| HOFFMAN-PAPPAS TEMPOROMANDIBULAR JOINT REPLACEMENT SYSTEM* |
Dr. David C. Hoffman,
an oral and maxillofacial surgeon, and Dr. Michael J. Pappas,
a mechanical and biomedical engineer, have collectively utilized
there experiences to design the Hoffman-Pappas (H-P) Temporomandibular
Joint Replacement. The extensive orthopaedic experience of
Dr. Pappas in the area of design and product development of
various joint replacements is evident in the H-P TMJ prosthesis.
The sound, clinically proven design concepts that have been
utilized are the use of materials that are not only biocompatable,
but are superior in wear performance and abrasive resistance,
to always provide the lowest possible contact stress via the
articulating surface geometry and allowing for the natural
motion required in the joint, and to allow for prosthetic
misalignments while still maintaining the maximum contact
area.
- Custom
CAD-CAM design allows precise fit for each patient
- Custom
fit titanium backed fossa adds stability
- Two
piece fossa allows for bearing exchange without removing
well fixed component
- Custom
ramus component allows for use in irregularly shaped or
deformed mandibular anatomy
- Condylar
head design increases contact area, while allowing for various
motions and misalignments
- One
piece titanium alloy condylar component with UltraCoat®?provides
superior mechanical and biological compatibility.
- Bearing
materials (UltraCoat® on UHMWPe) provide superior wear
characteristics to current joint prosthesis
- Locking
screw fixation for ramus allows maximum fixation without
micromovement
*
Available only under clinical investigation in the United
States
Device
Description
The Hoffman-Pappas
Temporomandibular joint replacement system consists of a mandibular
ramus component, fossa component and interlying fossa bearing.
The mandibular component is constructed from a single piece
of titanium bar stock and is used to replace the condylar
head while being secured to the lateral side of the ramus,
and is coated with UltraCoat®, a proprietary thin film
titanium nitride ceramic. The fossa is composed of a titanium
alloy fixturing cup and a ultra-high molecular weight polyethylene
(UHMWPe) bearing insert to replace the glenoid fossa and articulate
with the ramus prosthetic condylar head.
Mandibular
Component
The mandibular
component profile in the sagittal plane is one which allows
for bony coverage of the mandible in order to allow for appropriate
holes for screw fixation. The bone/prosthesis interface is
usually flat; however, a custom surface can be constructed
in certain situations where the surgeon deems necessary.
FLAT
INTERFACE
 |
CUSTOM
INTERFACE
|
The screw
fixation system used employs two types of fasteners. One is
a 2 mm x 8 or 10 mm self tapping screw. The other is a 3.5
mm anti-micromotion locking screw, which consists of a screw
that is secured to a counter-bored hole in the ramus component
and once proper seating is achieved, a smaller, tapered head
machine screw is placed into a tapped hole of the locking
screw to spread locking tabs and positively secure it to the
walls of the ramus component. To incorporate the two basic
movements of rotation in the sagittal plane and axial shifting,
the condylar head was designed to be a modified barrel that
would allow for these various motions while still maintaining
the largest contact area possible, hence providing a lower
contact stress.
In order
to provide for durability of the implant, a titanium nitride
(TiN) surface coating is applied to the entire component (UltraCoat®).
UltraCoat® is a near diamond hard, and highly biocompatible
coating that is ionically bonded to the substrate. When used
as a bearing surface and coupled with UHMWPe, the coating
greatly reduces wear in UHMWPe bearings and can reduce wear
by 2/3 when compared to Co-Cr/Poly wear couple14.
Fossa
Component
The fossa
component consists of a titanium alloy component and an UHMWPe
bearing insert. The bearing is fixed to the metal component
via a press fit, dovetail connection. In order to prevent
lateral dislocation of the bearing, a flexible locking tab
is machined onto the bearing and a corresponding notch on
the metal shell. Medial dislocation is prevented by the skull
anatomy. The bone-prosthesis interface is custom machined
for each patient and the overall shape is such to accommodate
the normal fossa for stability. A lateral flange extends from
the component superiorly with four to five holes for 2 mm
screws for fixation to the zygomatic arch of the skull. The
articulating surface of the bearing will accommodate the barrel
shaped head and allow for the various movements. An anterior
protrusion and posterior slope is present to prevent the anterior
dislocation as well as to provide proper alignment of the
components. The thickness of the polyethylene insert is such
to accommodate the maximum thickness of poly in a restricted
10 mm space. This shape also accommodates any misalignments
during implantation. Since the fossa is constructed from two
pieces, if necessary the bearing can be removed and replaced
without disturbing a well fixed fossa component.
FDA
Investigation Trial (United States)
The Hoffman-Pappas
Temporomandibular Joint Replacement system is currently under
clinical Investigation in the United States. For more information
about becoming a clinical investigator or a study subject
please contact Endotec at the address provided or Dr David
C. Hoffman at the address below.
 |
David
C. Hoffman DDS
256 Mason Avenue
C-bldg, 3rd floor
Staten Island,
NY 10305
Tel: (718) 226-1251
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Download 'TMJ System Brochure' as .pdf |
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