OBJECTIVE: Replacement teeth in reptiles and mammals develop from a successional dental lamina. In monophyodont (single generation) species such as the mouse, no successional lamina develops. We have selected a reptilian monophyodont species - the Veiled Chameleon (Chamaeleo calyptratus) - to investigate whether this is a common characteristic of species that do not have replacement teeth. Furthermore, we focus on the sequence of tooth initiation along the jaw, and tooth attachment to the bones. DESIGN: Embryos of the Veiled Chameleon were collected during the first 6 months of incubation (from the 5th to 24th week) at 7-day intervals. RESULTS: After five weeks of incubation, an epithelial thickening was present as a shallow protrusion into the mesenchyme. A week later, the epithelium elongated more deeply into the mesenchyme to form the dental lamina. The formation of all tooth germs along the jaw was initiated from the tip of the dental lamina. Development of a successional dental lamina was initiated during the pre-hatching period but this structure became markedly reduced during juvenile stages. MicroCT analysis showed the presence of a heterodont dentition in young chameleons with multicuspid teeth in the caudal jaw area and simpler monocuspid teeth rostrally. Unlike the pleurodont teeth of most reptilian species, chameleon teeth are acrodontly ankylosed to the bones of the jaw. Odontoblasts produced a layer of predentine that connected the dentine to the supporting bone, with both tooth and bone protruding out of the oral cavity and acting as a functional unit. CONCLUSIONS: Chameleons may provide new and useful information to study the molecular interaction at the tooth-bone interface in physiological as well as pathological conditions.

Department of Craniofacial Development and Stem Cell Biology and Department of Orthodontics King's College London Dental Institute Floor 27 Guy's Tower Guy's Hospital London Bridge SE1 9RT London UK

Department of Zoology Faculty of Science Charles University Albertov 6 128 43 Prague 2 Czech Republic; Institute of Experimental Medicine Academy of Sciences of the Czech Republic Vídeňská 1083 142 40 Prague 4 Czech Republic

Institute of Animal Physiology and Genetics v v i Academy of Sciences of the Czech Republic Veveri 97 602 00 Brno Czech Republic

Institute of Animal Physiology and Genetics v v i Academy of Sciences of the Czech Republic Veveri 97 602 00 Brno Czech Republic; Department of Anatomy Histology and Embryology Faculty of Veterinary Medicine University of Veterinary and Pharmaceutical Sciences Palackeho 1 3 612 42 Brno Czech Republic

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