Predictability of maxillary positioning: a 3D comparison of virtual and conventional orthognathic surgery planning

Accuracy of maxillary repositioning surgery in teaching hospitals using conventional model surgery

PURPOSE

The aim of this study was to assess the accuracy of maxillary repositioning surgery in teaching hospitals using conventional model surgery.

MATERIALS AND METHODS

A total of 73 patients undergoing single-piece LeFort I osteotomies in the maxilla and bilateral sagittal split osteotomies in the mandible were included in the study. Preoperative and immediate postoperative cone-beam CT were compared in computer software (Dolphin3D©). Maxillary landmarks relative to the vertical and horizontal reference lines were evaluated. The difference between the planned and achieved maxillary positions was measured. Distance error in millimeters and achievement ratio (achieved displacement/planned displacement*100) were calculated for different maxillary movements.

RESULTS

Midline correction and advancement were the most accurate movements with an overall mean distance error of 0.53 mm and 0.63 mm respectively while posterior impaction and setback were the least accurate movements with 1.38 mm and 1.76 mm mean discrepancies, respectively. A significant difference was observed only in setback movement regarding the discrepancy value (P < .05). Although setback and down-graft movements tended to under-correction, all other movements were overcorrected. As the magnitude of maxillary movements increases, the accuracy decreases. In severe displacements (≥ 8 mm), the accuracy declines significantly (P < .05).

CONCLUSION

Classic cast surgery and manually fabricated intermediate splints in teaching hospitals yield accurate and acceptable results in the majority of cases (84.6%). The accuracy of maxillary repositioning decreases as the magnitude of displacement increases.

OrthoCalc: The six degrees of freedom measurement workflow of rotational and displacement changes for maxilla positioning evaluation

BACKGROUND

This study is undertaken to establish the accuracy and reliability of OrthoCalc, a 3D application designed for the evaluation of maxillary positioning.

METHODS

We registered target virtual planned models, maxillary models from pre-operative and post-operative CT scans, and post-operative intra-oral scans to a common reference system, allowing for digital evaluation. To assess rotational changes, we introduced a novel measurement method based on virtual cuboid models. Displacement errors were calculated based on proposed registration matrices. We also compared OrthoCalc to established commercial medical software as a benchmark.

RESULTS

Statistical significance calculated showed no significant differences between OrthoCalc and commercial software. the biggest error of 0.04 degree in rotation change was found in the yaw. A maximum displacement change of 0.75 mm was found in the X direction.

CONCLUSIONS

Our study validates OrthoCalc as a precise and reliable tool for assessing maxillary position changes with six degrees of freedom in orthognathic surgery, endorsing its clinical utility.

[Comparison of the virtual surgical planning position of maxilla and condyle with the postoperative real position in patients with mandibular protrusion]

OBJECTIVE

To compare the difference between virtual surgical planning (VSP) position and postoperative real position of maxilla and condyle, and to explore the degree of intraoperative realization of VSP after orthognathic surgery.

METHODS

In this study, 36 patients with mandibular protrusion deformity from January 2022 to December 2022 were included. All the patients had been done bilateral sagittal split ramus osteotomy (SSRO) combined with Le Fort Ⅰ osteotomy under guidance of VSP. The VSP data (T0) and 1-week postoperative CT (T1) were collected, the 3D model of postoperative CT was established and segmented into upper and lower jaws in CCMF Plan software. At the same time, accor-ding to the morphology of palatal folds, the virtual design was registered with the postoperative model, and the unclear maxillary dentition in the postoperative model was replaced. Then the postoperative model was matched with VSP model by registration of upper skull anatomy that was not affected by the operation. The three-dimensional reference plane and coordinate system were established. Selecting anatomical landmarks and their connections of condyle and maxilla for the measurement, we compared the coordinate changes of marker points in three directions, and the angle changes between the line connecting the marker points and the reference plane to analyze the positional deviation and the angle deviation of the postoperative condyle and maxilla compared to VSP.

RESULTS

The postoperative real position of the maxilla deviates from the VSP by nearly 1 mm in the horizontal and vertical directions, and the anteroposterior deviation was about 1.5 mm. In addition, most patients had a certain degree of counterclockwise rotation of the maxilla after surgery. Most of the bilateral condyle moved forward, outward and downward (the average distance deviation was 0.15 mm, 1.54 mm, 2.19 mm, respectively), and rotated forward, outward and upward (the average degree deviation was 4.32°, 1.02°, 0.86°, respectively) compared with the VSP.

CONCLUSION

VSP can be mostly achieved by assistance of 3D printed occlusal plates, but there are certain deviations in the postoperative real position of maxilla and condyle compared with VSP, which may be related to the rotation axis of the mandible in the VSP. It is necessary to use patient personalized condylar rotation axis for VSP, and apply condylar positioning device to further improve surgical accuracy.

The impact of orthodontic-surgical treatment on facial expressions-a four-dimensional clinical trial

OBJECTIVE

The objective of this clinical trial was to compare facial expressions (magnitude, shape change, time, and symmetry) before (T0) and after (T1) orthognathic surgery by implementing a novel method of four-dimensional (4D) motion capture analysis, known as videostereophotogrammetry, in orthodontics.

METHODS

This prospective, single-centre, single-arm trial included a total of 26 adult patients (mean age 28.4 years; skeletal class II: n = 13, skeletal class III: n = 13) with indication for orthodontic-surgical treatment. Two reproducible facial expressions (maximum smile, lip purse) were captured at T0 and T1 by videostereophotogrammetry as 4D face scan. The magnitude, shape change, symmetry, and time of the facial movements were analysed. The motion changes were analysed in dependence of skeletal class and surgical movements.

RESULTS

4D motion capture analysis was feasible in all cases. The magnitude of the expression maximum smile increased from 15.24 to 17.27 mm (p = 0.002), while that of the expression lip purse decreased from 9.34 to 8.31 mm (p = 0.01). Shape change, symmetry, and time of the facial movements did not differ significantly pre- and postsurgical. The changes in facial movements following orthodontic-surgical treatment were observed independently of skeletal class and surgical movements.

CONCLUSIONS

Orthodontic-surgical treatment not only affects static soft tissue but also soft tissue dynamics while smiling or lip pursing.

CLINICAL RELEVANCE

To achieve comprehensive orthodontic treatment plans, the integration of facial dynamics via videostereophotogrammetry provides a promising approach in diagnostics.

TRIAL REGISTRATION NUMBER

DRKS00017206.

Managing Predicted Post-Orthognathic Surgical Defects Using Combined Digital Software: A Case Report

For facial abnormalities, recent developments in virtual surgical planning (VSP) and the virtual design of surgical splints are accessible. Software companies have worked closely with surgical teams for accurate outcomes, but they are only as reliable as the data provided to them. The current case's aim was to show a fully digitized workflow using a combination of three digital software to correct predicted post-upward sliding genioplasty defects. To reach our goal, we presented a 28-year-old man with long-face syndrome for orthodontic treatment. Before orthognathic surgery, a clinical and paraclinical examination was performed. For a virtual surgical plan, we used the dedicated surgical planning software NemoFab (Nemotec, Madrid, Spain) and Autodesk MeshMixer (Autodesk Inc., San Rafael, CA, USA). To create the design of the digital guides, DentalCAD 3.0 Galway (exocad GmbH, Darmstadt, Germany) and Autodesk MeshMixer (Autodesk Inc., San Rafael, CA, USA) were used. The patient had undergone bilateral sagittal split osteotomy in addition to Le Fort 1 osteotomy and genioplasty, followed by mandible base recontouring ostectomy. Stable fixation was used for each osteotomy. Based on our case, the current orthognathic surgery planning software was not able to perform all the necessary operations autonomously; therefore, future updates are eagerly awaited.