Partial dentures may be a thing of the past
This article
discusses treatment that may allow the replacement of lost bone
to be done far more simply. This would allow the placement
of implants to restore missing posterior teeth, eliminating
the need for partial dentures. Even with FDA procedures and protocols,
since
the materials are already being used on patients, when the
technique is standardized it should not take a long time before
it gets to the
dental mainstream.
Subject: Microscaffolding fits perfectly
in patient's jaw
In an operating room in Carle Hospital in Urbana,
Ill., on May 7, as scientists from the University of Illinois
(UI) and Sandia National
Laboratories watched, surgeon Michael Goldwasser fitted a highly
unusual ceramic prosthetic device into the mouth of an elderly
woman who had lost
most of her teeth and along with it, much of the bone of her
lower jaw.
From Sandi National Laboratory:
Sandia microscaffolding fits
perfectly in patient's jaw
Painless bone substitute could offer
new era for surgeons
ALBUQUERQUE, N.M. - In an operating room
in Carle Hospital in Urbana, Ill., on May 7, as scientists from
the University of Illinois (UI) and Sandia National Laboratories
watched, surgeon Michael Goldwasser
fitted a highly unusual ceramic prosthetic device into the mouth
of an elderly woman who had lost most of her teeth and along
with it, much of the bone of her lower jaw.
The fitting operation
was to determine whether the implant - created a thousand miles
away at Sandia in Albuquerque - had been accurately designed,
from its overall shape down to inclusion of a nerve groove.
"If it
fit like a sock on a rooster, our method wouldn't have worked, " Goldwasser
said.
Observers said it fit like a glove.
If approved by the Food and Drug Administration for in
vivo testing, the scaffoldlike structure - a layered mesh stronger
than bone, yet porous - would substitute for a portion of the
mandible, or lower jaw, until healthy, newly grown bone and blood
vessels could weave their
way through it like vines through a garden lattice. A patent
for the implant is pending.
The ceramic scaffolding would reduce
the pain, recovery time, and chances of infection of those needing
bone replacements in the jaw, as well as skull, spine, or other
bony areas. Other benefits include avoidance of longer surgeries,
more predictability of outcome, and lower health care costs.
The
device is built mainly of hydroxyapatite, a material already
approved by FDA for bodily implants, so approval of the new device
could be swift. The woman was reportedly pleased to be part of
an experiment that might benefit humanity, because the quality
of fit would determine whether scientists and doctors using computer
programs, modern communications, and machines a thousands miles
from each other could produce a prosthetic device that would
fit seamlessly in a patient's sensitive mouth - or, for that
matter, skull or spinal vertebrae - without the manufacturers
ever seeing the patient.
But because scientists have studied
the device's strength and permeability only in vitro (in the
lab), the woman then had to endure the standard method of bone
replacement, which by comparison seems almost medieval. This
involves cutting a several-square-inch piece of bone from her
pelvis, which is then power-sawn and drilled into the correct
shape in the operating room, a process that takes about an hour
and leaves the patient to endure a healing pelvis as well as
a healing mouth.
"Surgeons and patients would love to eliminate both
the bone retrieval and implant preparation processes," says Sandia
scientist Joe Cesarano, whose team fashioned the new implant. "This
test showed we can make artificial porous implants prior to surgery
that will fit
perfectly into the damaged region. The reconstructive procedure
would then only require attaching the implant and closing the
wound. "
A short course on bone implants
A surgeon uses the patient's
own bone to minimize rejection by the body. Harvesting bone,
however, creates new problems, says
Goldwasser. Not only is a new area of patient discomfort created
but the operation
requires more time and anesthetics. These raise the risks of
complications in the operation and in healing. "We could use cadaver
bones," he
says, "but then we face risks of rejection by the host and of possible
transfer of disease. "
The body may also dispose of the foreign bone
prematurely by absorbing it.
"What we want," Goldwasser says, "is a method
by which I can see a patient in Illinois, transmit X-ray information
to someone who can make a substitute part that would have the
porous properties that would allow bone to grow into it, yet
be strong enough for normal function. Here, this would mean mastication
and appearance. "
With the aid of UI bioengineering professor Russ
Jamison and graduate and Sandia summer student Jennifer Dellinger,
who were
experimenting with the growth of bone across porous surfaces
and needed a more regularly
porous substrate than those found in nature, he learned of a
device at Sandia that could do the job.
The Sandia device
The Sandia patented process called Robocasting,
led by Cesarano, was conceived and built to fashion defense components
out of
ceramics in a process that permitted manufacture of specialty
parts in a way no
ordinary mold or machining procedure could achieve. Situated
on a truck, it could make replacement parts on a battlefield,
instead of carrying millions of parts onto a site. It is also
being developed to form advanced catalyst supports that operate
like a maze (rather
than straight channels) to increase chemical reactivity.
Controlled
by a computer program, the machine dispenses liquefied ceramic
pastes, like toothpaste squeezed from a tube, to form
shapes of varying complexity along a prearranged path.
To create
the simulated bone scaffolding, the machine dispensed a hydroxyapatite
mixture in a child's Lincoln Log-like arrangement,
in cross-laid slivers each about as thick and as far apart as
the diameters of ten human hairs.
"Bone, blood vessels, and collagen love to grow into
a structure with pores of that size [500 microns]," says Cesarano. "The
material becomes a hard-tissue scaffold for promoting new bone
growth."
The trick in building it, he says, is that "the paste
has to be strong enough as it's being laid to set in place without under
support. "
Sandian
John Stuecker made the paste thicker than normal by increasing
the interparticle attractive forces. The changed procedure took
about six months to master.
Finally, the scaffolds are embedded
in wax and machined to exactly the right shape without splintering
the hydroxyapatite. The wax
is subsequently removed.
But what was that shape, and how was
it to be determined?
The UIUC connection
In part, by the spark of an idea from
Goldwasser and the diverse expertise linked together by Jamison.
"One by one, we linked together - even if only electronically
at first - the people whom I knew who could bring talent, skill,
and passion to the project. None of us working independently
could have accomplished the results we have, " he says.
Jamison involved
computer technologists and designers Ben Grosser and Janet Sinn-Hanlon
at UI's Beckman Institute to encode CAT
scan results into a computer program that could be shipped electronically
to Sandia,
where Michael Saavedra and David Gill created an interface to
machine the final shape.
Complicating the process was that while a CAT scan could
accurately delineate the diseased shape of an existing bone,
it could not
show what wasn't there: the exact dimensions of what the bone
would have looked
like, were it healthy. This required the potentially expensive
presence of the surgeon Goldwasser working with the computer
programmers to create
the dimensions of what should be there
but wasn't.
"Eventually, if it could be done electronically, it
may be a very simple thing and cost-effective, " he said.
"There is nothing inherently expensive about either
the materials or the process, " said Cesarano.
Using a CAD/CAM method
where a surgeon need only sketch the shape needed, a piece
might quickly and inexpensively take shape at
a remote site.
"We'll see if the clinician, the bioresearcher, and
the engineer can come up with a method to implement it," Goldwasser
said.
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Story available here [sandia.gov]