The hierarchy of stability and predictability in orthognathic surgery with rigid fixation: an update and extension

Abstract

A hierarchy of stability exists among the types of surgical movements that are possible with orthognathic surgery. This report updates the hierarchy, focusing on comparison of the stability of procedures when rigid fixation is used. Two procedures not previously placed in the hierarchy now are included: correction of asymmetry is stable with rigid fixation and repositioning of the chin also is very stable. During the first post-surgical year, surgical movements in patients treated for Class II/long face problems tend to be more stable than those treated for Class III problems. Clinically relevant changes (more than 2 mm) occur in a surprisingly large percentage of orthognathic surgery patients from one to five years post-treatment, after surgical healing is complete. During the first post-surgical year, patients treated for Class II/long face problems are more stable than those treated for Class III problems; from one to five years post-treatment, some patients in both groups experience skeletal change, but the Class III patients then are more stable than the Class II/long face patients. Fewer patients exhibit long-term changes in the dental occlusion than skeletal changes, because the dentition usually adapts to the skeletal change.

Figures

Figure 1

The extended hierarchy of stability, showing relative stability during the first postsurgical year.

Figure 2

A composite tracing for 42 patients in whom the maxilla was moved up >2 mm. With this surgical movement and rigid fixation, there is almost no relapse tendency. The tracing shows a small upward movement from immediate postsurgery to one year that is due to removal of the surgical splint.

Figure 3

A composite tracing for 40 patients in whom the mandible was advanced >2 mm. The only significant change is a shortening of ramus height due to remodeling at the gonial angle, which is expected after a ramus osteotomy.

Figure 4

The percentage of patients with horizontal change in maxillary cephalometric landmark positions after forward movement of the maxilla and rigid fixation. Note that 20% of this group show mild relapse (2–4 mm backward movement of anterior maxillary landmarks), with almost no chance of clinically problematic relapse (>4 mm). Forward movement of mandibular landmarks reflects splint removal and a tendency for the maxilla to move upward if it was moved down as well as advanced.

Figure 5

Stability after the combination of superior repositioning of the maxilla and advancement of the mandible: a, the percent of the patients with changes in the horizontal position of landmarks in the first 6 weeks postsurgery; b, the percent with changes from 6 weeks to 1 year.

Figure 6

The percentage of patients with changes in landmark positions after two-jaw surgery to correct jaw asymmetry, using rigid fixation: a, vertical; b, transverse. Vertically asymmetric change in the position of the maxilla is quite stable. The dental midlines and chin show >2 mm transverse relapse in about one-third of the patients.

Figure 7

The percent of patients with changes following transverse expansion of the maxilla with segmental osteotomy. Greater expansion usually occurs at the molars than premolars with this procedure, and the percentage with relapse also is greater at the molars.

Figure 8

Changes from one year to 5 years after mandibular advancement: a, the percentage of patients with changes in the horizontal position of landmarks; b, the percentage with changes in vertical position. Points B and Pg are as likely to move forward as backward long-term. Beyond one year postsurgery, one-third of the patients continue to experience backward and upward movement of gonion, indicating a loss of bone at the gonial angle as remodeling continues, but 20% have a net gain.

Figure 9

Changes from one year to 5 years after superior repositioning of the maxilla: a, the percentage of patients with changes in the vertical position of skeletal and dental landmarks; b, the percentage with changes in the vertical position of soft tissue landmarks. Although the long-term position of the maxilla is quite stable in 80% of the patients, 20% experience a downward movement, and when the downward movement occurs, parallel changes in the facial soft tissues occur.

Figure 10

Changes from one to 5 years after two-jaw surgery for Class II problems: a, the percentage of patients with changes in the horizontal position of landmarks; b, the percentage of patients with changes in linear dimensions and the mandibular plane angle (TFH = total face height). Note that one-third of the patients experienced >2 mm backward movement of points B and Pg, and half of these had >4 mm decrease, and one-third had >2 mm downward movement of the maxilla, but overjet increased >2 mm in only 8% and >4 mm in none. This reflects a forward movement of the teeth relative to the mandible in compensation for the skeletal change. The Co-Pg distance decreased >2 mm in 12%, with no decrease >4 mm.

Figure 11

Composite superimpositions of a group of 19 patients with mandibular setback done before 1995. Note the backward movement of the ramus from pre- to post-surgery, and the return of the inclination of the ramus to its original position at one year – which carries the chin forward. Controlling the inclination of the ramus at surgery seems to largely eliminate relapse after mandibular setback.

Figure 12

The percentage of patients with changes in the vertical position of the maxilla from immediate post-surgery to one year. Note that despite rigid fixation, nearly two-thirds of the patients had >2 mm upward movement of the anterior maxilla landmarks and 20% had >4 mm change. Moving the maxilla down is much more stable when a simultaneous ramus osteotomy is done (the preferred approach at UNC) or when a rigid interpositional graft is placed.