New model to explain tooth wear with implications for microwear formation and diet reconstruction

Abstract

Paleoanthropologists and vertebrate paleontologists have for decades debated the etiology of tooth wear and its implications for understanding the diets of human ancestors and other extinct mammals. The debate has recently taken a twist, calling into question the efficacy of dental microwear to reveal diet. Some argue that endogenous abrasives in plants (opal phytoliths) are too soft to abrade enamel, and that tooth wear is caused principally by exogenous quartz grit on food. If so, variation in microwear among fossil species may relate more to habitat than diet. This has important implications for paleobiologists because microwear is a common proxy for diets of fossil species. Here we reexamine the notion that particles softer than enamel (e.g., silica phytoliths) do not wear teeth. We scored human enamel using a microfabrication instrument fitted with soft particles (aluminum and brass spheres) and an atomic force microscope (AFM) fitted with silica particles under fixed normal loads, sliding speeds, and spans. Resulting damage was measured by AFM, and morphology and composition of debris were determined by scanning electron microscopy with energy-dispersive X-ray spectroscopy. Enamel chips removed from the surface demonstrate that softer particles produce wear under conditions mimicking chewing. Previous models posited that such particles rub enamel and create ridges alongside indentations without tissue removal. We propose that although these models hold for deformable metal surfaces, enamel works differently. Hydroxyapatite crystallites are "glued" together by proteins, and tissue removal requires only that contact pressure be sufficient to break the bonds holding enamel together. dental microwear | diet reconstruction | tooth wear

Mechanical modelling of tooth wear

“…That does not necessarily mean that phytoliths are the only wear agent, as other components of the food matrix like plant fibres, or properties of the food matrix that catch detached enamel particles or dust and keep them in the ingested bolus as additional abrasives, could also be responsible. Amorphous silica, which was used as an analogue of phytoliths in a recent study [6], has a role in the formation of microscale scratches. The diet containing most phytoliths also overwrote the striation from the initial polishing more quickly than the other non-sandy diets, suggesting tissue removal.…”

“…Despite the conclusion that phytoliths cause plastic deformation rather than removal of enamel, a recent ground-breaking study shows that phytoliths do in fact impact enamel [5]. Very recently, particles softer than enamel were reported to generate grooves, resulting from tissue loss and not plastic deformation, on enamel in macro-(aluminium and brass spheres) and nanoscale (amorphous silicon dioxide spheres) [6].…”

Seeds, browse, and tooth wear: a sheep perspective

“…2015; Xia et al. 2015). Controlled‐food experiments, by reducing the dietary breadth, allow for a direct quantification of the effect of each type of items separately (i.e., seed vs. browse vs. graze).…”

Dental microwear differences between eastern and southern African fossil bovids and hominins

“…Indeed, tissue removal is achieved with particles much softer than enamel. 33 In this light, it makes sense that primates known to consume phytolith-rich foods tend to have thicker tooth enamel 34 , that tell-tale siliceous plant opals have been found embedded in tooth enamel at the ends of microwear scratches 35 , and that experimental studies show cereals with different phytolith loads leave different microwear patterns 36 .…”