Biomedical Engineering Reference
In-Depth Information
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3
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Bioresorbable Ceramics
Bioresorbable implants are designed to degrade gradually with
time and be replaced with natural tissues [60]. It leads to tissue
regeneration, instead of their replacement. The rate of degradation
varies from one material to another. Calcium phosphate ceramics
(CPC) are bioresorbable ceramics (Table 3.28).
Ta b l e 3
.
28
Calcium phosphate ceramics (CPC)
Acronym Name Formula Ca/P
VCPA Monocalcium phosphate anhydrate Ca(H
2
PO
4
)
2
0.5
DCPA Dicalcium phosphate anhydrate CaHPO
4
1.0
OCP Octacalcium phosphate Ca
8
(HPO
4
)
2
(PO
4
)
4
5H
2
O1.33
TCP Alpha tricalcium phosphate Ca
3
(PO
4
)
2
1.5
TCP Beta tricalcium phosphate Ca
3
(PO
4
)
2
1.5
ACP Amorphous calcium phosphate Ca
x
(PO
4
)
y
n
H
2
O 1.1-1.5
HA Hydroxyapatite Ca
10
(PO
4
)
6
(OH)
2
1.67
cd-HA Calcium deicient hydroxyapatite Ca
9
(HPO
4
)(PO
4
)
2
OH 1.5
TetCP
Tetra calcium phosphate
Ca
4
(PO
4
)
2
O
2.0
The most widely used calcium phosphate based bioceramics
are hydroxyapatite (HAP) and
β
-tricalcium phosphate (
β
-TCP).
Hydroxyapatite has the chemical formula Ca
10
(PO
4
)
6
(OH)
2
, the Ca/P
ratio being 1.67 and possesses a hexagonal structure. It is the most
stable phase of various calcium phosphates. It is stable in body luid
and in dry or moist air up to 1200°C and does not decompose and
has shown to be bioactive due to its resorbable behavior.
Hydroxyapatite is the natural mineral phase of bone and teeth
and, hence, is compatible with the body environment as well as to
match closely some of the physical properties of bone. For biomedical
purposes, the carbonated apatite and luorapatite are the materials of
interest because of assumed similarity to bony apatite and decreased
solubility in aqueous solutions respectively [90]. It is important to
note, that carbonated luorapatite−gelatin nanocomposites were
grown by the double-diffusion technique within a gelatin gel [114].
Recent
studies have shown that irradiation of dental enamel by
carbon dioxide (CO
2
) laser irradiation, with
and
without luoride,
can inhibit the acid-induced surface dissolution of the carbonated
apatite (CAP) mineral of the tooth [105].
β
-tricalcium phosphate (
β
-TCP) is represented by the chemical
formula Ca
3
(PO
4
)
2
, the Ca/P ratio being 1.5.
β
-TCP shows an X-ray
