Three-dimensional virtual reality surgical planning and simulation workbench for orthognathic surgery

A new integrated computer system, the 3-dimensional (3D) virtual reality surgical planning and simulation workbench for orthognathic surgery (VRSP), is presented. Five major functions are implemented in this system: post-processing and reconstruction of computed tomographic (CT) data, transformation of 3D unique coordinate system geometry, generation of 3D color facial soft tissue models, virtual surgical planning and simulation, and presurgical prediction of soft tissue changes. The basic mensuration functions, such as linear and spatial measurements, are also included. The surgical planning and simulation are based on 3D CT reconstructions, whereas soft tissue prediction is based on an individualized, texture-mapped, color facial soft tissue model. The surgeon "enters" the virtual operatory with virtual reality equipment, "holds" a virtual scalpel, and "operates" on a virtual patient to accomplish actual surgical planning, simulation of the surgical procedure, and prediction of soft tissue changes before surgery. As a final result, a quantitative osteotomy-simulated bone model and predicted color facial model with photorealistic quality can be visualized from any arbitrary viewing point in a personal computer system. This system can be installed in any hospital for daily use.     

Three-Dimensional Soft Tissue Prediction Using Finite Elements Part I: Implementation of a New Procedure

Background and Aim:   

The prediction of soft tissue esthetics is important for achieving an optimal esthetic outcome in orthodontic treatment planning. Applicable procedures have so far been restricted to two-dimensional profile predictions that have not proven to be very reliable. The goal of this investigation was therefore to develop a novel finite element-based procedure that allows a three-dimensional, easily visualized, quantitative analysis and prediction of soft tissue behavior for the clinician. The procedure to be developed should be easy to handle and not entail any additional radiation exposure for the patient.     

Evaluation of soft tissue prediction accuracy for orthognathic surgery with skeletal class III malocclusion using maxillofacial regional aesthetic units

Objectives

This study aimed to evaluate the soft tissue prediction accuracy of patients undergoing orthognathic surgery to correct skeletal class III malocclusion using maxillofacial regional aesthetic units.

Materials and methods

Pre- and postoperative cone-beam computed tomography (CBCT) and 3D facial scans were taken for 58 patients who had undergone orthognathic surgery. The preoperative 3D facial scan was integrated with the preoperative CBCT using ProPlan CMF software. The software simulated the surgery and generated postoperative soft tissue prediction. The simulated 3D facial scan was then compared with the actual 3D facial scan obtained at least 6 months after the surgery by the maxillofacial regional aesthetic units and the facial soft tissue landmark points.

Results

The anatomical regions of the upper lip, lower lip, chin, right external buccal and left external buccal prediction were above 2.0 mm. As for the soft tissue landmarks, at chl, chr, ls, stm and li, the position of predicted scan was higher than that of the actual postoperative scan.

Conclusions

The accuracy of 3D soft tissue predictions using ProPlan CMF software in Skeletal III patients was clinically satisfactory according to maxillofacial regional aesthetic units combined with facial soft tissue landmark points. However, the accuracy of prediction still needed improvement in some areas.

Clinical relevance

The accuracy of soft tissue prediction can be analyzed more clearly through maxillofacial regional aesthetic units so that clinicians have a deeper understanding of the use of the software to predict soft tissue change after orthognathic surgery.

     

应用有限元法预测正颌术后三维软组织形变的初步探讨

目的:基于锥形束CT(CBCT)资料建立有限元模型,预测正颌术后三维软组织形变,探讨该方法的可行性与准确性。方法:选取下颌前突患者2例,于术前行颅颌面CBCT扫描,导入Mimics10.01软件,进行软、硬组织三维重建。采用Geomagic Studio11软件进行模型处理,并按实际情况进行手术模拟截骨,导入有限元分析软件AnsysWorkbench 11.0,建立线弹性有限元模型,加载位移后,经分析得出术后软组织三维模样,将其与术后6个月及以上的软组织三维重建图像对比,并进行定性及定量评价。结果:2例患者CBCT资料顺利进行有限元建模及预测,临床定性评价显示2例患者预测结果总体观察相似度高,但在口周及颊部相似度欠佳;Geomagic Qualify11定量检测显示,病例1误差小于2mm的区域为94.98%,病例2误差小于2mm的区域为90.71%。结论:采用线弹性有限元模型预测下颌前突正颌术后的软组织形态是可行的,可为临床提供较为可靠的参考。     

Computer-assisted three-dimensional surgical planing and simulation. 3D soft tissue planning and prediction

The purpose of this paper is to report a new technique for three-dimensional facial soft-tissue-change prediction after simulated orthognathic surgical planning. A scheme for soft tissue deformation, "Computer-assisted three-dimensional virtual reality soft tissue planning and prediction for orthognathic surgery (CASP)", is presented. The surgical planning was based on three-dimensional reconstructed CT visualization. Soft tissue changes were predicted by two newly devised algorithms: Surface Normal-based Model Deformation Algorithm and Ray Projection-based Model Deformation Algorithm. A three-dimensional color facial texture-mapping technique was also used for generating the color photo-realistic facial model. As a final result, a predicted and simulated patient's color facial model can be visualized from arbitrary viewing points.     

Soft tissue response and facial symmetry after orthognathic surgery

ObjectiveIn orthognathic surgery aesthetic issues and facial symmetry are vital parameters in surgical planning. Aim of this investigation was to document and analyze the results of orthognathic surgery on the base of a three-dimensional photogrammetric assessment, to assess the soft tissue response related to the skeletal shift and the alterations in facial symmetry after orthognathic surgery.Patients and methodsIn this prospective clinical trial from January 2010 to June 2011, 104 patients were examined who underwent orthognathic surgery due to mono- or bimaxillary dysgnathia. The standardized measurements, based on optical 3D face scans, took place one day before orthognathic surgery (T1) and one day before removal of osteosynthesis material (T2).ResultsSoft tissue changes after procedures involving the mandible showed significant positive correlations and strong soft tissue response (p < 0.05). The midfacial soft tissue response after maxillary advancement was only of minor extent (p > 0.05). The facial surfaces became more symmetric and harmonic with the exception of surgical maxillary expansion, but improvement of facial symmetry revealed no statistical significance.ConclusionSoft tissue response after orthognathic surgery and symmetry are only partially predictable, especially in the maxillary and midfacial region. Computer programs predicting soft tissue changes are not currently safely reliable and should not be used or with caution to demonstrate a patient potential outcome of surgery.     

Three-dimensional cone beam computed tomographic image reorientation using soft tissues as reference for facial asymmetry diagnosis

Objective:To investigate discrepancies in results of facial asymmetry analysis using different cone beam computed tomography (CBCT) image reorientation methods and the effectiveness of soft tissue as a reorientation reference for analysis of facial asymmetry.Materials and Methods:An asymmetric group of 30 patients with 4 mm or more of chin point (menton [Me]) deviation and a symmetric group of 30 patients with less than 4 mm of deviation of Me were chosen as study subjects. Three orientation methods were used to calculate and compare Me deviation values of the 60 subjects. Two methods used only skeletal landmarks for reference, and one method included the soft tissue landmarks around the eye. Preferences of an expert group for the facial midline as determined by each reorientation method were also examined.Results:The examinations showed significant discrepancies in Me deviation values between the three reorientation methods. The expert group showed the greatest preference for the facial midline reorientation method that incorporated soft tissue landmarks of the eye.Conclusions:These study findings suggest that the inclusion of soft tissue landmarks, especially those around the eyes, is effective for three-dimensional CBCT image reorientation for facial asymmetry analysis.     

Validation of new soft tissue software in orthognathic surgery planning

This study tests computer imaging software (SurgiCase-CMF^®, Materialise) that enables surgeons to perform virtual orthognathic surgical planning using a three dimensional (3D) utility that previews the final shape of hard and soft tissues. It includes a soft tissue simulation module that has created images of soft tissues altered through bimaxillary orthognathic surgery to correct facial deformities. Cephalometric radiographs and CT scans were taken of each patient before and after surgery. The surgical planning system consists of four stages: CT data reconstruction; 3D model generation of facial hard and soft tissue; different virtual surgical planning and simulation modes; and various preoperative previews of the soft tissues. Surgical planning and simulation is based on a 3D CT reconstructed bone model and soft tissue image generation is based on physical algorithms. The software rapidly follows clinical options to generate a series of simulations and soft tissue models; to avoid TMJ functional problems, pre-surgical plans were evaluated by an orthodontist. Comparing simulation results with postoperative CT data, the reliability of the soft tissues preview was >91%. SurgiCase^® software can provide a realistic, accurate forecast of the patient's facial appearance after surgery.     

Three-Dimensional Soft Tissue Prediction Using Finite Elements

BACKGROUND AND AIM: The goal of this study was to analyze the validity and prediction accuracy of a newly-developed procedure for three-dimensional soft tissue prediction based on Finite Element Method, and to compare the results with prediction produced using an existing two-dimensional prediction program (Dentofacial Planner Plus). PATIENTS AND METHODS: In twelve patients who underwent combined surgical-orthodontic treatment, profile prediction was generated using both procedures preoperatively and then compared at predefined measurement points with the patient's actual postoperative soft tissue status. RESULTS: The deviations observed depended on the facial region, whereby the prediction errors for both procedures were much greater in the lower facial third than in the midfacial third. Calculating in all the measurement points, the mean horizontal prediction error was 0.32 mm for the Finite Element Method and 0.75 mm for the Dentofacial Planner Plus. Overall, we were able to demonstrate the new procedure's superior validity and quality of visualization. In addition to profile prediction, the procedure allows a differentiated three-dimensional assessment of esthetically important regions such as the cheeks, nasolabial folds and the nasal wings. Additional X-radiation is not necessary in this risk-free and stress-free procedure. CONCLUSION: Three-dimensional soft tissue prediction employing finite element modeling is a useful aid for implementing esthetically-optimized treatment planning.     

A sparse principal component analysis of Class III malocclusions

Objectives:To identify the most characteristic variables out of a large number of anatomic landmark variables on three-dimensional computed tomography (CT) images. A modified principal component analysis (PCA) was used to identify which anatomic structures would demonstrate the major variabilities that would most characterize the patient.Materials and Methods:Data were collected from 217 patients with severe skeletal Class III malocclusions who had undergone orthognathic surgery. The input variables were composed of a total of 740 variables consisting of three-dimensional Cartesian coordinates and their Euclidean distances of 104 soft tissue and 81 hard tissue landmarks identified on the CT images. A statistical method, a modified PCA based on the penalized matrix decomposition, was performed to extract the principal components.Results:The first 10 (8 soft tissue, 2 hard tissue) principal components from the 740 input variables explained 63% of the total variance. The most conspicuous principal components indicated that groups of soft tissue variables on the nose, lips, and eyes explained more variability than skeletal variables did. In other words, these soft tissue components were most representative of the differences among the Class III patients.Conclusions:On three-dimensional images, soft tissues had more variability than the skeletal anatomic structures. In the assessment of three-dimensional facial variability, a limited number of anatomic landmarks being used today did not seem sufficient. Nevertheless, this modified PCA may be used to analyze orthodontic three-dimensional images in the future, but it may not fully express the variability of the patients.     

Computer-assisted midface reconstruction in Treacher Collins syndrome part 1: Skeletal reconstruction

IntroductionTreacher Collins syndrome (TCS) is a severe and complex craniofacial malformation affecting the facial skeleton and soft tissues. The palate as well as the external and middle ear are also affected, but his prognosis is mainly related to neonatal airway management. Methods of zygomatico-orbital reconstruction are numerous and currently use primarily autologous bone, lyophilized cartilage, alloplastic implants, or even free flaps. This work developed a reliable “customized” method of zygomatico-orbital bony reconstruction using a generic reference model tailored to each patient.MethodsFrom a standard computed tomography (CT) acquisition, we studied qualitatively and quantitatively the skeleton of four individuals with TCS whose age was between 6 and 20 years. In parallel, we studied 40 controls at the same age to obtain a morphometric database of reference. Surgical simulation was carried out using validated software used in craniofacial surgery.ResultsThe zygomatic hypoplasia was very important quantitatively and morphologically in all TCS individuals. Orbital involvement was mainly morphological, with volumes comparable to the controls of the same age. The control database was used to create three-dimensional computer models to be used in the manufacture of cutting guides for autologous cranial bone grafts or alloplastic implants perfectly adapted to each patient's morphology. Presurgical simulation was also used to fabricate custom positioning guides permitting a simple and reliable surgical procedure.ConclusionsThe use of a virtual database allowed us to design a reliable and reproducible skeletal reconstruction method for this rare and complex syndrome. The use of presurgical simulation tools seem essential in this type of craniofacial malformation to increase the reliability of these uncommon and complex surgical procedures, and to ensure stable results over time.     

Morphological differences of facial soft tissue contours from child to adult of Japanese males: A three-dimensional cross-sectional study

ObjectiveTo evaluate morphological differences of the facial soft tissue surface between male Japanese adults and children.Design20 adult Japanese males (average age 28 years) and 20 Japanese boys (average age 5.5 years) with normal occlusion were selected for this study. The images of the subjects’ facial surface were obtained with a 3-D laser scanner. To evaluate the three-dimensional morphological differences of the facial soft tissue, we transformed the coordinates of 16 facial landmarks to a new reference plane and compared the adults’ and children's facial form drawn to the same scale in the same coordinate system.ResultsThe morphological difference ratio of the lower facial area was higher than in the upper facial area, and the nose and lower face changed more forward than downward. The morphological difference ratio of the mid face width was smaller than other areas.ConclusionOur study suggests that the morphological facial soft tissue differences between Japanese adults and children are more forward and downward than laterally, manifesting in a facial form of adults that is deeper and narrow.     

基于二维DR的颅面硬组织与软组织拟合的研究

目的:以数字化X线摄影片(digital radiograph,DR)图像和激光扫描为数据源,三维重建颅面硬组织和软组织,并进行硬软组织的有效拟合,以期为治疗方案确定、手术方法选择和提高医患交流的水平提供平台.方法:在志愿者面部贴定铅点,拍摄头颅正侧位DR片.利用基于二维DR数据的颅面硬组织三维重建系统进行硬组织形变建模.获得颅面部硬组织模型.利用激光扫描数据进行面部软组织三维重建,获得面部软组织三维模型.然后通过铅点坐标的匹配,将颅面硬组织与面部软组织进行拟合.结果:分别重建了能反映真实颅面部组织结构的硬组织三维模型和面部软组织三维模型,并实现了颅面部硬组织与软组织的有效拟合.结论:本研究实现了颅颌面三维结构的有效重建和拟合,为进一步进行正颌手术模拟和容貌预测奠定了基础.拟合结果真实可靠,能够用于临床.     

Co-ordinate Grids for Three-dimensional Facial Measurement

Abstract

Alternative methods for recording the shape of the facial soft tissue integument in three dimensions are discussed. The requirements for and problems associated with head positioning are indicated, and a technique is described by which head positioning errors can be overcome. The results of three-dimensional analysis of a sample of human subjects are described, with particular reference to the method of analysis and orientation planes selected. Finally, possible clinical uses for three-dimensional recording are suggested.     

A computer system for the interactive planning and prediction of maxillofacial surgery

A computer system has been developed for the simulation of facial surgery with interactive three-dimensional graphic techniques and data derived from computed tomographic scans and a purpose-built laser scanning system. The simulation includes the surgery on the hard tissues, and modeling of the soft tissue for prediction of the postoperative facial appearance. The facilities available are described and an example of their use is given.     

Facial soft-tissue changes after rapid maxillary expansion analyzed with 3-dimensional stereophotogrammetry: A randomized,controlled clinical trial

Objective:To evaluate three-dimensional (3-D) soft tissue facial changes following rapid maxillary expansion (RME) and to compare these changes with an untreated control group.Materials and Methods:Patients who need RME as a part of their orthodontic treatment were randomly divided into two groups of 17 patients each. Eligibility criteria included having maxillary transverse deficiency with crossbite, and to be in the normal range according to body mass index. In the first group (mean age  =  13.4 ± 1.2 years), expansion was performed. The second group received no treatment initially and served as untreated control (mean age  =  12.8 ± 1.3 years). Skeletal and soft tissue changes were evaluated using posteroanterior cephalograms and 3-D facial images. The primary outcome of this study was to assess the soft tissue changes. The secondary outcomes were evaluation hard tissue and soft tissue relations. Randomization was done with preprepared random number tables. Blinding was applicable for outcome assessment only. MANOVA, t-test, and correlation analyses were used (P  =  .05).Results:In both groups, there was a general trend of increase for the transverse skeletal measurements, but these increases were more limited in the control group. Alar base width was greater in the treatment group (P  =  .002). Pogonion soft tissue point (P  =  .022) was located more posteriorly in the expansion group compared with the control group.Conclusions:Soft tissue changes between groups were similar, except for the alar base, which became wider in the treatment group. Weak correlations were found between the skeletal and soft tissue changes.     

正常人群面部软组织三维测量与X线头影测量的相关性分析

目的　比较正常的面部软组织三维测量与X线头影测量结果。方法　应用面部软组织数字化立体摄影测量与X线头影测量对标准正常进行面部软组织三维测量,并进行相关性分析。结果　面部软组织三维测量项目与对应的X线头影测量项目具备相关性。结论　面部软组织三维测量结果能够部分的反映其下硬组织的情况。     

Evaluation of soft tissue changes around the lips after bracket debonding using three-dimensional stereophotogrammetry

Objective:To evaluate the changes in soft tissue around the lips after orthodontic bracket debonding using three-dimensional (3-D) stereophotogrammetry.Materials and Methods:3-D facial images of 20 subjects (10 men and 10 women; mean age, 26.81 ± 7.23 years) were taken with a white light scanner before and after debonding the labial brackets. Two images acquired from each subject were superimposed, and 15 soft tissue landmarks around the lips were plotted and analyzed. Statistical analysis was performed using both paired and independent t-tests (P < .05).Results:There were no significant changes in position of any landmark on the x (left-right)- or y (vertical)-axes after removal of the brackets. However, the landmarks in the oral commissures and lower lip (LLP, −0.55 mm; Li, −0.44 mm; Ch-L, −0.56 mm, all P < .05) on the z (anteroposterior)-axis showed statistically significant differences. There were no significant positional changes of most landmarks on the x-, y-, or z- axes after bracket removal among the various genders and lip thicknesses.Conclusions:There was a slight retrusion in the oral commissure and lower lip areas after debonding, but no changes were found in the upper lip area. This study showed that 3-D stereophotogrammetry can be useful in evaluating facial soft tissue changes in orthodontic patients.     

Evaluating the relationship between dimensions of the upper airway and facial profile according to initial lateral cephalometric radiography in orthodontic patients in the north of Iran

PurposeDecreased upper airway dimensions due to adenoid enlargement may have unfavorable aesthetic and/or functional effects on the soft or hard tissue profile development. The aim of this study was to investigate the associations between adenoid sizes to upper airway size ratio (airway ratio) in the midsagittal plane and various types of soft and hard tissue facial profile convexity.Materials and methods251 lateral cephalometric images of pre-orthodontic healthy subjects with age group of 6?12, 13?18, 19?25 and 26?29 years, were collected. They were classified into four subgroups based on the airway ratio (grade 1: <1/4 í 100), (grade 2: 1/4?1/2 í 100), (grade 3:1/2?3/4 í 100) and (grade 4: >3/4 í 100). The radiographs were characterized as convex, normal and concave soft tissue facial profile according to the facial convexity angle. Cephalometric analyses were done using Dolphin imaging computer software 11.95. Kruskal Wallis test was used to evaluate differences between airway ratio and facial morphologies; the mandibular plane angle was compared between airway ratio subgroups by Chi square.ResultsAirway ratio was not significantly different (P = 0.241) between soft tissue facial convexity subgroups and within age subgroups. Mandibular plane angle was in a significant relation within airway ratio (p = 0.028).ConclusionThere was not any significant relation between decreased upper airway ratios and types of the soft or hard tissue facial profile convexity, however there was a significant relation between upper airway ratios and age subgroups. A significant revers correlation was seen between the mandibular plane angle and nasopharyngeal dimensions.     

Mathematical modeling and numerical simulation in maxillofacial virtual surgery

Computer-based surgery simulation is a rapidly emerging and increasingly important area of research that combines a number of disciplines for the common purpose of improving healthcare. The objective of this article is to provide a virtual surgery tool for accurately planning the aesthetic impact of hard and soft tissue movements in dentoskeletal malocclusions. The approach proposed here allows direct interaction with a completely three-dimensional (3D) computed tomography (CT) model of a solid, highly detailed structure of the head to obtain a realistic prediction of soft tissue behavior. We studied 25 patients who had facial malformations pre- and postoperatively with 3D hard and soft tissue CT studies, and maxillary or mandibular osteotomies were simulated. The postoperative 3D CT and facial outcomes were compared with the simulations. In 80% of the cases studied, the simulation-predicted changes, when compared with the clinical outcomes, were within the tolerance level (2 mm) established by maxillofacial surgeons.