Shunyao Shen

An eFace-Template Method for Efficiently Generating Patient-Specific Anatomically-Detailed Facial Soft Tissue FE Models for Craniomaxillofacial Surgery Simulation.

Accurate surgical planning and prediction of craniomaxillofacial surgery outcome requires simulation of soft-tissue changes following osteotomy. This can only be accomplished on an anatomically-detailed facial soft tissue model. However, current anatomically-detailed facial soft tissue model generation is not appropriate for clinical applications due to the time intensive nature of manual segmentation and volumetric mesh generation. This paper presents a novel semi-automatic approach, named eFace-template method, for efficiently and accurately generating a patient-specific facial soft tissue model. Our novel approach is based on the volumetric deformation of an anatomically-detailed template to be fitted to the shape of each individual patient. The adaptation of the template is achieved by using a hybrid landmark-based morphing and dense surface fitting approach followed by a thin-plate spline interpolation. This methodology was validated using 4 visible human datasets (regarded as gold standards) and 30 patient models. The results indicated that our approach can accurately preserve the internal anatomical correspondence (i.e., muscles) for finite element modeling. Additionally, our hybrid approach was able to achieve an optimal balance among the patient shape fitting accuracy, anatomical correspondence and mesh quality. Furthermore, the statistical analysis showed that our hybrid approach was superior to two previously published methods: mesh-matching and landmark-based transformation. Ultimately, our eFace-template method can be directly and effectively used clinically to simulate the facial soft tissue changes in the clinical application.

Image fusion in craniofacial virtual reality modeling based on CT and 3dMD photogrammetry.

Purpose The aim of this study was to demonstrate the feasibility of building a craniofacial virtual reality model by image fusion of 3-dimensional (3D) CT models and 3dMD stereophotogrammetric facial surface. Methods A CT scan and stereophotography were performed. The 3D CT models were reconstructed by Materialise Mimics software, and the stereophotogrammetric facial surface was reconstructed by 3dMD patient software. All 3D CT models were exported as Stereo Lithography file format, and the 3dMD model was exported as Virtual Reality Modeling Language file format. Image registration and fusion were performed in Mimics software. Genetic algorithm was used for precise image fusion alignment with minimum error. The 3D CT models and the 3dMD stereophotogrammetric facial surface were finally merged into a single file and displayed using Deep Exploration software. Errors between the CT soft tissue model and 3dMD facial surface were also analyzed. Results Virtual model based on CT-3dMD image fusion clearly showed the photorealistic face and bone structures. Image registration errors in virtual face are mainly located in bilateral cheeks and eyeballs, and the errors are more than 1.5 mm. However, the image fusion of whole point cloud sets of CT and 3dMD is acceptable with a minimum error that is less than 1 mm. Conclusions The ease of use and high reliability of CT-3dMD image fusion allows the 3D virtual head to be an accurate, realistic, and widespread tool, and has a great benefit to virtual face model.

Image-guided endoscopic navigation for the precise resection of a mandibular condylar osteochondroma.

Purpose The authors describe an intraoral approach to accessing the mandibular condyle using endoscopy combined with a navigation system and explore the feasibility of this technique for the precise excision of a benign tumor in the condyle. Methods The junction between the osteochondroma and the condyle was recognized and defined as the osteotomy line in a CT-based surgery planning software, and the surgical plan was then exported to a navigation system. A 4-mm–diameter 30-degree endoscope was placed in the wound with direct access to the entire condyle. Based on constant feedback from the navigation system in multiplanar and 3D views, the landmarks of the osteotomy line were identified, and precise tumor resection was achieved. Results The magnified endoscopic view allowed the condylar head and neck to be easily dissected with good illumination and clear visualization. The landmarks of the osteotomy line were transferred from the virtual surgical plan to the surgical field, and precise resection of the condylar tumor was achieved. Conclusion The combined technique reported in this paper could represent a valid minimally invasive approach to the ramus-condyle unit for direct visualization of the medial aspect of the condyle and precise resection of benign tumor located here.

A new approach of splint-less orthognathic surgery using a personalized orthognathic surgical guide system: A preliminary study

The purpose of this study was to evaluate a personalized orthognathic surgical guide (POSG) system for bimaxillary surgery without the use of surgical splint. Ten patients with dentofacial deformities were enrolled. Surgeries were planned with the computer-aided surgical simulation method. The POSG system was designed for both maxillary and mandibular surgery. Each consisted of cutting guides and three-dimensionally (3D) printed custom titanium plates to guide the osteotomy and repositioning the bony segments without the use of the surgical splints. Finally, the outcome evaluation was completed by comparing planned outcomes with postoperative outcomes. All operations were successfully completed using the POSG system. The largest root-mean-square deviations were 0.74mm and 1.93° for the maxillary dental arch, 1.10mm and 2.82° for the mandibular arch, 0.83mm and 2.59° for the mandibular body, and 0.98mm and 2.45° for the proximal segments. The results of the study indicated that our POSG system is capable of accurately and effectively transferring the surgical plan without the use of surgical splint. A significant advantage is that the repositioning of the bony segments is independent to the mandibular autorotation, thus eliminates the potential problems associated with the surgical splint.

Computer-Aided Design and Computer-Aided Manufacturing Hydroxyapatite/Epoxide Acrylate Maleic Compound Construction for Craniomaxillofacial Bone Defects.

AbstractThe aim of this study was to investigate the use of computer-aided design and computer-aided manufacturing hydroxyapatite (HA)/epoxide acrylate maleic (EAM) compound construction artificial implants for craniomaxillofacial bone defects. Computed tomography, computer-aided design/computer-aided manufacturing and three-dimensional reconstruction, as well as rapid prototyping were performed in 12 patients between 2008 and 2013. The customized HA/EAM compound artificial implants were manufactured through selective laser sintering using a rapid prototyping machine into the exact geometric shapes of the defect. The HA/EAM compound artificial implants were then implanted during surgical reconstruction. Color-coded superimpositions demonstrated the discrepancy between the virtual plan and achieved results using Geomagic Studio. As a result, the HA/EAM compound artificial bone implants were perfectly matched with the facial areas that needed reconstruction. The postoperative aesthetic and functional results were satisfactory. The color-coded superimpositions demonstrated good consistency between the virtual plan and achieved results. The three-dimensional maximum deviation is 2.12u200a±u200a0.65u200amm and the three-dimensional mean deviation is 0.27u200a±u200a0.07u200amm.No facial nerve weakness or pain was observed at the follow-up examinations. Only 1 implant had to be removed 2 months after the surgery owing to severe local infection. No other complication was noted during the follow-up period. In conclusion, computer-aided, individually fabricated HA/EAM compound construction artificial implant was a good craniomaxillofacial surgical technique that yielded improved aesthetic results and functional recovery after reconstruction.

Moving the mandible to the retruded contact position for simulating the hinge movement in virtual three-dimensional orthognathic surgery by integrating the plaster models.

The range of rotation of the mandible during virtual three-dimensional orthognathic surgery is small and may be similar to the hinge movement of the mandible. This current study offers a new method to move the mandible to the retruded contact position (RCP), a position of beginning hinge movement, during virtual three-dimensional orthognathic surgery. During this method, a three-dimensional skull model was reconstructed from the computed tomographic images in the Mimics software. Then the RCP in the patient could be obtained using Gothic arch tracer or swallowing method and was recorded using a wax plate, followed by transferring to plaster models. Subsequently, the plaster models in RCP were scanned using a dental surface scanner and imported into the Mimics software. Finally, we could move the mandible to the RCP based on the registration between the three-dimensional skull model and plaster model for simulating the hinge movement during virtual three-dimensional orthognathic surgery. This may be a small step forward for improving the accuracy of virtual three-dimensional orthognathic surgery.

A clinically validated prediction method for facial soft‐tissue changes following double‐jaw surgery

Purpose: It is clinically important to accurately predict facial soft‐tissue changes prior to orthognathic surgery. However, the current simulation methods are problematic, especially in anatomic regions of clinical significance, e.g., the nose, lips, and chin. We developed a new 3‐stage finite element method (FEM) approach that incorporates realistic tissue sliding to improve such prediction. Methods: In Stage One, soft‐tissue change was simulated, using FEM with patient‐specific mesh models generated from our previously developed eFace template. Postoperative bone movement was applied on the patient mesh model with standard FEM boundary conditions. In Stage Two, the simulation was improved by implementing sliding effects between gum tissue and teeth using a nodal force constraint scheme. In Stage Three, the result of the tissue sliding effect was further enhanced by reassigning the soft‐tissue‐bone mapping and boundary conditions using nodal spatial constraint. Finally, our methods have been quantitatively and qualitatively validated using 40 retrospectively evaluated patient cases by comparing it to the traditional FEM method and the FEM with sliding effect, using a nodal force constraint method. Results: The results showed that our method was better than the other two methods. Using our method, the quantitative distance errors between predicted and actual patient surfaces for the entire face and any subregions thereof were below 1.5 mm. The overall soft‐tissue change prediction was accurate to within 1.1 ± 0.3 mm, with the accuracy around the upper and lower lip regions of 1.2 ± 0.7 mm and 1.5 ± 0.7 mm, respectively. The results of qualitative evaluation completed by clinical experts showed an improvement of 46% in acceptance rate compared to the traditional FEM simulation. More than 80% of the result of our approach was considered acceptable in comparison with 55% and 50% following the other two methods. Conclusion: The FEM simulation method with improved sliding effect showed significant accuracy improvement in the whole face and the clinically significant regions (i.e., nose and lips) in comparison with the other published FEM methods, with or without sliding effect using a nodal force constraint. The qualitative validation also proved the clinical feasibility of the developed approach.

Titanium Mesh Shaping and Fixation for the Treatment of Comminuted Mandibular Fractures

PURPOSEnTreating comminuted mandibular fractures remains a challenge. In this study, we used titanium mesh to treat comminuted mandibular fractures.nnnMATERIALS AND METHODSnNine patients with traumatically comminuted mandibular fractures who received open reduction and internal stable fixation with titanium mesh were retrospectively reviewed. Open reduction-internal stable fixation was performed 7 to 10 days after primary debridement of the facial trauma. After the fractured mandible and the displaced fragments were reduced, the titanium mesh was reshaped according to the morphology of the mandible, and the reduced bone fragments were fixed with the reshaped titanium mesh and screws. Then, the surgical effects were evaluated during routine follow-up.nnnRESULTSnMost of the displaced fragments were preserved and exhibited a favorable shaping ability in restoring the morphology of the mandible during surgery. No intraoperative complications were encountered. In addition, all patients were infection free, with no obvious resorption in the fixed fragments after surgery. The mandible also exhibited favorable morphology and offered sufficient bone mass for dental implantation or a denture prosthesis.nnnCONCLUSIONSnWe conclude that titanium mesh shaping and fixation can effectively treat comminuted mandibular fractures with little bone fragment loss, little soft tissue exposure, a low infection rate, and favorable mandibular morphology.

Bioinformatic analysis of Msx1 and Msx2 involved in craniofacial development.

AbstractMsx1 and Msx2 were revealed to be candidate genes for some craniofacial deformities, such as cleft lip with/without cleft palate (CL/P) and craniosynostosis. Many other genes were demonstrated to have a cross-talk with MSX genes in causing these defects. However, there is no systematic evaluation for these MSX gene–related factors. In this study, we performed systematic bioinformatic analysis for MSX genes by combining using GeneDecks, DAVID, and STRING database, and the results showed that there were numerous genes related to MSX genes, such as Irf6, TP63, Dlx2, Dlx5, Pax3, Pax9, Bmp4, Tgf-beta2, and Tgf-beta3 that have been demonstrated to be involved in CL/P, and Fgfr2, Fgfr1, Fgfr3, and Twist1 that were involved in craniosynostosis. Many of these genes could be enriched into different gene groups involved in different signaling ways, different craniofacial deformities, and different biological process. These findings could make us analyze the function of MSX gens in a gene network. In addition, our findings showed that Sumo, a novel gene whose polymorphisms were demonstrated to be associated with nonsyndromic CL/P by genome-wide association study, has protein-protein interaction with MSX1, which may offer us an alternative method to perform bioinformatic analysis for genes found by genome-wide association study and can make us predict the disrupted protein function due to the mutation in a gene DNA sequence. These findings may guide us to perform further functional studies in the future.

A novel method to determine the potential rotational axis of the mandible during virtual three-dimensional orthognathic surgery.

Abstract During virtual three-dimensional orthognathic surgery in cases where an overlap or penetrability occurs between the 2 jaws due to the repositioning of the maxillary segment, it is necessary to establish a vertical opening of the mandible to obtain a relatively good relationship with the maxillary segment for the fabrication of an intermediate occlusal splint. However, there are few reports that address the precise definition of the rotational axis of the mandible during virtual surgery. Here, we present the idea that the mandible’s movement during virtual three-dimensional orthognathic surgery is similar to hinge movement in vivo and developed a method for locating the geometric center of the three-dimensional condyle using Hypermesh software combined with Mimics software. Subsequently, we defined the rotational axis of the mandible based on the located geometric centers of the bilateral condyles, and the mandible was then rotated around the defined axis from the retruded contact position to mimic the hinge movement. Preliminary results indicated that the presented method could approximately mimic the hinge movement of the mandible with a relatively high accuracy in a three-dimensional environment, which may improve the accuracy of virtual intermediate occlusal splint.