109
Recently, Alibardi and Segalla ( 2011 ) reported that the ultrastructural features of the
horny teeth of freshwater lamprey Lenthenteron zanandreai are reminiscent of similar
aspects present in the lamprey E. japonicus (Uehara et al. 1983 ). Electron- dense
bundles of keratin but no keratohyaline-like granules accumulated in the cytoplasm
of transitional cells that were incorporated in the dense stratum corneum of the
L. zanandreai tooth. Mature corneocytes were delimited by a cell corneous envelope
and formed corneous microridges on the tooth surface. Although the increase in
the electron density of the corneous layer suggested the presence of sulfur, the low to
absent reaction for sulfhydryl groups indicated that cysteine was largely oxidized to
form disulphide bonds in the corneous material of the teeth. A 2-dimensional electrophoretic analysis of the corneous material from the horny teeth showed the presence
of acidic proteins, most likely keratins of 45–66 kDa (Alibardi and Segalla 2011 ).
Based on the size, it is likely that acidic and basic non- keratin proteins of 16–20 kDa
were also present in the oral mucosa, generally in higher amounts than keratins. This
suggests that the low-molecular-weight basic proteins are likely associated with acidic
keratins to produce the dense corneous material of the tooth, a process that also occurs
in hard skin derivatives of other vertebrates like amphibians (Alibardi 2010a , b ).
Thus, the representatives of living agnatha possess, epithelially derived keratincontaining teeth, rather than the epidermal and dermally derived highly mineralized
“true teeth” of most other toothed vertebrates. Interestingly, it was possible to culture
the teeth from adult lampreys in vitro as reported by Langille and Hall ( 1988 ). These
authors reported that “ teeth cultured in L15-supplemented media for up to 14 days
at either 15 or 20 °C retained their structural and cellular integrity as observed
histologically, with no apparent cell outgrowth, ” (Langille and Hall 1988 ). It seems to
be necessary to repeat these experiments using modern tissue engineering technologies. In particular the infl uence of calcium, phosphate and carbonate sources on
development of these non-mineralized hard tissue structures should be studied.
3.2.3 Rostral Teeth
Another and very speculative example of “ non true teeth ” is rostral teeth of some
sawfi shes, which are actually a type of ray. While modern sawfi sh are related to the
Pristidae family, derived from a Greek word meaning “a sawyer or saw”; an ancient
sawfi sh family (Sclerorhynchidae) lived in primitive seas and have long since gone
extinct. Members of both families have the specifi c long, fl attened, blade-like
toothed rostrum, “a fl attened head and trunk, and a shark-like appearance and manner
of swimming,” (Wiley et al. 2008 ). The rostral teeth of the Pristidae are implanted
in socklets along the margin of a rostrum. This phenomenon—gomphosis (a type of
immovable articulation, as of a tooth inserted into its bony socket)—is one of the
rarer methods of attachment in pisces. These teeth are reputed to be held in the
socklets by cementum, and they grow from persistent pulps (Bradford 1957 ). It was
suggested (Miller 1974 ) that the rostral teeth do not arise in an alternate way as do
most tooth structures, and may indeed not be true teeth.
3.2 Teeth
Recently, Alibardi and Segalla ( 2011 ) reported that the ultrastructural features of the
horny teeth of freshwater lamprey Lenthenteron zanandreai are reminiscent of similar
aspects present in the lamprey E. japonicus (Uehara et al. 1983 ). Electron- dense
bundles of keratin but no keratohyaline-like granules accumulated in the cytoplasm
of transitional cells that were incorporated in the dense stratum corneum of the
L. zanandreai tooth. Mature corneocytes were delimited by a cell corneous envelope
and formed corneous microridges on the tooth surface. Although the increase in
the electron density of the corneous layer suggested the presence of sulfur, the low to
absent reaction for sulfhydryl groups indicated that cysteine was largely oxidized to
form disulphide bonds in the corneous material of the teeth. A 2-dimensional electrophoretic analysis of the corneous material from the horny teeth showed the presence
of acidic proteins, most likely keratins of 45–66 kDa (Alibardi and Segalla 2011 ).
Based on the size, it is likely that acidic and basic non- keratin proteins of 16–20 kDa
were also present in the oral mucosa, generally in higher amounts than keratins. This
suggests that the low-molecular-weight basic proteins are likely associated with acidic
keratins to produce the dense corneous material of the tooth, a process that also occurs
in hard skin derivatives of other vertebrates like amphibians (Alibardi 2010a , b ).
Thus, the representatives of living agnatha possess, epithelially derived keratincontaining teeth, rather than the epidermal and dermally derived highly mineralized
“true teeth” of most other toothed vertebrates. Interestingly, it was possible to culture
the teeth from adult lampreys in vitro as reported by Langille and Hall ( 1988 ). These
authors reported that “ teeth cultured in L15-supplemented media for up to 14 days
at either 15 or 20 °C retained their structural and cellular integrity as observed
histologically, with no apparent cell outgrowth, ” (Langille and Hall 1988 ). It seems to
be necessary to repeat these experiments using modern tissue engineering technologies. In particular the infl uence of calcium, phosphate and carbonate sources on
development of these non-mineralized hard tissue structures should be studied.
3.2.3 Rostral Teeth
Another and very speculative example of “ non true teeth ” is rostral teeth of some
sawfi shes, which are actually a type of ray. While modern sawfi sh are related to the
Pristidae family, derived from a Greek word meaning “a sawyer or saw”; an ancient
sawfi sh family (Sclerorhynchidae) lived in primitive seas and have long since gone
extinct. Members of both families have the specifi c long, fl attened, blade-like
toothed rostrum, “a fl attened head and trunk, and a shark-like appearance and manner
of swimming,” (Wiley et al. 2008 ). The rostral teeth of the Pristidae are implanted
in socklets along the margin of a rostrum. This phenomenon—gomphosis (a type of
immovable articulation, as of a tooth inserted into its bony socket)—is one of the
rarer methods of attachment in pisces. These teeth are reputed to be held in the
socklets by cementum, and they grow from persistent pulps (Bradford 1957 ). It was
suggested (Miller 1974 ) that the rostral teeth do not arise in an alternate way as do
most tooth structures, and may indeed not be true teeth.
3.2 Teeth