Trigeminal Somatosensory Evoked Potentials Research Articles

Topography and lateralization of long-latency trigeminal somatosensory evoked potentials

ObjectiveLong-latency trigeminal somatosensory evoked potentials (SSEPs) have not been sufficiently studied regarding their topography and lateralization. SSEPs are hypothesized to contribute to the evoked potentials after transcranial magnetic stimulation (TMS). This study focused on trigeminal SSEPs with latencies > 100 ms, potentially overlapping with TMS-evoked N100. MethodsIn 14 healthy subjects, the trigeminus was electrically stimulated on the left and right forehead, and time-course, topography, and lateralization of trigeminal SSEPs were examined in 64-channel electroencephalogram (EEG). SSEPs were then compared to TMS-evoked potentials when TMS was applied to the left and right dorsolateral prefrontal cortex. ResultsTrigeminal stimulation produced a somatosensory N140 with topographic maximum over centroparietal electrodes with larger amplitudes contra- than ipsilaterally to the stimulation. Contralateral potentials after TMS were partly comparable in their topography but differed in latencies. ConclusionsSSEPs generated by electrical stimulation of the trigeminus occurred over somatosensory areas with a contralateral lateralization. Therefore, contralateral potentials after TMS should be interpreted with caution, as they may include somatosensory components. SignificanceThe topography and lateralization of long-latency trigeminal SSEPs should be considered in future TMS-EEG designs.

Trigeminal somatosensory evoked potential test as an evaluation tool for infraorbital nerve damage.

BackgroundNeurosensory changes are frequently observed in the patients with mid-face fractures, and these symptoms are often caused by infraorbital nerve (ION) damage. Although ION damage is a relatively common phenomenon, there are no established and objective methods to evaluate it. The aim of this study was to test whether trigeminal somatosensory evoked potential (TSEP) could be used as a prognostic predictor of ION damage and TSEP testing was an objective method to evaluate ION injury.MethodsIn this prospective TSEP study, 48 patients with unilateral mid-face fracture (only unilateral blow out fracture and unilateral zygomaticomaxillary fracture were included) and potential ION damages were enrolled. Both sides of the face were examined with TSEP and the non-traumatized side of the face was used as control. We calculated the latency difference between the affected and the unaffected sides.ResultsTwenty-four patients recovered within 3 months, and 21 patients took more than 3 months to recover. The average latency difference between the affected side and unaffected side was 1.4 and 4.1 ms for the group that recovered within 3 months and the group that recovered after 3 months, respectively.ConclusionPatients who suffered ION damage showed prolonged latency when examined using the TSEP test. TSEP is an effective tool for evaluation of nerve injury and predicting the recovery of patients with ION damage.

P 117 Symptomatic trigeminal neuralgia (TN) – an electrophysiological case study

Introduction While idiopathic TN is associated with some delay in P19 response of the cortical trigeminal somatosensory evoked potential (T-SEP) in up to 50 % of patients, the blink reflex (BR) evoked by stimulation of the supraorbital nerve is usually not involved. We present a case of symptomatic TN in which the combination of electrophysiological findings was remarkable. Case report A 74 year-old man had a 3 month history of dull and diffuse pain of the left maxilla. Ten days before admission, he developed short-lasting attacks of severe sudden, sharp and stabbing pain in the left maxilla radiating to the temporal, frontal and mandibular regions of the left face. There were 1 to 4 attacks per day, no triggers could be identified. Neurological examination revealed hypaesthesia in the left face (V1-3) and mild asymmetry of the facial innervation due to peripheral paresis on the left. Other cranial nerve functions were normal, as was the rest of the neurological examination. Electrophysiology T-SEP of the left trigeminal nerve (simultaneous stimulation of upper and lower lip) revealed a delayed P19 response of 24.1 ms versus a normal response on the right of 20.1 ms. Blink reflex studies of the trigeminal and facial nerves were typical of an afferent lesion of the left trigeminal nerve with delays of ipsilateral R1 and ipsi- and contralateral R2 while these potentials were normal on the right ( Fig. 1 ). Electrical stimulation of the facial nerve at the foramen stylomastoideum and magnetic stimulation of the canalicular part of the facial nerve gave normal results, bilaterally. Finally, MRI of the head demonstrated a T1-contrast enhancing mass lesion in the region of the left cavum Meckeli, which reached to the cavernous sinus and the internal carotid artery, presumably of mesenchymal origin (meningeoma? Fig. 2) . Symptomatic pain control was achieved by administration of carbamazepine and pregabaline, and the patient awaited neurosurgical biopsy. Conclusion Our case demonstrates that TN is more likely to be of symptomatic than idiopathic or vascular compressive origin if not only T-SEP but also BR are abnormal, indicating a demyelinating lesion. MRI with thorough examination of the anatomical course of the TN is necessary to guide therapeutic decisions including neurosurgical intervention and biopsy.

Effect of Topical Anesthesia Using an Adhesive Patch and Anesthetic Solution.

We analyzed trigeminal somatosensory evoked potentials (TSEP) to the alveolar mucosa to investigate the efficacy of an amide local anesthetic, 2% lidocaine hydrochloride with 12.5 μg/mL epinephrine (Lido treatment) as a topical anesthetic. Eighteen consenting healthy adult volunteers were enrolled. A volume of 0.06 mL of Lido, 0.06 g of 20% benzocaine, or 0.06 mL of physiological saline (control) was instilled onto a hemostatic adhesive patch, which was then applied to the alveolar mucosa at the maxillary right canine for 5 minutes. An electrical stimulus approximately 5 times that of the sensory threshold was applied using a surface stimulation electrode. The trigeminal somatosensory evoked potential was recorded immediately, 5 minutes, and 10 minutes after removal of the patch. Positive P125 and P310 peaks and negative N100 and N340 peaks were observed as a result of the electrical stimulation. A significant decrease in the percentage change in amplitude of N100-P125 was observed in the Lido treatment immediately, 5 minutes, and 10 minutes after patch removal. In the Lido treatment, trigeminal somatosensory evoked potential amplitude at N100-P125 decreased significantly, suggesting that topical anesthesia produced by an amide local anesthetic may have a topical anesthetic effect as potent as that produced by an ester local anesthetic.

Trigeminal somatosensory-evoked potential

To reflect the extent of thermolesion of ganglion by testing the change of trigeminal somatosensory-evoked potential (TSEP) before and after ganglion radiofrequency thermocoagulation surgery (GRT), and evaluate long-term clinic effect by follow-up visiting of 1 year.Patients with idiopathic trigeminal neuralgia (TN) in the second division were enrolled between October 2014 and October 2015. They were treated with computed tomography-guided GRT and a follow-up visiting of 1 year. Bilateral TSEP measurements were performed 1 day before and 2 days after the GRT surgery. The latency and peak-to-peak amplitude of W2 and W3 were recorded.Immediate postprocedure pain relief (grades I–III) was 100% and 92.5% 1 year later. Facial numbness rate of grades III and IV was 70%, 40%, and 12.5%, respectively, at immediate, 2 days, and 1 year after GRT. No sever complications happened. The latency of W2 and W3 of patients who had no pain no numbness after 1 year of GRT was 1.74 ± 0.24 and 3.84 ± 0.66 ms, respectively, of TN side, and 1.71 ± 0.39 and 3.63 ± 0.85 ms of the healthy side before GRT. The amplitude of W2 and W3 was 1.13 ± 0.50 and 1.99 ± 1.09 uv, respectively, of TN side and 1.24 ± 0.40 and 1.89 ± 0.81 uv of the healthy side before GRT. There was no statistical difference of the latency and amplitude between 2 sides of W2 and W3 before surgery (P > 0.05). The latency of W2 and W3 delayed and the amplitude reduced especially in TN side after surgery comparing before (P < 0.001). And, comparisons of the latency and amplitude of W2 and W3 between TN side and the healthy side after surgery showed the latency of W2 and W3 delayed (W2: P = 0.02; W3: P = 0.01) and the amplitude of W2 reduced (P = 0.003), but the amplitude of W3 had no statistical difference (P = 0.22). The mean delayed latency and 95% confident interval of W2 and W3 were 0.22 ± 0.35 (0.1–0.34) ms and 0.35 ± 0.64 (0.14–0.57) ms, respectively. The mean decreased amplitude and 95% confident interval of W2 and W3 were 22 ± 24 (14–30)% and 23 ± 32 (12–34)%, respectively.GRT can make the latency delay and the amplitude decrease of TSEP. And the latency and amplitude of W2 and W3 can be considered reliable and safe reference for monitoring the extent of thermolesion.

Development of somatosensory-evoked potentials in foetal sheep: effects of betamethasone.

Antenatal glucocorticoids are used to accelerate foetal lung maturation in babies threatened with premature labour. We examined the influence of glucocorticoids on functional and structural maturation of the central somatosensory pathway in foetal sheep. Somatosensory-evoked potentials (SEP) reflect processing of somatosensory stimuli. SEP latencies are determined by afferent stimuli transmission while SEP amplitudes reveal cerebral processing. After chronic instrumentation of foetal sheep, mothers received saline (n=9) or three courses of betamethasone (human equivalent dose of 2×110μgkg-1 betamethasone i.m. 24h apart, n=12) at 0.7, 0.75 and 0.8 of gestational age. Trigeminal SEP were evoked prior to, 4 and 24h after each injection and at 0.8 of gestational age before brains were histologically processed. Somatosensory-evoked potentials were already detectable at 0.7 of gestation age. The early and late responses N20 and N200 were the only reproducible peaks over the entire study period. With advancing gestational age, SEP latencies decreased but amplitudes remained unchanged. Acutely, betamethasone did not affect SEP latencies and amplitudes 4 and 24h following administration. Chronically, betamethasone delayed developmental decrease in the N200 but not N20 latency by 2weeks without affecting amplitudes. In parallel, betamethasone decreased subcortical white matter myelination but did not affect network formation and synaptic density in the somatosensory cortex. Somatosensory stimuli are already processed by the foetal cerebral cortex at the beginning of the third trimester. Subsequent developmental decrease in SEP latencies suggests ongoing maturation of afferent sensory transmission. Antenatal glucocorticoids affect structural and functional development of the somatosensory system with specific effects at subcortical level.

A neurophysiological study of facial numbness in multiple sclerosis: Integration with clinical data and imaging findings

ObjectiveTo integrate neurophysiological findings with clinical and imaging data in a consecutive series of multiple sclerosis (MS) patients developing facial numbness during the course of an MS attack. MethodsNine consecutive patients with MS and recent-onset facial numbness were studied clinically, imaged with routine MRI, and assessed neurophysiologically with trigeminal somatosensory evoked potential (TSEP), blink reflex (BR), masseter reflex (MR), facial nerve conduction, facial muscle and masseter EMG studies. ResultsAll patients had unilateral facial hypoesthesia on examination and lesions in the ipsilateral pontine tegmentum on MRI. All patients had abnormal TSEPs upon stimulation of the affected side, excepting one that was tested following remission of numbness. BR was the second most sensitive neurophysiological method with 6/9 examinations exhibiting an abnormal R1 component. The MR was abnormal in 3/6 patients, always on the affected side. Facial conduction and EMG studies were normal in all patients but one. ConclusionsFacial numbness was always related to abnormal TSEPs. A concomitant R1 abnormality on BR allowed localization of the responsible pontine lesion, which closely corresponded with MRI findings. We conclude that neurophysiological assessment of MS patients with facial numbness is a sensitive tool, which complements MRI, and can improve lesion localization.

Comparison of lower lip hypoesthesia between hybrid fixation and conventional fixation following sagittal split ramus osteotomy

PurposeThe purpose of this study was to compare the recovery period of lower lip hypoesthesia between hybrid fixation and conventional fixation using absorbable plates and screw systems following sagittal split ramus osteotomy (SSRO). Subjects and methodsThe subjects were 66 patients (132 sides) who underwent bilateral SSRO setback surgery. They were divided into a hybrid fixation group (66 sides, 1 u-HA/PLLA plate and 4 mono-cortical screws and a bi-cortical screw in each side) and a conventional fixation group (66 sides, 1 u-HA/PLLA plate and 4 mono-cortical screws in each side). Trigeminal nerve hypoesthesia at the region of the lower lip was assessed bilaterally by the trigeminal somatosensory-evoked potential (TSEP) method. ResultsThe mean measurable periods were 8.1 ± 10.4 weeks in the hybrid fixation group, 5.1 ± 11.5 weeks in the conventional group with no significant difference. However, the maximum in the hybrid fixation group was 27 sides at 4 weeks postoperative and in the conventional fixation group was 37 sides at 1 week postoperative, and there was significant difference in the distribution of the measurable period (P < 0.0001). ConclusionThis study suggested that additional bi-cortical screws could affect the recovery of lower lip hypoesthesia after SSRO with bent absorbable plate fixation.

Evaluation of factors affecting recovery period in lower lip hypoesthesia after sagittal split ramus osteotomy in mandibular prognathism patients

PurposeThe purpose of this study was to evaluate the factors affecting the recovery period of lower lip hypoesthesia after sagittal split ramus osteotomy (SSRO) in mandibular prognathism patients using multivariate analysis, retrospectively. Subjects and methodsThe subjects were 222 patients (444 sides) who underwent bilateral SSRO setback surgery with and without Le Fort I osteotomy. Trigeminal nerve hypoesthesia at the region of the lower lip was assessed bilaterally by the trigeminal somatosensory-evoked potential (TSEP) method pre- and post-operatively. Recovery period was determined as the time when TSEP was first measurable post-operatively. Age, sex, presence or absence of third molars, setback amount and osteotomy type and fixation method were selected as covariates in the multivariate analysis. The factor affecting the recovery period in lower lip hypoesthesia was examined with Cox's proportional hazard regression. ResultsSex and osteotomy fixation method affected the recovery period in lower lip hypoesthesia significantly (P = 0.0132 and P = 0.0394). However, the other factors did not affect the recovery period. ConclusionThis study suggested that sex and osteotomy type and fixation method may affect the recovery period in lower lip hypoesthesia after SSRO setback surgery.

Differential diagnosis of the complex regional pain syndrome

Differential diagnosis of the complex regional pain syndrome

The differences in trigeminal system functional state in chronic and frequent migraine patients

Electrophysiological tools like trigeminal somato-sensory evoked potentials (TSSEP) are used for evaluation of trigeminal system (TS) functional state. The activity of the later is an important factor in migraine pathogenesis. The study aim was to analyze the TS functional state in chronic and frequent migraine patients in relation with age during the migraine attack (critic period) and in the interictal period on lateralized stimulation (left/right).

Assessment of bone healing and hypoesthesia in the upper lip after Le Fort I osteotomy with self-setting α-tricalcium phosphate and absorbable plates

PurposeThe purpose of this study was to evaluate hypoesthesia of the upper lip and bone formation using self-setting α-tricalcium phosphate (Biopex®) between the segments following Le Fort I osteotomy with bent absorbable plate fixation. Subjects and methodsThe subjects were 47 patients (94 sides) who underwent Le Fort I osteotomy with and without mandibular osteotomy. They were divided into a Biopex® group (48 sides) and a control group (46 sides). The Biopex® was inserted into the anterior part of the gap between the segments in the Biopex® group. Trigeminal nerve hypoesthesia at the region of the upper lip was assessed bilaterally by the trigeminal somatosensory-evoked potential (TSEP) method. The area of the Biopex® at the anterior part in the maxilla was assessed immediately after surgery and 1 year postoperatively by computed tomography (CT). ResultsThe mean measurable period and standard deviation were 13.2 ± 18.5 weeks in the control group, 14.5 ± 17.9 weeks in the Biopex® group, and there was no significant difference in TSEP. The area of the Biopex® after 1 year was significantly smaller than that immediately after surgery (right side: P = 0.0024, left side: P = 0.0001) and bone defects between the segments could not be found in the Biopex® group. In the control group, although the areas of bone defect after 1 year were significantly smaller than that immediately after surgery on the right side (P = 0.0133) and left side (P = 0.0469) in the frontal view, complete healing of the bone defects could be seen in 12 of 46 sides after 1 year. ConclusionThis study suggested that inserting Biopex® in the gap between the maxillary segments was useful for new bone formation and it did not prevent the recovery of upper lip hypoesthesia after Le Fort I osteotomy with absorbable plate fixation.

Measurement of somatosensory-evoked potential to evaluate function of the trigeminal nerve after rapid palatal expansion treatment in a rabbit model

The aim of this study was to evaluate whether high force or stress response occurs in rapid palatal expansion (RPE) on the skull base would affect the function of trigeminal nerve and its branches by measuring trigeminal somatosensory-evoked potential (TSEP). Twenty-four male New Zealand white rabbits were selected when they were 12-13 weeks old with mean weight around 3.05 ± 0.33 kg. A modified acrylic-bonded RPE appliance was used as an expansion tool. Through a series of TSEP measurements performed before the expansion treatment (T0), on the third day of the expansion (T1), at the end of the expansion process (T2), and after 10 days of retention (T3), function of the trigeminal nerve was analyzed with statistical models, including the Kruskal-Wallis test and paired t tests. A stable short-latency response represented by a "W" waveform was consistently identified on the TSEP spectram analysis. Within-subject comparisons between the experimental group and control group did not show significant differences on TSEP of maxillary nerve and of mandibular nerve. TSEP is a valuable technique for a comprehensive evaluation of the trigeminal system. Our study demonstrates that rapid palatal expansion is a safe orthopedic method regarding function of the trigeminal nerve during expansion and short-term retention period in young rabbits.

Effect of self-setting α-tricalcium phosphate between segments for bone healing and hypoaesthesia in lower lip after sagittal split ramus osteotomy

AimsThe aim of this study was to evaluate hypoaesthesia of the lower lip and bone formation using self-setting α-tricalcium phosphate (Biopex®) between the proximal and distal segments following sagittal split ramus osteotomy (SSRO) with bent absorbable plate fixation. Subjects and methodsThe subjects were 40 patients (80 sides) who underwent bilateral SSRO setback surgery. They were divided into a Biopex® group (40 sides) and a control group (40 sides). The Biopex® was inserted into the anterior part of the gap between the segments in the Biopex® group. Trigeminal nerve hypoaesthesia in the region of the lower lip was assessed bilaterally using the trigeminal somatosensory-evoked potential (TSEP) method. Ramus square, ramus length, and ramus width, the square of the Biopex® at the horizontal plane under the mandibular foramen were assessed preoperatively, immediately after surgery, and 1year postoperatively by computed tomography (CT). ResultsThe mean measurable period and standard deviation were 9.3±15.7weeks in the control group, 5.3±8.3weeks in the Biopex® group, and there was no significant difference. Ramus square after 1year was significantly larger than that prior to surgery and new bone formation was found between the segments in both groups (P<0.05). In the Biopex® group, the square of the Biopex® after 1year was significantly smaller than that immediately after surgery (P<0.05). ConclusionThis study suggested that inserting Biopex® in the gap between the proximal and distal segments was useful for new bone formation and it did not prevent the recovery of lower lip hypoaesthesia after SSRO with bent absorbable plate fixation.

Recordings of long-latency trigeminal somatosensory-evoked potentials in patients under general anaesthesia

Objective The reliability of intra-operative recordings of trigeminal scalp-induced somatosensory-evoked potentials (T-SSEP) is controversial. This investigation aimed to provide evidence that T-SSEP recordings are stable using standardised neurophysiological methodology and anaesthesiological regime. Methods We investigated 99 patients undergoing carotid endarterectomy under total intravenous anaesthesia (propofol/remifentanil infusion). Long-latency T-SSEPs were recorded from the scalp after simultaneously stimulating 2nd and 3rd branches of the trigeminal nerve. The analysis included visual assessments of traces and measurements of latencies and amplitudes of the N13 and P19 peaks of T-SSEP. Furthermore, additional groups of patients were investigated to identify changes in the parameters of T-SSEP that might correspond to different states of anaesthesia and artificial muscle activity. Results We reproducibly recorded T-SSEP responses in 99 patients with a mean latency of 12.4 ms (SD = 0.93) and amplitude of 5.7 μV (SD = 4.7). Collateral investigations concerning changes of T-SSEP caused by neuromuscular blockade improved independence of T-SSEP recordings to muscle relaxation in contrast to facial and cervical muscle activity. Conclusions We demonstrated the reliability of recording stable intra-operative T-SSEP responses with standardised electrophysiological and anaesthesiological regimes. Significance We provided evidence of the non-muscular origin of T-SSEPs recorded from the scalp.

Usefulness of trigeminal somatosensory evoked potentials to detect subclinical trigeminal impairment in multiple sclerosis patients.

Trigeminal somatosensory evoked potentials (TSEPs) by surface electric pulse stimulation were recorded in 30 normal subjects and in 70 multiple sclerosis (MS) patients, 13 of whom presenting clinical trigeminal impairment. We observed significant prolongation of all TSEPs parameters in MS group. TSEPs were abnormal in 45 patients (64.3%). Clinical and neurophysiological data agreed in 36 patients (51%) on 84 sides (60%). TSEPs were able to detect clinically silent lesions 54 times. TSEPs recording proves to be an additional useful test in MS multimodal evoked potential protocols.

The evaluation of surgical factors related to recovery period of upper lip hypoaesthesia after Le Fort I osteotomy

It is unclear whether surgical factors can affect the upper lip sensitivity. The aim of this study was to assess the factors that can affect the recovery period of hypoaesthesia of the upper lip after Le Fort I osteotomy, using trigeminal somatosensory evoked potential (TSEP) objectively. Twenty-nine patients with mandibular prognathism underwent Le Fort I osteotomy with and without artificial pterygoid plate fracture. Trigeminal nerve hypoaesthesia at the region of the upper lip was assessed bilaterally by the TSEP method. The distance between the infraorbital foramen and the osteotomy line (IO) or the nearest plate/screw position (IP) was measured on three-dimensional computed tomography (CT). The relationship between the recovery period in upper lip hypoaesthesia and surgical factors (these distances, movement amount, pterygoid plate fracture) were analysed statistically. The recovery period in upper lip hypoaesthesia did not significantly correlate with IO, IP and movement amount. There was no significant difference between pterygoid plate fracture group and non-fracture group. Temporary hypoaesthesia of upper lip after Le Fort I osteotomy could not be avoided, however, osteotomy line, plate/screw position and pterygoid plate fracture in Le Fort I osteotomy did not affect the recovery period of upper lip hypoaesthesia with TSEP.

Evaluation of trigeminal somatosensory evoked potential of patients with chronic masticatory muscle pain

To evaluate trigeminal function of patients with chronic masticatory muscle pain (MMP) using trigeminal somatosensory evoked potential (TSEP) and analyze mechanism of changes compared to the controls. Twelve chronic MMP patients and 12 matched controls participated in this study. TSEPs of bilateral masseter regions and inferior alveolar nerves were measured and compared between patient and control groups. The collected waves were concluded and those with appearance rate over 75% - 100% were selected. The latencies of waves were analyzed by use of the paired t test and independent-samples t test. Five stable-appearing waves were obtained and named P1, N1, P2, N2, P3. The latency of P1 was significant reduced in patients (P < 0.05). The latencies of other waves were prolonged, but only P2 and N2 in left were significantly changed (P < 0.05). TSEP latencies of chronic MMP patients changed in certain regular pattern and TSEP could be used as a parameter to disclose the trigeminal system abnormalities of the patients. The reduced latency of P1 might indicate the increasing conductivity of trigeminal nerves under level of ganglion Gasseri and the prolongation of latency of P2 was possibly related to inhibitory effects of the brain stem.

Relationship between recovery period of lower lip hypoesthesia and sagittal split area or plate screw position after sagittal split ramus osteotomy

The purpose of this study was to objectively evaluate the relationship between recovery of hypoesthesia of the lower lip after sagittal split ramus osteotomy (SSRO) with trigeminal somatosensory evoked potential (TSEP) and sagittal split area or plate screw position, using postoperative computerized tomography (CT). The subjects consisted of 58 patients (116 sides) with mandibular prognathism who underwent SSRO. The patients were divided into 2 groups. The Ob group, consisting of 62 sides, underwent the Obwegeser method. The OD group, consisting of 54 sides, underwent the Obwegeser-Dal Pont method. Trigeminal nerve hypoesthesia at the region of the lower lip was assessed bilaterally by the TSEP method. An electroencephalograph recording system (Neuropack Sigma; Nihon Koden, Tokyo, Japan) was used to analyze the potentials. Each patient was evaluated preoperatively and then postoperatively at 1 week, 2 weeks, 1 month, 3 months, 6 months and 1 year. Postoperative CT was performed in all cases to measure the sagittal split area (SSA) as well as the distance between the plate (the most medial point of screw) and the mental foramen (PM). Then comparisons between the 2 groups in recovery period of the lower lip, SSA, and PM were performed. Furthermore, the relationships between recovery period of hypoesthesia of the lower lip and SSA or PM were evaluated statistically. The average measurable period and standard deviation of TSEP of the lower lip was 3.4 +/- 5.5 weeks in the Ob group and 11.3 +/- 13.7 weeks in the OD group. There were significant differences between the Ob group and the OD group (P < .0001). The OD group showed significantly greater SSA and PM than the Ob group (P < 0.0001). This study suggested that recovery period of hypoesthesia of the lower lip after SSRO was strongly associated with SSA and PM.

A comparison of lower lip hypoesthesia measured by trigeminal somatosensory-evoked potential between different types of mandibular osteotomies and fixation

The purpose of this study was to compare objectively, the recovery of hypoestheia of the lower lip following orthognathic surgery using different procedures (sagittal split ramus osteotomy [SSRO]) and intra-oral vertical ramus osteotomy (IVRO)) and fixation methods (monocortical plate fixation and bi-cortical plate fixation). Hypoesthesia was evaluated using the trigeminal somatosensory-evoked potential (TSEP). The subjects consisted of 174 patients (348 sides) with mandibular prognathism with or without asymmetry, who underwent mandibular ramus osteotomies using different fixation types. The patients were divided into 4 groups. The OAM group consisted of 128 sides who had SSRO using the Obwegeser method with mono-cortical absorbable plate fixation, the ODTM group consisted of 84 sides who had the Obwegeser-Dal Pont method with mono-cortical titanium plate fixation, the OTB group consisted of 32 sides who had the Obwegeser method with bi-cortical titanium plate fixation and the VO group consisted of 104 sides who underwent IVRO according to the Bell method without fixation. Trigeminal nerve hypoestheia at the region of the lower lip was assessed bilaterally by the TSEP method. An electroencephalograph recording system (Neuropack Sigma; Nion Koden Corp., Tokyo, Japan) was used to analyze the potentials. Each patient was evaluated pre-operatively and then post-operatively at 1 and 2 weeks, 1, 3, and 6 months, and 1 year. The mean measurable period and standard deviation of TSEP of the lower lip in the OAM group was 5.2 +/- 9.9 weeks, 10.9 +/- 13.1 weeks in the ODTM group, 7.8 +/- 4.5 weeks in the OTB group, and 2.5 +/- 6.3 weeks in the VO group. There were significant differences between the OAM and ODTM groups (P < .0001), the ODTM and OTB groups (P = .0001), the OTB and VO groups (P = .0221), the OAM and VO groups (P < .0001), and the ODTM and VO groups (P < .0001). This study proved using objective measurements that the recovery period from hypoesthesia of the lower lip following orthognathic surgery was dependent on the surgical procedure. Recovery in lower lip hypoesthesia after IVRO was significantly earlier than SSRO.