Refining orthognathic outcomes: 3D accuracy with patient-specific implants for facial asymmetry correction

Abstract

This study evaluated the three-dimensional accuracy of maxillary and chin repositioning using patient-specific implants (PSIs) in non-syndromic patients with facial asymmetry. A retrospective cohort study was conducted at the University Hospital of Geneva between 2018 and 2023. Three-dimensional pre-operative planning and post-operative CT or CBCT scans of 21 patients with facial asymmetry were analyzed. Using 3D Slicer, images were imported and segmented, and the anterior surfaces of the maxilla and chin were extracted via Meshmixer. CloudCompare software calculated the distance between post-operative and pre-operative surface models using one million sample points. Boxplots visualized the distribution of signed Euclidean distances, and accuracy was assessed based on the proportion of values within ±2 mm. The mean difference between planned and actual post-operative surfaces was -0.9 mm for the maxilla and -0.5 mm for the chin. The proportion of values within the accuracy threshold was for the maxilla >90 % in 13 patients (62 %), 80-90 % in 5 patients (23.8 %), 50-80 % in 2 patients (9.5 %), and <50 % in 1 patient (4.8 %). For the chin, >90 % accuracy was observed in 7 patients (58.4 %), 50-80 % in 4 patients (33.3 %), and <50 % in 1 patient (8.3 %). These findings suggest that PSIs provide accurate maxillary and chin repositioning, with higher precision in maxillary repositioning. This study highlights the potential of PSIs to improve surgical outcomes in orthognathic procedures for facial asymmetry cases.

Keywords: CAD-CAM technology; Facial asymmetry; Orthognathic surgery; Patient-specific implants.

Figure 1

Intraoperative view of guided Le Fort I osteotomy. A) A cutting and drilling guide temporarily secured to the maxillary bone with monocortical screws. B) Maxillary repositioning and fixation using patient-specific 3D-printed plates.

Figure 2

Intraoperative view of guided genioplasty. A) A cutting and drilling guide temporarily secured to the mandibular bone with monocortical screws. B) Chin repositioning and fixation using patient-specific 3D-printed plates.

Figure 3

Bone segmentation of post-operative CT Images by using the Segment Editor module of 3D Slicer software.

Figure 4

Extraction of the anterior surface of the previously segmented maxilla by using Meshmixer software.

Figure 5

Post-operative surface models were registered onto pre-operative planning models using the SlicerCMF module in 3D Slicer. Initially, landmark-based transformation (3D rotation and translation) aligned the post-operative model with the reference bony segment. Manual adjustment refined the alignment for optimal superimposition, and the final transformation was applied to the target bony segment.

Figure 6

Distance between post-operative and pre-operative (reference) surface models was calculated using CloudCompare software. One million sample points were randomly distributed on the post-operative model, with the nearest triangle on the preoperative model identified for each. Signed Euclidean distances quantified surgical accuracy relative to the pre-operative planning.

Figure 7

Graphics showing the distribution of values between post-operative and pre-operative maxillary surface models.

Figure 8

Graphics showing the distribution of values between post-operative and pre-operative chin surface models.

Figure 9

Boxplots of differences between the planned and final results in the 21 patients who underwent maxillary surgery. Mean values (X) are displayed.

Figure 10

Boxplots of differences between the planned and final results in the 12 patients who underwent chin surgery. Mean values (X) are displayed.