Abstract
Tertiary dentine forms when an odontoblast is directly affected by stimuli, commonly through occlusal wear and caries. In this study the presence of tertiary dentine was recorded in three South African fossil hominin species (Australopithecus africanus, Homo naledi and Paranthropus robustus), and two extant great ape species (Gorilla gorilla gorilla and Pan troglodytes). Frequencies of tertiary dentine were calculated for each species based on macroscopic observations of teeth with dentine exposed through occlusal wear. Overall, the three hominin species have similar tertiary dentine frequencies ranging from 12% to 16.13%. In contrast, over 90% of permanent gorilla teeth with dentine visible show tertiary dentine. Chimpanzees fall between these extremes, with 47.21% of permanent teeth affected. Deciduous teeth follow the same pattern. Species variances are not related to differences in occlusal wear. Instead, some species appear predisposed to produce tertiary dentine earlier/faster, or more often, than other species. Therefore, tertiary dentine formation has the potential to provide useful information on fossil specimens. For example, the uniformly low frequency of tertiary dentine formation in hominins may relate to diet, or be due to thick enamel having a similar role in preventing loss of function of teeth, i.e., extending the life of a tooth. In contrast, tertiary dentine is clearly an important mechanism for normal dental function in gorillas, and may have evolved to help maintain shearing function.
Highlights
Primary dentine is produced during tooth formation by odontoblasts and is succeeded by secondary dentine, which is an ongoing, slow process (Rutherford et al 1995; Dean, 2017; Zuo et al 2018)
Gorillas have the highest prevalence with over 90% of permanent teeth with exposed primary dentine showing tertiary dentine islands
Most the gorilla examples are extremely dark, which may be caused by the amount of tertiary dentine formed or perhaps a denser tertiary dentine structure
Summary
Primary dentine is produced during tooth formation by odontoblasts and is succeeded by secondary dentine, which is an ongoing, slow process (Rutherford et al 1995; Dean, 2017; Zuo et al 2018). Tertiary dentine can be formed in two ways: reactionary dentine occurs when new dentine forms from the pre-existing odontoblasts; and reparative, in which new odontoblast cells are formed (Ricucci et al 2014; Carvalho and Lussi, 2017). In both types, tertiary dentine forms when teeth are directly affected by stimuli such as
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