When Teeth Twist: Distinct Mechanisms and Patterns of Enamel Wear from Rotational Forces-A Preliminary Investigation

Dental enamel possesses a unique anisotropic, heterogeneous hierarchical structure which enables a combination of high hardness and remarkable durability compared to other natural and synthetic biomaterials. Nevertheless, it undergoes mechanical degradation through fracture from concentrated overloads and/or progressive wear, both of which can compromise tooth function and longevity. Enamel wear is of particular interest to anthropology, as it is ubiquitous and enables researchers to discern the culture, behaviors, and ecologies of the study populations. Studies simulating dental wear in vitro often employ simplified loading configurations based on combinations of axial and lateral forces, which successfully reproduce the "classical" microwear features of pits and scratches, but do not capture the full complexity of in vivo loading conditions.

To conduct a preliminary in vitro investigation of previously underexplored rotationally induced occlusal mechanical wear in enamel.

Cyclic contact tests combining compression (50 N) and rotation (30°) are applied to human enamel specimens using a testing machine with decoupled biaxial (axial-torsion) actuators. Damage is characterized by electron and confocal microscopy.

Rotational forces produce abrasive wear with distinct microscopic damage patterns, involving transitions from quasi-plastic to brittle damage modes with an increasing number of contact cycles. After 10⁴ cycles, the macrowear volume is 0.0023 mm³.

Rotational microwear differs from "classical" pits and scratches associated with axial-lateral loading. Findings offer a framework for interpreting curved microscratches and provide a basis for future investigations. More broadly, they contribute to improving models of dental microwear and provide new insights in biomaterials science and anthropology.