Advances in interactive craniofacial surgery planning by 3D simulation and visualization

Application of three-dimensional reconstruction technology in dentistry: a narrative review

BACKGROUND

Three-dimensional(3D) reconstruction technology is a method of transforming real goals into mathematical models consistent with computer logic expressions and has been widely used in dentistry, but the lack of review and summary leads to confusion and misinterpretation of information. The purpose of this review is to provide the first comprehensive link and scientific analysis of 3D reconstruction technology and dentistry to bridge the information bias between these two disciplines.

METHODS

The IEEE Xplore and PubMed databases were used for rigorous searches based on specific inclusion and exclusion criteria, supplemented by Google Academic as a complementary tool to retrieve all literature up to February 2023. We conducted a narrative review focusing on the empirical findings of the application of 3D reconstruction technology to dentistry.

RESULTS

We classify the technologies applied to dentistry according to their principles and summarize the different characteristics of each category, as well as the different application scenarios determined by these characteristics of each technique. In addition, we indicate their development prospects and worthy research directions in the field of dentistry, from individual techniques to the overall discipline of 3D reconstruction technology, respectively.

CONCLUSIONS

Researchers and clinicians should make different decisions on the choice of 3D reconstruction technology based on different objectives. The main trend in the future development of 3D reconstruction technology is the joint application of technology.

On the Development of Virtual Reality Scenarios for Computer-Assisted Biomedical Applications

The modelling of virtual environments and scenarios is an important area of research for the development of new computer-assisted systems in the areas of engineering and medicine, particularly in the area of biomechanics and biomedical engineering. One of the main issues while designing a virtual environment is the level of realism, which depends on the computing capacity and the level of accuracy and usefulness of the generated data. Thus, the dilemma is between the aesthetic realism and the information utility. This paper proposes a methodology to develop low-cost and high-quality virtual environments and scenarios for computer-aided biomedical applications. The proposed methodology is based on the open-source software Blender and the Visualization Toolkit libraries (VTK). In order to demonstrate the usability of the proposed methodology, the design and development of a computer-assisted biomedical application is presented and analysed.

Multi-modal 3D Simulation Makes the Impossible Possible

B.Y. was born full term after a large vertex encephalocele was diagnosed prenatally. The unique challenge to repairing B.Y.'s encephalocele was a microcephalic skull and large proportion of likely functional extracranial brain tissue, which would need to be preserved. At Boston Children's Hospital, a simulation-based collaborative presurgical planning and rehearsal process, using both digital and 3D printed models, enabled successful technical completion and outcome of an otherwise inoperable case.

Autonomous bone reposition around anatomical landmark for robot-assisted orthognathic surgery

The purpose of this study was to develop a new method for enabling a robot to assist a surgeon in repositioning a bone segment to accurately transfer a preoperative virtual plan into the intraoperative phase in orthognathic surgery. We developed a robot system consisting of an arm with six degrees of freedom, a robot motion-controller, and a PC. An end-effector at the end of the robot arm transferred the movements of the robot arm to the patient's jawbone. The registration between the robot and CT image spaces was performed completely preoperatively, and the intraoperative registration could be finished using only position changes of the tracking tools at the robot end-effector and the patient's splint. The phantom's maxillomandibular complex (MMC) connected to the robot's end-effector was repositioned autonomously by the robot movements around an anatomical landmark of interest based on the tool center point (TCP) principle. The robot repositioned the MMC around the TCP of the incisor of the maxilla and the pogonion of the mandible following plans for real orthognathic patients. The accuracy of the robot's repositioning increased when an anatomical landmark for the TCP was close to the registration fiducials. In spite of this influence, we could increase the repositioning accuracy at the landmark by using the landmark itself as the TCP. With its ability to incorporate virtual planning using a CT image and autonomously execute the plan around an anatomical landmark of interest, the robot could help surgeons reposition bones more accurately and dexterously.

Bone and Skin-Supported Stereolithographic Surgical Guides for Cranio-Facial Implant Placement

PURPOSE

Osseointegrated skin-penetrating implants enhance the retention and stability of the craniofacial prostheses and provide the long-term comfort. However, to determine the implant locations is a great challenge facing the surgeon. Implants may either be located in conventional manner or by STL generated surgical guides.

MATERIALS AND METHODS

Present study reports the CT based 3D virtual modeling, preoperative virtual planning and the implant placement by using a STL surgical guide, in an anotia case.

RESULTS

Employed materials and the methods facilitated the implant surgery while improving the operational security.

CONCLUSIONS

CT based 3D virtual modeling of the surgical site, determining the implant locations virtually and the STL guided placement of the craniofacial implants, were found useful applications in order to facilitating the surgical intervention and providing prevention from complications.

Construction and validation of the midsagittal reference plane based on the skull base symmetry for three-dimensional cephalometric craniofacial analysis

OBJECTIVE

The objective of this study was to determine the reliable midsagittal (MS) reference plane in practical ways for the three-dimensional craniofacial analysis on three-dimensional computed tomography images.

METHODS

Five normal human dry skulls and 20 normal subjects without any dysmorphoses or asymmetries were used. The accuracies and stability on repeated plane construction for almost every possible candidate MS plane based on the skull base structures were examined by comparing the discrepancies in distances and orientations from the reference points and planes of the skull base and facial bones on three-dimensional computed tomography images.

RESULTS

The following reference points of these planes were stable, and their distribution was balanced: nasion and foramen cecum at the anterior part of the skull base, sella at the middle part, and basion and opisthion at the posterior part.

CONCLUSIONS

The candidate reference planes constructed using the aforementioned reference points were thought to be reliable for use as an MS reference plane for the three-dimensional analysis of maxillofacial dysmorphosis.

Rapid prototyping-assisted maxillofacial reconstruction

Rapid prototyping (RP) technologies have found many uses in dentistry, and especially oral and maxillofacial surgery, due to its ability to promote product development while at the same time reducing cost and depositing a part of any degree of complexity theoretically. This paper provides an overview of RP technologies for maxillofacial reconstruction covering both fundamentals and applications of the technologies. Key fundamentals of RP technologies involving the history, characteristics, and principles are reviewed. A number of RP applications to the main fields of oral and maxillofacial surgery, including restoration of maxillofacial deformities and defects, reduction of functional bone tissues, correction of dento-maxillofacial deformities, and fabrication of maxillofacial prostheses, are discussed. The most remarkable challenges for development of RP-assisted maxillofacial surgery and promising solutions are also elaborated.

Computer simulation surgery for mandibular reconstruction using a fibular osteotomy guide

In the present study, a fibular osteotomy guide based on a computer simulation was applied to a patient who had undergone mandibular segmental ostectomy due to oncological complications. This patient was a 68-year-old woman who presented to our department with a biopsy-proven squamous cell carcinoma on her left gingival area. This lesion had destroyed the cortical bony structure, and the patient showed attenuation of her soft tissue along the inferior alveolar nerve, indicating perineural spread of the tumor. Prior to surgery, a three-dimensional computed tomography scan of the facial and fibular bones was performed. We then created a virtual computer simulation of the mandibular segmental defect through which we segmented the fibular to reconstruct the proper angulation in the original mandible. Approximately 2-cm segments were created on the basis of this simulation and applied to the virtually simulated mandibular segmental defect. Thus, we obtained a virtual model of the ideal mandibular reconstruction for this patient with a fibular free flap. We could then use this computer simulation for the subsequent surgery and minimize the bony gaps between the multiple fibular bony segments.

Assessment of metal artifacts in three-dimensional dental surface models derived by cone-beam computed tomography

Objective

The aim of this study was to assess artifacts induced by metallic restorations in three-dimensional (3D) dental surface models derived by cone-beam computed tomography (CBCT).

Methods

Fifteen specimens, each with four extracted human premolars and molars embedded in a plaster block, were scanned by CBCT before and after the cavitated second premolars were restored with dental amalgam. Five consecutive surface models of each specimen were created according to increasing restoration size: no restoration (control) and small occlusal, large occlusal, disto-occlusal, and mesio-occluso-distal restorations. After registering each restored model with the control model, maximum linear discrepancy, area, and intensity of the artifacts were measured and compared.

Results

Artifacts developed mostly on the buccal and lingual surfaces. They occurred not only on the second premolar but also on the first premolar and first molar. The parametric values increased significantly with increasing restoration size.

Conclusions

Metallic restorations induce considerable artifacts in 3D dental surface models. Artifact reduction should be taken into consideration for a proper diagnosis and treatment planning when using 3D surface model derived by CBCT in dentofacial deformity patients.

The use of 3D planning in facial surgery: preliminary observations

Three-dimensional (3D) planning is becoming a more commonly used tool in maxillofacial surgery. At first used only virtually, 3D planning now also enables the creation of useful intraoperative aids such as cutting guides, which decrease the operative difficulty. In our center, we have used 3D planning in various domains of facial surgery and have investigated the advantages of this technique. We have also addressed the difficulties associated with its use. 3D planning increases the accuracy of reconstructive surgery, decreases operating time, whilst maintaining excellent esthetic results. However, its use is restricted to osseous reconstruction at this stage and once planning has been undertaken, it cannot be reversed or altered intraoperatively. Despite the attractive nature of this new tool, its uses and practicalities must be further evaluated. In particular, cost-effectiveness, hospital stay, and patient perceived benefits must be assessed.

Virtual planning for craniomaxillofacial surgery--7 years of experience

Contemporary computer-assisted surgery systems more and more allow for virtual simulation of even complex surgical procedures with increasingly realistic predictions. Preoperative workflows are established and different commercially software solutions are available. Potential and feasibility of virtual craniomaxillofacial surgery as an additional planning tool was assessed retrospectively by comparing predictions and surgical results. Since 2006 virtual simulation has been performed in selected patient cases affected by complex craniomaxillofacial disorders (n = 8) in addition to standard surgical planning based on patient specific 3d-models. Virtual planning could be performed for all levels of the craniomaxillofacial framework within a reasonable preoperative workflow. Simulation of even complex skeletal displacements corresponded well with the real surgical result and soft tissue simulation proved to be helpful. In combination with classic 3d-models showing the underlying skeletal pathology virtual simulation improved planning and transfer of craniomaxillofacial corrections. Additional work and expenses may be justified by increased possibilities of visualisation, information, instruction and documentation in selected craniomaxillofacial procedures.

Traditional and contemporary surgical approaches to the orbit

Traditional orbital approaches are nearly a century old and still comprise the foundation of techniques used today. Computer-assisted planning and intraoperative navigation have recently been reported with more prevalence in the literature. The purpose of this article was to review commonly used approaches to the orbit: old and new.

Management of obstructive sleep apnea in pediatric craniofacial anomalies

INTRODUCTION

Obstructive sleep apnea (OSA) is often associated with congenital craniofacial malformations such as Pierre-Robin Syndrome, Hemifacial Microsomia, Treacher Collins Syndrome resulting in decreased pharyngeal airway, which, in severe cases, leads to tracheostomy dependence. Some pediatric patients had tracheostomies done and others with severe respiratory distress were considered tracheostomy candidates.

MATERIALS AND METHODS

Twelve patients with severe respiratory distress without tracheostomy and ten patients with tracheostomy were treated by mandibular distraction osteogenesis using either external or internal devices. The expansion of mandibular framework was analyzed using bony cephalometric landmarks and computed tomography (CT).

RESULTS

The results demonstrated average mandibular elongation of 29 mm on each side using the external devices and 22 mm using the internal devices, and an increase in mandibular volume and pharyngeal airway. The group of patients with tracheostomies were decannulated and in the patients with respiratory distress there was improved airway with improvement of signs and symptoms of OSA with elimination of oxygen requirement.

CONCLUSIONS

Mandibular distraction is a useful method in younger children with OSA expanding the mandible and concomitantly advancing the base of tongue and hyoid bone increasing the pharyngeal airway. The external devices permit greater distraction length, the removal is simple but the devices are uncomfortable for the patients. On the other hand, the internal devices are more comfortable for patients but permit shorter distraction length and require a second operation for removal.

A method for mandibular dental arch superimposition using 3D cone beam CT and orthodontic 3D digital model

OBJECTIVE

The purpose of this study was to develop superimposition method on the lower arch using 3-dimensional (3D) cone beam computed tomography (CBCT) images and orthodontic 3D digital modeling.

METHODS

Integrated 3D CBCT images were acquired by substituting the dental portion of 3D CBCT images with precise dental images of an orthodontic 3D digital model. Images were acquired before and after treatment. For the superimposition, 2 superimposition methods were designed. Surface superimposition was based on the basal bone structure of the mandible by surface-to-surface matching (best-fit method). Plane superimposition was based on anatomical structures (mental and lingual foramen). For the evaluation, 10 landmarks including teeth and anatomic structures were assigned, and 30 times of superimpositions and measurements were performed to determine the more reproducible and reliable method.

RESULTS

All landmarks demonstrated that the surface superimposition method produced relatively more consistent coordinate values. The mean distances of measured landmarks values from the means were statistically significantly lower with the surface superimpositions method.

CONCLUSIONS

Between the 2 superimposition methods designed for the evaluation of 3D changes in the lower arch, surface superimposition was the simpler, more reproducible, reliable method.

CAD/CAM bilateral ear prostheses construction for Treacher Collins syndrome patients using laser scanning and rapid prototyping

Ear defects in patients affected by Treacher Collins syndrome necessitate the replacement of the existing anatomic residuals of the ears with custom-made prostheses. This paper describes a multidisciplinary protocol involving both medicine and computer-aided design/computer-aided manufacturing for manufacturing ear prostheses. Using innovative prototyping technologies together with conventional silicone processing procedures, a step-by-step procedure is presented. The complete workflow includes laser scanning of the defective regions of a patient's face, the use of 3D anatomic models from an ear digital library and rapid prototyping of both substructures for bar anchoring and moulds for silicone processing.

Computer-aided design and manufacturing construction of a surgical template for craniofacial implant positioning to support a definitive nasal prosthesis

AIM

To design a surgical template to guide the insertion of craniofacial implants for nasal prosthesis retention.

MATERIALS AND METHODS

The planning of the implant position was obtained using software for virtual surgery; the positions were transferred to a free-form computer-aided design modeling software and used to design the surgical guides. A rapid prototyping system was used to 3D-print a three-part template: a helmet to support the others, a starting guide to mark the skin before flap elevation, and a surgical guide for bone drilling. An accuracy evaluation between the planned and the placed final position of each implant was carried out by measuring the inclination of the axis of the implant (angular deviation) and the position of the apex of the implant (deviation at apex).

RESULTS

The implant in the glabella differed in angulation by 7.78°, while the two implants in the premaxilla differed by 1.86 and 4.55°, respectively. The deviation values at the apex of the implants with respect to the planned position were 1.17 mm for the implant in the glabella and 2.81 and 3.39 mm, respectively, for those implanted in the maxilla.

CONCLUSIONS

The protocol presented in this article may represent a viable way to position craniofacial implants for supporting nasal prostheses.

Development of a simulation system in mandibular orthognathic surgery based on integrated three-dimensional data

Purpose

Surgical simulation should reflect the 3D movement of dentition and the resultant movement of the osteotomized segments, which can influence surgical outcome. The present study was aimed at developing a new simulation system that enables virtual osteotomy of a given surgical situation and evaluation of the bony interference between the osteotomized segments of the mandible.

Subjects and methods

The data of 3D computer tomography (CT) for maxillomandibular dental casts were integrated into the standard coordinates of a 3D cephalogram. To evaluate the accuracy of the system, measurement errors of the 3D CT virtual model from a dry skull were compared with the computer simulation system and a contact-type 3D digitizer. To examine the clinical accessibility, 15 mandibular prognathism patients with mild to severe asymmetry were evaluated with the simulation program.

Results

The average error of measurement in all directions was 1.31 mm. It was possible to simulate various osteotomy procedures by conversion of the 3D coordinates of the dental cast and CT data into the standard coordinate system of a 3D cephalogram. Using this simulation system, it was possible to prevent condylar torque or segment malpositioning by removing the bony interference visualized by a 3D virtual model.

Conclusion

A new system, which enables the precise visualization of osteotomized segments and calculation of bony interference, was proposed in the present study. This new system provides an acceptable precision of treatment planning of orthognathic surgery, especially for facial asymmetry.

Computer planning and intraoperative navigation in cranio-maxillofacial surgery

Preoperative computer design and stereolithographic modeling combined with intraoperative navigation provide a useful guide for and possibly more accurate reconstruction of a variety of complex cranio-maxillofacial deformities. Although probably not necessary for routine use, the author's early experience confirms that of other surgeons with more than a decade of experience: computer-assisted surgery is indicated for complex posttraumatic or postablative reconstruction of the orbits, cranium, maxilla, and mandible; total temporomandibular joint replacement; orthognathic surgery; and complex dental/craniofacial implantology. Further study is needed to provide outcomes data and cost-benefit analyses for each of these indications.

Immediate facial rehabilitation in cancer patients using CAD-CAM and rapid prototyping technology: a pilot study

PURPOSE

This study describes the workflow in a procedure to create a provisional facial prosthesis for cancer patients using digital and rapid prototyping technologies without the need for supporting craniofacial implants.

MATERIALS AND METHODS

An integrated workflow procedure aimed at the construction of provisional silicone prosthesis was used to rehabilitate a facial disfigurement in a patient who had undergone ablative surgery of the midface. A laser scan of the defect was obtained, and a digital model of the patient's face was constructed using virtual mirroring of the healthy side and referencing the "Nose Digital Library."

RESULTS

The missing volume of the face was reconstructed, and a rapid-prototyped mold was devised to process the silicone prosthesis. A provisional eyeglasses-supported prosthesis designed with a CAD/CAM-projected titanium substructure was connected using the micro-components of implant prosthetic devices.

CONCLUSIONS

The workflow described herein offers a viable procedure for quickly restoring facial defects by means of provisional prosthetic rehabilitation.

Systematic contact-free 3D topometry of the soft tissue profile in cleft lips

OBJECTIVE

To evaluate the clinical application of three-dimensional (3D) imaging for the analysis of a broad variety of cleft lips and to conduct a systematic analysis.

DESIGN

This was a prospective study using a noncontact 3D laser scanner to acquire the preoperative 3D facial profiles. The data sets were analyzed qualitatively and quantitatively. The data were expressed by ratios and scores.

PATIENTS

Forty nonsedated patients (1 to 39 years, average age 2.7 years) with unilateral cleft lip, cleft lip and alveolus, or complete unilateral cleft in Cambodia.

RESULTS

The acquired 3D data sets (mean acquisition time: 2.5 seconds) from facial surfaces were of diagnostic quality in 27 of 40 patients (average age, 14.2 years). In these cases all anatomical structures could be mapped precisely by means of landmark positioning in the range of millimeters. A new method of systematic analysis could be elaborated, allowing for data set expression independent of size and growth factors. In children under age 3, the measuring procedure was of limited value because of motion artifacts and was successful in only 6% (1 of 15) of these patients.

CONCLUSION

The system offers a solid and precise tool for 3D imaging of the complex cleft lip anatomy in compliant patients and is useful for preoperative cleft assessment and follow-up. However, the application is limited in moving infants or uncooperative adults because of scanning time and acquisition method. The development of motion tracking and faster devices could eliminate motion artifacts.

[Lip, jaw, and palate clefts. Analysis of unilateral cleft lip using 3-D laser topometry]

INVESTIGATION

In most cases it is not sufficient to use photographs and plaster casts to document and analyze the three-dimensional morphology of lip, jaw, and palate clefts. The aim of this study was to evaluate the applicability of surface scanning with a 3-D laser topography scanner in patients with unilateral cleft lip.

PATIENTS AND METHODS

Three-dimensional surface scans of the face were performed pre- and postoperatively in 20 patients (3-35 years of age) with a 3-D laser topography scanner. All patients were suffering from nonoperated, one-sided cleft lip, cleft lip-jaw, or cleft lip-jaw and palate. The digital data sets were metrically analyzed and expressed on the basis of quotients, independent of size factors.

RESULTS

Using this 3-D laser scanner it was possible to acquire good quality three-dimensional data sets. Measurements were in the dimension of millimeters. Based on the data sets it was possible to provide the three-dimensional cleft morphology with reproducible landmarks and analyze the data. The postoperative symmetry of the face was controlled and objectively quantified. It is disadvantageous however that numerous views need to be taken to get the full image of the face and that the scanning process takes about 2 s.

CONCLUSION

The presented 3-D laser scanner renders a precise 3-D surface analysis of the lip and nose region in cleft patients. For lively infants or uncooperative adults, the system is suitable only to a limited extent due to the time-consuming scanning process.

Three-dimensional surface acquisition systems for the study of facial morphology and their application to maxillofacial surgery

BACKGROUND

There has been a growing interest in three-dimensional (3D) surface imaging devices over the last few years.

METHODS

This comprehensive review discusses the various emerging technologies in this field of 3D imaging and applies the use of technology to oral and maxillofacial imaging.

RESULTS

The paper shows that there is increased awareness and application of technology to the field.

CONCLUSION

3D surface acquisition technology is improving at a rapid pace and has a place in oral and maxillofacial surgery.

The use of a new 3D splint and double CT scan procedure to obtain an accurate anatomic virtual augmented model of the skull

Three-dimensional (3D) virtual planning of orthognathic surgery requires detailed visualization of the interocclusal relationship. The purpose of this study was to introduce the modification of the double computed tomography (CT) scan procedure using a newly designed 3D splint in order to obtain a detailed anatomic 3D virtual augmented model of the skull. A total of 10 dry adult human cadaver skulls were used to evaluate the accuracy of the automatic rigid registration method for fusion of both CT datasets (Maxilim, version 1.3.0). The overall mean registration error was 0.1355+/-0.0323 mm (range 0.0760-0.1782 mm). Analysis of variance showed a registration method error of 0.0564 mm (P < 0.001; 95% confidence interval = 0.0491-0.0622). The combination of the newly designed 3D splint with the double CT scan procedure allowed accurate registration and the set-up of an accurate anatomic 3D virtual augmented model of the skull with detailed dental surface.

A new navigation system based on cephalograms and dental casts for oral and maxillofacial surgery

Intraoperative navigation systems help surgeons to accurately carry out preoperative plans without injuring anatomically important structures. A system is evaluated that uses cephalograms instead of computed tomographic (CT) scans to create images. Three-dimensional (3D) dental casts provide registration between imaging data and the patient. Cephalograms are widely employed in orthognathic and oral and maxillofacial surgery and expose patients to lower doses of radiation than CT. The system uses a dental cast to register the operation field to a pair of frontal and lateral cephalograms. The cast is transformed to 3D data with a laser scanner and a programme that runs on a personal computer. 3D data describing the dental cast, cephalograms and the oral and maxillofacial region of the patient are integrated with specialized software. The optical tracking system for navigation uses charged-coupled-device (CCD) video cameras and light-emitting diodes (LEDs). Two CCD video cameras follow the 3D coordinates of LED assemblies attached to the head, lower jaw and a handpiece. Errors occurring when a dental cast was transformed to 3D data ranged from 0.08 to 0.21 mm. Mean errors were 0.71 mm (0.21-1.09 mm) for the right maxillary central incisor, 0.62 mm (0.04-1.69 mm) for the right maxillary 2nd molar and 1.02 mm (0.23-1.47 mm) for the left maxillary 2nd molar. This surgical navigation system is sufficiently accurate for use in oral and maxillofacial surgery.

Application of computer-assisted design in craniofacial reconstructive surgery using a commercial image guidance system

The technology of digital image guidance systems has transformed many aspects of neurosurgery, including intracranial tumor surgery, functional neurosurgery, and spinal surgery. Despite the central role of imaging studies in diagnosis and treatment planning, intraoperative image guidance has so far had very limited application to the surgical correction of craniofacial deformities, particularly those associated with craniosynostosis. The authors report an example of the marriage of computer-assisted design methods to a commercially available neurosurgical image-guidance system in the treatment of a case of anterior plagiocephaly due to unilateral coronal synostosis. They discuss the steps that must yet be taken to make this technology applicable to the management of craniosynostosis in infants.

CAD-CAM generated ear cast by means of a laser scanner and rapid prototyping machine

Sculpting a wax ear cast for use when making a definitive prosthesis for a patient who has had auricle ablative surgery, is challenging. It requires a skilled anaplastologist along with complex instrumentation able to perform facial laser scans and reproduce anatomic details. The aim of this article is to present a technique to create a cast by laser scanning a stone cast of the existing ear. A 3D laser scanner develops an integrated 3D digital image of the unaffected ear, which is copied and then mirrored. A rapid prototyping machine collects the necessary data to manufacture the definitive resin ear. This procedure is time and cost effective only if the technology is free of charge.

Prototype of simulation of orthognathic surgery using a virtual reality haptic device

A maxillofacial simulator can support education and training. In the present study, cutting, separation, and quantitative rearrangement of bone during orthognathic surgery were simulated by means of a haptic device with virtual tactile perception. Computed tomographic (CT) images of two patients with severe jaw deformity, one women and one man, were input into the device. In the woman, Le Fort I osteotomy of the maxilla and sagittal splitting ramus osteotomy of the mandible were initially simulated. During surgery with the haptic device, separation and rearrangement of the maxilla and the ramus of the mandible were initially processed. However, there was discrepancy and overlapping of the ramus with the mandible. Intraoral vertical osteotomy of the right ramus was then performed, with satisfactory results and less discrepancy and interference. The simulation was referred to at surgery, and satisfactory surgical assistance was postoperatively confirmed on CT images. The male patient had severe jaw deformity due to unequal growth between the ramuses, resulting in anterior crossbite. Sagittal splitting ramus osteotomy with rotation of the mandible was successfully simulated. Because of its versatility and functions, the present device was found to be useful for simulating various procedures for orthognathic surgery and thereby three-dimensionally determine surgical movements.

Comparison of the predicted surgical results following virtual planning with those actually achieved following bimaxillary operation of dysgnathia

AIM

To simulate the surgery of dysgnathia, several forms of computer software allowing two-dimensional 'virtual' planning are frequently used. However, in many cases it is not possible to transfer the virtual plan accurately to the surgical site. It is the purpose of this study to find the errors likely to occur when transferring the data.

METHODS

In 22 bimaxillary osteotomies for dysgnathia, the results of preoperative planning were compared with the surgical outcomes. The programme WinCeph 4.19 (Compudent) was used for cephalometric analyses and simulation of the operations.

RESULTS

Six major skeletal parameters were evaluated when comparing both the planned and the actual outcome, and the following results were recorded: Delta-SNA 1.53 degrees (+/-1.20), Delta-SNB 1.67 degrees (+/-1.29), Delta-ANB 1.62 degrees (+/-1.47), Delta-NL-NSL 3.9 degrees (+/-2.30), Delta-ML-NSL 3.6 degrees (+/-3.7) and Delta-ArGoMe 6.1 degrees (+/-4.6).

CONCLUSION

It was anticipated that the most important differences between planned and surgical outcomes were found to be in the vertical changes. Planning and data transfer was comparatively accurate with regard to sagittal data. Apart from several mechanical methods for data transfer, systems using navigation are therefore being discussed and used increasingly. They ensure accurate data transfer to the surgical site.

Three-Dimensional Osteotomy Planning in Maxillofacial Surgery Including Soft Tissue Prediction

Preoperative planning of complex osteotomies in craniomaxillofacial surgery, in conjunction with a surgeon's expertise, is essential for achieving an optimal result. However, the soft tissue changes that accompany facial bone movements cannot yet be accurately predicted. Bony tissue, because of its greater density, can be better predicted, but it alone does not account for the final aesthetic result. A new approach using not only three-dimensional (3-D) surface models of the patient's anatomy, but also a corresponding volumetric model, is discussed. This 3-D planning software was used in the treatment of 15 patients and was found to provide a good correlation between simulation and postoperative outcome.

Automated laser registration in image-guided surgery: evaluation of the correlation between laser scan resolution and navigation accuracy

Markerless patient registration based on the facial skin surface makes logistics prior to image-guided surgery much easier, as it is not necessary to place and measure registration markers. A laser scan registration of the surgical site takes the place of conventional marker-based registration. In a clinical study, the stability and accuracy of markerless patient registration was evaluated in 12 patients. Intraoral titanium markers served as targets for the infrared-pointer of the navigation system in order to check the accuracy of the markerless registration process. The correlation between laser scan resolution and navigation accuracy was checked using seven different laser scan resolutions (a cloud of 300,000 laser scan points down to 3750 laser scan points of the surgical site). The markerless patient registration was successful as long as high laser scan resolution was used (30,000 laser scan points and more): the titanium markers were detected with a mean deviation of 1.1 +/- 0.2 mm. Low resolution laser scans (6000 laser scan points of the surgical site and less) revealed inaccuracies up to 6 mm.

3D CT evaluation of masseter muscle morphology after setback osteotomy for mandibular prognathism

OBJECTIVE

Following mandibular setback osteotomy, changes in the direction, length, and cross-sectional area of the masseter muscle were studied by means of computerized tomography (CT) images generated with a 3-dimensional (3D) reconstructive technique.

STUDY DESIGN

Pre- and postoperative CT examinations were performed on 17 prognathic patients treated by sagittal split ramus osteotomy with rigid osteosynthesis and 13 patients treated by intraoral vertical ramus osteotomy without osteosynthesis. The pre- and postoperative masseter muscle direction and length were evaluated using 3D CT images observed from a lateral viewing angle. The cross-sectional area of the masseter muscle was first measured on an axial CT image of a selected slice level, following which the right-angle cross-sectional area of the muscle was revised using the measured area from the axial image.

RESULTS

Postoperatively, anterior tilting of the masseter muscle was observed; however, masseter muscle length was unchanged. Three months postoperatively, a significant reduction in the cross-sectional area of the masseter muscle was seen. A tendency to revert back to the normal dimension was seen between 6 months and 1 year postoperatively. No significant difference was noted between the 2 surgical techniques.

CONCLUSIONS

Three-dimensional computed tomography is an adequate imaging modality for masseter muscle evaluation. The results of this study suggest the masseter muscle may undergo reversible atrophy after mandibular setback osteotomy.

Fusion of computed tomography data and optical 3D images of the dentition for streak artefact correction in the simulation of orthognathic surgery

OBJECTIVE

To determine the limits of accuracy of fusion of optical three-dimensional (3D) imaging and computed tomography (CT) with and without metal artefacts in an experimental setting and to show the application of this hybrid system in 3D orthognathic surgery simulation.

METHODS

Ten plaster casts of dental arches were subjected to a CT scan and optical 3D surface imaging. Subsequently, the first molars in the plaster casts were supplied with metal restorations, bilaterally, and new CT scans and optical surface images were assessed. The registration of the surface data of the two imaging modalities of the study models without and with metal restorations was carried out. The mean distance between the two data sets was calculated. From a patient a CT scan of the skull as well as optical 3D images of plaster casts of the dental arches were acquired. Again the two imaging modalities were registered and virtual orthognathic surgery simulation was carried out.

RESULTS

The mean distance between the corresponding data points of CT and optical 3D surface images was 0.1262+/-0.0301 mm and 0.2671+/-0.0580 mm, respectively, for the plaster casts without and with metal restorations. The differences between these data were statistically significant (P<0.0005). For the patient case a mean difference of 0.66+/-0.49 mm and 0.56+/-0.48 mm for mandible and maxilla, respectively, was calculated between CT and optical surface data.

CONCLUSION

The accuracy of the fusion of 3D CT surface data and optical 3D imaging is significantly reduced by metal artefacts. However, it seems appropriate for virtual orthognathic surgery simulation, as post-operative orthodontics are performed frequently.

[Rapid prototyping in planning reconstructive surgery of the head and neck. Review and evaluation of indications in clinical use]

PURPOSE

The aim was to define the indications for use of rapid prototyping models based on data of patients treated with this technique.

PATIENTS AND METHODS

Since 1987 our department has been developing methods of rapid prototyping in surgery planning. During the study, first the statistical and reproducible anatomical precision of rapid prototyping models was determined on pig skull measurements depending on CT parameters and method of rapid prototyping.

RESULTS

Measurements on stereolithography models and on selective laser sintered models confirmed an accuracy of +/-0.88 mm or 2.7% (maximum deviation: -3.0 mm to +3.2 mm) independently from CT parameters or method of rapid prototyping, respectively. With the same precision of models multilayer helical CT with a higher rate is the preferable method of data acquisition compared to conventional helical CT. From 1990 to 2002 in atotal of 122 patients, 127 rapid prototyping models were manufactured: in 112 patients stereolithography models, in 2 patients an additional stereolithography model, in 2 patients an additional selective laser sinter model, in 1 patient an additional milled model, and in 10 patients just a selective laser sinter model.

CONCLUSION

Reconstructive surgery, distraction osteogenesis including midface distraction, and dental implantology are proven to be the major indications for rapid prototyping as confirmed in a review of the literature. Surgery planning on rapid prototyping models should only be used in individual cases due to radiation dose and high costs. Routine use of this technique only seems to be indicated in skull reconstruction and distraction osteogenesis.