An Improved Technique Using Dental Prostheses for Field Quantification of the Force Required by Primates for the Dental Penetration of Fruit

Tooth morphology is an important determinant of primate diet, setting potential limits on processable item size and material properties. Plunger-based commercial fruit firmness testers (penetrometers) have been used to estimate primate diet item hardness and, by proxy, bite force required for penetration. However, geometric forms and surface areas of penetrometer plungers and primate teeth differ considerably. Accurate bite force estimation is especially important with pitheciine primates as these penetrate fruit pericarps with their canines. To achieve more realistic bite force measures, we replaced a fruit penetrometer's standard plunger with a Cacajao calvus canine prosthesis. We compared indentation and penetration values for Hevea spruceana (Euphorbiaceae; hard-pericarp) and Mauritia flexuosa (Arecaceae; soft-pericarp) fruits (both natural Cacajao foods), and standard penetrometer head and canine prosthesis values for penetrating H. spruceana sulci. Compared to the canine prosthesis, a standard head overestimated the force needed to indent and penetrate H. spruceana fruit by more than twofold and, due to greater width, could not effectively penetrate a sulcus: sulcal penetrability data were easily retrieved with the canine prosthesis. We believe this new approach using dental prostheses has potential in the analysis of primate foraging mechanisms, especially for pitheciines for which canines are of paramount importance in accessing food.