Transcript A New Design Custom TMJ Prosthesis

A New Design Custom TMJ
Prosthesis
Philip McLoughlin
Eric Abel
Jyothi Chandramohan
Peter Bowman
Maxillofacial Unit, Ninewells Hospital
&
Dept of Biomechanical Engineering, Dundee University
Total Prosthetic TMJ
Replacement
• Well accepted guidelines
• Degenerative disease
• Standard or custom
Total Prosthetic TMJ
Replacement
• Falling age incidence
• Extensive surgery
• Removal of normal bone
• Similar condylar head design
Total Prosthetic TMJ
Replacement
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New custom design
More conservative?
Is it mechanically sound?
Potential for osseointegration?
Optimum manufacturing process?
Total Prosthetic TMJ
Replacement
• The Design
• The Mechanical testing
• Work in Progress
The Design
• Custom
• Excise diseased bone only
• Reduce access
• Orthopaedic Model?
The Design Investigation
• Mechanical loading
• Osseointegration
• Method of Manufacture
The Manufacture
• “Indirectly” from Stereolithographic
Models
• “Directly” by computer aided manufacture
Stress Analysis
• Finite element analysis
• Physiological Loading (100 N)
• Perfect and imperfect surgical fit
Finite Element Analysis
• Micro CT - X-TEK Benchtop
• Load into FE programme - ANSYS
• Apply load and measure total stresses
(von Mises stresses)
A
Finite Element Modelling (FEM)
A solid model is created from the CT scan.
The model is ‘meshed’ into elements.
Loads are applied.
Stresses are calculated.
Finite element software – COSMOS/ANSYS
A Meshed Model
FE Analysis
Physiological
loading
Leve
l
Prosthesis
stresses
No Bone Contact
Loading(N)
Stress(MPa)
100
220
200
280
300
530 (450)
Prosthesis-Bone Gap
Loading 300N
Gap(mm)
Stress(MPa)
0
10(neg)
0.25
24(neg)
0.50
270
0.75
395 (450)
FEA Conclusions
• In the unsupported prosthesis a sufficiently
high stress in the neck region would cause
failure.
• The magnitude of loading would be three
times the physiological normal.
FEA Conclusions
• That prosthesis bone contact would prevent
failure under extreme conditions.
• Even if there were not contact at the
prosthesis-bone interface, deflection of the
prosthesis would be limited if the gap were
small.
Work in Progress
Manufacturing
• Goal is to use direct CAD to CAM
manufacture.
• Will allow contact stresses to be controlled
during the design process.
Work in Progress
Titanium interface
• Electrolytic coating of the interface.
• Investigation and effects of integration.