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?