Biomedical Engineering Reference
In-Depth Information
ChronOS™ Inject (a brushite cement) samples exhibited a higher rate
of connective tissue formation and an insufficient osseointegration
[360]. α-BSM
was evaluated in a canine femoral slot model. New
bone was found to form in 3 weeks via an osteoconductive pathway.
After 4 weeks, only 1.7% of the implanted material was observed.
The hybrid bone possessed the strength of normal, unoperated
bone after 12 weeks. In 26 weeks, the boundary between old and
new bones was virtually indistinguishable, with only 0.36% of the
implant recognizable [169]. Neither influence on general health,
limb specific function and pain, nor associated complications with
α-BSM
®
®
application were found past 2 years in another study [361].
Norian SRS
®
was evaluated in canine tibial and femoral metaphyseal
defects. The cement appeared to be gradually remodeled over time,
with blood vessels penetrating through it. However, some amounts
of Norian SRS
®
were detected in the medullary area as long as 78
weeks after being implanted in dog femurs [32]. An interesting study
on the
resorption of three apatite cements (conventional,
fast-setting, and anti-washout) by osteoclasts if compared with a
similar resorption of sintered HA and a cortical bone revealed an
intermediate behavior of the cements: they were resorbed slower
than bone but faster than HA [362]. Furthermore, bone neo-formation
was seen 7 seven days after implantation of an α-TCP cement [363].
The biodegradation rate of the cements might be influenced by ionic
substitutions in calcium orthophosphates [364]. Evidences of the
direct contact of bone and a calcium orthophosphate cement without
soft tissue interposition might be found in literature [365, 366].
Different studies reported on both cement bioresorption and
the progress of bone formation around calcium orthophosphate
cements which in certain cases demonstrated both osteoconductive
and osteoinductive properties [367]. However, there are studies
in which the osteoinductive properties of calcium orthophosphate
cements were not confirmed [368]. Besides, inflammatory reactions
were noticed when the cement did not set [271]. As solubility of a
non-stoichiometric CDHA is higher than that of stoichiometric HA, α-
and β-TCP (Table 1.1) and the particle dimensions of a precipitated
CDHA is smaller than those of sintered calcium orthophosphates,
the biodegradability of apatite cements is always better than that
of dense bioceramics made of the sintered stoichiometric calcium
orthophosphates. For example, histologically, at 2 weeks, spicules
in vitro
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