219
– vasodentine in teleost fi sh, a tissue containing capillary canals instead of dentineal tubules (Hay 1912 ; Herold 1970 );
– plicidentine (infolded dentine) in sarcopterygians and the actinopterygian
Lepisosteus (Maxwell et al. 2011 ),
– mesodentine in acanthodian fi sh scales with Nostolepis -type histological
structure (Valiukevicius and Burrow 2005 ). Mesodentine “is characterized by
odontoblasts (odontocytes) trapped within the matrix, comparable with cellular
bone. Also similar to osteocytes these odontocytes demonstrate a reticulate (i.e.
non- polarized) branching pattern of cell processes. Like orthodentine, mesodentine is tubular,” (Sire et al. 2009 );
– semidentine has been reported as unique structure of the extinct group
Placodermi. “Similar to mesodentine, semidentine possesses embedded odontocytes within the matrix. However, the odontocyte cell processes are strongly
polarized, thus resembling a structural intermediate between the tubular appearance of orthodentine and mesodentine,” (Sire et al. 2009 );
– petrodentine in dipnoan fi sh (Smith 1984 , 1985 );
– elasmodine (isopedine) , a plywood-like collagenous dentine (Witzmann 2011 ).
Probably the hardest type of dentine is petrodentine. This hypermineralized tissue is
a functionally convergent structure with acrodin and enameloid in actinopterygian
and chondrichthyan marginal teeth. In marked contrast to the above two structures,
petrodentine forms entirely out of contact with any epithelium (Smith 1985 ), and is
produced by mesenchyme cells in the pulpal region. It was proposed that petrodentine is laid down by “ petroblasts ” which are modifi ed dentinoblasts (Denison 1974 ).
It has an extremely intimate anatomical relationship with the neighbouring “standard” dentine, often called osteodentine . Petrodentine forms a blade, supported on
both sides by dentine, but the dentine layer on one side is usually rather thin (Currey
and Abeysekera 2003 ). According to the modern defi nition (Reisz et al. 2004 ),
petrodentine is a hypermineralized tissue type, distinct from trabecular and circumpulpal dentine and bone, that approaches the hardness of enamel.
Dentine can be associated with some layers, which contain ions of metals other
than calcium. For example, the distal part of the durodentine tip of teleostean teeth
is occasionally provided with a very thin cap coloured by iron-oxid as reported by
Schmidt ( 1969 ). In mammals, reptiles and amphibians the iron-oxid coloration of
the tooth tip belongs exclusively to enamel. It is therefore concluded that the
coloured cap of the teleostean teeth is to be considered as a very thin enamel layer.
Hyaloine has been identifi ed as hypermineralized tissue that lacks on collagen
and that covers the surface of the post-cranial scutes in armored catfi sh (Teleostei:
Siluriformes) (Sire 1993 ). According to (Sire et al. 2009 ):
“Each scute initiates skeletogenesis via the osteogenic pathway: a bone primordium forms deep within the dermis and the presumptive scute grows by centrifugal
ossifi cation. Hyaloine matrix is deposited relatively late during development, once
the bony scute surface has come into close proximity with the basal surface of the
epidermis. Although outwardly similar to ganoine, hyaloine differs in that the superfi cial-most boundary of this tissue is always separated from the basalmost epidermal
4.2 Dentine and Dentine-Based Composite
– vasodentine in teleost fi sh, a tissue containing capillary canals instead of dentineal tubules (Hay 1912 ; Herold 1970 );
– plicidentine (infolded dentine) in sarcopterygians and the actinopterygian
Lepisosteus (Maxwell et al. 2011 ),
– mesodentine in acanthodian fi sh scales with Nostolepis -type histological
structure (Valiukevicius and Burrow 2005 ). Mesodentine “is characterized by
odontoblasts (odontocytes) trapped within the matrix, comparable with cellular
bone. Also similar to osteocytes these odontocytes demonstrate a reticulate (i.e.
non- polarized) branching pattern of cell processes. Like orthodentine, mesodentine is tubular,” (Sire et al. 2009 );
– semidentine has been reported as unique structure of the extinct group
Placodermi. “Similar to mesodentine, semidentine possesses embedded odontocytes within the matrix. However, the odontocyte cell processes are strongly
polarized, thus resembling a structural intermediate between the tubular appearance of orthodentine and mesodentine,” (Sire et al. 2009 );
– petrodentine in dipnoan fi sh (Smith 1984 , 1985 );
– elasmodine (isopedine) , a plywood-like collagenous dentine (Witzmann 2011 ).
Probably the hardest type of dentine is petrodentine. This hypermineralized tissue is
a functionally convergent structure with acrodin and enameloid in actinopterygian
and chondrichthyan marginal teeth. In marked contrast to the above two structures,
petrodentine forms entirely out of contact with any epithelium (Smith 1985 ), and is
produced by mesenchyme cells in the pulpal region. It was proposed that petrodentine is laid down by “ petroblasts ” which are modifi ed dentinoblasts (Denison 1974 ).
It has an extremely intimate anatomical relationship with the neighbouring “standard” dentine, often called osteodentine . Petrodentine forms a blade, supported on
both sides by dentine, but the dentine layer on one side is usually rather thin (Currey
and Abeysekera 2003 ). According to the modern defi nition (Reisz et al. 2004 ),
petrodentine is a hypermineralized tissue type, distinct from trabecular and circumpulpal dentine and bone, that approaches the hardness of enamel.
Dentine can be associated with some layers, which contain ions of metals other
than calcium. For example, the distal part of the durodentine tip of teleostean teeth
is occasionally provided with a very thin cap coloured by iron-oxid as reported by
Schmidt ( 1969 ). In mammals, reptiles and amphibians the iron-oxid coloration of
the tooth tip belongs exclusively to enamel. It is therefore concluded that the
coloured cap of the teleostean teeth is to be considered as a very thin enamel layer.
Hyaloine has been identifi ed as hypermineralized tissue that lacks on collagen
and that covers the surface of the post-cranial scutes in armored catfi sh (Teleostei:
Siluriformes) (Sire 1993 ). According to (Sire et al. 2009 ):
“Each scute initiates skeletogenesis via the osteogenic pathway: a bone primordium forms deep within the dermis and the presumptive scute grows by centrifugal
ossifi cation. Hyaloine matrix is deposited relatively late during development, once
the bony scute surface has come into close proximity with the basal surface of the
epidermis. Although outwardly similar to ganoine, hyaloine differs in that the superfi cial-most boundary of this tissue is always separated from the basalmost epidermal
4.2 Dentine and Dentine-Based Composite