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Human Jaw Motion SimulatorDepartment of Mechanical & Industrial Engineering
Northeastern UniversityBoston, MA 02115
April 17, 2007
By:B. Galer
N. HockenberryJ. Maloof
M. Monte-LowreyK. O’Donnell
Advisor and Sponsor:Prof. Sinan Muftu
Outline
• Motivation and Goals
• Project Stages
• Important Skull Components
• Muscles
• System Analysis and Control Development
• Design Details
• Results and Conclusions
Motivation
• Motivation– Over 10 million Americans are affected by TMJ disorders– 2 times as many woman as men suffer from TMJ disorders– Symptoms range from jaw click to limited movement, lock jaw,
and pain
• Purpose– Provide resource for analyzing the TMJ to allow for treatment of
TMJ disorders– To test prosthetics
Overall Project Goals
• Create physical model of a skull• Simulate jaw motions• LabVIEW interface• Virtual Matlab analysis
Stage Goals
• Stage I– Initial Setup and Jaw Closing
• Stage II– Jaw Opening (including opening to closing transition)
• Stage III– Jaw Clenching and Disc Adaptation (disc must be capable of
multiple forms of motion)
• Stage IV– Lateral Jaw Motion/ Chewing (realistic disc simulation must be
accomplished by this stage).
Background
Important Components of the Skull• Maxilla• Mandible • Muscles • Ligaments• Temporomandibular Joint• Articular disc
Muscles of Closing and Max Forces
Temporal120 lbs
Lateral pterygoid34 lbs
Masseter93 lbs
Muscle Assumptions and Constraints
• Muscles– Can only contract– Are symmetrical for either side of jaw– Act in a single plane– Will be simulated as acting as a single vector
through the center of the muscle.
Muscle attachments
• Koolstra Study 1992– Attachment points: On Jaw– Anchor points: On Skull– Zero point based on contact point
Muscle x (m) y (m)
MasseterAttachment 0.0204 -0.0605
Anchor 0.0338 0.0043
Lateral Pterygoid
Attachment 0.0032 -0.0044
Anchor 0.0239 0.0064
TemporalAttachment 0.0363 -0.018
Anchor 0.0167 0.0463
System Analysis and Control Development
Motion of the Human Jaw
• What motions are involved in closing the jaw?
• What assumptions must be made?
• How can the motion be controlled?
Assumptions• Compressive Force on disc is constant
• Disc moves with mandible
• Mandible Contact Point
oTaken while in fully closed position
oAlways perpendicular to articulating surface
Results of Assumptions• The Disc will be Left out of Model
• The Normal Force from the Articulating Surface Acts Directly on Contact Point
Physical Constraints of Mandible
• Constrained to single path of travel
• Mapped profile of the articulating surface
• Orientation of lower jaw found at predefined target positions
System Control
Anatomical Constraints Controllability
Available Knowledge
Control Knowledge
Physiologically Realistic
Value 5 4 3 2 1 Total
Force 1 2 1 1 2 20
Position 2 1 2 2 1 25
ForceStatically Indeterminate
Controllable with Tension or Slack Method
Definitive Research not Available
Control System Requires More Research
Physiologically Accurate
PositionAnatomically Constrained
Controllable with Length Adjustments
Information is Readily Available
Control System is Common and Simple
Not Physiologically Accurate
Positional Control
Articulating Surface
Attachments and Predicted Paths
Mandible
Anchor Points• Motion Tracking
•Constrained Orientations
•Varying Muscle lengths
• Matlab Program
•Variable surface profiles
•Variable tracking locations
•Creates positional output
• Control Method
•Control Muscle Lengths
Design Details
The Design
Frame
Muscle Decision Matrix
Total Control Precision Accuracy Complexity Resources Safety Cost
5 4 3 3 3 2 2
High End Motor 161 10 10 10 3 6 6 1
Standard Motor 164 8 8 7 7 8 6 7
Pneumatic 78 4 3 4 3 3 3 5
Hydraulic 63 5 3 4 1 1 1 3
Air Muscle 68 4 2 3 2 3 3 5
Muscle Wire 118 3 6 5 8 6 5 6
Polymer 118 3 6 5 8 6 5 6
Brushless Servo Motors
• High precision and accuracy
• Position control requires feedback
• AKM33E- Danaher Motion• 2.2NM torque• Built 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 Interface
• Can be run by any user• Allow easy future
changes to project• Feedback loop built into
program
Pulley System
• Pulleys used to increase torque
• Keeps motor cost low
• Allows for project expansion
Wire Attachments and Guides• Can only pull like
muscles
• Adjustable tension
Skull and Lubrication• Mimics Program
– Convert CT scan to 3-D model• SLA model to rubber-molded model• Attachment points tested for bending• Lubrication on joint
LubricatedSurface
ASurface
BCoefficient of Friction
No Teflon Delrin 0.45
No Teflon Teflon 0.5
No Delrin Delrin 0.45
Yes Teflon Delrin 0.08
Yes Teflon Teflon 0.06
Yes Delrin Delrin 0.1
Results and Conclusion
Virtual Analysis
Physical Analysis
Results
Virtual• Jaw Appeared to Open Improperly
• Negative Force Values
Physical• Separation at joint
Conclusions
Initial Assumptions Were Incorrect– Mandible Does Not Stay Perpendicular to the
Articulating Surface– Muscles Can Only Contract, Whereas Results
Suggested Expansion• Muscle Choices May be Incorrect or Over
Simplified
Updated Assumptions
Running the System
Special Thanks To• Prof. Sinan Muftu
• Prof. Greg Kowalski
• Prof. Rifat Sipahi
• Jeff Doughty
• Jon Doughty
• US Surgical
• Brian Weinberg & Prof. Constantinos Mavroidis’ lab
Questions?