Management of patients with trigeminal nerve injuries after mandibular implant placement
RICHARD A. KRAUT, D.D.S. and
OMAR CHAHAL, D.D.S.
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ABSTRACT
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Background. Placement of mandibular endosseous implants can result in damage to the lingual nerve, the inferior alveolar nerve or both nerves. All dentists who place mandibular implants should be aware of the appropriate early management of these injuries, as well as the appropriate time to refer patients with these injuries to a microneurosurgeon.
Overview. The lingual nerve is less likely to undergo spontaneous regeneration than is the inferior alveolar nerve, which is protected within the inferior alveolar canal. Since the inferior alveolar canal can be seen on most panoramic radiographs and on all high-quality computed tomographic scans, it is easier to avoid damage to the inferior nerve than to the lingual nerve, which is not visualized on radiographs and whose relationship to the posterior portion of the mandible varies from person to person.
Results. The authors reviewed one study that showed that lingual nerve repair helped 90 percent of patients. A second study found that patients who underwent lingual nerve repair reported a mean score of 7 on a scale from 0 to 10 in regard to the postoperative return of nerve function. Several other studies reported favorable patient responses to inferior alveolar nerve repair.
Conclusions and Clinical Implications. These results reinforce the need for early referral and intervention when inferior alveolar nerve injuries occur. Failure to refer patients with trigeminal nerve injury before distal nerve degeneration develops prevents minimization of the injury through microneurosurgical repair.
Placement of mandibular endosseous implants can result in damage to the lingual nerve, the inferior alveolar nerve or both nerves.1–6 The risk of nerve injury depends on multiple factors, including administration of inferior alveolar nerve block,7–12 the difficulty of the proposed procedure and the surgeon’s level of expertise. Inferior alveolar nerve lateralization and posterior alveolar distraction are high-risk procedures that are more likely to result in inferior alveolar nerve defect regardless of the surgeon’s experience; these procedures are further complicated if the patient has extremely dense bone.13
These results reinforce the need for early referral and intervention when inferior alveolar nerve injuries occur.
When the lingual or inferior alveolar nerve is injured, it is imperative that the surgeon recognize the injury and treat the patient appropriately. The purpose of this article is to examine ways to avoid, diagnose and manage nerve injuries associated with placement of mandibular endosseous implants.
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PREOPERATIVE PLANNING
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Altered sensation after mandibular implant placement is the result of trauma to any of the branches of the mandibular nerve, including the inferior alveolar, mental and lingual nerves.6,12–14 It is important for clinicians to perform a neurosensory examination of mandibular nerve function before placing the implant to determine whether there is pre-existing altered sensation. Great care must be taken when selecting possible sites for implant placement. Appropriate radiographic evaluation of the implant site is indicated.
When selecting implants based on preoperative panoramic images, clinicians must make sure that a marker of known dimension has been imaged in the area being considered for implant placement.6 We recommend a safety margin of 2 millimeters between the end of the implant and the canal when selecting the length of implants that are to be placed above the inferior alveolar canal (Figure 1
). Because of its greater precision, computed tomography enables the clinician to select an implant that will be 1 mm above the canal.6 Implant burs vary depending on the manufacturer and must be understood by the surgeon because the specified length (for example, a 10-mm marking) may not reflect an additional millimeter included for drilling efficiency.
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Figure 1. Panoramic radiograph with marking balls of known dimension in the area of the planned implants. The inferior alveolar canal has been marked to facilitate measurement of the space above the canal to determine the length of implants to be placed.
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When placing implants in proximity to the mental foramen, the clinician must take into consideration the anterior loop of the nerve (Figure 2), as well as the available bone above the mental foramen, because the inferior alveolar nerve often rises as it approaches the mental foramen (compared with its height in the molar region) (Figure 3).
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Figure 2. The mental nerve exits via a broad foramen, as seen in cross-sections 38 through 41; however, an anterior loop of the nerve appears in cross-sections 42 through 46. It is impossible to determine from the computed tomographic scan whether the radiolucency seen is an anterior loop of the mental nerve or an unusually large incisive nerve.
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Figure 3. The inferior alveolar nerve often rises as it approaches the mental foramina. This is clearly evident on the panoramic view in areas 35 through 45 and 95 through 87.
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INTRAOPERATIVE COMPLICATIONS
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Nerve damage after administration of an inferior alveolar nerve block is a documented, but very rare, intraoperative complication.7–12 Both the lingual and mental nerves are at risk during elevation of the mandibular mucoperiosteum.15 Careful flap design and elevation are important to avoid nerve injury while working on the buccal surface of the mandible in the region of the mental foramen or posterior mandible. The mental foramen may be located at or near the crest of an atrophic mandible (Figure 4). To avoid damage to the mental nerve in patients with atrophic mandibles, the clinician may need to make incisions in the area of the mental foramen that are lingual to the crest of the mandible.
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Figure 4. A. The nerve exits at the crest of the ridge in cross-sections 40 and 41. The incision must be on the lingual aspect of the mandible to avoid transecting the mental nerve when the symphysis is exposed at the time of implant placement and at the time of healing cap placement. B. Atrophic mandible in which the mental foramina are close to the crest of the ridge. The incision for implant placement must be on the lingual aspect of the crest to avoid transecting the mental nerves.
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The lingual nerve in the molar region typically is in close proximity to the lingual plate below the crest of the ridge. Anatomic dissections have demonstrated variation in the position of the lingual nerve. In a magnetic resonance study, Miloro and colleagues15 found that the nerve actually coursed over the retromolar pad in 10 percent of patients. In these cases, the nerve may be traumatized by flap elevation and retraction or during suturing.15 In addition, the lingual nerve may be damaged by direct implant encroachment.
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EVALUATION AND MANAGEMENT
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The most desirable outcome after nerve injury is spontaneous return of normal sensation. The likelihood of this occurring depends on both the severity of the injury and the nerve involved. Partial transection of the lingual nerve is less likely to result in spontaneous resolution of symptoms than is a similar injury involving the inferior alveolar nerve, which has a bony canal to contain and direct the regeneration fibers.
Lingual nerve injury.
Clinicians should document any unusual response (such as unusual pain or an electrical shock–like feeling) during administration of local anesthetic or during surgery. If a nerve injury is suspected, he or she should perform thorough, standardized tests to document the level of neurosensory function as soon as an injury is suspected (usually the day after surgery). The clinician should outline the area of decreased sensation on the patient’s tongue, record this area in the patient’s medical record and preferably photograph the tongue. The clinician should describe and document the nature of the altered sensation, as described by the patient (including duration, inducing factors, hyperesthesia, dysesthesia, anesthesia and loss of sense of taste with the use of salt and sugar).
The clinician should repeat the neurosensory examination and compare the results with the baseline examination results no later than one month after surgery. Total anesthesia or the development of hyperalgesia or spontaneous pain are predictors of poor response without surgical intervention, and should lead clinicians to make prompt referrals to a microneurosurgeon no later than one month after surgery. Signs of diminishing sensation or failure of sensation to improve on repeated testing also are indicators that normal sensation will not likely return spontaneously.
If a patient’s condition fails to show improvement or neurosensory function has deteriorated two months after the nerve injury occurred, the surgeon should promptly refer him or her to a microneurosurgeon. The microneurosurgeon often will want to perform his or her own neurosensory examination and may wish to repeat the examination one month later to avoid surgery in the case of a resolving injury. The goal of early referral is to allow the patient to undergo nerve repair within four months of the injury, thereby minimizing distal degeneration of the nerve.12
Robinson and colleagues16 studied 53 patients who underwent lingual nerve repair. They reported that patients generally considered the operation to be worthwhile, as indicated by a mean score of 7 on a scale from 0 (no change) to 10 (normal nerve function). Zuniga and colleagues17 conducted a study in which 90 percent of patients reported having experienced regeneration of fungiform taste receptors and recovered taste after undergoing lingual nerve repair; patients also expressed global satisfaction relative to the repair, as indicated by a mean score of 2.5 on a scale from 0 to 4. Although both of these studies reported excellent results, they clearly indicate variable responses and reflect the need for patients to have realistic expectations when they elect to undergo lingual nerve repair.
Inferior alveolar nerve injury.
As with lingual nerve injuries, clinicians should document unusual patient reactions occurring during surgery (such as sharp pain or an electrical shock–like sensation). If a nerve injury is suspected, the clinician should perform a thorough neurosensory examination and document the results the day after surgery (when the effects of the anesthetic should have worn off). The clinician also should record the patient’s subjective assessment of altered sensation. He or she should document nerve function by lightly touching the lip and chin with a wisp of cotton at the end of a cotton swab to determine sensitivity.
Use a soft brush to assess the patient’s ability to determine the direction of movement on the lip and chin (with the patient’s eyes closed), perform a 27-gauge needle test to determine the patient’s ability to perceive pain, and determine two-point discrimination on the lip and chin using a pointed caliper that is gradually opened to a distance of 1 centimeter. The final aspect of the neurosensory examination consists of temperature sensitivity testing on both the affected lip and part of chin and unaffected lip and part of chin. The clinician uses ice and a mirror handle warmed to 43 C to determine if the patient feels cold or heat.
The clinician should map any area of neurosensory deficit and photograph it to compare with future photographs. If an implant is potentially violating the canal, its depth should be decreased in bone (by unscrewing it a few turns) and left short of the canal or removed. Since the altered sensation may be due to an inflammatory reaction, a course of steroid treatment or a high dose of nonsteroidal anti-inflammatory medication (such as ibuprofen [800 milligrams] three times per day) should be prescribed for three weeks.
If improvement is noted at three weeks on the basis of a repeated neurosensory examination, the clinician can prescribe an additional three weeks of anti-inflammatory drug treatment. If, however, sensation has not improved by two months, the prognosis typically is poor, and we recommend referral to a microneurosurgeon. If the clinician notes improvement at two months, he or she should re-examine the patient at three and four months after the injury occurred. If the patient’s nerve function has not returned to the baseline level by four months, we recommend referral to a microneurosurgeon.
As early as 1985, Mozsary and Syers18 discussed guidelines for microsurgical reconstructive procedures in the treatment of inferior alveolar nerve injuries. Ruggiero,12 LaBanc and Van Boven,19 Colin and Donoff20 and Pogrel and Maghen21 reported favorable patient responses to inferior alveolar nerve repair, and all emphasized the need for repair before Wallerian degeneration of the distal portion of the inferior alveolar nerve has occurred (since this degeneration is a slow process, repair is possible four to six months after the injury has occurred).
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CONCLUSION
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Although uncommon, peripheral trigeminal nerve injury can occur after placement of mandibular implants. Practitioners who place implants must discuss the possibility of nerve injury with their patients and include this possibility in the consent forms. If nerve injury occurs or is suspected after the procedure, the clinician must inform the patient of its existence and make a timely referral to an appropriately trained microneurosurgeon if necessary.12,17–21
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Dr. Kraut is the director, Oral and Maxillofacial Surgery, Montefiore Medical Center, Department of Dentistry, 111 E. 210th St., Bronx, N.Y. 10467, e-mail "rkraut{at}montefiore.org". Address reprint requests to Dr. Kraut.
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FOOTNOTES
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At the time this study was conducted, Dr. Chahal was the chief resident, Oral and Maxillofacial Surgery, Montefiore Medical Center, Department of Dentistry, Bronx, N.Y. He now is a medical student, Louisiana State University Medical School, Shreveport.
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REFERENCES
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- Van Steenberghe D, Lekholm U, Bolender C, et al. Applicability of osseointegrated oral implants in the rehabilitation of partial eden-tulism: a prospective multicenter study on 558 fixtures. Int J Oral Maxillofac Implants 1990;5:272–81.[Medline]
- Ellies LG. Altered sensation following mandibular implant surgery: a retrospective study. J Prosthet Dent 1992;68:664–71.[Medline]
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- Bartling R, Freeman K, Kraut RA. The incidence of altered sensation of the mental nerve after mandibular implant placement. J Oral Maxillofac Surg 1999;57:1408–10.[Medline]
- Pogrel MA, Bryan J, Regezi J. Nerve damage associated with inferior alveolar nerve blocks. JADA 1995;126:1150–5.
- Pogrel MA, Thamby S. Permanent nerve involvement resulting from inferior alveolar nerve blocks. JADA 2000;131:901–7.
- Paxton MC, Hadley JN, Hadley MN, Edwards RC, Harrison SJ. Chorda tympani nerve injury following inferior alveolar injection: a review of two cases. JADA 1994;125:1003–6.
- Chang WK, Mulford GJ. Iatrogenic trigeminal sensorimotor neuropathy resulting from local anesthesia: a case report. Arch Phys Med Rehabil 2000;81:1591–3.[Medline]
- Krafft TC, Hickel R. Clinical investigation into the incidence of direct damage to the lingual nerve caused by local anesthesia. J Craniomaxillofac Surg 1994;22:294–6.[Medline]
- Ruggiero S. Trigeminal nerve injury and repair. N Y State Dent J 1996;62:36–40.
- Delcanho RE. Neuropathic implications of prosthodontic treatment. J Prosthet Dent 1995;73:146–52.[Medline]
- Rubenstein JE, Taylor TD. Apical nerve transection resulting from implant placement: a 10-year follow-up report. J Prosthet Dent 1997;78:537–41.[Medline]
- Miloro M, Halkias LE, Slone HW, Chakeres DW. Assessment of the lingual nerve in the third molar region using magnetic resonance imaging. J Oral Maxillofac Surg 1997;55:134–7.[Medline]
- Robinson PP, Loescher AR, Smith KG. A prospective, quantitative study on the clinical outcome of lingual nerve repair. Br J Oral Maxillofac Surg 2000;38(4):255–63.[Medline]
- Zuniga JR, Chen N, Phillips CL. Chemosensory and somatosensory regeneration after lingual nerve repair in humans. J Oral Maxillofac Surg 1997;55:2–13.[Medline]
- Mozsary PG, Syers CS. Microsurgical correction of the injured inferior alveolar nerve. J Oral Maxillofac Surg 1985;43:353–8.[Medline]
- LaBanc JP, Van Boven RW. Surgical management of inferior alveolar nerve injuries. Oral Maxillofac Surg Clin North Am 1992;4(2): 425–37.
- Colin W, Donoff RB. Restoring sensation after trigeminal nerve injury: a review of current management. JADA 1992;123:80–5.
- Pogrel MA, Maghen A. The use of autogenous vein grafts for inferior alveolar and lingual nerve reconstruction. J Oral Maxillofac Surg 2001;59:985–8.[Medline]
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ABSTRACT
PREOPERATIVE PLANNING
