Age-related changes in the tooth-bone interface area of acrodont dentition in the chameleon.
2016
Chameleon teeth develop as individual structures at a distance
from the developing jaw bone during the pre-hatching period and
also partially during the post-hatching period. However, in the
adult, all teeth are fused together and tightly attached to the
jaw bone by mineralized attachment tissue to form one
functional unit. Tooth to bone as well as tooth to tooth
attachments are so firm that if injury to the oral cavity
occurs, several neighbouring teeth and pieces of jaw can be
broken off. We analysed age-related changes in chameleon
acrodont dentition, where ankylosis represents a physiological
condition, whereas in mammals, ankylosis only occurs in a
pathological context. The changes in hard-tissue morphology and
mineral composition leading to this fusion were analysed. For
this purpose, the lower jaws of chameleons were investigated
using X-ray micro-computed tomography, laser-induced breakdown
spectroscopy and microprobe analysis. For a long time, the
dental pulp cavity remained connected with neighbouring teeth
and also to the underlying bone marrow cavity. Then, a
progressive filling of the dental pulp cavity by a mineralized
matrix occurred, and a complex network of non-mineralized
channels remained. The size of these unmineralized channels
progressively decreased until they completely disappeared, and
the dental pulp cavity was filled by a mineralized matrix over
time. Moreover, the distribution of calcium, phosphorus and
magnesium showed distinct patterns in the different regions of
the tooth-bone interface, with a significant progression of
mineralization in dentin as well as in the supporting bone. In
conclusion, tooth-bone fusion in chameleons results from an
enhanced production of mineralized tissue during post-hatching
development. Uncovering the developmental processes underlying
these outcomes and performing comparative studies is necessary
to better understand physiological ankylosis; for that purpose,
the chameleon can serve as a useful model species.
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