We would like to thank Nobel Biocare for their generous
sponsorship of speaker Steve Hurson for our March meeting of the Conejo Simi
Implant Study Club. Steve is a mechanical engineer by education who graduated
from Cal Poly San Louis Obispo and has over 30 years of experience in the
implant field.
Mr. Hurson brought to us knowledge that he has accumulated
from a long and industrious career at Nobel Biocare, spearheading the science
behind the product line. His topic today was to inform us on how we can increase
long term success by understanding the importance of proper screw preload,
properly matched components and an occlusal scheme that will not deteriorate
the system.
The original implants were all CP 1 (commercially pure
grade). Now the implants are CP 4. Large diameter fixtures have a CPA value of
680 and all the other have a CPA 0f 750.
The manufacturer starts with a large bar that is cold worked into a
smaller and smaller size. This creates a
work hardened bar stock. As the oxygen
and hydrogen and nitrogen levels go up the bar gets stronger. There will also be trace amounts of iron in
the implants. Some other companies use annealing to create their bar stock.
You can never
overstretch a prosthetic screw, this is a myth. It will break before it
stretches. You can’t make it too tight.
Steve described the preload of a screw to a stiff spring, like an old
garage spring, we try to tighten it to 75% of its induced tension of yield. Today’s
springs can be tightened 3 x tighter due to the stronger material used as compared
to 25 years ago. A problem with Ti
screws in Ti implants is the galling of the surfaces as they rub against each
other. Each time the screw is tightened it galls more and weakens the screw.
This led Nobel to develop Torqtite coated screws. Each tightening leads to the
small deposit of material and the screw can be tightened more. This coating
lasts for up to five tightenings before
the coating wears off.
Screw loosening many
times relates to poor management of occlusal forces. The longer the tooth the more negative impact
the horizontal forces will have on the screw system. Best results will come from loading implants
on their long axis in the posterior jaw, even if this requires the use of
shorter implants to achieve the proper position. Angled implants will place detrimental
horizontal forces on the screw system.
As a side note, this does not relate to all on four cases since this
load is held by the framework and dispersed over all the implants. It is important to note that aftermarket
screws do not have the high preload which will lead to a rocking motion and
screw failure. The tribe connection has
a longer screw and tube that goes 4mm into the implant so it is less likely to
rock. The conical connection is even
better as it has a 12-degree taper that stretches the implant wall and
hermetically seals the micro gap. These
connections are all tested at over 5 million cycles with torqtite screws.
Overall, screw loosening can be attributed to occlusal overload, lack of
screw preload and misfit components.
He advised all the attendees to purchase a 10x loupe so they
can evaluate the lab work prior to delivery. Always wash all the component with soap and water and rinse in saline
when they come from the lab, even sterilize if you can. Do not use peridex as it will cause the
periodontal tissues not to adhere to the abutment surface. Furthermore, do not allow the lab to glass
bead or grit blast the component. It
will create high points that can eventually lead to loosening. The but joint is the best connection to the
implant for multiple units as it sits passively on the shoulder of the implant. It is even better to use multiunit abutments
and move the micro gap further from the bone level, especially with the conical
connections that can be hermetically sealed.
Additionally he advised against probing around implants, as the
hemidesmisomal seal is broken each time and contaminated. This attachment is much different than the
bone implant level that consists of a 100 angstrom protein layer that the bone
adheres to.
Steve then spent time discussing the soft tissue seal around
dental implants and how important it is for good bone health and the prevention
of perimplantitis. He reviewed the role
of the hemidesmosmal attachment that occurs. There are three materials that
soft tissue will adhere to: Titanium, Zirconia, and PEET. It will not adhere to gold. This means that some sort of abutment is
needed to provide the best seal. Try to eliminate anything that would prevent
cell adherence to the restorative components.
So make sure the components are cleaned with soap and water and rinsed with
saline. Sterilize if possible. Do not
use peridex as a cleaner for final abutments of temporary abutments as it will
inhibit cell adhesion. A mirror finish
is no better than a machined surface in this regard. He is not an advocate of probing around
implants as he feels this leads to inoculation of the area with bacteria.
I hope this information helps to build a better
understanding of osseointergrated implants.