Dental Evolution

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Department of Pediatric Dentistry, Selcuk University, Faculty of Dentistry, Konya, Turkey
 
Abstract
Evolutionary and developmental biology are very complementary fields of research and study to that of comparative dental embryology, the latter arising in the last quarter of the nineteenth century. In order to achieve a suitable taxonomy for dental embryology, it is necessary to compare equivalent characteristics throughout existent and extinct species.

Evolutionary and developmental biology are very complementary fields of research and study to that of comparative dental embryology, the latter arising in the last quarter of the nineteenth century. In order to achieve a suitable taxonomy for dental embryology, it is necessary to compare equivalent characteristics throughout existent and extinct species.

1.1 Historical Perspectives

Histological studies of dental organs started to emerge in the nineteenth century. According to Louise J. Baume in his seminal work titled “The Biology of Pulp and Dentin,” the demonstration of tubular structures in dentin first took place between 1835 and 1851 (Baume 1980). While the recognition of the pulp/dentin relationship followed those discoveries in 1852–1863, peritubular and nerve structures were not shown until later, between 1863 and 1868. The ontogenical aspects and phylogeny of dentin were taken to this stage of definition between 1867 and 1906 (Baume 1980).
From agnathans, jawless vertebrates, to mammals, observed modifications showed the evolution of mammalian dental ontogeny. Fossil teeth provided evidence to compare the relationships between extant and extinct groups and established phylogeny of mammals (Rougier and Novacek 1998). As highly mineralized appendages found in the entrance of the alimentary canal of both invertebrates and vertebrates, teeth have many functions such as processing of food, phonetic articulation, and defense in humans (Koussoulakou et al. 2009). The fact that dermal structures are the origin of teeth in vertebrates has many implications in dental biology. Those dermal structures have been thought to spread secondarily to the mouth, and there they became associated with bones (Butler 1995). Odontodes, which are superficial dermal structures located outside the mouth in jawless fish, were followed by buccal teeth that were localized to the jaw margins (Koussoulakou et al. 2009). Reif has brought attention to the similarity of teeth to the dermal denticles (placoid scales) of elasmobranchs (Reif 1978), and Butler translates this knowledge by implying that teeth might have originated as products of the skin in jawless vertebrates, and furthermore that they subsequently spread to the mouth with the conversion of the mandibular arch into jaws in gnathostomes (vertebrate with jaws) (Butler 1995). Likewise, as the ancestor of teeth, odontodes was similar to placoid scales of recent sharks.
Most nonmammalian vertebrates have homodont dentition (all teeth of the same type). Human dentition is heterodont and diphyodont, which includes deciduous and permanent succession. While the dentition of animals with only one set of teeth throughout life is monophyodont, continuously replacing dentitions are polyphyodont (Fraser et al. 2006). The reduction in teeth number and generations (from polyphyodonty to oligodonty) and the increase in morphological complexity of teeth (from homodonty to heterodonty) represent important factors for mammalian diversification (Koussoulakou et al. 2009; Salazar-Ciudad and Jernvall 2010).
The reappearance of some teeth, which were lost over time, in birds is an interesting evolutionary concept (Chen et al. 2000). One of the central evolutionary principles known as Dollo’s law indicates that an organism is unable to return, even partially, to a previous stage already realized in the ranks of its ancestors (Tomic and Meyer-Rochow 2011). Obviously, under appropriate conditions, the lost odontogenic capacity of avian ectomesenchyme can be regained (Louchart and Viriot 2011). Possible explanations for this are the preserved odontogenic capacity in oral epithelium or a safeguard mechanism such as gene redundancy, since knockout mutations of most teeth-related genes do not cause developmental arrest. Moreover, those mutations cannot prevent the formation of dental lamina, which can be observed in birds, although their teeth were lost over 60 millions years ago (Chen et al. 2000; Koussoulakou et al. 2009). Understanding the rules governing the reacquisition of lost properties will provide a wide range of clinical and biological applications to impaired or lost teeth (Koussoulakou et al. 2009).
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Nov 16, 2015 | Posted by in General Dentistry | Comments Off on Dental Evolution
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