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Research – Lab for Physiology and Biomechanics of the Masticatory SystemCurrent Projects
01. Functional testing of diarthrodial joint soft tissues with in vivo acquired anatomical and kinematic information(Swiss National Science Foundation project # 325200-110067)Objective of this project is to gain knowledge of the mechanobiology of TMJ cartilage, by designing functional tests of cartilage tissue in general and TMJ disc tissue in particular. The long-term objective of this research is to understand the pathomechanics of TMJ degeneration and OA. We will take into account physiological conditions, thanks to our unique expertise in dynamic stereometry of the TMJ with real anatomic and kinematic data (s. project # 3), which yields an accurate 3D dynamic insight into the deformation of the joint space. As a matter of fact, thanks to the attachment of the jaw tracking references directly to the teeth, we are able to precisely relate the anatomy to the kinematics of the TMJ. This type of research can then be extended to other joints, in particular the knee, also providing functional tests for synthetic or tissue engineered replacement materials. 02. Mandibular kinematics and dynamicsScope of this project is a deeper and global insight into the mechanical aspects of jaw motion (Cell Tiss Org 180:54-68, 2005). Parts of this project are in collaboration with the Universities of Sydney and Western Sydney, Sydney NSW, Australia (Drs. G.M. Murray and J.A. Gal). New mechanical models such as the helical axis and the wrench axis are used to describe and characterize in a overall and compact way the kinematics of the mandible and the forces and torques acting on it. These quantities are extremely sensitive to jaw motion asymmetries and irregularities (J Dent Res 76:704:713, 1997 and 79:1566-1572, 2000) and are also useful to describe the contribution of the single masticatory muscles to any functional tasks (J Biomech 37:1405-1412, 2004). A jaw motion replicator based on the Stewart platform principle is being developed in order to move in real-time dental arch casts by means of the corresponding real jaw-tracking data. Beside the use of this replicator as a perfect articulator, the device will allow to perform more complex mechanical studies on whole craniomandibular models. 03. Dynamic stereometry of the temporomandibular jointAim of this project is to study the movement of the whole condyle in the fossa for didactic purposes and for the assessment of kinematic norms and irregularities of the temporomandibular joint (TMJ). The method, under constant development, consists in combining the three-dimensional software reconstruction of the joint structure (obtained by segmentation of a stack of tomographic images) with jaw movement data (obtained by means of optoelectronic tracking with 6 degrees-of-freedom) (Technology and Health Care, 2:193-207, 1994, Ann Acad Med Singapore, 24:11-16, 1995, Der Unfallchirurg, 261:106-114, 1997). It is thus possible not only to calculate and represent graphically the relative movement of the whole articular segments but also to perform quantitative measurements within the joint such as for instance the determination of time-varying intraarticular distances (Orthod Craniofac Res, 6-S1:37-47, 2003). 04. Development of a new optoelectronic tracking deviceGoal of this project is the development of a new jaw tracking device for the replacement of the optoelectronic system developed at our laboratory in the middle of the 80s (J Orofac Pain, 8:155-164, 1994). This system - based on improved optics and computation-intensive video signal processing - will have a much higher sampling rate and spatial resolution, a much lower geometric noise and will be able to host more than three linear cameras, thus increasing the field of view. The system will allow to record transient events lasting few milliseconds, such as sudden accelerations related to temporomandibular joint (TMJ) clicking, to measure variations in the condyle-fossa distance with higher accuracy, to animate both TMJs with single-sided recordings and to track jaw movements in unfavorable conditions, such as in animal experiments. 05. Non invasive analysis of temporomandibular joint loadingGoal of this project is the non invasive analysis of the TMJ loading under functional and parafunctional conditions. This is achieved by measuring the variation of the condyle-fossa distances (Med Engin Phys, 25:181-190, 2003). Joint loading is extrapolated from the variation of the area of minimum condyle-fossa distance under different loading conditions (unloaded jaw movements, chewing of different foods, clenching on a force transducer placed in different positions between the dental arches) (Habilitationsschrift PD Dr. L.M. Gallo, 2001). Preliminary results show that the loading patterns depend on the localization of the food or of the force transducer. The correlation of static data (clenching) with dynamic data (chewing) will validate the model. 06. Dynamic 3D biphasic finite element analysis of the temporomandibular joint discThis project is motivated by the hypothesis that magnitude and frequency of stresses applied to the collagen-glycosaminoglycan matrix of articular cartilage may play a role in the development of degenerative joint disease. In cooperation with the University of Nebraska Medical Center, Lincoln NE, USA (Drs. J.C. Nickel and L.R. Iwasaki) as well as Rensselaer Polytechnic Institute, Troy NY, USA (Dr. R.L. Spilker), we are investigating dynamically the stress, strain and pressure conditions within the temporomandibular joint disc, modeled as a biphasic tissue (J Biomech, 37:1787-1791, 2004). Since the TMJ disc material properties are anisotropic, we first analyzed the mediolateral velocity component of stress-fields responsible for plowing forces. As a first approximation, we located the stress-field of the TMJ disc in the area of minimum condyle-fossa distance. Preliminary results show that in asymptomatic joints the mediolateral velocity components vary between 35+17 and 40+19 mm/sec during unloaded jaw opening/closing movements of 0.5 and 1 Hz rate, with a corresponding energy dissipation estimated between 6 and 709 mJ (J Dent Res 79:1740-1746, 2000). Furthermore, a study on clicking TMJs (J Dent Res 83:480-484, 2004) showed that the mediolateral spread s of the stress-field trajectories was 2.4 ± 1.0 mm (s max = 4.9 ± 2.1 mm) with an aspect ratio a/h of 2.5 ± 1.6, both significantly greater than in controls (p<0.05). The stress-field trajectories of the controls coincided during opening/closing (s = 0.9 ± 0.2 mm, s max = 1.8 ± 0.8 mm, a/h = 1.6 ± 0.3). Clicking TMJs showed much less coincident stress-field paths and much “flatter” stress-fields than controls during jaw opening/closing as well as modifications of the shapes of bones and disc (J Orofac Pain 16:29-38, 2002, J Dent Res 83:480-484, 2004). 07. Animation of masticatory musclesAim of this project is the representation and the analysis of the activity of the whole masticatory musculature using inverse dynamics based on muscle Hill-models. For this purpose, origins and insertions of the masticatory muscles as well as their lines of action are obtained from stacks of tomograms recorded by means of magnetic resonance imaging (MRI). The muscle models are then animated by the application of corresponding jaw-tracking information and the data obtained compared with electromyographic (EMG) recordings. Beside a further non invasive insight into the physiology of the normal masticatory system, these studies can lead to a better understanding of the etiology of rapid transient events such as the temporomandibular joint clicking. 08. Magnetic resonance imaging of the temporomandibular jointThis project aims at the improvement of magnetic resonance imaging (MRI) techniques for the representation of the temporomandibular joint hard and soft tissues, i. e. the disc, under static as well as dynamic conditions. The studies are performed in collaboration with the Swiss Federal Institute of Technology, Zurich, Switzerland (Dr. D. Meier). The use of the echo planar imaging (EPI) technique and the optimization of the MRI parameters lowered the frame acquisition time to 0.2-0.3 sec. It is now therefore possible to record TMJ disc motion not only in real time but also non invasively. The optimization of the acquisition parameters also allowed to implement a multislice technique, so that the medial, central and lateral parts of the TMJ can now be visualized dynamically, thus providing a good insight into the movement of the whole disc. Preliminary results were the topic of three publications (J Orofac Pain 14:65-73, 2000, 14:128-139, 2000, and 16:29-38, 2002). These techniques will be used to study disc kinematics in normal and pathological temporomandibular joints and to validate software models of the disc deformation. 09. Electromyographic long-time recording of the activity of masticatory musclesAim of this project is to investigate whether muscle pain of patients with craniomandibular disorders can be at least precipitated by the overloading of masticatory muscles. For this purpose we record and analyze the functional and parafunctional electromyographic (EMG) signals of masticatory muscles. The studies are performed in cooperation with the University of Montreal QC, Canada (Dr. G.J. Lavigne) and with the University “Federico II” of Naples, Italy (Dres. A. Michelotti und M. Farella) (Eur J Oral Sc 113:380-385, 2005 und J Dent Res 84:644-648, 2005). EMG signals are recorded in the natural environment by means of small portable recorders developed at our laboratory or in sleep laboratories by means of polysomnography (J Sleep Res 6:259-263, 1997). For every contraction episode, the computer calculates occurrence time, intensity, duration, and the integral of the EMG signal over time. Data on the nocturnal activity patterns of a normal group in the natural environment have already been published (J Dent Res 78:1436-1444, 1999). Data from nocturnal bruxers or patients with craniomandibular disorders are compared to those of a normal population. In this context we are also investigating whether patients with craniomandibular disorders clench more often at daytime than asymptomatic subjects. 10. Real-time recognition of masticatory muscles activityAim of this project is the online processing of electromyographic (EMG) signals for the automatic classification of masticatory muscle activity and its implementation in portable recorders (J Oral Rehabil 22:455-462, 1995). The method is based on multivariate discriminant analysis algorithms and has already proven successful in a laboratory version (J Dent Res 77:1541-1548, 1998). Besides providing an immediate analysis of oral function and parafunction and data storage with an efficient data compression, the system can also be useful in biofeedback therapy. New modern low-power high-speed integrated circuitry for signal acquisition and processing is needed for complete miniaturization. |
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