Anteroposterior Discrepancies

Correction of significant skeletal discrepancies requires either modification of facial growth, dentoalveolar compensation, or orthognathic surgery. Selection and timing of the appropriate treatment alternative is often based upon the extent of the jaw discrepancy in combination with the presence or absence of favorable growth. The plan selected carries with it the expectation by both the clinician and the patient that the final outcome will be a stable, well-functioning occlusion with a favorable aesthetic outcome.

This chapter will focus on the orthognathic procedures commonly used to correct anteroposterior skeletal deformities with particular emphasis on posttreatment stability.

Class II Malocclusion: Mandible Moved Forward with Mandibular Plane Maintained or Rotated Clockwise

Since the primary etiology of the Class II malocclusion is mandibular retrognathia, the most common orthognathic procedures used in the correction is the bilateral sagittal split osteotomy (BSSO) with rigid internal fixation and distraction osteogenesis (DO). Accordingly, these two procedures will be the focus of this section dealing with the advancement or lengthening of the mandible in the correction of mandibular retrognathia.

Retrospective Studies

Twenty nongrowing subjects who underwent sagittal ramus osteotomies and rigid fixation were examined by Kirkpatrick et al. (1987). Cephalograms were analyzed before, immediately after, and at least 6 months following surgery to evaluate skeletal stability. A mean horizontal relapse of 0.42 mm (8%) and a mean vertical increase in lower face height of 0.2 mm were found 6 months after surgery. Both were statistically insignificant. The mean backward rotation of the mandible of 0.55 degrees found 6 months after surgery was statistically significant but considered to be clinically insignificant. Kirkpatrick and colleagues concluded that surgical mandibular advancement with rigid fixation is a very reliable and stable procedure.

Forty-three patients who underwent surgical lengthening of the mandible using an inverted L osteotomy, bone grafting, and rigid internal fixation between the mandibular segments were evaluated by Barer et al. (1987). This was a retrospective cephalometric analysis for longitudinal skeletal and dental changes. Postoperative response (mean 1 year, 9 months) was found to demonstrate a high level of stability with some individual variation. No propensity for relapse was observed in any postoperative time interval. Condylar repositioning postoperatively appeared to be an important factor in those patients who exhibited any relapse tendency. They stated that overall postoperative stability of this external surgical/fixation technique appeared to be significantly improved compared with previously documented techniques.

Witt (1991) evaluated the long-term stability of intentionally increasing lower anterior face height with mandibular sagittal split osteotomies. During the presurgical orthodontic phase, the mandibular curve of Spee was maintained to ensure the clockwise rotation of the distal segment with maximum increase in facial height during surgery. Lateral cephalometric radiographs were taken and evaluated on 24 adult Class II patients at the following time intervals: before surgery, following surgery, and at a mean of 4 years, 6 months posttreatment. Witt found that a statistically significant increase in lower anterior facial height took place and that this increase in facial height was determined to be statistically stable long term.

A retrospective cephalometric analysis for rotational and linear stability of the proximal and distal segments of the mandible was conducted by Knaup, Wallen & Bloomquist (1993) in 41 patients who underwent bilateral sagittal ramus osteotomy for large mandibular advancements. The patients were grouped by the number of screws used in fixation, three versus four 2-mm bicortical screws, and matched for the amount of advancement measured from changes in mandibular body length. The group with four fixation screws did receive significantly larger advancements relative to the cranial base than did the group with three screws. However, the pattern of postoperative change was similar for the two groups. There was no higher rate of relapse seen in those patients with high mandibular plane angles, genioplasties, mandibular constriction with symphyseal osteotomy, or open bites preoperatively, nor did the number of screws used in fixation affect changes seen in those patients.

Bailey, Cevidanes & Proffit (2004) evaluated data from the University of North Carolina Dentofacial Program containing over 1,400 patients with at least 1 year posttreatment follow-up. They found that mandibular advancement in patients with short or normal face height and less than 10 mm of advancement is one of the two most stable orthognathic procedures, along with superior repositioning of the maxilla. They stated that both these procedures can be highly stable, defined as more than 90% chance of less than 2-mm change at landmarks and almost no chance of more than 4 mm of change during the first postsurgical year.

A study to identify contributing factors associated with skeletal relapse by analyzing cephalometric changes after bilateral sagittal split osteotomy for advancement was published by Eggensperger et al. (2004). The study included 30 consecutive patients treated with mandibular advancement with a mean age of 23 years. Radiographs taken immediately before surgery, at 1 week, and at 14 months were evaluated. The sample was further divided into hyper- and hypodivergent facial patterns. Measured at B point, skeletal relapse was 1.3 mm (30%) after mean advancement of 4.4 mm. The magnitude of the surgical movement correlated with skeletal relapse. Eggensperger and colleagues found, however, that the correlation was not linear. Advancement of greater than 7 mm was associated with an increased tendency to relapse. The hyperdivergent retrognathic patients had a 30% higher relapse rate, whereas patients with hypodivergent facial patterns showed less relapse.

Prospective Studies

A prospective comparison of skeletal stability following BSSO advancement of the mandible fixed with titanium or biodegradable bicortical screws was published by Ferretti & Reyneke (2002). Forty consecutive patients underwent mandibular advancement, with BSSO performed using a standardized technique. In 20 patients, rigid fixation was achieved by means of titanium bicortical screws; the other 20 patients were fixed with biodegradable copolymer screws made of poly-L-lactic acid (82%) and polyglycolic acid (18%). Lateral cephalograms were obtained 1 week preoperatively, 1 week postoperatively, and after a minimum of 6 months postoperatively. Relevant skeletal points were traced and digitized to evaluate 2-D skeletal change. They found that there was no statistically significant difference in long-term stability between the two groups.

A prospective study was conducted by Borstlap et al. (2004) involving a 2-year follow-up on a group of patients who underwent BSSO for advancement (n = 222) of the mandible and who were treated in seven institutions following the same treatment protocol. They found that the mean skeletal relapse at pogonion of the whole group after 2 years was 0.9 mm. They also reported a relationship between the amount of advancement and relapse. The tendency for both horizontal and vertical movement was the same; the larger the surgery effect, the larger the relapse. Finally, they noted that patients with a high mandibular plane angle may be more prone to relapse.

Randomized Trials

Ow and Cheung (2009a) also conducted a randomized controlled trial comparing the skeletal stability of bilateral sagittal split osteotomy (BSSO) and mandibular distraction osteogenesis (DO) for moderate mandibular advancement. Their trial consisted of 14 Class II patients with mandibular hypoplasia requiring mandibular advancement of between 6 and 10 mm. They were randomized into two groups for either BSSO or DO. Serial lateral cephalographs were taken at 2 weeks, 6 weeks, 6 months, and 12 months following surgery for the assessment of skeletal stability. They found no significant difference in horizontal or vertical skeletal relapse between the two groups at every postoperative time period. They concluded that other patient-related factors need to be considered when selecting techniques.

Reviews

BSSO and DO are the most common techniques currently used to surgically correct mandibular retrognathia. Schreuder et al. (2007) reviewed the literature on these two procedures to determine the differences in response, if any, between them. They stated that some support was found in the literature for DO having advantages over BSSO in the surgical treatment of low and normal mandibular plane angle patients requiring greater than 7 mm of advancement. In all other retrognathic patients, the treatment outcomes of BSSO and DO appeared to be comparable.

A systematic review was done by Joss and Vassalli (2009) to evaluate horizontal relapse and causes in bilateral sagittal split advancement osteotomy with rigid fixation of different types. Twenty-four articles were finally included. Six studies were prospective, and 18 were retrospective. The range of postoperative study records was 6 months to 12.7 years. They found that the short-term relapse for bicortical screws was between 1.5% and 32.7%, for miniplates between 1.5% and 18.0%, and for bioresorbable bicortical screws between 10.4% and 17.4% at point B. The long-term relapse for bicortical screws was between 2.0% and 50.3%, and for miniplates between 1.5% and 8.9% at point B. They concluded the bicortical screws of titanium, stainless steel, or resorbable material show little difference regarding skeletal stability compared to miniplates in the short-term. A greater number of studies with larger skeletal long-term relapse rates were evident in patients treated with bicortical screws instead of miniplates. They also concluded that patients with a low mandibular plane angle have increased vertical relapse, whereas patients with a high mandibular plane angle have more horizontal relapse. Advancements in the range of 6 to 7 mm or more are predisposed to horizontal relapse.

An evidence-based review comparing the skeletal stability and complications of BSSO and mandibular DO in the treatment of mandibular hypoplasia was published by Ow and Cheung (2009b). Based on the articles evaluating stability, patients undergoing BSSO or DO with an advancement or lengthening of between 6 and 10 mm showed similar mean skeletal relapse of 15.0% and 17.1%, respectively, within postoperative months 6 to 12. Greater skeletal relapse was reported for BSSO patients with high mandibular plane angles compared with normal mandibular plane angle patients (29.6% vs. 11.3%). The authors concluded that both BSSO and DO showed similar relapse rates for mandibular advancements between 6 and 10 mm. Both techniques may also share similar risk factors for skeletal relapse.

Summary

The retrospective studies indicate a relapse rate of 8% to 30%. The prospective studies report larger amounts of relapse with larger surgical movements, and one randomized clinical trial reports that DO and BSSO display comparable stability up to 12 months. The review articles also indicate that larger surgical movements display larger amounts of relapse, with some differences in stability between patients with low and high mandibular plane angles. Overall, mandibular advancement that maintains or increases the mandibular plane angle (distal segment rotated clockwise) appears to be a relatively stable procedure.

Class II Malocclusion: Mandible Moved Forward with Mandibular Plane Rotated Counterclockwise

Historically, open bite closure through counterclockwise rotation of the mandible and intermaxillary wire fixation was discontinued because of the instability associated with this technique. Correction of open bite deformities with maxillary surgical impaction became the standard of care. Currently, the development of rigid internal fixation has allowed clinicians to again close anterior open bite discrepancies in the mandible using bilateral split osteotomies to autorotate the mandibular distal segment counterclockwise. Closure of an anterior open bite through counterclockwise rotation of the mandible offers several advantages. It might be possible to limit surgery to a single jaw, in this case the mandible, rather than using a bimaxillary procedure. Single-jaw surgery would significantly reduce the cost to the patient, making treatment more affordable. Another major advantage is the elimination of the potentially adverse aesthetic changes associated with maxillary LeFort impaction in patients with certain pretreatment facial characteristics. The jury appears to be “still out” regarding the long-term stability of open bite closure in the mandible, but preliminary data suggest that this procedure is at least as stable as maxillary impaction alone (Joondeph & Bloomquist 2004).

Retrospective Studies

A preliminary report on the stability of bilateral sagittal split osteotomy and rigid internal fixation (Oliveira & Bloomquist 1997) to close anterior open bite malocclusion looked at 10 patients who had completed orthodontics and were at least 1 year out of surgery. They were evaluated cephalometrically at three time periods for dental and skeletal changes. They concluded that although their sample was small, their data suggested that the use of bilateral split osteotomy and 2-mm bicortical screws for the closure of anterior open bite is a relatively stable procedure.

A cephalometric study to compare the skeletal stability and the time course of postoperative changes in high-angle and low-angle Class II patients after mandibular advancement surgery was conducted by Mobarak et al. (2001). Their sample consisted of 61 consecutive mandibular retrognathic subjects who were treated with BSSO and rigid fixation. The patients were divided according to the preoperative mandibular plane angle; the 20 patients with the lowest mandibular plane angle (20.8 degrees +/– 4.9) constituted the low-angle group, and the 20 cases with the highest mandibular plane angle (43.0 degrees +/– 4.0) represented the high-angle group. Lateral cephalograms were taken at six time intervals: immediately before surgery, immediately after surgery, 2 and 6 months after surgery, and 1 and 3 years after surgery. Results demonstrated that the high-angle and low-angle groups had different patterns of surgical and postoperative changes. High-angle patients were associated with both a higher frequency and greater magnitude of horizontal relapse. Although 95% of the total relapse took place during the first 2 months after surgery in the low-angle group, high-angle patients demonstrated a more continuous relapse pattern, with a significant proportion (38%) occurring late in the follow-up period.

Frey et al. (2007) investigated predictors of long- and short-term stability of surgical mandibular advancements with bilateral sagittal split osteotomy. They evaluated 127 Class II patients who received mandibular advancement through BSSO with either rigid internal fixation or wire osteosynthesis. Multiple linear regression analyses were done to assess the association of predictor variables with posttreatment horizontal and vertical B-point movement through 2 years. They found that counterclockwise rotation of the mandibular plane angle was associated with greater horizontal and vertical relapse at all time periods except 8 weeks. Wire osteosynthesis, larger advancements, younger age, and genioplasty were significantly associated with relapse. The authors concluded that surgically closing the mandibular plane angle is associated with late horizontal and vertical relapse, whereas fixation type is related to early B-point movement. Large advancements with forward and upward repositioning of the mandible, genioplasty, and young age also pla/>