Human Jaw Motion Simulator Department of Mechanical & Industrial Engineering Northeastern...

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  • Human Jaw Motion Simulator

    Department of Mechanical & Industrial EngineeringNortheastern UniversityBoston, MA 02115

    April 17, 2007By:B. GalerN. HockenberryJ. MaloofM. Monte-LowreyK. ODonnell

    Advisor and Sponsor:Prof. Sinan Muftu

  • OutlineMotivation and GoalsProject StagesImportant Skull ComponentsMusclesSystem Analysis and Control Development Design DetailsResults and Conclusions

  • MotivationMotivationOver 10 million Americans are affected by TMJ disorders2 times as many woman as men suffer from TMJ disordersSymptoms range from jaw click to limited movement, lock jaw, and pain

    PurposeProvide resource for analyzing the TMJ to allow for treatment of TMJ disordersTo test prosthetics

  • Overall Project GoalsCreate physical model of a skullSimulate jaw motionsLabVIEW interfaceVirtual Matlab analysis

  • Stage GoalsStage IInitial Setup and Jaw ClosingStage IIJaw Opening (including opening to closing transition)Stage IIIJaw Clenching and Disc Adaptation (disc must be capable of multiple forms of motion)Stage IVLateral Jaw Motion/ Chewing (realistic disc simulation must be accomplished by this stage).

  • Background

  • Important Components of the SkullMaxillaMandible Muscles LigamentsTemporomandibular JointArticular disc

  • Muscles of Closing and Max ForcesTemporal120 lbsLateral pterygoid34 lbsMasseter93 lbs

  • Muscle Assumptions and ConstraintsMusclesCan only contractAre symmetrical for either side of jawAct in a single planeWill be simulated as acting as a single vector through the center of the muscle.

  • Muscle attachmentsKoolstra Study 1992Attachment points: On JawAnchor points: On SkullZero point based on contact point

    Musclex (m)y (m)MasseterAttachment0.0204-0.0605Anchor0.03380.0043

    Lateral PterygoidAttachment0.0032-0.0044Anchor0.02390.0064


  • System Analysis and Control Development

  • Motion of the Human JawWhat motions are involved in closing the jaw?

    What assumptions must be made?

    How can the motion be controlled?

  • AssumptionsCompressive Force on disc is constantDisc moves with mandibleMandible Contact PointTaken while in fully closed positionAlways perpendicular to articulating surfaceResults of AssumptionsThe Disc will be Left out of ModelThe Normal Force from the Articulating Surface Acts Directly on Contact Point

  • Physical Constraints of MandibleConstrained to single path of travelMapped profile of the articulating surfaceOrientation of lower jaw found at predefined target positions

  • System Control

    Anatomical ConstraintsControllabilityAvailable KnowledgeControl KnowledgePhysiologically RealisticValue54321TotalForce1211220Position2122125

  • Positional Control Motion TrackingConstrained OrientationsVarying Muscle lengths Matlab ProgramVariable surface profiles Variable tracking locationsCreates positional output Control MethodControl Muscle Lengths

  • Design Details

  • The Design

  • Frame

  • Muscle Decision Matrix

    TotalControlPrecisionAccuracyComplexityResourcesSafetyCost5433322High End Motor1611010103661Standard Motor1648877867Pneumatic784343335Hydraulic635341113Air Muscle684232335Muscle Wire1183658656Polymer1183658656

  • Brushless Servo Motors

    High precision and accuracyPosition control requires feedback

    AKM33E- Danaher Motion2.2NM torqueBuilt in encoder

  • Controlling the Motors

    NI PCI-7344 four axis servo/step motion controller MDM-2100 integrated three axis servo drive with power supply

  • LabVIEW InterfaceCan be run by any userAllow easy future changes to projectFeedback loop built into program

  • Pulley SystemPulleys used to increase torqueKeeps motor cost lowAllows for project expansion

  • Wire Attachments and GuidesCan only pull like musclesAdjustable tension

  • Skull and LubricationMimics ProgramConvert CT scan to 3-D modelSLA model to rubber-molded modelAttachment points tested for bendingLubrication on joint

    LubricatedSurface ASurface BCoefficient of FrictionNoTeflonDelrin0.45NoTeflonTeflon0.5NoDelrinDelrin0.45YesTeflonDelrin0.08YesTeflonTeflon0.06YesDelrinDelrin0.1

  • Results and Conclusion

  • Virtual Analysis

  • Physical Analysis

  • ResultsVirtual Jaw Appeared to Open Improperly Negative Force ValuesPhysical Separation at joint

  • ConclusionsInitial Assumptions Were IncorrectMandible Does Not Stay Perpendicular to the Articulating SurfaceMuscles Can Only Contract, Whereas Results Suggested ExpansionMuscle Choices May be Incorrect or Over Simplified

  • Updated Assumptions

  • Running the System

  • Special Thanks ToProf. Sinan MuftuProf. Greg KowalskiProf. Rifat SipahiJeff DoughtyJon DoughtyUS SurgicalBrian Weinberg & Prof. Constantinos Mavroidis lab

  • Questions?

    **Our project is the Human Jaw Motion Simulator. The project team consists of myself Bryan Galer, Katelyn ODonnell, Jim Maloof, Nate Hockenberry, and Mia Monte-Lowrey. Our advisor and sponsor is Prof. Sinan Muftu**Today we will be presenting to you some background on our project followed by some details on the design and we will conclude with our results.**The temporomandibular joint or TMJ is the joint that provides motion to your jaw, allowing you to do things such as talk and eat. Unfortunately for a person suffering from a TMJ disorder as is the case for over 10 million Americans; they can experience a range of symptoms from audible clicks to pain and lock jaw performing these simple tasks. The purpose for our project is to provide a resource that would allow for further studies of the TMJ. It is our hope that this will eventually lead to improved testing of prosthetics or possible treatment of TMJ disorders.The goal of our project was to create a physical model of the skull that will mechanically simulate the jaw motions and be controlled through a LabVIEW interface. To aid with this goal and to analyze the system a virtual Matlab program was needed.**Unlike the knee or elbow the left and right joints of the jaw arent independent of each other resulting in a system with six degrees of freedom. There is also limited information on the forces and reactions of the jaw. Due to the complexity of the system a decision was made to divide the project into stages with the final result being a model of the human jaw for research purposes. Our focus is stage one, which is the initial set-up and closing motion.****There are many components to the skull. The maxilla is the upper jaw and the mandible is the lower moveable part of the jaw. the muscles create tension to move and hold the jaw, and the ligaments connect the bones to prevent overextension of the joint. The TMJ is where the maxilla and mandible interact. In the joint there is an articular disc which transmits force over the bone and decreases the friction in the joint.*Shown here are the three muscles chosen to represent the closing motion of the jaw along with values for their maximum forces. The Temporal muscle aids is closing the jaw by pulling it up and back. The masseter pulls the jaw up and aids in rotating. The lateral pterygoid helps the stability of the jaw. These choices were based on studies by Prof. Koolstra at the University of Amsterdam. In addition, muscles that created repetitive forces were removed.*The movements of the muscles is limited by certain constraints and assumptions. Muscles can only contract, meaning they can only apply tension. Each side of the jaw has the same set of muscles, and we assumed that they will act symmetrically. Although in reality muscles act in 3 dimensions, we assumed they act on a single plane. This allowed for calculations to be made on 2-D system. While some muscles are broad and cover a large area we assumed the force each muscle exerts acts through the center of the muscle to make replication more feasible.***The locations of the muscle attachments were based on another study by Koolstra. Using MRI they determined the points where the muscles attach. Based on the averaged values we came up with the locations shown here for muscle attachment points on the mandible, and the anchor points on the skull. The zero location was based on the point of contact when the mandible is completely closed.****My wordingIn order to create a working model of the human jaw, there were a few questions that had to be addressed. LikeWhat motions are involved in closing the jaw? What assumptions are needed to constrain the motion? And lastly, how can this motion be controlled?Due to the complex and unique nature of the mandibles movement, it is necessary to make assumptions that constrain the motion. The key assumption is that the point of contact between the mandible and the maxilla remains perpendicular to the slope of the articulating surface while the jaw closes. It is also assumed that the disc moves with the mandible and that the compressive load remains constant. These assumptions allow for the disc to be excluded from this simulation. The compressive force on the disc will be represented by a constant normal force imposed by the maxillas articulating surface at the contact point.

    *With the assumptions made, the lower jaw was geometrically constrained to a single path of travel. A cross section of the TMJ was taken so that the profile of articulating surface could be mapped. This profile was then used to calculate the orientation of lower jaw at predefined target positions as shown here.

    *Once the initial system analysis was completed, 2 possible control methods emerged to simulate the motion of the lower jaw: force and position. A static analysis of