Oral Maxillofac Surg (2009) 13:213–219 DOI 10.1007/s10006-009-0175-3
ORIGINAL ARTICLE
Inferior alveolar nerve lateral transposition Bruno Ramos Chrcanovic & Antônio Luís Neto Custódio
Published online: 4 October 2009 # Springer-Verlag 2009
Abstract Purpose We determined the outcomes of 18 inferior alveolar nerve lateral transposition procedures in 15 consecutive patients. The advantages and disadvantages of this technique are discussed. Results The surgical protocol for inferior alveolar nerve transposition, followed by implant placement, presented excellent results, with complete recovery of the sensitivity within 6 months after the surgical procedure. Discussion Inferior alveolar nerve transposition is an option for prosthetic rehabilitation in cases of moderate or even severe bone reabsorption for patients that do not tolerate removable dentures. Conclusions It is concluded that inferior alveolar nerve transposition can be safely and predictably performed with low risk to the mental nerve sensibility. Each patient should be advised of the chance of permanent nerve deficit throughout the distribution of the mental nerve. Alternative restorative solutions should also be considered.
B. R. Chrcanovic (*) Av. Raja Gabaglia, 1000/1209—Gutierrez, Belo Horizonte, MG-CEP 30441-070, Brazil e-mail:
[email protected] A. L. N. Custódio Departamento de Odontologia, Pontifícia Universidade Católica de Minas Gerais, Av. Dom José Gaspar, 500 Prédio 45—Coração Eucarístico, Belo Horizonte, MG 30535-610, Brazil e-mail:
[email protected] A. L. N. Custódio Oral and Maxillofacial Surgery Department, School of Dentistry, Pontifícia Universidade Católica De Minas Gerais, Belo Horizonte, Brazil A. L. N. Custódio Department of Morphology, Institute of Biological Sciences, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
Keywords Mandibular nerve surgery . Paresthesia . Dental implants
Introduction Rehabilitation of edentulous posterior mandibular regions with advanced ridge resorption using implants has anatomical, surgical, and biological problems [14]. Osseointegrated dental implants are often placed in the posterior mandible, mostly for support of fixed restorative prostheses. In many cases the bone has atrophied, such that sufficiently long fixtures cannot be placed without encroaching on the inferior alveolar nerve (IAN). In that situation, restorative options include use of short fixtures, onlay bone grafting to increase ridge height, and more complicated and detailed imaging studies to allow positioning of implants alongside and not into the nerve canal during the procedure. Another option is to move the IAN laterally from its canal by either nerve lateralization or nerve transposition. Inferior alveolar nerve dysfunction may be the result of trauma, disease, or iatrogenic injury [30, 43]. Hypoesthesia, paresthesia, and hyperesthesia [37] are the most common postoperative complications after IAN lateral transposition and indeed of any surgery whereby a peripheral nerve is moved from its physiological site [16]. There are two main variations of the technique, either involving the mental foramen or not. As a biomechanical advantage, IAN transposition presents an increase in resistance to occlusal forces and promotes a good proportion between the implant and the prosthesis [38]. As a negative point, this type of technique does not recover the alveolar ridge anatomy, temporarily weakens the mandible, and particularly presents the risk that eventual sensory alterations may be permanent [3]. IAN transposition generally causes some degrees of sensory
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alterations, like hypoesthesia (partial loss of sensitivity) and paresthesia (abnormal response to stimuli) [45]. Nerve lesion occurs due to ischemia caused by distension of the nerve during the surgical procedure or by its chronic compression/distension after surgery [31]. The aim of the present study is to report a sequence of patients who underwent IAN transpositions with their longterm subjective sensory assessment, with a literature review.
Surgical technique A mucosal incision superior to the mental foramen is extended from the site of the canine tooth to the second molar region. The mental nerve is identified, and the periosteum is freely dissected from the surrounding mandibular bone (Fig. 1). A unicortical lateral osteotomy is then fashioned around the mental foramen and is extended inferiorly and anteriorly so any “loop” of nerve is not interfered with during the osteotomy. Minimal retraction of the nerve is required, and there is no need for dissection of the nerve as it enters the soft tissue of the lip and chin. A curette is plunged into the mandibular canal in the proximal direction. In fact, the curette will be put between the bone and the nerve. This procedure is done to protect the nerve. When the curette is plunged into the canal, the corticocancellous bone can be removed by a small round bur. The buccal bone can be removed about 2 to 3 mm, then the curette will be plunged into the canal again, and this procedure can be repeated posteriorly along the canal (Fig. 2). With the cortex removed, it is relatively easy to remove any remaining overlying bone with an instrument and to tease the nerve out of the mandible (Fig. 3). The incisive branch is severed with a scalpel, and the mental nerve and its IAN proximal portion can be freed
Fig. 1 The mental nerve is identified
Fig. 2 A curette is put between the bone and the nerve. This procedure is done to protect the nerve while the bur removes bone
from the canal. Once this has been done, the implants can be placed under direct vision through the canal and into or through the inferior cortex (Figs. 4 and 5). Finally, the excised bone can be replaced laterally around the implants as a bone graft (Fig. 6). The IAN can then be left to lie passively alongside. In essence, the mental foramen has been moved posteriorly. Figures 7 and 8 show radiographs before and after IAN transposition. All patients were submitted for 10 sessions (four times a week) of low level laser (LLL) application, beginning just after the surgery. A photon-plus GaAlAs diode laser (LLL) system was used. The unit had a contact probe with a laser beam diameter of 0.5 cm. The system delivers a 70 mW output that emits a wavelength of 780 nm. The irradiance used was 6.0 J/cm2 per treatment site. It was also prescribed for all patients one pill of Citoneurin© 5000 UI (vitamin B1 100 mg+vitamin B6 100 mg+vitamin B12 5,000 μg) every
Fig. 3 Inferior alveolar neurovascular plexus being removed out of the mandible
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Fig. 4 Insertion of implants according to the surgical prosthetic guide
8 h for 10 days. The area of sensibility was identified with a simple anesthesia needle. A diagram was used in objective neurosensory assessment. The area of sensibility of each patient was monitored monthly. The percentage of improvement was obtained by subtracting the initial area of loss of sensibility from the final area after 6 months. The neurological examinations were not performed by a neurologist, but by the same oral and maxillofacial surgeon.
Results Fifteen patients (10 women and five men) underwent a total of 18 IAN transpositions, with an average age of 46 years. Two women and one man underwent bilateral surgery. A total of 25 dental implants were placed; three did not integrate. All patients reported initial change in sensation (paresthesia). The surgical protocol followed with complete recovery of the sensitivity within 6 months in all patients
Fig. 5 Implants placed
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Fig. 6 The excised bone can be replaced laterally around the implants as a bone graft
(2 months, one case; 4 months, seven cases; 5 months, five cases; and 6 months, five cases).
Discussion Kan et al. [18] pointed out that the amount of bone superior to the IAN canal is often insufficient for placement of fixtures of the desirable length. In addition, the bone that is present superior to the IAN canal is often of poorer quality than its cortical counterpart. These factors and the fact that shorter implants have been associated with higher failure rates [13, 24] have led to the development of methods of IAN displacement that allow placement of longer fixtures; with these methods the inferior cortex of the mandible is engaged, which leads to greater initial stability. Apart from longer implants, IAN transposition allows for use of a greater number of implants, which improves the overall strength of the final prosthesis [22]. With nerve lateralization the IAN is exposed, and traction is used to deflect it laterally, while the implants are placed. The IAN is then left to fall back in against the
Fig. 7 Presurgical panoramic radiography
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According to Hirsch and Brånemark [14] the cause of the impaired nerve function noticed is most probably due to an impairment of the metabolic supply due to the disturbed microvascular flow of the nerve fibers caused by mechanical trauma. Subjective tests have shown that the fibers responsible for heat and pain sensitivity can better withstand compressive and traumatic ischemic events than the larger fibers supplying the receptors responsible for tactilediscriminatory sensitivity [31]. Fig. 8 Postsurgical panoramic radiography with implants
fixtures. There is no interference with the incisive nerve. With nerve transposition a corticotomy is done about the mental foramen, and the incisive nerve is transected such that the mental foramen is repositioned more posteriorly. Advantages and risks of IAN transposition The advantages of IAN transposition include the ability to place longer fixtures and to engage two cortices for initial stability. Using this technique avoids the need for additional radiation-intensive and costly imaging studies. Simple panoramic radiography and clinical examination are all that is required. The inherent risk of this surgical procedure is damage to the IAN, with resultant neurosensory disturbance to the mental nerve. It is therefore important to establish the relative risk of this occurring since avoiding such problems is the very reason the procedure is done in the first place. Minimum quantity of remaining bone required to perform the technique The literature presents a report of mandibular fracture after IAN transposition and implant placement in the posterior region of an atrophic mandible, more emphatically stressing the need for making small osteotomies and presence of adequate bone remainder for performing the technique [19]. A minimum quantity of approximately 8 mm of remaining bone above the mandibular canal is required [35]. In situations with minimal bone height above the mandibular canal, autogenous bone graft before IAN transposition and implant placement must be considered. Loss of sensation of lower lip and chin Transposition of the IAN also results in the loss of sensation of its terminal incisive branch. This is of no consequence for people who are edentulous in the anterior mandible, but it may cause some disturbance to residual dental and periodontal sensibility in any remaining anterior teeth [29]. The major clinical difficulty associated with IAN transposition is temporary or permanent dysfunction of the nerve, which patients report as altered sensation of the lower lip and chin.
Loss of sensibility as a result of stretching of the nerve The total IAN lateral transpositioning is likely to be the most traumatic maneuver for the nerve. It should be recalled that 10–17% traction is enough for fibers to even temporarily lose their conduction ability [39]. Moreover, mental nerve damage can be the result of an overstretched mucoperiosteal flap in the premolar area. Whenever the non-osseous portion of the mental nerve becomes exposed and the flap is stretched with a view to preserving it, some degree of injury is unavoidable. As a matter of fact a spatula-caused traction can lead to nerve twisting even in areas far away from the inured one [31]. Therefore, more severe stretch injury may result in partial lesion of the axons and of their myelin sheaths. Wallerian degeneration of the distal segment ensues from axonal regeneration of the nerve stump toward the periphery within the endothelial sheaths serving as a guide. Functional recovery depends on the nervous fiber regeneration ability and speed, which may vary between 1 and 3 mm a day [26]. Loss of sensibility as a result of vascular damage Vascular damage can also jeopardize nerve function and recovery. Inferior alveolar artery revascularization initiates the regeneration process. Blood arterial pressure helps maintain the canal size and promotes bone remodeling in the surgical site (with no appropriate revascularization, the canal becomes obstructed in about 12 months after surgery). Nerve regeneration goes hand in hand with bone remodeling, directing the growth of the nerve proximal stump toward the distal end of the injured nerve, thus preventing haphazard growth [2, 11]. Morrison et al. [29] says that since this surgery is delicate, it is best performed under a general anesthetic to eliminate patient movement and to maximize access. Retrospective papers Jensen and Nock [16] were the first to report an IAN transposition for the placement of osseointegrated implants in the posterior mandible area. In 1992 Rosenquist [34] reported on 10 IAN transposition operations with implant placement involving mental foramen osteotomy. He reported persistent nerve dysfunction in 20% regions after 6 months. At 1 year neurosensory function of all 10 mental nerves was tested normal. Also in 1992,
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Friberg et al. [10] reported 22.2% impaired function of the nerve after 6 months. In 1993 Smiler [40] also reported a low incidence of permanent neurosensory dysfunction with this procedure, stating that none of the 10 patients he described had permanent disturbance of sensation in the mental nerve distribution. In 1994 Jensen et al. [15] reported on nine sites at which IAN transposition with mental foramen osteotomy and incisive nerve transection was performed for placement of posterior mandibular implants. On follow-up at 6 months, sensation in the mental nerve distribution was normal at seven sites, whereas one site was paresthetic and one site was hypoesthetic. In 1995, in a study of 24 posterior mandibular segments where IAN transposition was performed during placement of implants, only three sites were abnormal on the basis of objective assessment (12.5%), and all sites were reported as normal on the basis of subjective assessment [14]. In 1999 Nocini et al. [31] assessed the inferior alveolar dysfunction after his transposition in 10 patients. They found that certain sensory dysfunctions after surgery were present in all but one patient after 7 months to 2 years postoperatively. In 2002 Morrison et al. [29] performed 26 IAN transpositions. All of the patients reported initial change in sensation lasting approximately 1 month. Four patients reported that the change in sensation was persistent. However, the reported incidence of neurosensory disturbance of the mental nerve after this procedure is not always low. In an investigation of the long-term neurosensory outcome of IAN displacement with and without mental foramen osteotomy, nine of the 21 operations involved mental foramen osteotomy and incisive nerve transection, whereas 12 involved IAN lateralization without incisive nerve transection [18]. Neurosensory testing over a mean follow-up period of 41 months included light touch, brush stroke direction, and two-point discrimination. In the patients who underwent mental foramen osteotomy, seven of the nine sites tested abnormal with objective assessment, whereas only four of the 12 sites in the nerve lateralization group tested abnormal. Overall, neurosensory deficits existed at 11 of the 21 sites tested. Statistical comparison of nerve conduction data showed that partial and total lateral IAN transposition had the same effect on IAN recovery over 6 months after surgery, indicating that the former procedure may be most adequate to maintain the continuity of the nerve [31]. Identifying and assessing the frequency and severity of nerve damage following IAN transposition as well as recovery potential is difficult. Clinical-neurosensory evaluations are biased by the patient’s own sensitivity, the stimulus-evoking technique, and the examiner’s interpretation, and thus cannot yield objective results [17, 44]. Females were at higher risk of developing postoperative complications than men, and mainly women and older
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persons have the most severe discomfort after oral nerve damage [7, 37]. According to Ozen et al. [32] it can be stated that females are less likely to undergo spontaneous recovery following nerve injury than male subjects. The process of nerve regeneration after compression or less severe crush injuries usually requires several weeks to 6 months. If there is no sensory recovery during this time, permanent loss of continuity in the nerve trunk should be expected [42]. There is generally little improvement in sensation on the injured side when assessed either by objective means or subjectively by the patient 9 months after compression injury and 12 months after nerve section [4, 12]. Low level laser therapy LLL therapy can be used for the treatment of nerve injuries [32]. Because LLL is relatively noninvasive, its ability to stimulate injured nerves without surgical intervention is desirable [33]. There are some studies reported in the treatment of IAN injury, in both subjective and objective neurosensory impairment after LLL treatment of IAN paresthesia [20, 21, 25]. Clinical studies of the effects of LLL therapy on injured nerves have revealed an increase in nerve function and improved capacity for myelin production [27]. In a previous blind clinical trial Khullar et al. [20] investigated the effects of LLL treatment using a GaAlAs laser on sensory perception in a 15-patient population after a longstanding postsurgical IAN injury. The average time after injury before starting treatment was 33.4 months. Six patients received real LLL treatment, while the seven received placebo laser treatment. The results demonstrated an overall significant improvement in mechanosensory perception subsequent to laser treatment compared with the placebo LLL treated group. The patient in the real-lasertreated group showed a 44% improvement after LLL treatment. Midamba and Haanaes [25] have also reported subjective improvement in patients suffering from IAN injuries for more than 6 months. An average subjective improvement was found (71.1%) after 20 LLL GaAlAs treatments. More recently, Miloro et al. [27] reported a positive LLL effect both on neural regeneration in surgically created defects and on neurosensory recovery after sagittal ramus osteotomy [28]. They found significant improvement in neurosensory recovery after a bilateral sagittal split osteotomy and also noted that LLL therapy may be a useful adjunct to promote neural wound healing in surgically created defects. Brugnera et al. [6] treated two groups of patients with lesions to the inferior alveolar and mental nerves with LLL in their study. All cases of paresthesia were due to surgical interventions. The first group was identified as immediate and was treated within 2–15 days after the injury, while the history of injury for the second group was 30–365 days. In the first group 72.7%
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achieved absolute recovery and 18.3% showed relative improvement, whereas the improvement for the latter group was only 27.7%. The use of piezosurgery to avoid nerve damage Piezosurgery (Mectron Piezosurgery Device, Mectron, Genova, Italy) is a recently developed system for cutting bone with microvibrations [8]. The device, with an oscillation of 20– 200 μm, cuts mineralized tissue exactly and smoothly, while adjacent soft tissue and nerves remain unharmed because surgical action ceases when the scalpel comes into contact with non-mineralized tissues [41]. The technique has shown to be feasible in IAN transposition, since it favors smaller osteotomies and preservation of the vascularnervous bundle [5, 36]. The longer time required for the operation has been reported as a disadvantage [23]. The use of short implants Another treatment option that should be considered, taking into account the vertical discrepancy between the arches, is the use of short implants that have shown high rates of success [1]. Nevertheless, it is pointed out that biomechanics is related to the denture design, which is directly associated with the mean rates of success and failure, and the use of short implants and dentures with excessive lever arms is a factor for failure [9].
Conclusions Avoiding IAN damage during any surgical procedures is an important goal because of the forensic and ethical issues and the neurological sequelae, which may impair the oral function related to the nerve injury. However, a certain degree of nerve injury may be expected to occur during this demolitive surgical approach [16]. Although objective testing may reveal sensory changes in most cases, nerve transposition is a worthwhile surgical procedure that does not cause severe sensory complaints [31]. Our 18 cases with complete recovery of the sensitivity, within 6 months after the surgical procedure, help to support this. Before undergoing this procedure, each patient should be advised of the chance of permanent nerve deficit throughout the distribution of the mental nerve [3]. Alternative restorative solutions should also be considered.
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