Maxillofacial Surgery Simulation Research Articles

Digital setting of postoperative planned occlusion using occlusal contact points on a dental cast model in digital maxillofacial surgery.

This study analyzed the accuracy of digital occlusion settings for maxillofacial surgery simulation using occlusal contact points obtained from dental cast models. Twenty-nine paired dental cast models of patients were used. The orthodontist set the dental cast for postoperative planned occlusion in the articulator. In the experimental group, a digital dental cast was placed in the occlusion state between the maxillary cast and the mandibular cast by the paired points matching method according to the more than four paired occlusal contact points. In the control group, the obtained digital dental cast data and occlusal lateral surface scan data were used to create maxillary and mandibular digital occlusions of the dental cast. Significantly greater error occurred when occlusion was set based on paired points matched by occlusal contact points than when direct intraoral scanning was used. This paired points matching method may be considered an alternative in cases in which superimposition using occlusal surfaces or the external surface of dental cast models is difficult in the clinical setting. However, the occlusal surface-based method for digital dental casts is recommended for digital planned occlusion in maxillofacial simulation.

The Application of Rapid Prototyping in Prosthodontics

Dentists have used rapid prototyping (RP) techniques in the fields of oral maxillofacial surgery simulation and implantology. With new research emerging for molding materials and the forming process of RP techniques, this method is becoming more attractive in dental prosthesis fabrication; however, few researchers have published material on the RP technology of prosthesis pattern fabrication. This article reviews and discusses the application of RP techniques for prosthodontics including: (1) fabrication of wax pattern for the dental prosthesis, (2) dental (facial) prosthesis mold (shell) fabrication, (3) dental metal prosthesis fabrication, and (4) zirconia prosthesis fabrication. Many people could benefit from this new technology through various forms of dental prosthesis production. Traditional prosthodontic practices could also be changed by RP techniques in the near future.

Gradient field based inhomogeneous volumetric mesh deformation for maxillofacial surgery simulation

This paper presents a novel inhomogeneous volumetric mesh deformation approach by gradient field manipulation, and uses it for maxillofacial surgery simulation. The study is inspired by the state-of-the-art surface deformation techniques based on differential representations. Working in the volumetric domain instead of on only the surface can preserve the volumetric details much better, avoid local self-intersections, and achieve better deformation propagation because of the internal mesh connections. By integrating the mesh cell material stiffness parameter into our new discrete volumetric Laplacian operator, it is very convenient to incorporate inhomogeneous materials into the deformation framework. In addition, the system matrix for solving the volumetric harmonic field to handle the local transformation problem is the same used for Poisson reconstruction equation, thus it requires solving essentially only one global linear system. The system is easy to use, and can accept explicit rotational constraints, or only translational constraints to drive the deformation. One typical maxillofacial surgery case was simulated by the new methodology with inhomogeneous material estimated directly from CT data, and compared to the commonly used finite element method (FEM) approach. The results demonstrated that the deformation methodology achieved good accuracy, as well as interactive performance. Therefore, the usage of our volumetric mesh deformation approach is relevant and suitable for daily clinical practice.

Maxillofacial surgery simulation using a mass-spring model derived from continuum and the scaled displacement method

Development of a maxillofacial surgery simulation software capable of predicting a patient's appearance after surgery. We have derived a new mass-spring model (MSM) equivalent to a linear finite element (FE) model for cubic elements. In addition, we propose the scaled displacement method as a new method to perform the simulation more realistically. The average error of eight soft tissue landmarks measured between 0.37 and 2.01 mm except from a landmark that had an error of 4.44 mm; values close to those obtained with the linear FE method. On the other hand, the scaled displacement method allows avoiding punctual stress concentration and bending effects making a much more realistic simulation in the region of the bone cut. Good results have been achieved with our two proposed methods. In addition, the simple way in which MSM can be parallelized makes it an interesting alternative to FE method.

Maxillo-facial surgery simulation with a simple patient specific material model

In this paper we develop an elasto-dynamic model of the human arm that includes effects of neuro-muscular control upon elastic deformation in the limb. The elasto-dynamic model of the arm is based on hybrid parameter multiple body system variational projection principles presented in the companion paper. Though the technique is suitable for detailed bone and joint modeling, we present simulations for simplified geometry of the bones, discretized as Rayleigh beams with elongation, while allowing for large deflections. Motion of the upper extremity is simulated by incorporating muscle forces derived from a Hill-type model of musculotendon dynamics. The effects of muscle force are modeled in two ways. In one approach, an effective joint torque is calculated by multiplying the muscle force by a joint moment arm. A second approach models the muscle as acting along a straight line between the origin and insertion sites of the tendon. Simple arm motion is simulated by utilizing neural feedback and feedforward control. Simulations illustrate the combined effects of neural control strategies, models of muscle force inclusion, and elastic assumptions on joint trajectories and stress and strain development in the bone and tendon.

An Approach for the High-Level Specification of QoS-Aware Grid Workflows Considering Location Affinity

Many important scientific and engineering problems may be solved by combining multiple applications in the form of a Grid workflow. We consider that for the wide acceptance of Grid technology it is important that the user has the possibility to express requirements on Quality of Service (QoS) at workflow specification time. However, most of the existing workflow languages lack constructs for QoS specification. In this paper we present an approach for high level workflow specification that considers a comprehensive set of QoS requirements. Besides performance related QoS, it includes economical, legal and security aspects. For instance, for security or legal reasons the user may express the location affinity regarding Grid resources on which certain workflow tasks may be executed. Our QoS-aware workflow system provides support for the whole workflow life cycle from specification to execution. Workflow is specified graphically, in an intuitive manner, based on a standard visual modeling language. A set of QoS-aware service-oriented components is provided for workflow planning to support automatic constraint-based service negotiation and workflow optimization. For reducing the complexity of workflow planning, we introduce a QoS-aware workflow reduction technique. We illustrate our approach with a real-world workflow for maxillo facial surgery simulation.

GEMSS: Grid-infrastructure for Medical Service Provision

The European GEMSS Project is concerned with the creation of medical Grid service prototypes and their evaluation in a secure service-oriented infrastructure for distributed on demand/supercomputing. Key aspects of the GEMSS Grid middleware include negotiable QoS support for time-critical service provision, flexible support for business models, and security at all levels in order to ensure privacy of patient data as well as compliance to EU law. The GEMSS Grid infrastructure is based on a service-oriented architecture and is being built on top of existing standard Grid and Web technologies. The GEMSS infrastructure offers a generic Grid service provision framework that hides the complexity of transforming existing applications into Grid services. For the development of client-side applications or portals, a pluggable component framework has been developed, providing developers with full control over business processes, service discovery, QoS negotiation, and workflow, while keeping their underlying implementation hidden from view. A first version of the GEMSS Grid infrastructure is operational and has been used for the set-up of a Grid test-bed deploying six medical Grid service prototypes including maxillo-facial surgery simulation, neuro-surgery support, radio-surgery planning, inhaled drug-delivery simulation, cardiovascular simulation and advanced image reconstruction. The GEMSS Grid infrastructure is based on standard Web Services technology with an anticipated future transition path towards the OGSA standard proposed by the Global Grid Forum. GEMSS demonstrates that the Grid can be used to provide medical practitioners and researchers with access to advanced simulation and image processing services for improved preoperative planning and near real-time surgical support.