Bilateral sagittal split osteotomy (BBSO) is the most frequent used surgical technique for correcting mandibular deformities and characterized as a highly stable and predictable surgical orthognatic procedure for mandibular advancement [1,2]. A positive correlation between the amount of advancement and relapse has been described in several studies [3-5] and it has been concluded that an advancement of 5 mm or more could predispose to horizontal relapse [6,7].

To minimize horizontal skeletal relapse, BSSO in combination with postoperative skeletal intermaxillary fixation has been advocated [8,9]. However, studies assessing skeletal relapse after BSSO with rigid internal fixation (RIF) and skeletal elastic intermaxillary fixation (IMF) compared to no skeletal elastic IMF has never previously been conducted.

Therefore, the objective of the present study is to estimate the amount of skeletal relapse after single-jaw bilateral sagittal split osteotomy advancement in combination with postoperative skeletal elastic intermaxillary fixation versus no skeletal intermaxillary fixation.

Patients

From January 2008 to December 2011 a total of 92 consecutively (75 females and 17 males) patients were treated at the Department of Oral and Maxillofacial Surgery, Aalborg University Hospital with BSSO to correct Class II malocclusion. Surgery was performed after the rate of growth was determined to have declined to adult levels. BSSO was performed by 3 senior maxillofacial surgeons and no concomitant surgical procedures were performed.

The inclusion criteria were:

Preoperatively the patients were evaluated and the indication for postoperative skeletal elastic IMF was assessed by the surgeon based on the following criteria: 1) preorthodontic open bite, 2) tongue habits, 3) morphological slender condyles estimated radiographically. The skeletal elastic IMF was activated starting one week postoperatively by connecting the 2 wires with 3 elastics and worn 24 hours a day for the following 8 weeks. The patients were allowed to deactivate the IMF 3 times a day for 1 hour duration. In addition the elastics were used for further 8 weeks nocturnal.

A total of 66 patients were excluded from the study due to:

Finally 26 patients were included in the study. Thirteen patients were postoperatively treated with skeletal elastic IMF and 13 patients were treated without IMF (Table 1).

Description of procedures

Preoperatively

All patients were seen approximately 14 days preoperatively for the final treatment planning by the responsible surgeon. The treatment plan was conducted by a clinical evaluation of the patient [10], dental cast models, standard lateral cephalometric radiographs (T1/preoperative), and surgical imaging program (Dolphin Imaging & Management Solutions and Patterson Technology, Chatsworth, CA, USA). Derived from these registrations the occlusal splint was fabricated.

Surgical technique

The surgical procedure was conducted in general anaesthesia with nasotracheal intubation, supplemented by local anaesthesia. Initially the intraoperative splint was ligated to the maxillae, before BSSO was performed according to the modified method presented by Hunsuck [11]. The distal segment of the mandible was positioned in the wafer and temporary IMF was initiated by 0.4 mm wires and rubber bands, before the proximal segment was seated by hand. RIF was performed at the vertical osteotomy line using L-shaped, Y-shaped or 2 straight plates and 5 mm screws (Stryker Corporate, Kalamazoo, Mi, USA). The type of fixation was chosen by an individual preference of the surgeon. At the anterior part of the ramus of the mandible 2-holes plate was used for ostheosynthesis. Finally the temporary IMF and the intraoperative wafer were removed.

Preoperatively allocated to postoperative skeletal elastic IMF had a 0.6 mm ligature inserted subcortical in the symphysis region and the spina nasalis anterior by a vestibular approach (Figure 1). The ligature from the upper and lower jaw entered the oral cavity through the previously addresses incisions and were cut and bent hook-shaped at the level of the brackets. Finally the mucosa was sutured with resorbable sutures.

Follow-up regimen

The patients were included in a maintenance program involving 1 day (T2/baseline), 1 week, 3 weeks, 8 weeks, 6 months and 18 months (T3/follow-up) postoperatively follow-up at the Department of Oral and Maxillofacial Surgery, Aalborg, Denmark, respectively. Additionally, the patients were included in an individual maintenance program by their orthodontist.

Outcome measures

The primary outcome measures were:

The secondary outcome measures were:

Standard lateral cephalometric radiographs were obtained 14 days preoperatively (T1), immediately postoperatively (T2) (Figure 2), and 18 months (T3) after surgery. Tracing of the digitized radiograph was performed on a personal computer (Por-DiosW, Institute of Orthodontic Computer Science, Middelfart, Denmark) [13], by one calibrated examiner (JH). The correction of magnification was based upon the known distance of the ruler. Magnification, brightness, contrast, and gamma adjustment were used for image enhancement.

An XY-coordinate system was created on the radiograph using the cephalometric Sella-Nasion-line (SN-line) rotated down 7° anteriorly [14,15] as the x axis, and a vertical plane perpendicular to it through sella as the y axis, so that changes in landmark locations were registered as x, y coordinates.

Furthermore B-point, Pog, gonion (Go), gnathion (Gn) were also registered. Mandibular plane angle (MP-angle) was defined as the angle between the SN-line and the Gonion-Gnathion-line (Mandibular plane) [12].

Statistical analysis

Data management and analysis including calculation of descriptive statistics were performed using Excel (Microsoft, Redmond, WA, USA) and Stata (StataCorp, College Station, Texas, USA). The results were reported by proportions (%), mean, and 95% confidens interval (95% CI). Correlations between measurements were evaluated with Spearman rank correlation and analysis of variance was performed evaluating difference between the groups and the vertical facial types.

Skeletal IMF

The mean advancement at B-point and Pog was 6.44 mm and 7.22 mm, respectively (Table 2). Relapse at follow-up at B-point was -0.74 mm and -0.29 mm at Pog. There was no correlation between the amount of advancement and the amount of relapse at B-point (rho = 0.29, P = 0.34) nor Pog (rho = 0.38, P = 0.2) (Figure 3 and 4).

No skeletal IMF

The mean advancement at B-point and Pog was

6.3 mm and 6.45 mm, respectively (Table 2). Relapse at follow-up at B-point was -0.97 mm and -0.86 mm at Pog. There was no correlation between the amount of advancement and the amount of relapse at B-point (rho = 0.35, P = 0.25), but at Pog there was (rho = 0.58, P = 0.04) (Figure 3 and 4).

There was no statistical significant difference between the skeletal IMF group and the no skeletal group regarding advancement nor relapse at B-point or Pog (P > 0.05 for all groups).

Vertical facial type

Seven patients were categorized as short facial types with a relapse of 17% at both B-point and Pog. In the average facial type group, 13 patients were included with a relapse of 13% at B-point and 5% at Pog. The long facial types were characterized with a relapse of 12% at B-point and 7% at Pog (Table 3). The amount of advancement was statistical significant larger in the long facial group than the short and average group (B-point P = 0.01, Pog = 0.047). There was no statistical significant difference between the groups regarding relapse (P > 0.05 for all groups).

No patients were reoperated.

The skeletal stability after mandibular advancement with or without anterior skeletal fixation was retrospectively assessed in 26 patients with a mean follow-up of 19 month. Measurements on standard lateral cephalometric radiographs obtained preoperatively, immediately postoperatively, and after a mean follow-up of 19 month demonstrated no statistically difference in skeletal relapse between the 2 treatment modalities. Additionally no statistical significant (P > 0.05) correlation between the amount of advancement and relapse was presented in the skeletal IMF-group. On the other hand a significant correlation between the amount of advancement and relapse was revealed in the no skeletal IMF group at Pog.

A total mean relapse of 14% and 8% after 19 month follow-up was seen at B-point and Pog, respectively. The relapse percentage demonstrates relative post-operatively stability approximately equal to previously described long-term (≥ 18 months) results [16]. Skeletal stability must be considered a multifactorial phenomenon where factors as the amount of advancement, the type and material of fixation, low and high mandibular plane angle, skills and experience of the surgeon, and proper management of the proximal segment, soft tissue and muscles may contribute to relapse [7]. Challenging patients with slim condyles and/or tongue habits may also add to a higher frequency of relapse [7]. Finally, the length of follow-up period contributes to the variance of relapse which is described in the literature [17].

This study demonstrated diversity in the correlation between the amount of advancement and relapse. The skeletal IMF group demonstrated no correlation between the amount of advancement and relapse while the no skeletal IMF group at Pog revealed a correlation. Diverse conclusions have been reached addressing this topic previously. A minority of studies proved no correlation between the amount of advancement and relapse [17,18], whereas the majority of studies assessing relapse after BBSO demonstrated a positive correlation between the amount of advancement and relapse [7,19]. Relapse being a multifactorial phenomenon as previously addressed may explain the difference of correlation between amount of advancement and relapse.

The long facial type group was advanced more than the other 2 groups, but there was no significant difference (P > 0.05) between the groups regarding relapse. Long facial types have been described to have a higher amount of relapse after BSSO than short facial types [5,17,20-22]. In the present study this was not validated which can be explained by few patients in the 2 groups (7 and 6 patients).

The present study is characterized by some limitations, including the relative small number of patients and a retrospective study design. The inclusion criterion regarding removal of the wafer preoperatively and thereby reduction of included patients was chosen for the most accurate comparison between the baseline and the follow-up radiographs. The study design is weakened by some degree of selection-bias by grouping the patient by an individual assessment in a skeletal IMF group and in a no skeletal IMF group. Direct comparison with other studies involving mandibular advancement in combination with elastic skeletal IMF was not possible since no other studies regarding this topic, to our knowledge, have been published. Technically the placement of the wire is uncomplicated during surgery, but patients described soreness and discomfort using the skeletal IMF, especially from the wire in the mandible.

Single-jaw mandibular bilateral sagittal split osteotomy is characterized as a stable and predictable treatment modality to correct Class II occlusion. This study demonstrated no difference of relapse between the skeletal intermaxillary fixation group and the no skeletal intermaxillary fixation group. Because of selection-bias and the reduced number of patients it still remains inconclusive whether to recommend skeletal intermaxillary fixation or not in the prevention of relapse after mandibular advancement. However, postoperative skeletal elastic intermaxillary fixation may minimize relapse in patients with anterior open bite, tongue habits and slim condyles. Further randomized clinical trials with larger study groups are needed before final conclusions can be made regarding this topic.