Objective:

To prospectively evaluate the incidence of change in light-touch sensation in the innervated area of the lower alveolar nerve after bilateral sagittal-split osteotomy (BSSO) with attention on the time it takes to rebuild the function of the inferior alveolar nerve.

Materials and Methods:

The sample consisted of 30 women and 20 men with a mean age of 22.14 ± 3.30 years. The neurosensory test was conducted with a 20-mm long monofilament of suture material Prolene (3-0) connected to a plastic holder. These tests were performed 1 day before surgery and every 2 weeks during first 2 months after surgery. After that, patients were tested once every month until the end of the first year.

Results:

All patients had a disturbance of light-touch sensation after BSSO, but none of these changes was permanent. The average duration of hypoesthesia was 6.6 ± 1.2 with a range from 4 to 9 months. The average duration of hypoesthesia for women was 6.27 ± 1.0 months, and men had hypoesthesia for 7.1 ± 1.2 months on average. This difference was statistically significant. The two oldest female patients, who were 33 and 37 years old at the time of the surgery, experienced altered sensitivity for only 4 months.

Conclusions:

After BSSO, all patients experienced disturbed light-touch sensation in the innervated area of the lower alveolar nerve. A faster recovery in the oldest patients and a statistically significant difference between the sexes should be interpreted with caution.

Considering the importance of esthetics in recent years, it is not surprising that the number of patients treated with orthognathic surgery is increasing. Bilateral sagittal-split osteotomy (BSSO) is the most commonly performed orthognathic surgical intervention in Europe and the United States.1 BSSO was introduced by Trauner and Obwegeser in 1957 and was modified and improved by Dal Pont et al.2 

This operation is a well-documented, safe, and standardized procedure with impaired postoperative function of the inferior alveolar nerve as the main disadvantage.3 Numbness or altered function of the nerve has been reported to occur in between 9% and 85% of patients,4 but some authors argue that it reaches 100% immediately after surgery.5 Interindividual surgical skills and patient age have been documented to be general factors that influence postoperative nerve function and time to regeneration.6 Genioplasty and a large amount of mandibular movement are also cited as risk factors, especially in older patients.7 

Impaired nerve function also appeared with our patients. This report is a prospective evaluation of the following:

  • Incidence of change in light-touch sensation in the innervated area of the lower alveolar nerve after BSSO

  • Time it takes to rebuild the function of the inferior alveolar nerve

  • Correlation of recovery time and patients' sex and age

Patients and Methods

The study was a prospective clinical trial that lasted from 2005 to 2007. Subjects were recruited from the Department of Oral and Maxillofacial Surgery, University Hospital Dubrava. This study followed the Declaration of Helsinki on medical protocol and ethics, and the Ethical Review Board of University hospital Dubrava approved the study. On the basis of similar studies, it was decided that the sample should consist of 50 patients who were first operated on with BSSO for mandibular setback. Patients who were treated with BSSO and genioplasty were excluded. The same investigator, the orthodontist who treated all the patients, performed all measurements. The sample consisted of 30 women and 20 men, with a mean age of 22.14 ± 3.3 years. The statistical analysis included descriptive statistical methods, Student's t-test for independent samples and a correlation test with a level of statistical significance P < .05.

Surgical Treatment

All patients were operated on by two surgeons who used the same operating methods. The surgical treatment of patients included BSSO modified by Dal Pont for mandibular setback and rigid fixation with three bicortical titanium screws 2 mm in diameter on both sides. Neither a postoperative splint nor intermaxillary fixation was used; only elastics for guidance were used for 3 weeks.

Neurosensory Evaluation

The neurosensory test was conducted with a 20-mm long monofilament of suture material Prolene (3-0) connected to a plastic holder. A maximum applied force of about 2 g is achieved when the monofilament bends on the skin. Several points in the inferior alveolar nerve innervation area were tested. Patients' answers were positive or negative. In the case of one negative response, all tests were considered negative, with no complete recovery. The test is designed for testing large, myelinated, slow adaptive nerve fibers.

The test was conducted by the orthodontist and was always conducted in the same place. The patient was relaxed and lying horizontally on the dental chair with his or her eyes closed. These tests were performed 1 day before surgery and every 2 weeks during first 2 months after surgery. After that, patients were tested once every month until the end of the first year. If the patient did not return for a particular follow-up visit, but displayed negative results on a subsequent visit, then the missed visit was considered negative. On the next control test, patients with positive results were excluded from the study. All preoperative tests were positive.

The study included 50 patients, 30 women and 20 men. The average age of patients was 22.14 ± 3.3 years with a range of 18 to 37 years. Figure 1 shows the homogeneity of the sample with respect to age. Because we planned 14 measurements for each patient, the total number of measurements should have been 700. However, because some patients missed some follow-up visits, a total of 663 (94.71% of planned) measurements were performed. None of the patients was excluded from study because of a positive test after a previously missed control.

Figure 1

Homogeneity of the sample with respect to age.

Figure 1

Homogeneity of the sample with respect to age.

Close modal

All patients had disturbance of light-touch sensation after BSSO, but none of these changes was permanent. The average duration of hypoesthesia was 6.6 ± 1.2 months with a range from 4 to 9 months (Figure 2).

Figure 2

Average duration of hypoesthesia.

Figure 2

Average duration of hypoesthesia.

Close modal

The average duration of hypoesthesia for women was 6.27 ± 1.2 months, and men had hypoesthesia for 7.1 ± 1.0 months on average. On the basis of the t-test, this difference was statistically significant (t  =  −2.507, df  =  48, P  =  .016). Patient age and duration of hypoesthesia were significantly negatively correlated in women (r  =  −0, 394; P  =  0.005). The two oldest female patients, who were 33 and 37 years old at the time of the surgery, experienced altered sensitivity for only 4 months. The correlation was not significant for male patients, but the age range varied from 19 to 24 years.

The percentage of patients with impaired function of the inferior alveolar nerve after BSSO varies considerably in the literature.7 These differences are probably the result of the varying time that had elapsed since surgery when the research was performed and use of nonstandardized testing methods. There are doubts about whether changes in sensation should be tested with subjective or objective tests. Westmark et al.8 showed a positive correlation between tests with the monofilament and subjective tests, which were used in our evaluation of this method. Although some authors consider the recovery of sensation after a lesion of the inferior alveolar nerve to be stabilized 18 months after the trauma, according to general opinion, a 12-month follow-up period is sufficient for nerve regeneration to occur and to enable neurological data monitoring.9 

Our results show the incidence of hypoesthesia to be 100% of patients immediately after surgery, and the quickest recovery was after 4 months. Macintosh et al. as cited by Akal et al.8 reported that 85% of patients had this complication immediately after surgery. Kim et al.11 studied postoperative complications after BSSO and found 96 sensory disturbances among 116 patients. Our findings confirm those of Phillips et al.,5 who found this altered sensation in 99% of patients.

Recovery time also varied in different studies. In the study by Nesari et al.,4 2 months after BSSO, approximately 62% of the sites showed decreased function or numbness. The incidence of disorder decreased to 38% at 6 months, which is lower than the figure reported in other studies. Al-Bishri et al.12 showed 37% of sensory disturbances after sagittal-split osteotomy without genioplasty, but we do not know the exact time after surgery. Unlike other research, frequent checkups in our study provide more precise tracking of functional return. Notably, methods differ in almost all research efforts, and standardization is necessary for a better comparison of results.

Another example that demonstrates the extensive variability of results in studies is permanent sensory dysfunction, which ranges from 0 to 72%.2 With the methods used in this study, all patients had positive neurosensory tests after 9 months.

According to the results of our study, there was a statistically significant difference between the duration of hypoesthesia and sex in all patients. It is interesting to see how these differences emerged. Only two female patients were older than 30 years, and their recovery lasted only 4 months, while the other patients ranged in age from 18 to 26 years. The situation is similar for the correlation of age and duration of hypoesthesia. The two oldest patients had the shortest recovery time, which contradicts the results of other authors.7,13 This result may be a consequence of altered bone structure in the elderly and easier osteotomy procedures, which can lead to less nerve trauma. Given that all patients displayed nerve recovery, we were unable to examine the situation with persistent hypoesthesia after 1 year. Moreover, patients who had genioplasty were not included in the study. In that case, younger patients would have better potential for nerve recovery. However, because only two patients were older than 30 years, caution in interpreting these results is necessary, as is further research with a larger sample.

Methods of this study with very frequent checkups brought new insights about the return of nerve function after orthognathic surgery. We would like to point out that this method with simple neurosensory test only gave insight into the recovery of large, myelinated, slow adaptive nerve fibers. Future research should take into account other types of nerve fibers as well as the difference between left and right side.

  • After BSSO, all patients experienced disturbed light-touch sensation in the innervated area of the lower alveolar nerve. The average time to recovery was 6.6 ± 1.2 months, with a range of 4 to 9 months.

  • Although the study showed the fastest recovery in the oldest patients, caution is needed because of the small number of patients older than 30 years.

  • Statistically significant difference between the sexes should also be interpreted with caution, because this difference may have been caused by the inclusion of patients older than 30 years.

This work has been supported by Croatian Ministry of Science, Education and Sport Grant No. 065-1080057-0429.

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