Evaluation of alveolar nerve function after surgical lengthening of the mandible by a bilateral sagittal split osteotomy or distraction osteogenesis

Abstract

This study compares the effects of bilateral sagittal split osteotomy (BSSO) and distraction osteogenesis (DO) for lengthening the mandible regarding loss of function of the inferior alveolar nerve (IAN). In a retrospective cohort study design, the function of the IAN was tested with a Weinstein monofilament 3.22, 1 year after the surgical procedure in 65 patients (35 BSSO; 30 DO). This was defined as the upper limit for normal function. Of 130 IAN studied (70 BSSO, 54%; 60 DO, 46%), nerve function was disturbed in 23 (18%). In this group, 14 cases (61%) had undergone BSSO and 9 (39%) DO. One-hundred and seven nerves had no neurosensory IAN changes; of these BSSO had been performed in 56 cases (52%) and DO in 51 cases (48%). After eliminating confounding factors, there was no significant difference in the occurrence of neurosensory changes between the treatment options (DO versus BSSO, odds ratio: 1.254 with 95% CI: 0.366–4.300). In conclusion, there was no difference in IAN function between patients treated with BSSO or DO for lengthening the mandible.

Surgical lengthening of the mandible is one of the most commonly performed orthognathic procedures in western Europe. Since the first description of a bilateral sagittal split osteotomy (BSSO) by T rauner and O bwegeser in 1957, there have been several modifications, including D al P ont (1961) and H unsuck (1968). Much has been published on the complications of these procedures, including loss of function of the inferior alveolar nerve (IAN) ranging from 0% to 75% 1 year after surgery . M cCarthy introduced distraction osteogenesis (DO) for lengthening the mandible in 1992. The principle of DO is based on Ilizarov’s experiments in the 1950s . In DO, new bone is generated by gradual distraction of two bony segments after callus formation. New bone is formed along the tension lines, and active histogenesis occurs in tissues including the skin, fascia, blood vessels, nerves, muscles ligament, cartilage and periosteum . There are several reports on the surgical outcome of this procedure . In small, retrospectively described, series of patients, loss of function of the IAN after DO was reported to be low compared with BSSO .

In this study, patients who were treated with BSSO or DO and who suffered a permanent loss of function of the IAN were evaluated and compared with patients from the same cohort without sensory disturbances. Skeletal stability in this group, after more than 1 year, is described by V os et al. . The main goal was to evaluate IAN function in relation to the surgical procedure and compare the results with those in the group without sensory distortion.

Materials and methods

A retrospective cohort study was carried out in 65 patients who underwent a mandibular lengthening procedure between 2001 and 2004. In 30 patients, DO was performed, while a BSSO was carried out in the other 35 patients . Patients and their parents were informed about both procedures, including the reported risks for the alveolar nerve. The decision to use intra-oral DO or BSSO for mandibular advancement primarily depended on the choice of the patient, their parents and the surgeon.

At least 1 year after surgery, the patients were screened for IAN function. Objective screening of the sensibility of the lower lip and chin area was performed with simple neurological tests using cotton swabs, pin prick tests and Semmes Weinstein monofilament 3.22. This filament was chosen as the upper normal limit for the detection threshold in the cutaneous region of the lower lip and chin . The patients were not tested prior to surgery but none reported sensory disturbance before surgery. The separate stimuli of the neurological tests were applied four times to the skin in the area of interest. Right and left side were tested separately. A positive response to a stimulus was scored in cases in which there were at least 75% correct responses out of 4 applied stimuli (3 out of 4 stimuli correct).

In both groups, surgery was performed under general anaesthesia. Preoperatively 2 g Kefzol (cefazoline) and 0.5 mg/kg dexamethasone were given intravenously. Postoperatively another 10 mg dexamethasone was given intravenously after 8 and 16 h.

BSSO

The BSSO was carried out according to Obwegeser/Dal Pont modified by H unsuck . After infiltration of the mucosa with Ultracaine (articaine), an incision and mucoperiosteal flap was performed in the region of the planned osteotomy. Following stripping of the temporalis muscle insertion, the medial site of the mandibular ramus was exposed. A periosteal elevator was then introduced subperiosteally on the medial aspect of the ramus, above the foramen. IAN was identified at the lingula, and care was taken not to overstretch the inferior mandibular nerve. With a Lindemann bur the medial horizontal osteotomy cut was made, just above the lingula and parallel with the occlusal plane. After completion of the oblique and buccal cuts, the lower border of the mandible was cut with the Lindemann bur. The osteotomy of the mandible was carried out using a splitting forceps on the upper border and an elevator on the buccal osteotomy site.

After advancement, a thin interocclusal acrylic splint (wafer) was placed with intermaxillary wire fixation. Titanium miniplates (Synthes GmbH, Solothurn, Switzerland) (Synthes 2.0) with monocortical screws were used for fixation of the fragments ( Fig. 1 ).

Fig. 1
Titanium miniplates with monocortical screws were used for fixation of the fragments.

BSSO

The BSSO was carried out according to Obwegeser/Dal Pont modified by H unsuck . After infiltration of the mucosa with Ultracaine (articaine), an incision and mucoperiosteal flap was performed in the region of the planned osteotomy. Following stripping of the temporalis muscle insertion, the medial site of the mandibular ramus was exposed. A periosteal elevator was then introduced subperiosteally on the medial aspect of the ramus, above the foramen. IAN was identified at the lingula, and care was taken not to overstretch the inferior mandibular nerve. With a Lindemann bur the medial horizontal osteotomy cut was made, just above the lingula and parallel with the occlusal plane. After completion of the oblique and buccal cuts, the lower border of the mandible was cut with the Lindemann bur. The osteotomy of the mandible was carried out using a splitting forceps on the upper border and an elevator on the buccal osteotomy site.

After advancement, a thin interocclusal acrylic splint (wafer) was placed with intermaxillary wire fixation. Titanium miniplates (Synthes GmbH, Solothurn, Switzerland) (Synthes 2.0) with monocortical screws were used for fixation of the fragments ( Fig. 1 ).

Fig. 1
Titanium miniplates with monocortical screws were used for fixation of the fragments.

DO

The mucosa was infiltrated with Ultracaine. After exposing the mandibular body and angle, the buccal osteotomy was made with a Lindemann bur just behind the second molar. The lower border of the mandible was cut. The third molar, if present, was removed. With a fissure bur a cut was made distal to the second molar from buccal to lingual. The mono-directional distractor device (Zurich Distractor, Martin GmbH & Co, Tuttlingen, Germany) was adapted and placed ( Fig. 2 ). After removing the screws and the distractor device the osteotomy was completed. The distractor device was reinstalled in the marked position and fixed on each side with three monocortical screws. The most dorsal screws were placed transcutaneously. Before closure of the wounds, the functioning of the distractor device was checked. After a latency period of 5–7 days, distraction twice a day was started, resulting in a 1.0 mm lengthening per day ( Fig. 3 ). Distraction was continued until a Class I occlusion was achieved and guiding elastics were placed ( Fig. 4 ). After a consolidation period of 8–10 weeks the devices were removed under general anaesthesia.

Fig. 2
The mono-directional distractor device was adapted and placed.

Fig. 3
Panoramic radiograph after corticotomy and placement of the disractors.

Fig. 4
Distraction continued with 1 mm per day until a Class I occlusion was achieved and guiding elastics were placed.

Data analysis

Student’s t -tests and χ 2 -tests were performed to compare the different variables between the groups. Logistic regression analysis was used to compare the proportion of patients with a neurosensory IAN change with patients with normal IAN function between groups and to eliminate possible confounding and effect modification. Statistical analyses were performed with SPSS 16 software.

Results

One hundred and thirty IANs were tested: 70 BSSO (54%); 60 DO (46%) ( Table 1 ). In 23 nerves, the function was disturbed (18%). In this group, 14 cases (61%) had undergone BSSO and 9 (39%) had undergone DO. In the 14 nerves with sensory disturbance in the BSSO group, 3 nerves had complete anaesthesia, in 11 hypoaesthesia/paraesthesia was present. In the DO group with sensory disturbance 2 of the 9 nerves showed complete anaesthesia. In the group with sensory disturbance, the mean age was 33 years. In the group without neurosensory IAN changes, a BSSO had been performed in 56 nerves (52%) and DO in 51 (48%). The mean age in this group was 26 years ( Table 2 ). Although there was a significant difference in gender distribution between the BSSO and DO groups, the sensory disturbances were equally distributed between males and females ( Tables 3 and 4 ). The mean age in the group with sensory changes was significantly higher than in the group with normal nerve function due to a large difference in the age of the female patients ( p = 0.011) ( Table 5 ). For males, the mean advancement was comparable in both groups ( p = 0.141), but for females, the advancement was significantly larger in the group with sensory changes ( p = 0.025) ( Table 6 ). Males were equally at risk as females (odds ratio: 0.968 with 95% CI: 0.376–2.492) and, surprisingly, in the whole group a younger age (<25 years) was not associated with a lower risk of nerve dysfunction (odds ratio: 0.505 with 95% CI: 0.203–1.253). Logistic regression analyses showed that age, gender and advancement were confounding the primary outcome (nerve function) of the study. After eliminating the confounding factors, there was no significant difference in the occurrence of neurosensory changes between both treatment options (DO versus BSSO, odds ratio: 1.254 with 95% CI: 0.366–4.300) ( Table 7 ).

Table 1
Patient characteristics.
BSSO (percent) DOG (percent) Total
Patients 35 30 70
Number of nerves 70 60 130
Male, number of nerves 14 (20) 32 (53.3) 46
Female, number of nerves 56 (80) 28 (46.7) 84
Mean age (years) 32.54 21.60
Minimum age (years) 19 16
Maximum age (years) 53 44
Mean advancement (mm) 7.37 8.00

Table 2
Age distribution; normal versus sensory disturbed patients.
Statistics
Normal N = 107
Mean age 26
Median 21
Minimum 16
Maximum 53
Sensory disturbed N = 23
Mean age 33
Median 28
Minimum 17
Maximum 53
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Feb 8, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Evaluation of alveolar nerve function after surgical lengthening of the mandible by a bilateral sagittal split osteotomy or distraction osteogenesis
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