Research Article: Ambient occlusion and PCV (portion de ciel visible): A new dental topographic metric and proxy of morphological wear resistance

Date Published: May 1, 2019

Publisher: Public Library of Science

Author(s): Michael A. Berthaume, Julia Winchester, Kornelius Kupczik, Alistair Robert Evans.


Recently, ambient occlusion, quantified through portion de ciel visible (PCV) was introduced as a method for quantifying dental morphological wear resistance and reconstructing diet in mammals. Despite being used to reconstruct diet and investigate the relationship between dental form and function, no rigorous analysis has investigated the correlation between PCV and diet. Using a sample of platyrrhine and prosimians M2s, we show average PCV was significantly different between most dietary groups. In prosimian, insectivores had the lowest PCV, followed by folivores, omnivores, frugivores, and finally hard-object feeders. In platyrrhines, omnivores had the lowest average PCV, followed by folivores, frugivores, and finally hard-object feeders. PCV was correlated to two topographic variables (Dirichlet normal energy, DNE, and relief index, RFI) but uncorrelated to three others (orientation patch count rotated, OPCR, tooth surface area, and tooth size). The OPCR values here differed greatly from previously published values using the same sample, showing how differences in data acquisition (i.e., using 2.5D vs. 3D surfaces) can lead to drastic differences in results. Compared to other popular topographic variables, PCV performed as well or better at predicting diet in these groups, and when combined with a metric for size, the percent of successful dietary classifications reached 90%. Further, using an ontogenetic series of hominin (Paranthropus robustus) M2s, we show that PCV correlates well with probability of wear, with PCV values being higher on the portions of the occlusal surface that experience more wear (e.g., cusps and crest tips, wear facets) than the portions of the tooth that experience less. This relationship is strongest once wear facets have begun to form on the occlusal surface. These results highlight the usefulness of PCV in quantifying morphological wear resistance and predicting diet in mammals.

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Dental topography has become a popular method for inferring diet from tooth shape in mammals [1,2]. While methods for quantifying tooth shape in a dietary manner have existed for decades (e.g. shearing quotient and ratio [3–8]), it wasn’t until the development of advanced scanning techniques and homology-free metrics that species with dissimilar occlusal morphologies could be directly compared in large scale analyses [9,10].

We used a sample of 209 primate minimally worn mandibular second molars (LM2s), representing two groups (Prosimii, n = 111; Platyrrhini, n = 110) and five dietary categories (insectivore, folivore, omnivore, frugivore, and hard-object feeder) to test the relationship between average molar PCV and diet. The majority of this sample was used in previous dental topographic studies [11,15,18,19], and are freely available at [26]. Five teeth obtained from were not part of the aforementioned studies (see supplementary information for specimen list).

Averages and standard deviations of dental topographic values for each group and dietary category are presented in Fig 3 and Table 2. Raw values are published in the supplementary material (S1 Table). PCV is generally highest for hard-object feeders, followed by frugivores, omnivores, folivores, and lowest for insectivores (S2 Table). Results from two-way ANOVAs indicated significant interactions between group and diet factors for all topographic variables except OPCR (Table 1). As such, one-way ANOVAs were used to examine the effect of diet on topographic variables in platyrrhines and prosimians separately. One-way ANOVAs revealed all topographic variables except OPCR were correlated to diet, though it should be noted that OPCR did significantly vary with diet in the two-way ANOVA (Table 3). Tukey HSD results showed differences between dietary categories occurred more often for PCV, DNE, and RFI in prosimians (Table 4), and more often for SA and tooth size in platyrrhines (Table 5). Significant correlations occurred between many of the variables, with PCV being negatively correlated to DNE and RFI, and uncorrelated to OPCR, SA, and tooth size (Table 6).

Average ambient occlusion, quantified through PCV, differed significantly between dietary categories in two major primate groups, and performed as good or better than the other metrics at predicting diet from tooth shape (Tables 3 and 7). In prosimians, insectivores had the lowest average PCV values, followed by folivores, omnivores, frugivores, and hard-object feeders. In platyrrhines, omnivores had the lowest average PCV values, followed by folivores, frugivores, and hard-object feeders (Table 2).

Recently, average ambient occlusion, quantified through PCV, was introduced as new dental topographic variable for quantifying morphological wear resistance, which could be used to predict dietary categories in primates. Here, we show a strong correlation between PCV and diet in two groups of primates, platyrrhines and prosimians, and that it performs as well or better than other topographical variables at predicting diet in Primates. Finally, we show how it is correlated to dental wear in a series of P. robustus teeth, and how it can be used to predict the parts of the tooth which will interact with the tooth, and, if the tooth has even low levels of wear, can be used to predict which parts of the tooth will wear further.




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