215
– The evolutionary link between fi sh scales and teeth is more substantial. Scales in
teleost fi sh evolved from the dermal armour covering the body of ancient
vertebrates.
– The structural and developmental similarities of fi sh dermal armour and mammalian teeth has led to the suggestion that teeth evolved by internalisation of
dentine containing dermal armour ‘odontodes’ into the oral cavity.
– Teeth evolved from fi sh dermal armour,” (Sharpe 2001 ).
Thus, each kind of fi sh scales possess both mineral and organic components, some
of them are the same as in vertebrate teeth. Therefore, I fi nd it necessary to introduce here briefl y the corresponding compounds and biocomposites.
4.1 Enamel and Enameloid
Mature dental enamel is an example of highly mineralized hard tissue with respect
to hierarchically structured hydroxyapatite crystals (up to 95 % by weight). Both
chemistry and exceptionally organized structure of enamel make it the hardest substance in the human body with specifi c functional properties. According to Hu et al.
( 2007 ), dental enamel has no physiological means of repair outside of the remineralization and protective potential provided by saliva because of its acellularity (Hu
et al. 2007 ). The ultrastructure of enamel “resembles a perfect pattern for knitting or
croche,” (Moradian-Oldak 2009 ). Hierarchical organization of mature enamel can
be represented in the following way:
– Nanoscale: long fl uoridated calcium hydroxyapatite crystals;
– Microscale: the crystals are aligned together in bundles to form 3 μm to 5 μm
diameter prisms or rods.
The diameter of such enamel prism has approximately the same size as an enamelmaking cell, or ameloblast. The extracellular environment between dentine and ameloblasts is that space where the formation of tooth enamel takes place initially, before
the tooth erupts. The formation (amelogenesis) and development of enamel in vivo is
a very complex process that includes gene expression, protein secretion, folding and
assembly, and calcifi cation. Margolis et al. ( 2006 ) defi ned enamel amelogenesis as
“the result of highly orchestrated extracellular processes that regulate the nucleation,
growth, and organization of forming mineral crystals,” (Margolis et al. 2006 ).
Although there are lot of open questions concerning understanding of the mechanism
of enamel formation in different animal taxa as well as in human (see for detail Nanci
2003 ; Moradian–Oldak and Paine 2008 ), the common hypothesis is still based on
crucial roles of protein-mineral and protein-protein interactions.
During collar enamel formation in actinopterigian fi sh ( Polypterus senegalus ),
an amorphous fi ne enamel matrix without any presence of fi brillar collagen was
recently found by Sasagawa and co-workers ( 2012 ) between the dentine and ameloblast layers. These authors characterized this type of enamel as follow:
4.1 Enamel and Enameloid
– The evolutionary link between fi sh scales and teeth is more substantial. Scales in
teleost fi sh evolved from the dermal armour covering the body of ancient
vertebrates.
– The structural and developmental similarities of fi sh dermal armour and mammalian teeth has led to the suggestion that teeth evolved by internalisation of
dentine containing dermal armour ‘odontodes’ into the oral cavity.
– Teeth evolved from fi sh dermal armour,” (Sharpe 2001 ).
Thus, each kind of fi sh scales possess both mineral and organic components, some
of them are the same as in vertebrate teeth. Therefore, I fi nd it necessary to introduce here briefl y the corresponding compounds and biocomposites.
4.1 Enamel and Enameloid
Mature dental enamel is an example of highly mineralized hard tissue with respect
to hierarchically structured hydroxyapatite crystals (up to 95 % by weight). Both
chemistry and exceptionally organized structure of enamel make it the hardest substance in the human body with specifi c functional properties. According to Hu et al.
( 2007 ), dental enamel has no physiological means of repair outside of the remineralization and protective potential provided by saliva because of its acellularity (Hu
et al. 2007 ). The ultrastructure of enamel “resembles a perfect pattern for knitting or
croche,” (Moradian-Oldak 2009 ). Hierarchical organization of mature enamel can
be represented in the following way:
– Nanoscale: long fl uoridated calcium hydroxyapatite crystals;
– Microscale: the crystals are aligned together in bundles to form 3 μm to 5 μm
diameter prisms or rods.
The diameter of such enamel prism has approximately the same size as an enamelmaking cell, or ameloblast. The extracellular environment between dentine and ameloblasts is that space where the formation of tooth enamel takes place initially, before
the tooth erupts. The formation (amelogenesis) and development of enamel in vivo is
a very complex process that includes gene expression, protein secretion, folding and
assembly, and calcifi cation. Margolis et al. ( 2006 ) defi ned enamel amelogenesis as
“the result of highly orchestrated extracellular processes that regulate the nucleation,
growth, and organization of forming mineral crystals,” (Margolis et al. 2006 ).
Although there are lot of open questions concerning understanding of the mechanism
of enamel formation in different animal taxa as well as in human (see for detail Nanci
2003 ; Moradian–Oldak and Paine 2008 ), the common hypothesis is still based on
crucial roles of protein-mineral and protein-protein interactions.
During collar enamel formation in actinopterigian fi sh ( Polypterus senegalus ),
an amorphous fi ne enamel matrix without any presence of fi brillar collagen was
recently found by Sasagawa and co-workers ( 2012 ) between the dentine and ameloblast layers. These authors characterized this type of enamel as follow:
4.1 Enamel and Enameloid