Korean J Orthod.  2020 Sep;50(5):324-335. 10.4041/kjod.2020.50.5.324.

Positional changes in the mandibular proximal segment after intraoral vertical ramus osteotomy: Surgery-first approach versus conventional approach

• Jung S
• Choi Y
• Park JH
• Jung YS
• Baik HS

• KMID: 2506467
• DOI: http://doi.org/10.4041/kjod.2020.50.5.324

Abstract

Objective
To compare postoperative positional changes in the mandibular proximal segment between the conventional orthognathic surgery (CS) and the surgery-first approach (SF) using intraoral vertical ramus osteotomy (IVRO) in patients with Class III malocclusion.
Methods
Thirty-eight patients with skeletal Class III malocclusion who underwent bimaxillary surgery were divided into two groups according to the use of preoperative orthodontic treatment: CS group (n = 18) and SF group (n = 20). Skeletal changes in both groups were measured using computed tomography before (T0), 2 days after (T1), and 1 year after (T2) the surgery. Three-dimensional (3D) angular changes in the mandibular proximal segment, condylar position, and maxillomandibular landmarks were assessed.
Results
The mean amounts of mandibular setback and maxillary posterior impaction were similar in both groups. At T2, the posterior portion of the mandible moved upward in both groups. In the SF group, the anterior portion of the mandible moved upward by a mean distance of 0.9 ± 1.0 mm, which was statistically significant (p < 0.001). There were significant between-group differences in occlusal changes (p < 0.001) as well as in overjet and overbite. However, there were no significant between-group differences in proximal segment variables. Conclusions: Despite postoperative occlusal changes, positional changes in the mandibular proximal segment and the position of the condyles were similar between CS and SF, which suggested that SF using IVRO achieved satisfactory postoperative stability. If active physiotherapy is conducted, the proximal segment can be adapted in the physiological position regardless of the occlusal changes.

Keyword

Surgery-first approach; Intraoral vertical ramus osteotomy; Computed tomography; Proximal segment

Figure

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  Figure 1 Landmark points used for superimposition of three-dimensional computed tomography images and point P. A, Lambda point. B, The image shows evaluation of the accuracy of superimposition using a color diagram. Errors within 0–0.2 mm are displayed in green, while a difference of > 1.0 mm is shown in gray. C, The prechiasmatic groove point (point P, The vertical and transverse midpoint of prechiasmatic groove). SO, Supraorbital foramen; ZFF, zygomaticofacial foramen.

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  Figure 2 Construction of the co-ordinate system and reference planes. A, Horizontal plane (FH plane) and midsagittal plane (MSP). B, Coronal plane and FH plane. C, Proximal segment plane (PxP) and mandibular plane (MP). R-Po, Right porion (the highest midpoint on the roof of external auditory meatus); L-Or, left orbitale (the lowest point on the infraorbital margin of each orbit); Na, nasion (the junction of the frontal nasal suture at the most posterior on the curve at the bridge of the nose); Go-post, the most prominent posterior point of ramus posterior border; Cp, the most prominent posterior point of condyle.

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  Figure 3 Landmark points for the mandibular segments. A, Distal segment. ① B point; ② MF, mental foramen; ③ F, mandibular foramen. B, Proximal segment. ① MCP, Medial condylar head point; ② LCP, lateral condylar head point; ③ Cp, the most prominent posterior point of condyle; ④ Go-post, the most prominent posterior point of ramus posterior border; ⑤ CON, uppermost point on the condyle.

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  Figure 4 Evaluation of positional changes in the mandibular proximal segment after surgery. A, Coronal change. (+), Lateral flaring from the midsagittal plane (MSP). B, Sagittal change. (+), Clockwise rotation. C, Horizontal change. (+), Outward rotation from MSP.

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  Figure 5 Evaluation of angular changes in the mandibular proximal segment before (T0), immediately after (T1), and 1 year after (T2) treatment with the surgery-first approach (SF) or the conventional orthognathic surgery approach (CS) using intraoral vertical ramus osteotomy. A, Horizontal change. B, Sagittal change. C, Coronal change.

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