What’s the Big Fuss
About Implant Surfaces?
T
here are over 500 different manufacturers of
endossseous dental implants today. Most are “me
too” copies of already existing implants. There are
only two basic shapes, Press fit (push in) or Threaded. The
press fit has parallel walls with a rounded end whereas the
threaded is shaped like a wood screw. (Figures 1 & 2)
Almost all implants today are made from 6/4 Titanium
Alloy (6% Aluminum and 4% Vanadium). At one time
Commercially Pure (C.P.) Titanium was used but
C.P.Titanium is quite soft and relatively weak, whereas 6/4
Titanium Alloy is 60% stronger and better able to withstand
greater loads. Zirconium implants are entering the market
now but scientific data is lacking sufficiently to prevent
them having much credibility today.
There are several factors that affect the degree and
quality of the bone that attaches to the implant. These
factors are:
1. The degree of surface area or roughness.
2. The type of material comprising the surface of the
implant.
3. The degree of contamination of the implant surface.
Dr. Harold Bergman
1. The rougher the surface,
the greater the surface area.
Figure 1 —
Press Fit Implant
38
Figure 2 —
Threaded Implant
The greater the surface area, the more potential
bone/implant interface surface. The greater the potential
bone/implant interface surface the less stress that will be
distributed to the attached bone.
All implants are machined on Computerized Numerically
Controlled (CNC) machines frequently by the same
manufacturer of other implant systems. (Figure 3) Once the
implant is machined, the surface is relatively smooth,
appears relatively shiny to the eye and has a minimal
degree of roughness (Figure 4). The original Nobelpharma
CPOI — Vol. 2 No. 2 — Summer 2011
Figure 3 — CNC Machine
implants were machined from C.P.Titanium with the surface of the implant
receiving no further treatment than machining. To the best of my
knowledge this surface is no longer offered.
To further enhance the surface roughness, almost all “non coated”
implants today are usually acid etched and/or grit blasted (AEGB) with a
biocompatable grit such as aluminum oxide (Figure 5). This gives the
implant a dull , matte appearance when viewed with the naked eye. To
separate themselves from the copies, most of the “big” companies are
touting their surface “coatings” as being unique and have named this
AEGB with names such as “Tiunite” or “SLA” coatings. In reality, these are
not “coatings” but are simply an AEGB process similar to other
manufacture’s finishes.
To obtain even additional surface area a coating can be sintered or
plasma sprayed with titanium or hydroxylapatite (HA) or both (Figure 6).
During the plasma spray procedure, tiny titanium or HA granules are
melted at extremely high temperatures in excess of 15,000C and sprayed
on to the implant surface at a very high speed, close to the speed of
sound. This results in a roughened, granular surface.
Another method to increase surface area is by the sintering process.
(Figure 7) Small balls of titanium are layered on the surface of the implant,
then heated sufficiently to melt the surface of the titanium balls. The
surface of the balls are melted together leaving interstices, an affect
similar to that found when a box of chocolates is heated enough to melt
the surface, then cooled, allowing spaces between the chocolates.
Figure 4 — Machined surface
Figure 5 — Grit blasted surface
Figure 6 — Plasma spray surface
2. The type of material comprising
the surface of the implant.
Most metals will oxidize when exposed to air or water. We are all familiar
with the oxidized surface of a “rusty” nail containing iron. Many of us who
have boated on the ocean will also recognize the loss of the shininess with
aluminum fittings on boats as the aluminum oxidizes. Titanium is no
exception to oxidization. Within a millisecond of exposure to air or water,
titanium will oxidize forming a titanium oxide layer. The oxide layer has a
structure similar to that found with bone. It is this titanium oxide layer to
which the bone bonds, not the titanium. Most implants today are made
from 6/4 Titanium Alloy, (6% Vanadium, 4% Aluminum, 90% Titanium).
The alloy is 60% stronger than C.P. Titanium. Even though the titanium
CPOI — Vol. 2 No. 2 — Summer 2011
Figure 7 — Sintered surface
39
immediate loads and achieve better bone contact in less
dense and decreased amounts of bone. All these features
have been well documented over 25 years of scientific
study.
One of the features of HA is that of osteoconductivity.
Osteoconductivity induces bone to form on the HA surface.
(Figure 10) When an implant is placed into an osteotomy
site in the bone, the bone will lay down new bone on the
cut surface of the bone. (Figure 11) After the implant is
placed into the osteotomy site, new bone is laid down on
the old bone surface and travels from the cut bone surface
until it contacts the surface of the implant. By having bone
form on the HA surface as well as on the cut bone surface,
bone grows from the surface of the HA as well as from
the surface of the cut bone during the osseointegration
process. This results in the formation of a quicker, stronger
bone/implant interface.
This feature of HA coating and the advantages it offers is
especially important with the advent and popularity of
immediate loading of the implant. (Figure 12)
Figures 8 and 9 — HA Coated Implants
3. The degree of contamination
of the implant surface.
alloy contains elements other than titanium, the titanium
oxide layer will form on titanium alloy as long as there is a
minimum of 85% titanium in the alloy with the Vanadium
and Aluminum not reaching the surface of the oxide layer
In many cases, the titanium implants’ surface is coated
with Hydroxylapatite (HA). (Figures 1,8 & 9) Hydroxylapatite
forms the total mineral content of bone representing 60%
by weight. HA can be obtained from cadavers, from
animals, from coral and made synthetically. Hydroxylapatite
coatings on titanium implants have qualities that titanium
oxide surfaces do not possess. These features include
enhanced osseointegration at earlier stages, greater initial
implant/bone strengths, quicker initial implant/bone
attachment, higher initial success rates, withstand greater
Figure 10 — Bone on HA and bone surfaces
40
For these surfaces to function properly it is also necessary
that they be free of any contamination such as oils, bacteria
and debris. Most implants today are packaged by the
manufacturer sterile and clean. Once the implant is
removed from the package it is critical not to contaminate
the surface by touching it with gloved or ungloved hands.
Figure 11 — Bone on bone surface only
CPOI — Vol. 2 No. 2 — Summer 2011
Figure 12 — Immediate load implants
Figure 13 — Connective tissue interface
Ungloved hands will transmit oils to the surface. Gloved hands can
contaminate the surface with talc. Both oils and talc will prevent bone from
integrating with the implant surface. When this occurs, a connective tissue
interface ensues. (Figure 13)
Once contaminated by body fluids from another person, it is imperative
that the implant NOT be used in another patient due to cross contamination
of bacteria, viruses and allergens. Re-sterilization will not eliminate the
problem as sterilization does not kill viruses nor eliminates foreign protein.
Regardless of the surface texture of titanium or the type of implant surface
or the degree of contamination of the implant surface, when an implant is
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Figure 14 — Perio ligament
Figure 15 — Non integration
placed into an osteotomy site, osteoblasts will lay down
new bone on the cut surface of the osteotomy site and
migrate to the surface of the implant.
Should the quality of the implant surface be clean and
bacteria/virus/allergen free, the bone should attach to
the titanium surface of the implant with a glycoprotein
“crazy glue”. This bone to implant union is known as
“osseointegration”. “Osseointegration” is defined as “On
the light microscope level, the attachment of bone to the
implant without an intervening connective tissue layer.”
As you can see on the radiograph of a tooth (Figure 14),
there is a clear radiolucency about the tooth indicating
the connective tissue layer. Compare that with an
osseointegrated implant (Figure 14) there is no
radiolucency. The X Ray (Figure 15) shows a radiolucency
around the implant which can be indicative of non
integration. The histological photo (Figure 16) shows the
bone attached directly to the implant. Should the implant
surface be coated with HA, bone will grow from the surface
of the HA as well as from during the cut bone surface.
(Figure 10) This results in bone growing from both sides of
the osteotomy site resulting in the formation of a quicker,
stronger bone/implant interface Instead of a glycoprotein
joint attachment between bone and the implant, the
bone/implant interface intermingles. (Figure 17) The
structure of the HA is similar to that of bone. There is no
joint and the interface is difficult to determine at the
microscopic level.
A tooth has a specialized connective tissue interface with
bone, the periodontal ligament. (Figure 18) Should the
implant surface be contaminated, or the bone severely
traumatized during surgery or the site become infected,
bone growth in the area will be jeopardized and a
connective tissue interface will ensue. This connective tissue
Figure 16 —
Integration
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Figure 17 —
HA/bone interface
Figure 18 —
Perio ligament
CPOI — Vol. 2 No. 2 — Summer 2011
interface is NOT a periodontal ligament which is a highly specialized
connective tissue.
Should an implant be overloaded after osseointegration occurs, the bone
interface can fail and become a connective tissue interface. Once connective
tissue has formed, the chance of a bone/implant interface reattaching is
minimal. Not only does surface area affect the degree of bony interface
between the implant and the bone, the feature that determines the ability of
the bone to adhere to the implant is the material that actually forms on the
surface of the implant.
So Why the Big Fuss About Implant Surfaces? It is the quality, quantity and
type of surface that determines the type of implant interface with the bone,
either bony integration or connective tissue. You would be very wise to ensure
your implants are all they claim to be. n
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