Biomedical Engineering Reference
In-Depth Information
9.3 Bone Formation Around
Dental Implants
in one case, the sandblasted and acid-etched
surface was manufactured so as to maintain
the chemical activity of the titanium oxide.
This approach makes the surface hydrophilic,
whereas most other implant surfaces are hydro-
phobic. The hydrophilic surface reacts quickly
with the blood, and the response of bone cells
to the surface is enhanced. A study of the mini-
pig maxilla found that bone apposition on the
chemically modifi ed, sandblasted, acid-etched
implant surface was signifi cantly greater after
2
When teeth are missing or have to be removed,
endosseous titanium implants can be inserted
in the alveolar bone and the missing tooth or
teeth attached to the implants by means of a
screw or cement. This procedure has a success
rate of over
%. Early implant placement pro-
cedures required waiting periods of
90
9
months for bone to surround the implant
surface following the osteotomy and insertion
of the implant [
6
to
to
4
weeks than that on the control surfaces
[
). Another study found that the
amount of torque required to remove the modi-
fi ed implant was greater than that needed for
the control [
10
] (Fig.
9
.
4
]. The amount of time needed
was predicated on healing taking place against
a relatively smooth titanium surface of the
machined implant. Interestingly, success rates
with implants with machined surfaces were
much lower when the bone was composed of a
larger fraction of cancellous and a lesser frac-
tion of cortical bone [
8
,
9
]. With these studies as a basis,
a randomized, controlled clinical trial was ini-
tiated. Sites for two implants were prepared in
the posterior areas of either jaw bone (where
the bone quality is relatively low), and the two
types of implant were inserted according to a
random schedule [
27
]. Such bone is typically
found in the maxilla and in the posterior man-
dible, with the denser bone found in the ante-
rior mandible. To establish implants in bone
that was less dense required signifi cant
advances in implant therapy.
Subsequent experimental studies have indi-
cated that bone apposition is more complete
and faster if implants have surfaces that are less
smooth than when the titanium surface is
machined [
33
]. Implant stability was
measured by means of resonance frequency.
This technique uses a device that stimulates a
transducer on top of the implant, which pro-
vides a value for the relative stability of the
implant. Weekly readings were obtained on
each implant for
47
months.
Preliminary results indicated that the implant
with the modifi ed surface became stable sig-
nifi cantly more quickly than the control. Thus,
the animal and human studies gave compara-
ble results, indicating how implant surface
characteristics enhance bone apposition to the
implant surface. This procedure also improves
patient care because the implant becomes stable
more quickly. Consequently, the patient has
less opportunity to interfere with early healing
during function.
Another strategy to enhance bone apposition
around implants is to place a bone-replacement
graft or bone-stimulating agent around the
implant. This is particularly indicated if a space
or gap exists between the implant and the bone,
a situation that tends to arise if the implant is
inserted into the extraction socket immedi-
ately after tooth removal (Fig.
6
weeks and again at
3
]. For this reason, much effort has
been spent in trying to optimize the roughness
of the titanium surface. Studies in mini-pigs
have found that a titanium surface produced by
sandblasting and acid etching induces the best
bone apposition in comparison with four other
roughness procedures [
16
]. The advantage of
this procedure was confi rmed in an in vivo
canine study [
11
]. This implant, with the sand-
blasted and acid-etched surface, was then uti-
lized in a large multicenter international
prospective human clinical trial and was shown
to induce bone healing in half the time required
in the conventional procedure [
21
]. The new
procedure made it possible to insert teeth only
6
17
weeks after bone drilling, with success rates
in the
). It also arises
if an implant is inserted into an area where
bone has healed but where new bone has not
fi lled the tooth socket completely. This happens
more frequently as dental implant therapy
becomes more widespread and the patient is
pushing to have missing teeth replaced more
quickly.
9
.
5
% range. This signifi cant
advance in the dental implant fi eld has been
confi rmed in other studies in which rough sur-
faces were prepared differently.
Recent efforts to obtain even faster rates of
bone healing have centered on changing the
surface chemistry of the titanium. For example,
97
% to
99
