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 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)

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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. A Meshed Model Finite element software – COSMOS/ANSYS

FE Analysis Leve l Physiological loading Prosthesis stresses

No Bone Contact

Prosthesis-Bone Gap Loading 300N

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.