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A comparison of lower lip hypoesthesia measured by trigeminal somatosensory-evoked potential between different types of mandibular osteotomies and fixation
A comparison of lower lip hypoesthesia measured by trigeminal somatosensory-evoked potential between different types of mandibular osteotomies and fixation Yukari Hashiba, DDS,a Koichiro Ueki, DDS, PhD,b Kohei Marukawa, DDS, PhD,b Mayumi Shimada, DDS, PhD,b Kan Yoshida, DDS, PhD,b Chika Shimizu, DDS,a Shamiul Alam, DDS,a and Kiyomasa Nakagawa, DDS, PhD,c Kanazawa, Japan KANAZAWA UNIVERSITY
Purpose. 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). Patients and Methods. 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 postoperatively at 1 and 2 weeks, 1, 3, and 6 months, and 1 year. Results. 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). Conclusion. 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. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2007;104:177-85)
Orthognathic surgical procedures have been described extensively with good results having been reported for the variety of different treatments.1 Two surgical procedures are used most often for mandibular osteotomies of mandibular prognathism, namely the sagittal split ramus osteotomy (SSRO)2 and the intraoral vertical ramus osteotomy (IVRO).1 The SSRO technique was first described by Trauner and Obwegeser,2 with many modifications of the technique having been introduced a
Graduate Student, Department of Oral and Maxillofacial Surgery, Graduate School of Medicine, Kanazawa University. b Clinical Fellow, Department of Oral and Maxillofacial Surgery, Graduate School of Medicine, Kanazawa University. c Associate Professor, Department of Oral and Maxillofacial Surgery, Graduate School of Medicine. Received for publication May 25, 2006; returned for revision Oct 5, 2006; accepted for publication Nov 9, 2006. 1079-2104/$ - see front matter © 2007 Mosby, Inc. All rights reserved. doi:10.1016/j.tripleo.2006.11.038
with the aim of minimizing morbidity and maximizing the stability of the procedure. These modifications included the variations described by Dal Pont,3 Hunsuck,4 and Epker.5 It is generally recognized that the vertical buccal cut of the Obwegeser-Dal Pont method is positioned more anteriorly than in the Obwegeser method. One of the major complications after orthognathic surgery is lower and upper lip hypoesthesia. Karas et al.6 reported that in comparison with other surgical procedures such as a Le Fort I osteotomy, IVRO, or genioplasty, the SSRO caused the highest percentage of postsurgical neurosensory damage assessed by static light touch (SLT), moving touch discrimination (MTD), and 2-point discrimination (TPD). Lemke et al.7 also reported that rigid fixation resulted in more anesthesia in mental nerve distribution compared to wire fixation when tested by brush stroke determination. 177
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Standard sensory testing modalities include the following parameters: threshold of light touch perception, 2-point discrimination threshold, temperature sensitivity,7 and trigeminal somatosensory-evoked potentials (TSEP).8-12 The TSEP method is noninvasive, highly objective, and extremely reliable and can be used to investigate trigeminal sensory hypoesthesia of the lower lip after mandibular ramus osteotomy. In simple sensory tests such as 2-point sensory discrimination, collection of output data depends on the patient’s view with their bias, even if input data such as stimulating pressure is objective. However, TSEP data are directly collected from the patient’s electroencephalography derived from the cerebral cortex so that data of TSEP could be more objective and reliable. Thus, a difference between objective and subjective assessment may occur. Furthermore, there may also be a difference between actual return of feeling and registration of nerve conduction. Advancements in the field of neurophysiology have revealed posttraumatic change in the central nervous system. Functional disturbance in the central nervous system after peripheral nerve injury is known as central sensitization.13,14 Actual return of feeling may not always occur with recovery in peripheral nerves. However, there are no reports on the use of TSEP to assess the difference in recovery period of lip hypoesthesia after SSRO (Obwegeser-Dal Pont method and Obwegeser method) or IVRO. There are also no studies using TSEP that have investigated whether different fixation methods and surgical procedures affect the recovery of lip hypoesthesia after surgery. The purpose of this study was therefore to determine objectively using TSEP whether differences in surgical procedures and fixation methods influenced the recovery of hypoesthesia of the upper and lower lip following orthognathic surgery. SUBJECTS AND METHODS The subjects comprised 174 Japanese adults (45 males, 129 females) presenting with jaw deformities, diagnosed as mandibular prognathism with or without mandibular asymmetry, or mandibular prognathism with or without bimaxillary asymmetry. At the time of orthognathic surgery, the mean age of the patients was 24.1 years (standard deviation 6.5 years; range 15-45 years). Informed consent was obtained for all the patients who underwent mandibular ramus osteotomy. The patients who could agree with the informed consent were selected as the subjects in this study. However, the distribution of surgical procedures was not equal in our facility so that the sample number of each group was different.
Fig. 1. Schematic drawing of the procedure and fixation in the OAM group. A, Osteotomy line. B, Plate position from lateral view. C, Plate position from axial view.
The total 348 sides of the 174 patients were divided into 4 groups as follows: ●
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OAM group: 128 sides underwent the Obwegeser method with monocortical absorbable plate fixation (straight PLLA [poly-L-lactic acid] plate: 28 ⫻ 4.5 ⫻ 1.5 mm with 4 screws [2 ⫻ 8 mm], Fixorb-MX; Takiron Co., Osaka, Japan) (Fig. 1). ODTM group: 84 sides underwent the ObwegeserDal Pont method with monocortical titanium plate fixation (long mini-plate: 4 holes/burr, 8-mm thickness 1.0 mm and 4 screws [2 ⫻ 7 mm] Würzburg titanium miniplate system, Leibinger Co, Freiburg, Germany) (Fig. 2). OTB group: 32 sides underwent the Obwegeser method with bicortical titanium plate fixation (long mini-plate: 4 holes/burr 8-mm thickness 1.0 mm and 4 screws [2 ⫻ 14 mm and 2 ⫻ 5 mm] Universal Mandible fixation module, Stryker Leibinger Co, Freiburg, Germany). The 2 posterior screws were bicortical and the 2 anterior screws were monocortical (Fig. 3). At the site of fixation, an osseous step was formed, depending on the amount of setback. Bent plates were used to maintain the condyle in its original position in both groups, so that a small gap remained between the bone fragments at the anterior part of the juncture site space in the SSRO.15 VO group: 104 sides underwent IVRO according to the Bell method without fixation (Fig. 4).
The purpose of the study was explained to all patients before the operation, and their informed consent
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Fig. 4. Schematic drawing of the procedure in the VO group.
Fig. 2. Schematic drawing of the procedure and fixation in the ODTM group. A, Osteotomy line. B, Plate position from lateral view. C, Plate position from axial view.
Fig. 3. Schematic drawing of the procedure and fixation in the OTB group. A, Osteotomy line. B, Plate position from lateral view. C, Plate position from axial view.
was obtained for the measurement of TSEP. The patients then underwent bilateral setback surgery for mandibular prognathism or unilateral setback and unilateral slight advance surgery for mandibular asymmetry. The same surgeons carried out all the procedures.
Postoperative intermaxillary fixation was maintained with 0.4-mm wires and intermaxillary fixation (IMF) screws (2 ⫻ 8 mm, Stryker Leibinger) for 1 to 7 days in the SSRO groups and for 1 to 2 weeks in the IVRO groups. Intermaxillary elastic traction was performed in all patients. Trigeminal nerve hypoesthesia was assessed bilaterally by the TSEP method. The methodology and values of TSEP have been described previously in our preliminary studies.10-12 The electrodes were placed exactly under the highest point of the vermilion border and on the mucosa of the lower lip. An electroencephalograph recording system (Neuropack Sigma; Nihon Koden Corp, Tokyo, Japan) was used to measure the potentials (Fig. 5). The right and left sides were measured separately so that a total of 348 sides could be assessed. Each patient was evaluated preoperatively and then postoperatively at 1 and 2 weeks; 1, 3, and 6 months; and 1 year. Trigeminal hypoesthesia was assessed by the latency of P1 and N2 in the recorded TSEP spectra. An earlier pilot study in healthy volunteers showed that these peaks produced an accurate figure and tended to result in better reproducibility. Measurable periods of TSEP were defined as periods before the peaks of N1 (N13), P1 (P17), N2 (N27), P2 (P36), and N3 (N46) that were identified clearly as early components of the TSEP wave. Actual data were recorded as latency period (msec) in each peak (Fig. 6). The measurable period was determined as the time when TSEP was first measurable postoperatively. Measurement of TSEP after surgery was continued until TSEP became measurable. Statistical analysis of the data was carried out using StatView version 4.5 software (ABACUS Concepts, Inc, Berkeley, CA). Differences between the groups were analyzed using the Kruskal-Wallis test and the
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Fig. 5. Pictures of TSEP measure instruments. A, An electroencephalograph recording system (Neuropack Sigma; Nihon Koden Corp, Tokyo, Japan). B, Electrode box. C, The modified electrostimulus clip.
Fig. 6. TSEP wave form. Measurable periods of TSEP were defined as those periods before the peaks of N1, P1, N2, P2, and N3 that were clearly identified on early components of the TSEP wave. Amplitude value (V) and latency periods (msec) are shown in this graph.
Mann-Whitney U test, with statistical significance being inferred at P ⬍ .05. The amount of setback of all the sides was also recorded with the correlation between the measurable period of TSEP and the amount of setback in each side being examined using simple regression analysis. RESULTS There were no complications such as fracture of the proximal segments or abnormal bleeding during surgery. After surgery, no patient had a wound infection or dehiscence, bone instability or nonunion, or long-term malocclusion. The average measurable period and standard devia-
tion of TSEP of the lower lip in the OAM group was 5.2 ⫾ 9.9 weeks, 10.9 ⫾ 13.1weeks in the ODTM group, 7.8 ⫾ 4.5 weeks in the OTB group, and 2.5 ⫾ 6.3 weeks in the VO group. There was significant difference among the 4 groups with the Kruskal-Wallis test. Although there were significant differences between the OAM and ODTM groups (P ⬍ .001), the ODTM and OTB groups (P ⫽ .001), the OTB and VO groups (P ⫽ .022), the OAM and VO groups (P ⬍ .001), and the ODTM and VO groups (P ⬍ .001), there were no significant differences between the OAM and OTB groups (P ⫽ .3082) with the Mann-Whitney U test (Fig. 7). In the OAM group, TSEP was measurable within 1 week in 74 (57.8%) of 128 sides of the lower lip, within 2 weeks in 88 sides (68.8%), within 1 month in 99 sides (77.3%), within 3 months in 109 sides (78.0%), within 6 months in 116 sides (85.2%), and within 1 year in 120 sides (93.8%). Recovery of TSEP was negative response 1 year postoperatively in the remaining 8 sides. In 30 (35.7%) of 84 sides of the lower lip in the ODTM group, TSEP was measurable within 1 week, in 36 sides (42.9%) within 2 weeks, in 45 sides (53.6%) within 1 month, in 59 sides (70.2%) within 3 months, in 75 sides (89.3%) within 6 months, and in 80 sides (95.2%) it recovered within 1 year. Four sides remained immeasurable 1 year postoperatively. In the OTB group, 20 (62.5%) of 32 sides of the lower lip had TSEP measurable within 1 week, in 22
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Fig. 7. The mean measurable period and standard deviation of TSEP of the lower lip. *Significant difference at P ⬍ .05.
sides (68.8%) within 2 weeks, in 29 sides (90.1%) within 1 month, while 3 sides showed negative response 1 year postoperatively. TSEP was measurable within 1 week in 91 (87.5%) of 104 sides of the lower lip in the VO group, within 2 weeks in 96 sides (92.3%), within 1 month in 99 sides (95.2%), within 6 months 103 sides (99.0 %), and within 1 year it had recovered in all 104 sides (100%). Within-subject comparisons in the OAM group showed there were significant differences in TSEP in N1 (P ⫽ .001), P1 (P ⬍ .001), N2 (P ⫽ .001), and P2 (P ⬍ .001) with Kruskal-Wallis test (Fig. 8). In the ODTM group, there were significant differences in N1 (P ⬍ .001), P1 (P ⬍ .003), N2 (P ⬍ .001), and P2 (P ⫽ .001) (Fig. 9). In the OTB group, there were significant differences in N1 (P ⫽ .028), P1 (P ⫽ .012), N2 (P ⫽ .001), and P2 (P ⫽ .003), although there were no data after more than 3 months so that the data within 1 month could be calculated (Fig. 10). In the VO group, there was a lack of numbers after more than 3 months so that statistical calculation could not be performed with the Kruskal-Wallis test (Fig. 11). No significant correlations were found between the measurable period of TSEP and amount of setback (R ⫽ 0.095, adjusted R2 ⫽ 0.006, RMS Residual ⫽ 3.841, P ⫽ .0819) (Fig. 12). DISCUSSION TSEP, a somatosensory evoked potential of the peripheral nerves has been used previously to investigate the causal factors of trigeminal sensory hypoesthesia that occurs after SSRO.10-12,16-18 This method is highly objective and reliable as the potential changes of cerebral origin can be detected on the scalp in human subjects following electrical stimulation of the peripheral nerves. Factors known to cause postoperative tri-
geminal nerve hypoesthesia include medial periosteal dissection, exposure of the alveolar nerve during the split, compression injury at the time of fixation and postoperative swelling.19,20 Our previous study using horizontal images of computed tomography showed that the distance between the mandibular canal and the split surface correlated with TSEP latency recovery.12 In the present study, the ODTM group had a slower recovery from hypoesthesia than the OAM, OTB, and VO groups. As the monocortical fixation method was performed in the OAM and ODTM groups, this surgical procedure may have contributed to the difference in the recovery period in TSEP observed in these groups. There was no significant difference between the OAM and OTB groups, indicating that fixation methods may affect the recovery period of TSEP. The VO group showed the earliest obvious signs of recovery of TSEP. In short, the Obwegeser-Dal Pont method delayed the recovery period of hypoesthesia of the lower lip and was associated with a higher incidence of lower lip hypoesthesia than the Obwegeser method. However, the results of this study suggested that monocortical or bicortical fixation methods did not influence the recovery period from hypoesthesia. With regards to the effect of the fixation method, Lemke et al.7 reported that rigid fixation resulted in more anesthesia in the mental nerve distribution than wire fixation when tested with brush stroke direction. Fujioka et al.21 also reported that monocortical osteosynthesis caused less damage to the inferior alveolar nerve. Some surgeons have suggested that compressive forces can occur when fixing the 2 mandibular segments together, resulting in the nerve being sandwiched. Takeuchi et al.22 reported that in SSRO setback cases, the distance between the mental foramen and the mandibular ramus always decreased, and that this change may cause trigeminal nerve hypoesthesia by compression of the nerve trunk because of posterior shifting of the proximal segments. There is evidence that wire fixation and monocortical fixation is less likely to cause direct trauma and has no risk of compressing the segments.7 Merrill23 showed, in an experimental study in dogs, that within 6 months of a simple crush of the inferior alveolar nerve that the axons had completely regenerated. However, a considerable reduction in the number of regenerated axons occurred when the same nerve injury was complicated by bony compression, with decompression of the nerves facilitating the recovery of an increased number of axons and also the degree of myelination. Although compression has been considered as a cause, proper use of screws as “positional” screws should prevent compressive forces. In this study, depending on the amount of setback, an osseous step was formed at the site of fixation. In the OAM,
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1 3 1 3
SUH
SRVWZ
SRVWZ
SRVWP
SRVWP
SRVWP
SRVW\
Fig. 8. Average latency period of TSEP in the OAM group. Error bar shows the standard deviation.
(msec) 1 3 1 3
SUH
SRVWZ
SRVWZ
SRVWP
SRVWP
SRVWP
SRVW\
Fig. 9. Average latency period of TSEP in the OBTM group. Error bar shows the standard deviation.
ODTM, and OTB groups, bent plates were used to maintain the condyle in its original position in all groups, so that a small gap remained between the bone fragments at the anterior part of the juncture site space. Therefore, compression between segments did not occur in these groups, possibly explaining why no significant difference was observed between monocortical and bicortical screw fixation. The main difference between the Obwegeser-Dal Pont and Obwegeser methods was the difference of the area of split. In other words, the area of the split surface at the region anterior to the mandibular foramen was related to the latency period of TSEP. However, the
results of the VO group showed that the area of split surface at the posterior region of the mandibular foramen was not related to the latency period of TSEP. The wide bony contact in SSRO has the disadvantage of hypoesthesia of the lower lip, although it has an advantage during segmental fixation. In fact, the inferior alveolar nerve was not damaged, resulting in the branches being distributed widely in the mandibular bone at the region anterior to the mandibular foramen. The osteotomy and split may injure the inferior alveolar nerve and also its branches. We found that the inferior alveolar nerve could be protected by careful operation; however, injury to the branches could not be avoided.
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(msec) 1 3 1 3
SUH
SRVWZ
SRVWZ
SRVWP
SRVWP
SRVWP
SRVW\
Fig. 10. Average latency period of TSEP in the OTB group. Error bar shows the standard deviation.
(msec) 1 3 1 3
SUH
SRVWZ
SRVWZ
SRVWP
SRVWP
SRVWP
SRVW\
Fig. 11. Average latency period of TSEP in the VO group. Error bar shows the standard deviation.
Decrease in sensation of the lower lip following IVRO was also observed. Nerve sensation of the lower lip may not be distributed by only the branches of the inferior alveolar nerve through the mandibular canal, but also by the branches through the gingival, oral mucosa, and any other surrounding tissue. It was considered that the slight sensory change in the lower lip could be detected after IVRO. On the other hand, our previous study demonstrated that prolonged latency of TSEP was caused by medial periosteal dissection and was extended further after splitting of the sagittal bone and fixation.11 TeerijokiOksa et al.24 reported that low corpus height and the
location of the mandibular canal near the inferior border of the mandible may increase the risk of injury to the inferior alveolar nerve. The location length and area of the dissection and osteotomy line may also affect hypoesthesia of the lower lip. The anterior osteotomy line in the Obwegeser-Dal Pont method was positioned more anteriorly than in the Obwegeser method, resulting in the incision and dissection area of the Obwegeser-Dal Pont method being necessarily larger and more anterior to that of the Obwegeser method. Fixation of the segments in the Obwegeser-Dal Pont method may result in the location of the screw on the titanium plate to sometimes
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Recovery in lower lip hypoesthesia after IVRO was significantly earlier than SSRO.
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REFERENCES
10 7.5 5 2.5 0 -2.5 -5 -7.5 -10
0
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Measurable period of TSEP Y = 4.944 + .033 * X; R^2 = .009
Fig. 12. Simple regression analysis between the setback amount and the measurable period of TSEP.
be close to the mental foramen. This position of the screw may have also affected the results. Posnick et al.25 reported a high percentage of subjective and objective neurosensory deficits in a group of adolescent patients who had undergone both a sagittal osteotomy and genioplasty. They attributed this to the “double crush syndrome” during which 2 serial and simultaneous constraints of axoplasmic flow occurred in the inferior alveolar nerve. A similar situation may occur after plate fixation in the Obwegeser-Dal Pont method. This theory had been described previously for peripheral nerves. However, Upton and McComas26 also evaluated the influence of concomitant surgical procedures on the incidence of postoperative nerve alteration and did not find a higher percentage of deficits associated with multiple procedures. It was not possible in this study to compare the use of PLLA or titanium plates in the same procedure, and therefore it is necessary to examine whether fixation material affects hypoesthesia following osteotomy in future studies. Although there was no significant association between the amount of setback and the measurable period of TSEP in this study, the smaller setback side tended to show earlier recovery. In general, IVRO was performed more frequently in cases of asymmetry so that the setback amount was smaller than with SSRO. Therefore, it was difficult to judge which factor, procedure, or setback amount had marked effects on neurosensory disturbances of the lower lip following surgery. CONCLUSION This study provided objective proof that the recovery period from hypoesthesia of the lower lip following orthognathic surgery was dependent on the surgical procedure.
1. Bell WH (editor). Mandibular prognathism. In: Modern practice in orthognathic and reconstructive surgery. Philadelphia (PA): Saunders; 1992. p. 61, 2111-37. 2. Trauner R, Obwegeser H. The surgical correction of mandibular prognathism and retrognathia and consideration of genioplasty: surgical procedures to correct mandibular prognathism and reshaping the chin. Oral Surg Oral Med Oral Pathol 1957;10:677-89. 3. Dal Pont G. Retromolar osteotomy for the correction of prognathism. J Oral Surg 1961;19:42-7. 4. Hunsuck EE. A modified intraoral sagittal splitting technique for the correction of mandibular prognathism. J Oral Surg 1968;26:249-52. 5. Epker B. Modifications in the sagittal osteotomy of the mandible. J Oral Surg 1977;35:157-9. 6. Karas ND, Boyd SB, Sinn DO. Recovery of neurosensory function following orthognathic surgery. J Oral Maxillofac Surg 1990;48:124-34. 7. Lemke RR, Rugh JD, Van Sickels J, Bays RA, Clark GM. Neurosensory differenced after wire and rigid fixation in patients with mandibular advancement. J Oral Maxillofac Surg 2000;58:1354-9. 8. de Beukelaer JG, Smeele LE, van Ginkel FC. Is short-term neurosensory testing after removal of mandibular third molars efficacious? Oral Surg Oral Med Oral Pathol 1998;85:366-70. 9. Jones DL, Wolford LM. Intraoperative recording of trigeminal evoked potentials during orthognathic surgery. Int J Orthod Orthognath Surg 1990;5:167-74. 10. Nakagawa K, Ueki K, Matsumoto N, Takatsuka S, Yamamoto E, Ooe H. The assessment of trigeminal sensory nerve paraesthesia after bilateral sagittal split osteotomy: modified somatosensory evoked potentials recording method. J Craniomaxillofac Surg 1997;25:97-101. 11. Nakagawa K, Ueki K, Takatsuka S, Daisuke T, Yamaomoto E. Somatosensory-evoked potential to evaluate the trigeminal nerve after sagittal split osteotomy. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001;91:146-52. 12. Nakagawa K, Ueki K, Takatsuka S, Yamamoto E. Trigeminal nerve hypesthesia after sagittal split osteotomy in setback cases: correlation of postoperative computed tomography and longterm trigeminal somatosensory evoked potentials. J Oral Maxillofac Surg 2003;61:898-903. 13. Coderre TJ, Katz J, Vaccarino AL, Melzack R. Contribution of central neuroplasticity to pathological pain: review of clinical and experimental evidence. Pain 1993;52:259-85. 14. McQuay HJ, Carroll D, Jadad AR, Glynn CJ, Jack T, Moore RA, et al. Dextromethorphan for the treatment of neuropathic pain: a double-blind randomized controlled crossover trial with integral n-of-1 design. Pain 1994;59:127-33. 15. Ueki K, Nakagawa K, Takatsuka S, Yamamoto E. Plate fixation after mandibular osteotomy. Int J Oral Maxillofac Surg 2001;30:490-6. 16. Bennett AJ, Wastell DG, Barker GR, Blackburn CW, Rood JP. Trigeminal somatosensory evoked potentials: a review of the literature as applicable to oral dysesthesias. Int J Oral Maxillofac Surg 1987;16:408-15. 17. Narita Y, Nagai M, Kuzuhara S. Trigeminal somatosensory evoked potentials before, during and after an inferior alveolar nerve block in normal subjects. Psychiatry Clin Neurosci 1997;51:241-7.
OOOOE Volume 104, Number 2 18. Vriens JPM, Pasman JW. Assessment of trigeminal nerve function by means of short-latency somatosensory evoked potentials after microneurosurgical repair. J Craniomaxillofac Surg 1994;22:156-62. 19. August M, Marchena J, Conady J Kaban L. Neurosensory deficit and functional impairment after sagittal split osteotomy: a longterm follow-up study. J Oral Maxillofac Surg 1998;56:1231-5. 20. Leira JI, Gihuus-Moe OT. Sensory impairment following sagittal splitosteotomy for correction of mandibular retrognathism. Int J Adult Orthodon Orthognath Surg 1991;6:161-7. 21. Fujioka M, Akiyoshi H, Fuji T. Comparative study of inferior alveolar distribution restoration after sagittal split osteotomy by means of bicortical versus monocortical osteosynthesis. Plast Reconstr Surg 1998;102:37-41. 22. Takeuchi T, Furusawa K, Hirose I. Mechanism of transient mental nerve paraesthesia in sagittal split mandibular ramus osteotomy. Br J Oral Maxillofac Surg 1994;32:105-8. 23. Merrill RG. Further studies in decompression for inferior alveolar nerve injury. J Oral Surg 1966;24:233-8.
Hashiba et al. 185 24. Teerijoki-Oksa T, Jääskeläinen SK, Forssell K, Forssell H, Vähätalo K, Tammisalo T, et al. Risk factors of nerve injury during mandibular sagittal split osteotomy. Int J Oral Maxillofac Surg 2002;31:33-9. 25. Posnick JC, Al-Qattan MM, Stepner NM. Alteration in facial sensibility in adolescents following sagittal split and chin osteotomies of the mandible. Plast Reconstr Surg 1996;97:920-7. 26. Upton AR, McComas AJ. The double crush in nerve entrapment syndrome. Lancet 1973;2: 359-62. Reprint requests: Yukari Hashiba, DDS Department of Oral and Maxillofacial Surgery Graduate School of Medicine Kanazawa University 13-1 Takaramachi Kanazawa 920-8641, Japan [email protected]
Purpose. 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). Patients and Methods. 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 postoperatively at 1 and 2 weeks, 1, 3, and 6 months, and 1 year. Results. 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). Conclusion. 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. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2007;104:177-85)
Orthognathic surgical procedures have been described extensively with good results having been reported for the variety of different treatments.1 Two surgical procedures are used most often for mandibular osteotomies of mandibular prognathism, namely the sagittal split ramus osteotomy (SSRO)2 and the intraoral vertical ramus osteotomy (IVRO).1 The SSRO technique was first described by Trauner and Obwegeser,2 with many modifications of the technique having been introduced a
Graduate Student, Department of Oral and Maxillofacial Surgery, Graduate School of Medicine, Kanazawa University. b Clinical Fellow, Department of Oral and Maxillofacial Surgery, Graduate School of Medicine, Kanazawa University. c Associate Professor, Department of Oral and Maxillofacial Surgery, Graduate School of Medicine. Received for publication May 25, 2006; returned for revision Oct 5, 2006; accepted for publication Nov 9, 2006. 1079-2104/$ - see front matter © 2007 Mosby, Inc. All rights reserved. doi:10.1016/j.tripleo.2006.11.038
with the aim of minimizing morbidity and maximizing the stability of the procedure. These modifications included the variations described by Dal Pont,3 Hunsuck,4 and Epker.5 It is generally recognized that the vertical buccal cut of the Obwegeser-Dal Pont method is positioned more anteriorly than in the Obwegeser method. One of the major complications after orthognathic surgery is lower and upper lip hypoesthesia. Karas et al.6 reported that in comparison with other surgical procedures such as a Le Fort I osteotomy, IVRO, or genioplasty, the SSRO caused the highest percentage of postsurgical neurosensory damage assessed by static light touch (SLT), moving touch discrimination (MTD), and 2-point discrimination (TPD). Lemke et al.7 also reported that rigid fixation resulted in more anesthesia in mental nerve distribution compared to wire fixation when tested by brush stroke determination. 177
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Standard sensory testing modalities include the following parameters: threshold of light touch perception, 2-point discrimination threshold, temperature sensitivity,7 and trigeminal somatosensory-evoked potentials (TSEP).8-12 The TSEP method is noninvasive, highly objective, and extremely reliable and can be used to investigate trigeminal sensory hypoesthesia of the lower lip after mandibular ramus osteotomy. In simple sensory tests such as 2-point sensory discrimination, collection of output data depends on the patient’s view with their bias, even if input data such as stimulating pressure is objective. However, TSEP data are directly collected from the patient’s electroencephalography derived from the cerebral cortex so that data of TSEP could be more objective and reliable. Thus, a difference between objective and subjective assessment may occur. Furthermore, there may also be a difference between actual return of feeling and registration of nerve conduction. Advancements in the field of neurophysiology have revealed posttraumatic change in the central nervous system. Functional disturbance in the central nervous system after peripheral nerve injury is known as central sensitization.13,14 Actual return of feeling may not always occur with recovery in peripheral nerves. However, there are no reports on the use of TSEP to assess the difference in recovery period of lip hypoesthesia after SSRO (Obwegeser-Dal Pont method and Obwegeser method) or IVRO. There are also no studies using TSEP that have investigated whether different fixation methods and surgical procedures affect the recovery of lip hypoesthesia after surgery. The purpose of this study was therefore to determine objectively using TSEP whether differences in surgical procedures and fixation methods influenced the recovery of hypoesthesia of the upper and lower lip following orthognathic surgery. SUBJECTS AND METHODS The subjects comprised 174 Japanese adults (45 males, 129 females) presenting with jaw deformities, diagnosed as mandibular prognathism with or without mandibular asymmetry, or mandibular prognathism with or without bimaxillary asymmetry. At the time of orthognathic surgery, the mean age of the patients was 24.1 years (standard deviation 6.5 years; range 15-45 years). Informed consent was obtained for all the patients who underwent mandibular ramus osteotomy. The patients who could agree with the informed consent were selected as the subjects in this study. However, the distribution of surgical procedures was not equal in our facility so that the sample number of each group was different.
Fig. 1. Schematic drawing of the procedure and fixation in the OAM group. A, Osteotomy line. B, Plate position from lateral view. C, Plate position from axial view.
The total 348 sides of the 174 patients were divided into 4 groups as follows: ●
●
●
●
OAM group: 128 sides underwent the Obwegeser method with monocortical absorbable plate fixation (straight PLLA [poly-L-lactic acid] plate: 28 ⫻ 4.5 ⫻ 1.5 mm with 4 screws [2 ⫻ 8 mm], Fixorb-MX; Takiron Co., Osaka, Japan) (Fig. 1). ODTM group: 84 sides underwent the ObwegeserDal Pont method with monocortical titanium plate fixation (long mini-plate: 4 holes/burr, 8-mm thickness 1.0 mm and 4 screws [2 ⫻ 7 mm] Würzburg titanium miniplate system, Leibinger Co, Freiburg, Germany) (Fig. 2). OTB group: 32 sides underwent the Obwegeser method with bicortical titanium plate fixation (long mini-plate: 4 holes/burr 8-mm thickness 1.0 mm and 4 screws [2 ⫻ 14 mm and 2 ⫻ 5 mm] Universal Mandible fixation module, Stryker Leibinger Co, Freiburg, Germany). The 2 posterior screws were bicortical and the 2 anterior screws were monocortical (Fig. 3). At the site of fixation, an osseous step was formed, depending on the amount of setback. Bent plates were used to maintain the condyle in its original position in both groups, so that a small gap remained between the bone fragments at the anterior part of the juncture site space in the SSRO.15 VO group: 104 sides underwent IVRO according to the Bell method without fixation (Fig. 4).
The purpose of the study was explained to all patients before the operation, and their informed consent
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Fig. 4. Schematic drawing of the procedure in the VO group.
Fig. 2. Schematic drawing of the procedure and fixation in the ODTM group. A, Osteotomy line. B, Plate position from lateral view. C, Plate position from axial view.
Fig. 3. Schematic drawing of the procedure and fixation in the OTB group. A, Osteotomy line. B, Plate position from lateral view. C, Plate position from axial view.
was obtained for the measurement of TSEP. The patients then underwent bilateral setback surgery for mandibular prognathism or unilateral setback and unilateral slight advance surgery for mandibular asymmetry. The same surgeons carried out all the procedures.
Postoperative intermaxillary fixation was maintained with 0.4-mm wires and intermaxillary fixation (IMF) screws (2 ⫻ 8 mm, Stryker Leibinger) for 1 to 7 days in the SSRO groups and for 1 to 2 weeks in the IVRO groups. Intermaxillary elastic traction was performed in all patients. Trigeminal nerve hypoesthesia was assessed bilaterally by the TSEP method. The methodology and values of TSEP have been described previously in our preliminary studies.10-12 The electrodes were placed exactly under the highest point of the vermilion border and on the mucosa of the lower lip. An electroencephalograph recording system (Neuropack Sigma; Nihon Koden Corp, Tokyo, Japan) was used to measure the potentials (Fig. 5). The right and left sides were measured separately so that a total of 348 sides could be assessed. Each patient was evaluated preoperatively and then postoperatively at 1 and 2 weeks; 1, 3, and 6 months; and 1 year. Trigeminal hypoesthesia was assessed by the latency of P1 and N2 in the recorded TSEP spectra. An earlier pilot study in healthy volunteers showed that these peaks produced an accurate figure and tended to result in better reproducibility. Measurable periods of TSEP were defined as periods before the peaks of N1 (N13), P1 (P17), N2 (N27), P2 (P36), and N3 (N46) that were identified clearly as early components of the TSEP wave. Actual data were recorded as latency period (msec) in each peak (Fig. 6). The measurable period was determined as the time when TSEP was first measurable postoperatively. Measurement of TSEP after surgery was continued until TSEP became measurable. Statistical analysis of the data was carried out using StatView version 4.5 software (ABACUS Concepts, Inc, Berkeley, CA). Differences between the groups were analyzed using the Kruskal-Wallis test and the
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Fig. 5. Pictures of TSEP measure instruments. A, An electroencephalograph recording system (Neuropack Sigma; Nihon Koden Corp, Tokyo, Japan). B, Electrode box. C, The modified electrostimulus clip.
Fig. 6. TSEP wave form. Measurable periods of TSEP were defined as those periods before the peaks of N1, P1, N2, P2, and N3 that were clearly identified on early components of the TSEP wave. Amplitude value (V) and latency periods (msec) are shown in this graph.
Mann-Whitney U test, with statistical significance being inferred at P ⬍ .05. The amount of setback of all the sides was also recorded with the correlation between the measurable period of TSEP and the amount of setback in each side being examined using simple regression analysis. RESULTS There were no complications such as fracture of the proximal segments or abnormal bleeding during surgery. After surgery, no patient had a wound infection or dehiscence, bone instability or nonunion, or long-term malocclusion. The average measurable period and standard devia-
tion of TSEP of the lower lip in the OAM group was 5.2 ⫾ 9.9 weeks, 10.9 ⫾ 13.1weeks in the ODTM group, 7.8 ⫾ 4.5 weeks in the OTB group, and 2.5 ⫾ 6.3 weeks in the VO group. There was significant difference among the 4 groups with the Kruskal-Wallis test. Although there were significant differences between the OAM and ODTM groups (P ⬍ .001), the ODTM and OTB groups (P ⫽ .001), the OTB and VO groups (P ⫽ .022), the OAM and VO groups (P ⬍ .001), and the ODTM and VO groups (P ⬍ .001), there were no significant differences between the OAM and OTB groups (P ⫽ .3082) with the Mann-Whitney U test (Fig. 7). In the OAM group, TSEP was measurable within 1 week in 74 (57.8%) of 128 sides of the lower lip, within 2 weeks in 88 sides (68.8%), within 1 month in 99 sides (77.3%), within 3 months in 109 sides (78.0%), within 6 months in 116 sides (85.2%), and within 1 year in 120 sides (93.8%). Recovery of TSEP was negative response 1 year postoperatively in the remaining 8 sides. In 30 (35.7%) of 84 sides of the lower lip in the ODTM group, TSEP was measurable within 1 week, in 36 sides (42.9%) within 2 weeks, in 45 sides (53.6%) within 1 month, in 59 sides (70.2%) within 3 months, in 75 sides (89.3%) within 6 months, and in 80 sides (95.2%) it recovered within 1 year. Four sides remained immeasurable 1 year postoperatively. In the OTB group, 20 (62.5%) of 32 sides of the lower lip had TSEP measurable within 1 week, in 22
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Fig. 7. The mean measurable period and standard deviation of TSEP of the lower lip. *Significant difference at P ⬍ .05.
sides (68.8%) within 2 weeks, in 29 sides (90.1%) within 1 month, while 3 sides showed negative response 1 year postoperatively. TSEP was measurable within 1 week in 91 (87.5%) of 104 sides of the lower lip in the VO group, within 2 weeks in 96 sides (92.3%), within 1 month in 99 sides (95.2%), within 6 months 103 sides (99.0 %), and within 1 year it had recovered in all 104 sides (100%). Within-subject comparisons in the OAM group showed there were significant differences in TSEP in N1 (P ⫽ .001), P1 (P ⬍ .001), N2 (P ⫽ .001), and P2 (P ⬍ .001) with Kruskal-Wallis test (Fig. 8). In the ODTM group, there were significant differences in N1 (P ⬍ .001), P1 (P ⬍ .003), N2 (P ⬍ .001), and P2 (P ⫽ .001) (Fig. 9). In the OTB group, there were significant differences in N1 (P ⫽ .028), P1 (P ⫽ .012), N2 (P ⫽ .001), and P2 (P ⫽ .003), although there were no data after more than 3 months so that the data within 1 month could be calculated (Fig. 10). In the VO group, there was a lack of numbers after more than 3 months so that statistical calculation could not be performed with the Kruskal-Wallis test (Fig. 11). No significant correlations were found between the measurable period of TSEP and amount of setback (R ⫽ 0.095, adjusted R2 ⫽ 0.006, RMS Residual ⫽ 3.841, P ⫽ .0819) (Fig. 12). DISCUSSION TSEP, a somatosensory evoked potential of the peripheral nerves has been used previously to investigate the causal factors of trigeminal sensory hypoesthesia that occurs after SSRO.10-12,16-18 This method is highly objective and reliable as the potential changes of cerebral origin can be detected on the scalp in human subjects following electrical stimulation of the peripheral nerves. Factors known to cause postoperative tri-
geminal nerve hypoesthesia include medial periosteal dissection, exposure of the alveolar nerve during the split, compression injury at the time of fixation and postoperative swelling.19,20 Our previous study using horizontal images of computed tomography showed that the distance between the mandibular canal and the split surface correlated with TSEP latency recovery.12 In the present study, the ODTM group had a slower recovery from hypoesthesia than the OAM, OTB, and VO groups. As the monocortical fixation method was performed in the OAM and ODTM groups, this surgical procedure may have contributed to the difference in the recovery period in TSEP observed in these groups. There was no significant difference between the OAM and OTB groups, indicating that fixation methods may affect the recovery period of TSEP. The VO group showed the earliest obvious signs of recovery of TSEP. In short, the Obwegeser-Dal Pont method delayed the recovery period of hypoesthesia of the lower lip and was associated with a higher incidence of lower lip hypoesthesia than the Obwegeser method. However, the results of this study suggested that monocortical or bicortical fixation methods did not influence the recovery period from hypoesthesia. With regards to the effect of the fixation method, Lemke et al.7 reported that rigid fixation resulted in more anesthesia in the mental nerve distribution than wire fixation when tested with brush stroke direction. Fujioka et al.21 also reported that monocortical osteosynthesis caused less damage to the inferior alveolar nerve. Some surgeons have suggested that compressive forces can occur when fixing the 2 mandibular segments together, resulting in the nerve being sandwiched. Takeuchi et al.22 reported that in SSRO setback cases, the distance between the mental foramen and the mandibular ramus always decreased, and that this change may cause trigeminal nerve hypoesthesia by compression of the nerve trunk because of posterior shifting of the proximal segments. There is evidence that wire fixation and monocortical fixation is less likely to cause direct trauma and has no risk of compressing the segments.7 Merrill23 showed, in an experimental study in dogs, that within 6 months of a simple crush of the inferior alveolar nerve that the axons had completely regenerated. However, a considerable reduction in the number of regenerated axons occurred when the same nerve injury was complicated by bony compression, with decompression of the nerves facilitating the recovery of an increased number of axons and also the degree of myelination. Although compression has been considered as a cause, proper use of screws as “positional” screws should prevent compressive forces. In this study, depending on the amount of setback, an osseous step was formed at the site of fixation. In the OAM,
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1 3 1 3
SUH
SRVWZ
SRVWZ
SRVWP
SRVWP
SRVWP
SRVW\
Fig. 8. Average latency period of TSEP in the OAM group. Error bar shows the standard deviation.
(msec) 1 3 1 3
SUH
SRVWZ
SRVWZ
SRVWP
SRVWP
SRVWP
SRVW\
Fig. 9. Average latency period of TSEP in the OBTM group. Error bar shows the standard deviation.
ODTM, and OTB groups, bent plates were used to maintain the condyle in its original position in all groups, so that a small gap remained between the bone fragments at the anterior part of the juncture site space. Therefore, compression between segments did not occur in these groups, possibly explaining why no significant difference was observed between monocortical and bicortical screw fixation. The main difference between the Obwegeser-Dal Pont and Obwegeser methods was the difference of the area of split. In other words, the area of the split surface at the region anterior to the mandibular foramen was related to the latency period of TSEP. However, the
results of the VO group showed that the area of split surface at the posterior region of the mandibular foramen was not related to the latency period of TSEP. The wide bony contact in SSRO has the disadvantage of hypoesthesia of the lower lip, although it has an advantage during segmental fixation. In fact, the inferior alveolar nerve was not damaged, resulting in the branches being distributed widely in the mandibular bone at the region anterior to the mandibular foramen. The osteotomy and split may injure the inferior alveolar nerve and also its branches. We found that the inferior alveolar nerve could be protected by careful operation; however, injury to the branches could not be avoided.
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(msec) 1 3 1 3
SUH
SRVWZ
SRVWZ
SRVWP
SRVWP
SRVWP
SRVW\
Fig. 10. Average latency period of TSEP in the OTB group. Error bar shows the standard deviation.
(msec) 1 3 1 3
SUH
SRVWZ
SRVWZ
SRVWP
SRVWP
SRVWP
SRVW\
Fig. 11. Average latency period of TSEP in the VO group. Error bar shows the standard deviation.
Decrease in sensation of the lower lip following IVRO was also observed. Nerve sensation of the lower lip may not be distributed by only the branches of the inferior alveolar nerve through the mandibular canal, but also by the branches through the gingival, oral mucosa, and any other surrounding tissue. It was considered that the slight sensory change in the lower lip could be detected after IVRO. On the other hand, our previous study demonstrated that prolonged latency of TSEP was caused by medial periosteal dissection and was extended further after splitting of the sagittal bone and fixation.11 TeerijokiOksa et al.24 reported that low corpus height and the
location of the mandibular canal near the inferior border of the mandible may increase the risk of injury to the inferior alveolar nerve. The location length and area of the dissection and osteotomy line may also affect hypoesthesia of the lower lip. The anterior osteotomy line in the Obwegeser-Dal Pont method was positioned more anteriorly than in the Obwegeser method, resulting in the incision and dissection area of the Obwegeser-Dal Pont method being necessarily larger and more anterior to that of the Obwegeser method. Fixation of the segments in the Obwegeser-Dal Pont method may result in the location of the screw on the titanium plate to sometimes
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Recovery in lower lip hypoesthesia after IVRO was significantly earlier than SSRO.
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REFERENCES
10 7.5 5 2.5 0 -2.5 -5 -7.5 -10
0
10
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Measurable period of TSEP Y = 4.944 + .033 * X; R^2 = .009
Fig. 12. Simple regression analysis between the setback amount and the measurable period of TSEP.
be close to the mental foramen. This position of the screw may have also affected the results. Posnick et al.25 reported a high percentage of subjective and objective neurosensory deficits in a group of adolescent patients who had undergone both a sagittal osteotomy and genioplasty. They attributed this to the “double crush syndrome” during which 2 serial and simultaneous constraints of axoplasmic flow occurred in the inferior alveolar nerve. A similar situation may occur after plate fixation in the Obwegeser-Dal Pont method. This theory had been described previously for peripheral nerves. However, Upton and McComas26 also evaluated the influence of concomitant surgical procedures on the incidence of postoperative nerve alteration and did not find a higher percentage of deficits associated with multiple procedures. It was not possible in this study to compare the use of PLLA or titanium plates in the same procedure, and therefore it is necessary to examine whether fixation material affects hypoesthesia following osteotomy in future studies. Although there was no significant association between the amount of setback and the measurable period of TSEP in this study, the smaller setback side tended to show earlier recovery. In general, IVRO was performed more frequently in cases of asymmetry so that the setback amount was smaller than with SSRO. Therefore, it was difficult to judge which factor, procedure, or setback amount had marked effects on neurosensory disturbances of the lower lip following surgery. CONCLUSION This study provided objective proof that the recovery period from hypoesthesia of the lower lip following orthognathic surgery was dependent on the surgical procedure.
1. Bell WH (editor). Mandibular prognathism. In: Modern practice in orthognathic and reconstructive surgery. Philadelphia (PA): Saunders; 1992. p. 61, 2111-37. 2. Trauner R, Obwegeser H. The surgical correction of mandibular prognathism and retrognathia and consideration of genioplasty: surgical procedures to correct mandibular prognathism and reshaping the chin. Oral Surg Oral Med Oral Pathol 1957;10:677-89. 3. Dal Pont G. Retromolar osteotomy for the correction of prognathism. J Oral Surg 1961;19:42-7. 4. Hunsuck EE. A modified intraoral sagittal splitting technique for the correction of mandibular prognathism. J Oral Surg 1968;26:249-52. 5. Epker B. Modifications in the sagittal osteotomy of the mandible. J Oral Surg 1977;35:157-9. 6. Karas ND, Boyd SB, Sinn DO. Recovery of neurosensory function following orthognathic surgery. J Oral Maxillofac Surg 1990;48:124-34. 7. Lemke RR, Rugh JD, Van Sickels J, Bays RA, Clark GM. Neurosensory differenced after wire and rigid fixation in patients with mandibular advancement. J Oral Maxillofac Surg 2000;58:1354-9. 8. de Beukelaer JG, Smeele LE, van Ginkel FC. Is short-term neurosensory testing after removal of mandibular third molars efficacious? Oral Surg Oral Med Oral Pathol 1998;85:366-70. 9. Jones DL, Wolford LM. Intraoperative recording of trigeminal evoked potentials during orthognathic surgery. Int J Orthod Orthognath Surg 1990;5:167-74. 10. Nakagawa K, Ueki K, Matsumoto N, Takatsuka S, Yamamoto E, Ooe H. The assessment of trigeminal sensory nerve paraesthesia after bilateral sagittal split osteotomy: modified somatosensory evoked potentials recording method. J Craniomaxillofac Surg 1997;25:97-101. 11. Nakagawa K, Ueki K, Takatsuka S, Daisuke T, Yamaomoto E. Somatosensory-evoked potential to evaluate the trigeminal nerve after sagittal split osteotomy. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001;91:146-52. 12. Nakagawa K, Ueki K, Takatsuka S, Yamamoto E. Trigeminal nerve hypesthesia after sagittal split osteotomy in setback cases: correlation of postoperative computed tomography and longterm trigeminal somatosensory evoked potentials. J Oral Maxillofac Surg 2003;61:898-903. 13. Coderre TJ, Katz J, Vaccarino AL, Melzack R. Contribution of central neuroplasticity to pathological pain: review of clinical and experimental evidence. Pain 1993;52:259-85. 14. McQuay HJ, Carroll D, Jadad AR, Glynn CJ, Jack T, Moore RA, et al. Dextromethorphan for the treatment of neuropathic pain: a double-blind randomized controlled crossover trial with integral n-of-1 design. Pain 1994;59:127-33. 15. Ueki K, Nakagawa K, Takatsuka S, Yamamoto E. Plate fixation after mandibular osteotomy. Int J Oral Maxillofac Surg 2001;30:490-6. 16. Bennett AJ, Wastell DG, Barker GR, Blackburn CW, Rood JP. Trigeminal somatosensory evoked potentials: a review of the literature as applicable to oral dysesthesias. Int J Oral Maxillofac Surg 1987;16:408-15. 17. Narita Y, Nagai M, Kuzuhara S. Trigeminal somatosensory evoked potentials before, during and after an inferior alveolar nerve block in normal subjects. Psychiatry Clin Neurosci 1997;51:241-7.
OOOOE Volume 104, Number 2 18. Vriens JPM, Pasman JW. Assessment of trigeminal nerve function by means of short-latency somatosensory evoked potentials after microneurosurgical repair. J Craniomaxillofac Surg 1994;22:156-62. 19. August M, Marchena J, Conady J Kaban L. Neurosensory deficit and functional impairment after sagittal split osteotomy: a longterm follow-up study. J Oral Maxillofac Surg 1998;56:1231-5. 20. Leira JI, Gihuus-Moe OT. Sensory impairment following sagittal splitosteotomy for correction of mandibular retrognathism. Int J Adult Orthodon Orthognath Surg 1991;6:161-7. 21. Fujioka M, Akiyoshi H, Fuji T. Comparative study of inferior alveolar distribution restoration after sagittal split osteotomy by means of bicortical versus monocortical osteosynthesis. Plast Reconstr Surg 1998;102:37-41. 22. Takeuchi T, Furusawa K, Hirose I. Mechanism of transient mental nerve paraesthesia in sagittal split mandibular ramus osteotomy. Br J Oral Maxillofac Surg 1994;32:105-8. 23. Merrill RG. Further studies in decompression for inferior alveolar nerve injury. J Oral Surg 1966;24:233-8.
Hashiba et al. 185 24. Teerijoki-Oksa T, Jääskeläinen SK, Forssell K, Forssell H, Vähätalo K, Tammisalo T, et al. Risk factors of nerve injury during mandibular sagittal split osteotomy. Int J Oral Maxillofac Surg 2002;31:33-9. 25. Posnick JC, Al-Qattan MM, Stepner NM. Alteration in facial sensibility in adolescents following sagittal split and chin osteotomies of the mandible. Plast Reconstr Surg 1996;97:920-7. 26. Upton AR, McComas AJ. The double crush in nerve entrapment syndrome. Lancet 1973;2: 359-62. Reprint requests: Yukari Hashiba, DDS Department of Oral and Maxillofacial Surgery Graduate School of Medicine Kanazawa University 13-1 Takaramachi Kanazawa 920-8641, Japan [email protected]