One-year assessment of surgical outcomes in Class III patients using cone beam computed tomography

Abstract

The purpose of this study was to apply a novel method to evaluate surgical outcomes at 1 year after orthognathic surgery for Class III patients undergoing two different surgical protocols. Fifty patients divided equally into two groups (maxillary advancement only and combined with mandibular setback) had cone beam computed tomography (CBCT) scans taken pre-surgery, at splint removal, and at 1-year post-surgery. An automatic cranial base superimposition method was used to register, and shape correspondence was applied to assess, the overall changes between pre-surgery and splint removal (surgical changes) and between splint removal and 1-year post-surgery at the end of orthodontic treatment (post-surgical adaptations). Post-surgical maxillary adaptations were exactly the same for both groups, with 52% of the patients having changes >2mm. Approximately half of the post-surgical changes in the maxilla for both groups were vertical. The two-jaw group showed significantly greater surgical and post-surgical changes in the ramus, chin, and most of the condylar surfaces (P<0.05). Post-surgical adaptation on the anterior part of the chin was also more significant in the two-jaw group (P<0.05). Regardless of the type of surgery, marked post-surgical adaptations were observed in the regions evaluated, which explain the adequate maxillary-mandibular relationship at 1-year post-surgery on average, with individual variability.

Fig. 1

Magnitude of displacement is shown by the color map from green (0 mm) to red (5 mm). The directionality is expressed by the vector arrows.

Fig. 2

Regions of interest selected for the study: 1, maxilla; 2, right and left condyle posterior surface; 3, right and left condyle medial pole; 4, right and left condyle lateral pole; 5, right and left condyle superior surface; 6, right and left posterior border ramus; 7, anterior part of the chin; 8, inferior border of the mandible.

Fig. 3

Percentage of patients with changes (>2 mm and <−2 mm) between pre-surgery and splint removal (S1) for each anatomic region. Maxilla-only group.

Fig. 4

Percentage of patients with changes (>2 mm and <−2 mm) between splint removal and 1 year post-surgery (S2) for each anatomic region. Maxilla-only group.

Fig. 5

Example of condylar displacement in a maxilla-only surgery patient. 1 and 2: semi-transparency of condylar changes in two different superimpositions. In 1 the condyle is moved postero-superiorly, and in 2 the condyle has returned to approximately the original position. A: condyle model of T1 and vectors showing changes to T2. B: condyle model of T2 and vectors showing changes to T3. C: only the vectors from image B showing its inward movement. This patient had an approximate 2.5 mm of movement in opposite directions for A and B at the posterior and superior condylar surfaces.

Fig. 6

Percentage of patients with changes (>2 mm and <−2 mm) between pre-surgery and splint removal (S1) for each anatomic region. Two-jaw group.

Fig. 7

Percentage of patients with changes (>2 mm and <−2 mm) between splint removal and 1 year post-surgery (S3) for each anatomic region. Two-jaw group.

Fig. 8

Two-jaw surgery patient. A: posterior view of the ramus showing lateral displacement. B: superior view of the condyle of the same patient showing its rotation. Note that the medial pole is displaced more than the lateral pole for surgical movements and post-surgical adaptation.

Fig. 9

Gonial angle pushed back after surgery and returning to its initial position.

Fig. 10

Example of maxillary vertical relapse. A and B: vectors representing forward and downward movement of the maxilla from T1 to T2. C and D: vectors from T2 to T3 showing that the post-surgical adaptation was mostly vertical (approximately 4 mm).

Fig. 11

Clockwise rotation after surgery due to maxillary repositioning and counterclockwise rotation after maxillary post-surgical adaptation.