A new technique for recording sensory conduction velocity of the inferior alveolar nerve

Differential Diagnosis of Chronic Neuropathic Orofacial Pain: Role of Clinical Neurophysiology

Orofacial pain syndromes encompass several clinically defined and classified entities. The focus here is on the role of clinical neurophysiologic and psychophysical tests in the diagnosis, differential diagnosis, and pathophysiological mechanisms of definite trigeminal neuropathic pain and other chronic orofacial pain conditions (excluding headache and temporomandibular disorders). The International Classification of Headache Disorders 2018 classifies these facial pain disorders under the heading Painful cranial neuropathies and other facial pains. In addition to unambiguous painful posttraumatic or postherpetic trigeminal neuropathies, burning mouth syndrome, persistent idiopathic facial and dental pain, and trigeminal neuralgia have also been identified with neurophysiologic and quantitative sensory testing to involve the nervous system. Despite normal clinical examination, these all include clusters of patients with evidence for either peripheral or central nervous system pathology compatible with the subclinical end of a continuum of trigeminal neuropathic pain conditions. Useful tests in the diagnostic process include electroneuromyography with specific needle, neurography techniques for the inferior alveolar and infraorbital nerves, brain stem reflex recordings (blink reflex with stimulation of the supraorbital, infraorbital, mental, and lingual nerves; jaw jerk; masseter silent period), evoked potential recordings, and quantitative sensory testing. Habituation of the blink reflex and evoked potential responses to repeated stimuli evaluate top-down inhibition, and navigated transcranial magnetic stimulation allows the mapping of reorganization within the motor cortex in chronic neuropathic pain. With systematic use of neurophysiologic and quantitative sensory testing, many of the current ambiguities in the diagnosis, classification, and understanding of chronic orofacial syndromes can be clarified for clinical practice and future research.

Inferior alveolar nerve injuries associated with mandibular fractures

The study evaluates the incidence of inferior alveolar nerve injuries in mandibular fractures, the duration of their recovery, and the factors associated with them. Fifty-two patients with mandibular fractures involving the ramus, angle, and body regions were included in this study; the inferior alveolar nerve was examined for neurological deficit posttraumatically using sharp/blunt differentiation method, and during the follow-up period the progression of neural recovery was assessed. The incidence of neural injury of the inferior alveolar nerve was 42.3%, comminuted and displaced linear fractures were associated with higher incidence of inferior alveolar nerve injury and prolonged recovery time, and recovery of inferior alveolar nerve function occurred in 91%.Fractures of the mandible involving the ramus, angle, and body regions, and comminuted and displaced linear fractures are factors that increase the incidence of inferior alveolar nerve injuries. Missile injuries can be considered as another risk factor.

Difficult diagnosis of facial pain: A case report and mini-review

This case report elucidates pitfalls of clinical and radiologic investigations of neuropathic pain due to trigeminal pathology, and utility of neurophysiologic examination when diagnosing facial pain. Our patient was a 63-year-old woman who developed acute, severe facial pain, first located behind the left eye. Neuralgic exacerbations, paresthesia within lower face on the left and restricted mouth opening occurred during the course of the disease with gradual progression. Brain MRI and CT scans were interpreted as normal at 4 and 10 months after symptom onset. At 9 months, detailed neurophysiologic examination showed severe chronic mandibular neuropathy at the left oval foramen with more prominent disturbance of the thick myelinated nerve fibers than the small fibers suggesting compressive etiology. Guided by the neurophysiologic findings, 11 months after the onset of the symptoms, a new brain MRI with contrast enhancement revealed metastatic adenocarcinoma of the left temporal bone along the mandibular nerve, exactly matching the site indicated by the neurophysiologic examination. Neurophysiologic tests offer cost-effective, sensitive tools for screening and accurate level diagnostics of neuropathy and neuropathic pain, which can be utilized also in the diagnosis of facial pain. In addition, whenever there are progressing neurologic deficits or neurophysiologic signs indicating expansive lesion, despite initially normal findings in the brain imaging studies, repeated MRI examinations are warranted, preferably focusing to the ‘neurophysiologic region of interest’ to avoid radiologic sampling errors. As no isolated technique achieves 100% diagnostic accuracy, only rational combinations of different methods will result in correct diagnosis of facial pain without unnecessary delays. Treatment of neuropathic pain is often delayed because of difficulties in reaching the correct diagnosis. During the work-up, many differential diagnostic alternatives have to be considered, also in patients with chronic orofacial pain. Table 1 shows the most important differential diagnoses of orofacial pain.

Surgical risk factors and maxillary nerve function after Le Fort I osteotomy

PURPOSE

Data on intraoperative risk factors for long-term postoperative complications after Le Fort I osteotomy (LFO) are limited. The aim of this study was to describe prospectively the overall postoperative changes in maxillary nerve function after LFO, and to correlate these changes with a number of possible intraoperative risk factors.

PATIENTS AND METHODS

Twelve men and 13 women (mean +/- standard deviation: aged 25+/-10 years) participated in 4 sessions: 1 before LFO (baseline), and the rest at 3, 6, and 12 months after LFO. At each session, somatosensory sensitivity was assessed for the skin, oral mucosa, and teeth, using quantitative sensory tests at either 1 cutaneous point or on a 5 x 5 point matrix reproduced on the skin. In addition, all patients were asked to report their perceived differences in somatosensory sensitivity and their overall satisfaction with the LFO.

RESULTS

The thresholds of tactile stimuli on the gingiva and palate were increased 12 months after LFO (P< .001). Significant increases in 2-point discrimination detection thresholds (P< .01) and increased sensitivity to heat (P< .01) and cold (P< .001) in the infraorbital region were also recorded 12 months after LFO. Correspondingly, self-reported complaints of changed sensation under the eyes (P< .01), upper lip (P< .01), gingiva (P< .001), palate (P< .01), and teeth (P< .01) were reported during the entire postoperative period. Intraoperative risk factors were identified and correlated with postoperative changes in somatosensory sensitivity. Segmentation of the maxilla was associated with an increase in tactile thresholds at the palate and gingiva (P< .05), as were self-reported complaints involving the palate and gingiva (P< .001), whereas maxillary impaction was related to lower-tooth pulp pain thresholds when compared with maxillary lowering (P< .01). All patients expressed satisfaction with LFO, despite signs of somatosensory disturbances in up to 64% of patients.

CONCLUSION

Numerous changes in postoperative somatosensory function are to be expected after LFO. In most patients, these changes are minor, and some are dependent on intraoperative procedures. Nonetheless, all patients reported satisfaction with the surgical results, and would recommend the procedure to others.

Sensory action potentials of the maxillary nerve: a methodologic study with clinical implications

PURPOSE

Recently, recording of sensory nerve action potentials (SNAPs) of the inferior alveolar nerve (IAN) was described and is used as a diagnostic test of traumatic neuropathic trigeminal disorders. The technique is limited to IAN damage; therefore, we adapted the technique to the maxillary nerve, which is also frequently injured by either trauma or orthognathic surgery.

PATIENTS AND METHODS

Fourteen healthy volunteers participated in this methodologic study in which the infraorbital nerve (ION) was stimulated with 2 needle electrodes. The SNAPs were recorded from the maxillary nerve with a unipolar needle electrode close to the foramen rotundum.

RESULTS

The mean latency of the SNAPs was 0.73 ms (95% CI, 0.55 to 0.85 ms) with a 0.08+/-0.09 ms interside difference. The mean baseline to peak amplitude was 31.3+/-7.0 microV (95% CI, 24.2 to 38.3 microV) with a 6.5+/-32.4 microV interside difference. Repeated tests within a session test demonstrated no significant differences in the latency data (ANOVA: P= .225) or amplitude data (ANOVA: P= .44). Stimulus-response curves indicated that the SNAPs saturated at 5.1+/-4.4 mA stimulus intensity. In 1 subject, stimulation of the mental nerve elicited SNAPs (latency: 1.6 ms; amplitude 38 microV) in accordance with published values. A local anesthetic block of the ION was associated with a distinct decay of the SNAP in 1 subject.

CONCLUSION

We suggest that SNAPs of the maxillary nerve can be a valuable technique for a comprehensive examination of the trigeminal system.

Neurophysiologic and quantitative sensory testing in the diagnosis of trigeminal neuropathy and neuropathic pain

This study investigated the utility of neurophysiologic examination and thermal quantitative sensory testing (QST) in the diagnosis of trigeminal neuropathy and neuropathic pain. Fifty-eight patients (14 men), 34 with sensory deficit within the inferior alveolar nerve (IAN) and 24 within the lingual nerve (LN) distribution, were included. Twenty-six patients (45%) reported neuropathic pain. Patients underwent blink reflex (BR) test and thermal QST; sensory neurography was done to the IAN patients. Results of clinical sensory testing were available from the charts of 48 patients revealing abnormal findings in 77% of the IAN and in 94% of the LN patients. The BR test was abnormal in 41%, neurography in 96%, and QST in 91% of the IAN patients. In the LN group, BR was abnormal in 33%, and QST in 100% of the patients tested. Neurophysiologic tests and QST verified the subjective sensory alteration in all but 2 IAN patients, both with old injuries, and 4 LN patients who did not undergo QST. When abnormal, thermal QST showed elevation of warm and cold detection thresholds (hypo/anesthesia), hypoalgesia was less marked, and heat allodynia was only occasionally present. Contralateral thermal hypoesthesia after unilateral injury was found in 14 patients. It was associated with the occurrence of neuropathic pain (P=0.016). Axonal Abeta afferent damage was less severe in the IAN patients with pain than in those without pain (P=0.012). Neurophysiologic tests and thermal QST provide sensitive tools for accurate diagnosis of trigeminal neuropathy and study of pathophysiological features characteristic to human neuropathic pain.

Neurophysiological assessment of trigeminal nerve reflexes in disorders of central and peripheral nervous system

The trigeminal nerve and nuclei (the trigeminal complex) are unique in the human body with regard to their anatomical and physiological characteristics. They are also special regarding the lesions in which they are involved, both at the peripheral level because of the susceptibility of some terminal branches, and at the nuclei because of their large size and the large amount of connections with other centers. Conventional magnetic resonance imaging studies are often not sufficiently informative to demonstrate very tiny lesions that could be responsible for an important damage in the brainstem. Therefore, clinical neurophysiology and specifically, the techniques used in the study of the trigeminal functions, remain as convenient diagnostic and research tools to document clinically evident lesions or uncover subclinical abnormalities. This review is focussed on the clinical applicability of the study of trigeminal reflexes, including methods employed in the documentation of focal lesions of peripheral branches, trigeminal involvement of peripheral neuropathies, specific lesions of the trigeminal ganglia, central nervous dysfunctions causing abnormalities in the excitability of trigeminal neurons, and the possible use of trigeminal nerve reflexes in the study of facial pain syndromes and headache.

Morphometric Analysis of Implant-Related Anatomy in Caucasian Skulls

BACKGROUND

Sequelae related to implant placement/advanced bone grafting procedures are a result of injury to surrounding anatomic structures. Damage may not necessarily lead to implant failure; however, it is the most common cause of legal action against the practitioner. This study aimed to describe morphological aspects and variations of the anatomy directly related to implant treatment.

METHODS

Morphometric analyses were performed in 22 Caucasian skulls. Measurements of the mental foramen (MF) included height (MF-H), width (MF-W), and location in relation to other known anatomical landmarks. Presence or absence of anterior loops (AL) of the inferior alveolar nerve (IAN) was determined, and the mesial extent of the loop was measured. Additional measurements included height (G-H), width (G-W), thickness (G-T), and volume (G-V) of monocortical onlay grafts harvested from the mandibular symphysis area, and thickness of the lateral wall (T-LW) of the maxillary sinus. The independent samples t test, and a two-tailed t test with equal variance were utilized to determine statistical significance to a level of P < 0.05. Multiple regression analyses were performed to determine if each one of these measurements was affected by age and gender.

RESULTS

The most common location of the MF in relation to teeth was found to be below the apices of mandibular premolars. The mean MF-H was 3.47 +/- 0.71 mm and the mean MF-W was 3.59 +/- 0.8 mm. The mean distance from the MF to other anatomical landmarks were: MF-CEJ = 15.52 +/- 2.37 mm, MF to the most apical portion of the lower cortex of the mandible = 12.0 +/- 1.67 mm, MF to the midline = 27.61+/- 2.29 mm, and MF-MF = 55.23 +/- 5.34 mm. A high prevalence of AL was found (88%); symmetric occurrence was a common finding (76.2%), with a mean length of 4.13 +/- 2.04 mm. The mean size of symphyseal grafts was: G-H = 9.45 +/- 1.08 mm, G-W = 14.5 +/- 3.0 mm, and G-T = 6.15 +/- 1.04 mm, with an average G-V of 857.55 +/- 283.97 mm3 (range: 352 to 1,200 mm3). The mean T-LW of the maxillary sinus was 0.91 +/- 0.43 mm.

CONCLUSION

Implant-related anatomy must be carefully evaluated before treatment due to considerable variations among individuals, in order to prevent injury to surrounding anatomical structures and possible damage.

Recovery of nerve injury after mandibular sagittal split osteotomy. Diagnostic value of clinical and electrophysiologic tests in the follow-up

The diagnostic value of several clinical, quantitative sensory tests (brush-stroke directional discrimination (BSD), touch detection threshold (TD), warm/cold (W/C) and sharp/blunt discrimination (S/B)), and electrophysiologic tests (mental nerve blink reflex (BR), nerve conduction study (NCS), cold (CDT), and warm (WDT) detection thresholds) in the recovery of inferior alveolar nerve (IAN) injury was evaluated in a prospective 1-year follow-up study of 20 patients after bilateral sagittal split osteotomy (BSSO). The subjective sensory alteration was assessed from patients' drawings. The predictive values of different tests at 2 weeks were determined in relation to the subjective sensory recovery at 12 months. The most pronounced recovery of the nerve damage occurred during the first 3 months according to all measures used. After 3 months, the electrophysiologic tests, especially the NCS, indicated significant further improvement. Except for the TD test, all other clinical test results were normal already at 3 months postoperatively. At early and late controls, the NCS and the thermal quantitative sensory testing could best verify the subjective sensory alteration, and most accurately assess the degree of thick and thin fibre dysfunction. At 1 year, the nerve dysfunction, as revealed by the NCS, corresponded with the figures of sensory alteration reported by the patients (35% R, 40% L). The W/C, BSD, S/B and WDT tests had the best early positive predictive values. Electrophysiologic tests had higher negative predictive values compared to clinical tests.

Conduction velocity of the rabbit facial nerve: a noninvasive functional evaluation

The aim of this study was to evaluate standardized conduction velocity data for uninjured facial nerve and facial nerve repaired with autologous graft nerves and synthetic materials. An evaluation was made measuring the preoperative differences in the facial nerve conduction velocities on either side, and ascertaining the existence of a positive correlation between facial nerve conduction velocity and the number of axons regenerated postoperatively. In 17 rabbits, bilateral facial nerve motor action potentials were recorded pre- and postoperatively. The stimulation surface electrodes were placed on the auricular pavilion (facial nerve trunk) and the recording surface electrodes were placed on the quadratus labii inferior muscle. The facial nerves were isolated, transected and separated 10 mm apart. The gap between the two nerve ends was repaired with autologous nerve grafts and PTFE-e (polytetrafluoroethylene) or collagen tubes. The mean of maximal conduction velocity of the facial nerve was 41.10 m/s. After 15 days no nerve conduction was evoked in the evaluated group. For the period of 2 and 4 months the mean conduction velocity was approximately 50% of the normal value in the subgroups assessed. A significant correlation was observed between the conduction velocity and the number of regenerated axons. Noninvasive functional evaluation with surface electrodes can be useful for stimulating and recording muscle action potentials and for assessing the functional state of the facial nerve.

An evaluation of clinical and electrophysiologic tests in nerve injury diagnosis after mandibular sagittal split osteotomy

The yield of clinical sensory tests and electrophysiologic tests in the diagnostics of inferior alveolar nerve (IAN) damage after bilateral sagittal split osteotomy (BSSO) was studied. The diagnostic value of these tests was evaluated by comparing the test results to the degree of nerve damage at the end of the operation as documented by means of the intraoperative nerve conduction recording of the IAN. Twenty patients undergoing BSSO were analysed preoperatively and 2 weeks postoperatively. The frequency of the IAN disturbance ranged from 10% to 94% depending on the test method and the test site used. Of the clinical sensory tests, the touch detection threshold (TD) test was the most sensitive and clinically useful test. It also correlated best with the electrophysiologically verified intraoperative nerve damage (R = -0.603, P = 0.017 on the right, R = -0.626, P = 0.01 on the left). The blink reflex and quantitative cold detection threshold tests were almost as often abnormal as the TD-test, but nerve conduction study (NCS) was the most sensitive (88%) of all clinical and electrophysiologic tests. The frequency of abnormal findings in the electrophysiologic tests indicating IAN injury, 75% on the right side and 90% on the left side, corresponded exactly with the figures of subjective sensory alteration. Almost all electrophysiologic tests showed obvious associations with the objectively verified IAN damage. All tests, except the NCS, showed only moderate sensitivity. Specificity of the tests was generally high, the only exceptions being the TD test and the NCS. To increase the diagnostic accuracy of the testing and to detect different types of damage in different nerve fibre populations, a combination of different sensory and electrophysiologic tests is recommended.

Risk factors of nerve injury during mandibular sagittal split osteotomy

There is little objective data about whether surgical technique or mandibular anatomy are a risk for inferior alveolar nerve (IAN) injury during bilateral sagittal split osteotomy (BSSO). Orthodromic sensory nerve action potentials (SNAPs) of the IAN were continuously recorded on both sides in 20 patients with mandibular retrognathia during BSSO operation. Changes in latency, amplitude, and sensory nerve conduction velocity (SNCV) at baseline and at different stages of the operation were analyzed. The SNAP latencies prolonged, the amplitudes diminished, and the SNCVs slowed down during BSSO (P = 0.0000 for all parameters). The most obvious changes occurred during surgical procedures on the medial side of the mandibular ramus. There was a clear tendency towards more disturbed IAN conduction with longer duration of these procedures (right side R = -0.529. P = 0.02; left side R = -0.605, P = 0.006). Exposure or manipulation of the IAN usually had no effect on nerve function, but the IAN conduction tended to be more disturbed in cases with nerve laceration. Low corpus height (R = 0.802, P = 0.001) and the location of the mandibular canal near the inferior border of the mandible (R = 0.52, P = 0.02) may increase the risk of IAN injury. There was no correlation between the age of the patients and the electrophysiological grade of nerve damage.

Sensory nerve conduction study of the mental nerve

We describe a technique for sensory nerve conduction study of the mental nerve. A monopolar recording needle is placed near the mandibular foramen using the same approach as that for routine inferior alveolar nerve block in dentistry, and a surface reference electrode is positioned over the ipsilateral mastoid process. Sensory nerve action potentials to stimulation of the mental nerve at the chin can be reliably recorded orthodromically in normal healthy subjects. The method is simple and well tolerated and provides a useful means to evaluate mental nerve function electrophysiologically.

Intraoperative monitoring of the inferior alveolar nerve during mandibular sagittal-split osteotomy

In order to evaluate the risk of nerve injury and to prevent iatrogenic damage at different stages of bilateral sagittal-split osteotomy (BSSO) of the mandible, we monitored the function of the inferior alveolar nerve (IAN) continuously on both sides in 13 orthognathic patients undergoing BSSO. The IAN was stimulated at the mental foramen with two monopolar needle electrodes fixed to the dental splint, and the orthodromic sensory nerve action potentials (SNAP) of the IAN were recorded with a silver-wire electrode inserted near the oval foramen on each side. The latencies, amplitudes, and sensory nerve conduction velocities at baseline, after medial opening, sawing, splitting, eventual manipulation, and fixation of the mandible were analyzed. The monitoring method functioned technically well in 25 of 26 nerves. Both the surgical technique and the duration of medial opening had conspicuous effects on the function of the IAN, which led us to modify the medial approach. When finer instruments were used for retraction and the duration of medial opening was shortened to less than 10 min, the SNAP of the IAN was always preserved at this stage. Monitoring of the IAN also prevented nerve injury during splitting and fixation. This technique for intraoperative monitoring of the IAN seems to be a feasible and promising tool for objective evaluation of intraoperative events and for prevention of nerve injury during BSSO.