FUNDAMENTALS OF HYDROXYAPATITE AND RELATED CALCIUM PHOSPHATES - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 19

2.4 Related Calcium Phosphates 35

2.4.1 Amorphous Calcium Phosphates (ACP) 35

2.4.2 Dicalcium Phosphate Dihydrate (DCPD) 36

2.4.3 Octacalcium Phosphate (OCP) 38

2.4.4 Tricalciumphosphate ( α - TCP, β - TCP) 38

2.4.5 Tetracalcium Phosphates (TTCP) 39

2.5 Biologic Apatites and Related Calcium Phosphates 39

2.6 Calcium Phosphate - Based Biomaterials 40

Acknowledgments 45

References 46

2.1 OVERVIEW

Several types of calcium phosphates occur in nature and in biologic systems.
These apatites or tricalcium phosphates incorporate different ions. In biologic
systems, besides the carbonate apatite which comprise the mineral phase of the
calcifi ed tissues (enamel, dentin, cementum, bone), there are other calcium
phosphates (amorphous calcium phosphate, dicalcium phosphate, octacalcium
phosphate and magnesium-substituted tricalcium phosphates.) Calcium phos-
phates of synthetic or biologic origin are used as bone graft materials or as
coatings on orthopedic and dental implants.
A brief review of the physico-chemical properties of hydroxyapatite and re-
lated calcium phosphates and their medical and dental applications are presented
in this chapter.

2.2 INTRODUCTION

Calcium phosphates occur in biologic systems (Table 2.1) and in nature (Table
2.2). Apatites (specially, substituted apatites) are the most commonly occurring
calcium phosphate compounds. For example, most of the mineral apatites incor-
porate fl uoride (F-apatite), chloride (Cl-apatite), carbonate (dahllite) or fl uoride
and carbonate (staffellite), with few occurrences of unsubstituted calcium
hydroxyapatite, HA (Table 2.2). The mineral phase of calcifi ed human tissues
(for example, enamel, dentin, cementum, bone), previously idealized as calcium
hydroxyapatite, HA or fl uor-apatite [5,19,50] is associated with minor constitu-
ents such as magnesium, sodium, and carbonate, and has been determined as a
carbonate-substituted apatite, CHA [57,59,64,107]. The mineral phases of some
fi sh enameloids and special shells are CHA or carbonate and F-substituted apa-
tite (CFA) [72,86] .
Mixtures of CHA and other calcium phosphates occur in pathologic calcifi ca-
tions, for example, kidney or urinary stones, dental calculus, vascular calcifi cations
and other soft-tissue calcifi cations (lung, skin, joints), calcifi ed deposits found in
heart valves prostheses, and so on. [64,112]. CHA and other calcium phosphates
also occur in diseased states (for example, tooth enamel or dentin caries) [63,97].