PADOVA STUDY CLUB

Interesting how the perceptions related to the top couple of mm of the
implant have evolved. The Core-Vent was blasted to the top and the top was
placed 1mm above the crest to make it easier to find the submerged implant. when
the plastic plug cemented into the hex hole was removed and the abutment placed,
the tissue cuff was similar to what you see with the Astra as the soft tissue
grew over the top of the implant. The ITI implant's TPS surface was placed level
with the crest, but that surface was too rough and porous to
allow maintenance of tissue health if it become exposed in the crevice. The
Branemark machined surface implant, while experiencing initial bone loss of a
few mm (probably do to countersinking), led people to believe that a smooth neck
was desirable (machined is not polished - no one polishes the neck). 3i under
the urging of Dennis Tarnow, designed the Osseotite implant with a 3mm long
machined neck below which was the acid etched surface, but acid etching is a
chemical polishing processes, so Osseotite was actually smoother from the
standpoint of depth of irregularities, than the machined neck of the same
implant. SLA is an aluminous oxide blasted surface that has subsequently
been acid etched to remove the aluminous oxide imbedded particles. Problem
is that this double surface treatment rounds the threads. Astra blasts with
Titanium Oxide, leaving the particles imbedded, but now follows up with etching
with HFl acid that leaves Fl ions on the surface. Astra claims this speeds
osseointegration. The Screw-Vent of the late 1980's and early 1990's etched with
HFl acid, also leaving Fl ions. After the results of the VA studies on
various surfaces and designs of Core-Vent's products, I decided that
etching left too smooth a surface and went to blasting with tri-calcium
phosphate  (RBM or SBM trade names standing for Resorbable or Soluble Blast
Media). This creates a similar roughness to SLA but preserves the sharpness of
the threads and the cutting grooves. I focused in the mid-1990's on what I
called Selective surface, with the top 1mm of the implant left machined,
the midsection either blasted with SBM or coated with HA, and the apical third
left machined for the sharpest possible cutting grooves for self-taping. There
is nothing wrong with leaving 1mm of the top of the implant machined
because more often than not, the ridge is not perfectly flat so if the
implant is placed level with the lingual crest of the ridge, the 1mm of
machined shiny metal is exposed on the labial (not under bone), and a smooth
surface in the soft tissue is thought to be beneficial. With the advent of the
Tapered Screw-Vent in 1998, there was no need to leave the apical few mm
machined because a tapered implant does not cut leading threads all the way down
the socket... only in the last few mm of the socket and only if you use step
drills that make the socket with narrow parallel walls in this area. The
one-stage ScrewPlus and Advent implants from Paragon Implant Company, now sold
by Zimmer, ran the SBM surface (Zimmer calls it MTX) to the crest of the ridge
because those implants with the longer necks sometimes are set 1mm  into
the bone in which case you would have 2mm of a machined neck below the crest if
you started out with a 1mm machined neck like the two-stage Screw-Vent.
Generally speaking, bringing a medium rough, blasted surface to the crest of the
bone would be hard to criticize today. Nobel took it farther than I think is
necessary by extending their TiUnite surface 1mm above the crest on its
one-stage implants while leaving it level with the bone on its new Groovy
two-stage Replace Select implants. This left 3i out in the cold with no theory
or rational to support its Osseotite 3mm smooth neck since it got
this from the Branemark implant and Nobel was abandoning this theory of needing
a machined neck... SO 3i now runs its Osseotite surface to the top. That is
the problem with implants that just copy someone else without adopting a
philosophy of their own... when the company being copied changes, you have
to abandon the very thing you claimed was so important. The new generation
of surfaces, TiUnite, Osseospeed, SLActive, Friadent's blasted/etched surfaces
are all claiming faster integration at the 2-4 week period all compared
only to their own older surfaces. I would like to see any of them compare
their surfaces to the RBM/SBM surfaces or better yet, to HA coated surfaces. And
so what if you get a 20% more bone contact or torque resistance in the
2-4th week? If you load the implant immediately and the bone is dense
enough to provide adequate stability for immediate loading, what happens a few
weeks later does not matter. If the implant was overloaded initially its fate is
sealed within the first week. If you are not going to load the implant
immediately, then by 10 weeks, even the SLA and SLActive have the same bone
contact, as does TiUnite.

 

Jerry Niznick