Biomedical Engineering Reference
In-Depth Information
implants. Even small gaps may lead to relative micro-motions between implant and the
tissue, which increases the risk of implant loosening over time due to formation of zones of
fibrous tissues at the implant-tissue interface. Early loading of implants is of particular
interest for dental implants (Vercaigne et al, 1998). The use of surface coatings technology is
today an established method to reduce the problem with poor interfacial stability for
implants. With coatings technology, structural characteristics of the implant (e.g. strength,
ductility, low weight or machinability) may be combined with surface properties promoting
tissue integration. There are several established coating deposition techniques, e.g. physical
vapour deposition (sputtering) and thermal spraying techniques. Coatings based on calcium
phosphates are the most used ones.
This section deals with coatings deposited with established methods, with the aim of
improving particularly the early stage anchoring of metal implants to bone tissue by
exploring
in vivo
hydration of coatings or pastes based on chemically curing ceramics. The
study focuses on calcium aluminate in the form of coatings and paste. Results are presented
from an implantation study with flame-sprayed coating on titanium implants and uncoated
implants augmented with a calcium aluminate paste in the hind legs of rabbits. Implants
were applied with the paste composed of a mixture of CaO·Al
2
O
3
and CaO·2Al
2
O
3
. The
paste was applied manually as a thin layer on the threaded part of the implant just before
implantation. The uncoated and coated implants were sterilised with hot dry air at 180 ºC
for 2 hrs. Female albino adult New Zealand White rabbits with a body weight around 2.5 kg
were used. Each animal received four implants, two in each hind leg. Implants were placed
in the distal femoral metaphysis as well as in the proximal tibial metaphysis. Surgery
followed standard procedure. The implants were screwed into predrilled and threaded
cavities. Necropsy took place after 24 hrs, 2 and 6 weeks (Axen et al, 2005).
No negative effects of the implants on the general welfare of the animals were observed. The
healing progressed in a normal and favourable way. As for the removal torque recordings,
all calcium aluminate coatings types provided an improved implant anchoring to bone
tissue after
in vivo
hydration, as compared to that of the pure metal implants. Implants on
the tibia and femur side of the knee gave similar removal torques. Table 15 provides average
values from both tibia and femur sides.
Implant type 24 hrs (n) 2 weeks (n) 6 weeks (n)
Flame spraying 7.0 (8) 7.0 (8) 25 (6)
Paste augmentation 6.6 (8) 15 (6) 13 (4)
Rf-PVD 12 (4) - - 10 (4)
Uncoated reference 3.8 (8) 5.7 (6) 14 (4)
Table 15. Removal torque (Ncm) for dental implants in rabbit hind legs (tibia and femur).
24 hrs after implantation, calcium aluminate in-between the implant and tissue increased the
removal torque to about double that of the uncoated reference implants, independently of
means of application (coatings or paste). This is considered to be attributable to the point-
welding according to integration mechanism 6 above. Two weeks after implantation,
implants combined with paste augmentation provide the highest removal torque; flame
sprayed coatings also improve the torque relative to the uncoated system. Six weeks after
implantation, all systems are relatively similar (considering the uncertainty due to scatter
and statistics), apart from the sprayed system which shows significantly higher values.
