who also responds to the signaling. Overall, the process is incredibly complex and
subject to many forms of feedback controlled by a large number of biochemical
triggers such as hormones that are circulating in the blood stream.
6.1.2.2 Tooth
The structure and organization of tooth enamel and dentine, like bone, derive from a
highly complex system designed to withstand specific types of mechanical stress.
Enamel, which is on the outside of the tooth, is much less tough than bone because it
has close to 95 wt.% hydroxyapatite (human bone on average is around 65 wt.%)
but gains some structural resistance by interweaving long ribbon-like crystals into
an inorganic fabric. Interestingly, enamel starts out with a high proportion of
proteins (mainly amelogenin and enamelin), which are progressively removed as
the biomineral matures to produce the high mineral volume fraction of the erupted
tooth. Dentine, on the other hand, which resides within the central regions of the
tooth, contains collagen and is more similar in structure and composition to bone.
A principal cause of the general increase in dental health in many societies is the
use of fluoride in drinking water and in numerous toothpastes. The F ion is readily
incorporated into the hydroxyapatite lattice where it stabilizes the lattice and
reduces the solubility of the mineral phase. Interestingly, fish teeth consist of a
structure very similar to enamel (called enameloid) but contains high levels of
natural fluoride. For example, the fluoride concentration in shark enameloid is over
1,000 times compared with that in human enamel.
6.2 Hierarchical Structure of Calcium Carbonate-Based
Biomineral in Aquatic Organisms
Many natural biominerals have been found to have hierarchical structure, such as
human bone, human enamel, nacre, ivory, etc.
Living organisms make up hierarchically organized materials through selforganization from precursors in aqueous solution, and scientists have developed
various biomimetic techniques to prepare and organize building blocks. It is
believed that an exquisite association of organic and inorganic compounds is
required for the construction of bioinorganic superstructures; therefore, understanding the roles of macromolecules in the biomineralization process is a significant
challenge in biomimetic materials. For example, the discovery of calcitic
microlenses in brittlestars, chiral morphologies with stereochemical recognition,
and the handedness of a snail shell bring out hidden elaborate structures and
properties of biominerals. The nacreous layer has attracted the interest of
researchers in a broad range of disciplines, especially in terms of its detailed
structure, defects in different scales, incorporated macromolecules, mechanical
6 Principles of Calcium-Based Biomineralization
153
subject to many forms of feedback controlled by a large number of biochemical
triggers such as hormones that are circulating in the blood stream.
6.1.2.2 Tooth
The structure and organization of tooth enamel and dentine, like bone, derive from a
highly complex system designed to withstand specific types of mechanical stress.
Enamel, which is on the outside of the tooth, is much less tough than bone because it
has close to 95 wt.% hydroxyapatite (human bone on average is around 65 wt.%)
but gains some structural resistance by interweaving long ribbon-like crystals into
an inorganic fabric. Interestingly, enamel starts out with a high proportion of
proteins (mainly amelogenin and enamelin), which are progressively removed as
the biomineral matures to produce the high mineral volume fraction of the erupted
tooth. Dentine, on the other hand, which resides within the central regions of the
tooth, contains collagen and is more similar in structure and composition to bone.
A principal cause of the general increase in dental health in many societies is the
use of fluoride in drinking water and in numerous toothpastes. The F ion is readily
incorporated into the hydroxyapatite lattice where it stabilizes the lattice and
reduces the solubility of the mineral phase. Interestingly, fish teeth consist of a
structure very similar to enamel (called enameloid) but contains high levels of
natural fluoride. For example, the fluoride concentration in shark enameloid is over
1,000 times compared with that in human enamel.
6.2 Hierarchical Structure of Calcium Carbonate-Based
Biomineral in Aquatic Organisms
Many natural biominerals have been found to have hierarchical structure, such as
human bone, human enamel, nacre, ivory, etc.
Living organisms make up hierarchically organized materials through selforganization from precursors in aqueous solution, and scientists have developed
various biomimetic techniques to prepare and organize building blocks. It is
believed that an exquisite association of organic and inorganic compounds is
required for the construction of bioinorganic superstructures; therefore, understanding the roles of macromolecules in the biomineralization process is a significant
challenge in biomimetic materials. For example, the discovery of calcitic
microlenses in brittlestars, chiral morphologies with stereochemical recognition,
and the handedness of a snail shell bring out hidden elaborate structures and
properties of biominerals. The nacreous layer has attracted the interest of
researchers in a broad range of disciplines, especially in terms of its detailed
structure, defects in different scales, incorporated macromolecules, mechanical
6 Principles of Calcium-Based Biomineralization
153