Toyohiko Hayashi

Computer-aided determination of occlusal contact points for dental 3-D CAD

Present dental CAD systems enable us to design functional occlusal tooth surfaces which harmonize with the patient’s stomatognathic function. In order to avoid occlusal interferences during tooth excursions, currently available systems usually use the patient’s functional occlusal impressions for the design of occlusal contact points. Previous interfere-free design, however, has been done on a trial-and-error basis by using visual inspection. To improve this time-consuming procedure, this paper proposes a computer-aided system for assisting in the determination of the occlusal contact points by visualizing the appropriate regions of the opposing surface. The system can designate such regions from data of the opposing occlusal surfaces and their relative movements can be simulated by using a virtual articulator. Experiments for designing the crown of a lower first molar demonstrated that all contact points selected within the designated regions completely satisfied the required contact or separation during tooth excursions, confirming the effectiveness of our computer-aided procedure.

A physiological control of chewing-like jaw movement for robotized jaw simulator JSN/2A

In order to reproduce a chewing-like movement In a robotized jaw simulator, JSN/2A, the authors employed a physiological and adaptive control scheme, which optimizes open-close movement first, and then gradually transfers it into a chewing-like movement by asymmetrizing bilateral control-parameter values. This strategy was verified to be effective to obtain a life-like and reproducible trajectory.

Functions of masseter and temporalis muscles in the control of temporomandibular joint loading--a static analysis using a two-dimensional rigid-body spring model.

Masticatory forces or bite forces applied to the teeth are known to generate a compressive force on the temporomandibular joint (TMJ). This intra-articular force is referred to as TMJ loading. TMJ loading is considered to be controlled to a certain extent by the stomatognathic system, so as not to exceed a certain limit. In order to clarify the control mechanism of the TMJ during biting, the controllability of TMJ loading through coordinated activities of the masticatory muscles has been numerically analyzed using a static two-dimensional jaw model. This model consists of a rigid-body model of the jaws and a spring model of the articular disk, which includes three dominant muscle force vectors representing the masseter, temporalis and lateral pterygoid muscles. The bite force vector is assumed to be applied solely at the first molar. Static equilibrium analyses suggest that coordinated activities of the masseter muscle and anterior portion of the temporalis muscle can minimize TMJ loading and concentrate the stress within the articular disk to the intermediate zone of the disk, and that the activity of the posterior portion of the temporalis muscle has the possibility of reducing TMJ loading.

Preliminary study of 6 degrees of freedom measurement of scapula movement using a motion capture system

Summary form only given. The shoulder joints vulnerability to injury, especially while engaged in sports, makes it a frequent focus of the orthopedists attention. We investigated the mechanics of its motion, using a purpose-built camera setup able to detect, in six degrees of freedom, a set of round plastic markers attached to the skin, above bony landmarks. Since a given section of skin is able to slide in any direction, within a limited range, over the skeleton, the indicators deviate from their landmarks according to the degree of body movement. We established a set of landmarks that would lessen the influence of the skins mobility, in order to measure scapula movement accurately.

Development of a physiological knee motion simulator

Several kinds of knee motion simulator systems have been developed for the accurate analysis of knee biomechanics. Knee motion simulators, however, are not recognized for their practical use because of difficulties in design and control. In this study, a wire-driven knee simulator which generates physiological knee motion has been developed. Physiological three-dimensional tibia motion against the femur can be generated by the simulator. Many clinical studies have been performed to analyze the length displacement pattern of the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL). We assume that the physiological knee motion can be realized if the length displacement patterns of the ACL and PCL against the knee flexion angle are the same as the experimental data obtained from the literature. A fuzzy neural control policy, one of the most effective intelligent control policies. has been applied for control of the simulator. Applying the fuzzy neural control policy, human knowledge and experience can be reflected and adaptive/learning ability can be incorporated in the controller. On-line learning of the fuzzy neural controller is carried out to minimize a fuzzy controlled evaluation function using the back-propagation learning algorithm. The effectiveness of the proposed simulator has been evaluated by experiments using a model bone.

Denture Prosthetic Treatment by the Assistance of Videofluorography.

The purpose of this clinical study was to show that videofluorography (VF) is a useful tool for diagnosis of mastication and swallowing. A series of modifications of a VF system allowed a relaxed posture for the patient and easy orientation of the patients head under the condition of low-level X-ray exposure. Visual analyses using this system were effective, especially in denture prosthetic treatment, as follows:1. The habitual retracted tongue position during mastication was a cause of lower complete denture instability.2. A palatal reshaping prosthesis improved the disphagia that bothered a patient after partial excision of the tongue and mandible due to oral floor cancer.3. Distal extention of the denture base to the space left after a segmental mandible resection could improve mastication and swallowing.4. The potential risk of aspiration pneumonia in an elderly patient who had a cerebral infarction history and who wore new complete dentures.5. A patients strong demand to masticate food by himself after total glossectomy and mandibulectomy was satisfied by a prosthesis as a substitute for the tongue and teeth.The results suggested that VF imaging analysis was available to evaluate masticatory function in denture wearers.