Age‐related changes in the tooth–bone interface area of acrodont dentition in the chameleon

Abstract

Chameleon teeth develop as individual structures at a distance from the developing jaw bone during the prehatching 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 microcomputed 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.

Mosasaurs and snakes have a periodontal ligament: timing and extent of calcification, not tissue complexity, determines tooth attachment mode in reptiles

“…; Dosedělová et al. ). This in turn may confound our understanding of dental tissue complexity in modern reptiles and should therefore be explored further in other squamates.…”

“…; Dosedělová et al. ), where a single, ‘bone of attachment’‐like tissue has been described, there are two important reasons for this type of histological study to be pursued further in other squamate lineages. First, the acrodont dentitions of chameleonids and Sphenodon consist of an extremely reduced periodontium and an apomorphic relationship of the teeth to their attachment tissues and the jawbones (Kieser et al.…”

The Permian reptile Opisthodontosaurus carrolli: a model for acrodont tooth replacement and dental ontogeny

“…; Dosedělová et al. ). These extant taxa exhibit many adaptations to extreme wear, making them excellent developmental models for studies of wear resistance and how a dentition can remain functional for an extended period of time in spite of a lack of replacement (Cooper et al.…”

“…; Dosedělová et al. ). These wear adaptations have also become intimately linked with the acrodont condition, just as the lack of replacement has become a part of the definition of acrodonty (Zaher & Rieppel, ; Smirina & Ananjeva, ).…”

“…; Dosedělová et al. ). This in‐filling of the pulp cavity through ontogeny is absent in Opisthodontosaurus .…”