Human Jaw Motion Simulator Department of Mechanical Industrial

Human Jaw Motion Simulator Department of Mechanical & Industrial Engineering Northeastern University Boston, MA 02115 April 17, 2007 By: B. Galer N. Hockenberry J. Maloof M. Monte-Lowrey K. 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 Lab. VIEW 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 Temporal 120 lbs Lateral pterygoid 34 lbs Masseter 93 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 Masseter Lateral Pterygoid Temporal x (m) y (m) Attachment 0. 0204 -0. 0605 Anchor 0. 0338 0. 0043 Attachment 0. 0032 -0. 0044 Anchor 0. 0239 0. 0064 Attachment 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 o. Taken while in fully closed position o. Always 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 25 Force Position Statically Indeterminate Anatomically Constrained Controllable with Tension or Slack Method Controllable with Length Adjustments Definitive Research not Available Information is Readily Available Control System Requires More Research Control System is Common and Simple Physiologically Accurate Not Physiologically Accurate

Positional Control Anchor Points • Motion Tracking • Constrained Orientations • Varying Muscle lengths Articulating Surface • Matlab Program • Variable surface profiles • Variable tracking locations Attachments and Predicted Paths • Creates positional output • Control Method • Control Muscle Lengths Mandible

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 3 3 5 Hydraulic 63 5 3 4 1 1 1 3 Air Muscle 68 4 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 • AKM 33 E- Danaher Motion • 2. 2 NM 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

Lab. VIEW 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 Lubricated Surface A Surface B Coefficient of Friction No Teflon Delrin 0. 45 No Teflon 0. 5 No Delrin 0. 45 Yes Teflon Delrin 0. 08 Yes Teflon 0. 06 Yes 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?