Biomineralization: Tooth Enamel Formation - Bioinspiration: From Nano to Micro Scales - page 158

Chapter 5
Biomineralization: Tooth Enamel Formation
Mayumi Iijima, Kazuo Onuma, and Toru Tsuji
Abstract Tooth enamel is composed of well-crystallized apatite that elongates in
the c-axis direction with a highly organized orientation. How do these crystals form?
It is still an unanswered question, despite enormous efforts made on answering it.
Chapter 5 briefly reviews the physicochemical studies on clarifying the mech-
anism of enamel apatite formation. These studies revealed that enamel apatite
crystals are formed in a fluid with discrete inorganic and organic compositions. The
activity of inorganic ions changes dynamically during the formation process under
strict cellular control, and it provides an adequate driving force for nucleation and
successive growth. These processes include a dynamic equilibrium of inorganic ions
and a transition of unstable intermediates to more stable phases. The composition
and solubility of the forming enamel crystals also change dynamically. Because
of this complex situation, several formation mechanisms of enamel apatite crystals
have been proposed, and researchers have yet to reach a consensus on the subject.
Crystal formation takes place in a gel-like enamel matrix, composed of spherical
aggregates of amelogenin molecules. Amelogenin is a major component of the
enamel matrix and regulates crystal formation by cooperating with enameline
(minor matrix protein) and inorganic fluid components. Once enamel formation is
M. Iijima ( )
Asahi University School of Dentistry, Oral Functional Science and Rehabilitation, Dental
Materials Science, 1851-1 Hozumi, Mizuho, Gifu, 501-0296, Japan
e-mail: [e-mail]
K. Onuma
National Institute of Advanced Industrial Science & Technology, Central 6, 1-1-1 Higashi,
Tsukuba, Ibaraki, 305-8566, Japan
e-mail: [e-mail]
T. Tsuji
Advanced Research Centers, Keio University, 3-14-1, Hiyoshi, Kohoku-ku,
Yokohama, 223-8522, Japan
e-mail: [e-mail]