) was used to secure the tube (Figure 8). Moreover, removing fluids and debris from the surgical field using a vacuum can be safely performed without the risk of direct nerve tissue dehydration.

After implant placement, the protective tube was removed, and the IAN was repositioned inside the exposed canal. The buccal fat pad graft was used to cover the partially exposed IAN (Figure 9). Primary tension-free sutures (3-0 Vicryl Rapide, Ethicon) of the surgical wound were used at the end of the surgery (Figure 10). All surgeries were performed by the same surgeon (the first author), who has 20 years of experience as a maxillofacial specialist and about 15 years of experience in nerve transposition procedures.

All patients received 1 g amoxicillin–clavulanic acid and 8 mg dexamethasone intraoperatively. Patients were instructed to maintain a soft diet for 6 weeks. They were prescribed 875 mg amoxicillin–clavulanic acid twice a day and short-term corticosteroid therapy (Decadron, 6 mg/d) for 1 week after the procedure.¹¹  Oral complex vitamin B (1500 mcg/d) was prescribed for 6 weeks to promote IAN recovery.¹² 

IAN neurosensory impairment was assessed 1, 3, 6, and 12 months after the procedure, using the light touch test and sensitivity mapping by applying moderate pressure with a periodontal probe to depress the skin by 1–2 mm. The sensory testing was independently performed by the first 2 authors. All patients underwent a panoramic X-ray (Planmeca, ProMAX 3D classic, Helsinki, Finland) or a computed tomography scan (Ingenuity 128, Philips, Haifa, Israel) within 48 hours following surgery.

Subject ratings of sensory disturbances at follow-ups (either “yes” or “no”) were collected, and a 2-sided chi-square test was performed to evaluate the changes between subsequent and initial follow-ups. Statistical analyses were performed using GraphPad Prism 7. Significance levels were **P < .01, ***P < .001, and ****P < .0001.

A total of 46 IANT procedures were performed in 31 patients (26 females and 5 males, age range 21–68 years) (Table 1). Sixteen procedures were unilateral, and 15 were bilateral. Overall, 149 implants were inserted. Eight onlay bone grafts from the calvaria or ramus of patients were harvested simultaneously to implant insertion and IANT. One implant failed 4 weeks after the operation due to a jaw fracture, and a second failed 4 months after the procedure due to insufficient osseointegration. The success rate of the implants during the follow-up period (6–60 months) was 98.6%. Sensory impairment was documented in 47.8% of the treated sites at 1 month (22/46 sites), 21.7% of the sites at 3 months (10/46 sites), 6.5% of the sites after 6 months (3/46 sites), and 2.2% of the sites at 12 months (1/46 sites) postsurgery (Figure 11). Four cases of hyperesthesia, 16 cases of hypoesthesia, and 26 cases of paraesthesia were recorded. All but 1 case was resolved by the end of the 12 months of follow-up. The remaining case was resolved after 16 months. All patients received a fixed prosthesis over the implants 3–4 months after the surgery.

Posterior edentulous mandibular segments with severe atrophy are a challenging setting for dental implant placement. IAN repositioning procedures have been used as an alternative to standard treatment options, such as short implants or bone grafting, prior to implant placement in patients lacking sufficient bone height for conventional posterior dental implant treatment. In this article, we presented our experience with the tubing technique for IAN preservation during IANT procedures. The incidence of sensory disturbances recorded 1 month after the operation was 47.8% and dropped to 2.2% by 12 months postsurgery. The implantation success rate following IANT was 98.6%.

Short dental implants decrease costs and have a cumulative survival rate of 92.3%.¹³  Another standard treatment is the utilization of bone grafting prior to implant placement. However, the need for 2 surgical procedures increases costs and treatment time and adds a potential risk for donor site morbidity. IAN repositioning enables the use of standard implants, which increases primary stability and lowers the risk of bone loss in comparison to short implants placed under similar circumstances.¹⁴  However, IANT is still considered a technique-sensitive procedure associated with several morbidities, such as fracture of the mandible, which is regarded as a rare complication,¹⁵  and initial change in sensation, which occurs in most cases. In a review by Abayev and Juodzbalys,⁶  99.47% of IANT procedures resulted in transient neurosensory disturbance, with 0.53% of procedures ending with permanent neurosensory disruption. Neurosensory disturbances resulting from IAN injury include hypoesthesia (partial loss of sensation), paresthesia (abnormal response to stimuli), and hyperesthesia (hypersensitivity to all stimuli). In these cases, patient quality of life can be significantly impaired.¹⁵  Several modifications of the standard inferior alveolar nerve repositioning method followed by immediate placement of dental implants have been published to reduce the risk of neurosensory disturbance.^16–20  Metzger et al¹⁶  demonstrated that piezosurgery for IANT resulted in a lower degree of injury compared to the use of conventional rotary burs. Khojasteh et al²¹  reported that the placement of platelet-rich fibrin and collagen membranes over the exposed IAN accelerated neural healing within 6 months and reduced the duration of discomfort reported by patients.²¹ 

The Seddon²²  and Sunderland²³  classifications are the 2 most widely used nerve injury grading scales. Seddon described the 3 basic types of nerve injuries. Neurapraxia, a first-degree injury, is the most common response to blunt trauma, causing a temporary sensory dysfunction. Axonotmesis is a second-degree injury leading to axonal loss while the connective tissue layers are preserved. Neurotmesis is a third-degree and the most severe nerve injury, where the nerve is physically divided and no conduction is present. Sunderland described 5 degrees of peripheral nerve injury. The first degree corresponds to neurapraxia and focal demyelination and the second degree to axonotmesis with intact neuronal stroma. The third, fourth, and fifth degrees involve injury to endoneurial tubes, perineurium, and epineurium.

Nerve injury may arise from compromised nerve integrity due to tearing, stretching, twisting, and partial or complete transection of the nerve bundles. Minimizing the trauma inflicted to the exposed neurovascular bundle during surgery may reduce the incidence of neurosensory disturbance. According to our accumulated experience with IANT before dental implant placement, injuries to the IAN are classified as either mechanical or physiological. We define mechanical nerve injuries as direct damage inflicted during the following surgical steps: canal exposure osteotomies, release of the mental nerve with its anterior loop from the mental foramen, extraction and lateral mobilization of the nerve out of the canal, and dental implant drilling and placement. Intraoperative injuries to peripheral nerves, in general, and to the IAN can result from direct damage to the nerve due to pressure, traction, thermal injury, or local ischemia.²⁴  During exposure of the IAN, compromised blood supply to the nerve due to bundle mobilization (nerve and its blood vessels), ischemia, or blunt suction may lead to nerve injury.²⁵  In addition, suction used to clear the surgical field may accelerate the dehydration of neurovascular tissues. Such a phenomenon has been documented in the context of the optic nerve, in which direct optic nerve dehydration was recorded during pars plana vitrectomy procedures, leading to functional impairment.²⁶  Further investigations of this phenomenon may shed more light on mechanisms of nerve deterioration due to dehydration.

Once the IAN is mobilized out of the mandibular canal, adequate retraction and preservation of the bundle are crucial for preventing nerve injuries during dental implant placement.⁶  Several methods designed to protect the IAN during transposition surgery have been described.^8,9  De Vasconcelos et al.²⁷  used a delicate spatula as a nerve retractor, while Rosenquist and others introduced vessel loops to facilitate nerve retraction.^28–33  Hashemi^8,9  and Mahmood-Hashemi³⁴  proposed using green cloths, a piece of a suture cover, and half of the rubber piston taken from dental anesthetic cartridges for the retraction of the IAN during implant insertion. Hassani et al³⁵  introduced a low-thickness elastic tape, such as a sterile latex Penrose drain, as a straightforward method to retract and protect nerves deflected outside of the canal during transposition. While the methodologies mentioned above provide partial coverage of the neurovascular bundle, the tubing technique proposed herein offers complete coverage along the entire length of exposed IANs. In the tubing technique, the nerve is fully protected by a suction catheter, commonly used to remove surgical debris and irrigation. This method provides several advantages, including continuous protection of deflected nerves and full compatibility with suction during the operation. In addition, the technique protects the nerve bundle during drilling of the implant sites and implant placement. In cases where simultaneous bone augmentations and onlay block fixations³⁶  or removal of screws from previous surgeries are required, IAN tubing can be an excellent option for nerve preservation. In addition, there is no need to retract the exposed IAN during the operation, rendering the technique entirely passive and eliminating the risk of stretching injury. Additional advantages of the tubing technique include its cost-effectiveness, simplicity, and complete visualization of the IAN throughout the entire procedure, reducing the risk of contact injury to the wrapped nerve.

Limitations of this research include the focus on a specific method, although novel, with no comparison to other methods mentioned in the literature. In addition, a relatively small patient cohort is presented. Further research on the technique will be needed to determine whether it provides benefits with regard to the risk of neurological disorders.

During IAN repositioning prior to placement of implants at posterior segments of atrophic jaws, nerve preservation is of utmost importance to avoid postoperative sensory disturbance. The IAN tubing technique described in the current work is a safe and straightforward procedure providing passive IAN protection. This surgical technique may be a significant addition to the armamentarium of clinicians aiming to treat edentulous patients with atrophied jawbones.

Abbreviations

IAN:

inferior alveolar nerve

IANT:

inferior alveolar nerve transposition

IANL:

inferior alveolar nerve lateralization

CBCT:

cone-beam computed tomography

We would like to thank Dr Ensaf Safori for her beautiful and informative illustrations, which explain the tubing technique and contribute to the article.