Lay summary authored by Ian Towle. The paper can be read in Open Quaternary: http://doi.org/10.5334/oq.48
It is well known that the outer layer of a tooth, enamel, can’t repair after it has been removed through injury, wear or a cavity. However, the underlying dentine can ‘heal’ to a certain extent, in the form of new material formation called tertiary dentine. This form of dentine forms in response to disease and wear to protect the underlying pulp chamber, and therefore ultimately protects the individual against abscesses and infection.
Tertiary dentine can be easily distinguished on the surface of a tooth, with its much darker appearance compared to the original dentine. It is not known if certain species have evolved to produce tertiary dentine in response to stimuli sooner, or at a quicker rate, than others.
The aim of this study was to begin to address this question by comparing the frequency of tertiary dentine in different species of primate, and to see if some species produce this material quicker than others in response to wear.
The results show that gorillas have by far the highest rate of tertiary dentine formation, with over 90% of teeth with dentine exposed through wear showing tertiary dentine. Gorillas likely evolved this high rate as protection against heavy wear, with early/more tertiary dentine formation keeping the tooth functioning for longer.
In contrast, hominins (humans and our closely related fossil relatives), exhibit a remarkably low and uniform rate of tertiary dentin formation, with all species showing a frequency of around 15%. Chimpanzees fall between these extremes, with 47% of worn teeth showing ‘healing’. Why humans and our close relatives produce tertiary dentine slower and/or later than other great apes is not known, but it may be because we evolved different ways to cope with heavy wear and dental disease, such as evolving thick enamel, or it may instead relate to dietary and behavioural differences.
When more species have been studied it will be possible to give further insight into what drives tertiary dentine formation on an evolutionary scale. If, as seems likely, diet plays a crucial role, then the presence of this material in the fossil record may be useful for reconstructing diet in extinct species.
Read the paper here:
Towle, I., 2019. Tertiary Dentine Frequencies in Extant Great Apes and Fossil Hominins. Open Quaternary, 5(1), p.2. DOI: http://doi.org/10.5334/oq.48