Relevance of 3D virtual planning in predicting bony interferences between distal and proximal fragments after sagittal split osteotomy

Modification of Sagittal Split Osteotomy in Class II Asymmetry: Optimizing Bone Contact between Proximal and Distal Segments

BACKGROUND

Computer-assisted surgical simulation (CASS) allows more precise orthognathic surgery. However, few studies have evaluated associations between CASS-designed bilateral sagittal split osteotomy (SSO) and bone contact surface in class II mandibular asymmetry. This study aims to evaluate the effects of using computer-assisted simulation and design modification of SSO to improve bony contact in skeletal class II asymmetry.

METHODS

This retrospective analysis reviewed 28 patients with class II asymmetry who underwent orthognathic surgery, including 15 with modified SSO (group CS) and 13 with conventional SSO (group C). Modified SSO was designed under CASS. Operative characteristics, postoperative outcomes, and complications were collected and compared between the two groups.

RESULTS

Bony contact was found at the distal end of the proximal segment in all group CS patients, while bone gap was noted in all group C patients ( P < 0.05). Moreover, bone graft was used in four group C patients but was not used in all cases in group CS patients ( P < 0.05). A trend toward lower operative time or perioperative bleeding was noted in group CS, but without statistical significance. After 1-year follow-up, inferior alveolar nerve disturbances were noted in two group CS patients and one group C patient. Palpable bone gap with uneven jaw line was noted in two group C patients 1 year after surgery and one patient received fat graft treatment.

CONCLUSION

The simulation-based SSO modification provides appropriate contact surface and eliminates the bone gap between proximal and distal segments in class II asymmetry.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, III.

Enhancing skeletal stability and Class III correction through active orthodontist engagement in virtual surgical planning: A voxel-based 3-dimensional analysis

INTRODUCTION

Skeletal stability after bimaxillary surgical correction of Class III malocclusion was investigated through a qualitative and quantitative analysis of the maxilla and the distal and proximal mandibular segments using a 3-dimensional voxel-based superimposition among virtual surgical predictions performed by the orthodontist in close communication with the maxillofacial surgeon and 12-18 months postoperative outcomes.

METHODS

A comprehensive secondary data analysis was conducted on deidentified preoperative (1 month before surgery [T1]) and 12-18 months postoperative (midterm [T2]) cone-beam computed tomography scans, along with virtual surgical planning (VSP) data obtained by Dolphin Imaging software. The sample for the study consisted of 17 patients (mean age, 24.8 ± 3.5 years). Using 3D Slicer software, automated tools based on deep-learning approaches were used for cone-beam computed tomography orientation, registration, bone segmentation, and landmark identification. Colormaps were generated for qualitative analysis, whereas linear and angular differences between the planned (T1-VSP) and observed (T1-T2) outcomes were calculated for quantitative assessments. Statistical analysis was conducted with a significance level of α = 0.05.

RESULTS

The midterm surgical outcomes revealed a slight but significantly less maxillary advancement compared with the planned position (mean difference, 1.84 ± 1.50 mm; P = 0.004). The repositioning of the mandibular distal segment was stable, with insignificant differences in linear (T1-VSP, 1.01 ± 3.66 mm; T1-T2, 0.32 ± 4.17 mm) and angular (T1-VSP, 1.53° ± 1.60°; T1-T2, 1.54° ± 1.50°) displacements (P >0.05). The proximal segments exhibited lateral displacement within 1.5° for both the mandibular right and left ramus at T1-VSP and T1-T2 (P >0.05).

CONCLUSIONS

The analysis of fully digital planned and surgically repositioned maxilla and mandible revealed excellent precision. In the midterm surgical outcomes of maxillary advancement, a minor deviation from the planned anterior movement was observed.

3D simulation of interosseous interference in sagittal split ramus osteotomy for mandibular asymmetry

BACKGROUND

The purpose of this study was to evaluate the pattern of predicted interosseous interference and to determine the influencing factor to volume of bony interference using a computer-assisted simulation system. This retrospective study recruited 116 patients with mandibular prognathism who had undergone sagittal split ramus osteotomy (SSRO) with or without maxillary osteotomy. The patients were divided into 3 groups according to the amount of menton (Me) deviation: less than 2 mm (Group 1), 2-4 mm (Group 2), and more than 4 mm (Group 3). Changes in the distal segments following BSSRO and the volume of the interosseous interference between the proximal and distal segments were simulated after matching preoperative occlusion and postoperative expected occlusion with the cone-beam computed tomography data. Ramal inclinations and other skeletal measurements were analyzed before surgery, immediately after surgery, and at least 6 months after surgery.

RESULTS

The anticipated interosseous interference was more frequently noted on the contralateral side of chin deviation (long side) than the deviated site (short side) in Groups 2 and 3. More interference volume was predicted at the long side (186 ± 343.9 mm3) rather than the short side (54.4 ± 124.4 mm3) in Group 3 (p = 0.033). The bilateral difference in the volume of the interosseous interference of the osteotomized mandible was significantly correlated with the Me deviation (r =  - 0.257, p = 0.009) and bilateral ramal inclination (r = 0.361, p < 0.001). The predictor variable that affected the volume of the osseous interference at each side was the amount of Me deviation (p = 0.010).

CONCLUSION

By using the 3D simulation system, the potential site of bony collision could be visualized and successfully reduced intraoperatively. Since the osseous interference can be existed on any side, unilaterally or bilaterally, 3D surgical simulation is necessary before surgery to predict the osseous interference and improve the ramal inclination.

Clinical Stability of Bespoke Snowman Plates for Fixation following Sagittal Split Ramus Osteotomy of the Mandible

Maxillofacial skeletal surgery often involves the use of patient-specific implants. However, errors in obtaining patient data and designing and manufacturing patient-specific plates and guides can occur even with accurate virtual surgery. To address these errors, bespoke Snowman plates were designed to allow movement of the mandible. This study aimed to compare the stability of bespoke four-hole miniplates with that of a bespoke Snowman plate for bilateral sagittal split ramus osteotomy (SSRO), and to present a method to investigate joint cavity changes, as well as superimpose virtual and actual surgical images of the mandible. This retrospective study included 22 patients who met the inclusion criteria and underwent orthognathic surgery at a university hospital between 2015 and 2018. Two groups were formed on the basis of the plates used: a control group with four-hole bespoke plates and a study group with bespoke Snowman plates. Stability was assessed by measuring the condyle-fossa space and superimposing three-dimensional virtual surgery images on postoperative cone-beam computed tomography (CBCT) scans. No significant differences were observed in the condyle-fossa space preoperatively and 1 year postoperatively between the control and study groups. Superimposing virtual surgery and CBCT scans revealed minimal differences in the landmark points, with no variation between groups or timepoints. The use of bespoke Snowman plates for stabilizing the mandible following SSRO exhibited clinical stability and reliability similar to those with bespoke four-hole plates. Additionally, a novel method was introduced to evaluate skeletal stability by separately analyzing the condyle-fossa gap changes and assessing the mandibular position.

Comparison of Artificial Intelligence-Based Applications for Mandible Segmentation: From Established Platforms to In-House-Developed Software

Medical image segmentation, whether semi-automatically or manually, is labor-intensive, subjective, and needs specialized personnel. The fully automated segmentation process recently gained importance due to its better design and understanding of CNNs. Considering this, we decided to develop our in-house segmentation software and compare it to the systems of established companies, an inexperienced user, and an expert as ground truth. The companies included in the study have a cloud-based option that performs accurately in clinical routine (dice similarity coefficient of 0.912 to 0.949) with an average segmentation time ranging from 3'54″ to 85'54″. Our in-house model achieved an accuracy of 94.24% compared to the best-performing software and had the shortest mean segmentation time of 2'03″. During the study, developing in-house segmentation software gave us a glimpse into the strenuous work that companies face when offering clinically relevant solutions. All the problems encountered were discussed with the companies and solved, so both parties benefited from this experience. In doing so, we demonstrated that fully automated segmentation needs further research and collaboration between academics and the private sector to achieve full acceptance in clinical routines.

Fully automatic segmentation of the mandible based on convolutional neural networks (CNNs)

OBJECTIVES

To evaluate the accuracy of automatic deep learning-based method for fully automatic segmentation of the mandible from CBCTs.

SETTING AND SAMPLE POPULATION

CBCT-derived mandible fully automatic segmentation.

METHODS

Forty CBCT scans from healthy patients (20 females and 20 males, mean age 23.37 ± 3.34) were collected, and a manual mandible segmentation was carried out by using Mimics software. Twenty CBCT scans were randomly selected and used for training the artificial intelligence model file. The remaining 20 CBCT segmentation masks were used to test the accuracy of the CNN automatic method by comparing the segmentation volumes of the 3D models obtained with automatic and manual segmentations. The accuracy of the CNN-based method was also assessed by using the DICE Score coefficient (DSC) and by the surface-to-surface matching technique. The intraclass correlation coefficient (ICC) and Dahlberg's formula were used respectively to test the intra-observer reliability and method error. Independent Student's t test was used for between-groups volumetric comparison.

RESULTS

Measurements were highly correlated with an ICC value of 0.937, while the method error was 0.24 mm³ . A difference of 0.71 (±0.49) cm³ was found between the methodologies, but it was not statistically significant (P > .05). The matching percentage detected was 90.35% (±1.88) (tolerance 0.5 mm) and 96.32% ± 1.97% (tolerance 1.0 mm). The differences, measured as DSC in percentage, between the assessments done with both methods were, respectively, 2.8% and 3.1%.

CONCLUSION

The tested deep learning CNN-based technology is accurate and performs as well as an experienced image reader but at much higher speed, which is of significant clinical relevance.

Correction of Condylar Displacement of the Mandible Using Early Screw Removal following Patient-Customized Orthognathic Surgery

OBJECTIVE

Orthognathic surgery (OGS) is a surgical intervention that corrects dentofacial deformities through the movement of maxillary and mandibular segments to achieve adequate masticatory function, joint health, and facial harmony. However, some patients present with occlusal discrepancies, condylar sag, and/or temporomandibular disorders after OGS. Various methods have been employed to solve these problems after surgery. This study aimed to evaluate the effectiveness of early screw removal in patients with occlusal discrepancies after OGS using three-dimensional cone-beam computed tomography (CBCT).

METHODS

In 44 patients with dentofacial deformities, patient-customized OGSs with customized plates were performed to correct facial deformities using customized guides with computer-aided surgical simulation. Of the 44 patients, eight patients complained of occlusal discrepancies and temporomandibular disorders after OGS. These eight patients underwent screw removal under local anesthesia around four weeks. The temporomandibular joint spaces at three time points (pre-surgical, post-surgical, and after screw removal) in the sagittal and coronal planes were compared using CBCT.

RESULTS

Eight patients showed an increase in joint space on CBCT images immediately after surgery (T1), but after early screw removal (T2), these spaces almost returned to their pre-surgical state, and the temporomandibular joint problem disappeared.

CONCLUSIONS

The removal of screws located in the distal segment under local anesthesia between three and four weeks post-surgically may be a treatment option for patients with post-OGS occlusal discrepancies, condylar sag, and/or temporomandibular disorder.