title: 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.
authors.affiliation: Tribology Research Institute, Key Laboratory of Advanced Technologies of Materials, Ministry of Education of China, Southwest Jiaotong University, Chengdu 610031, People's Republic of China;
authors.forename: Jing
authors.initials: J
authors.lastname: Xia
authors.affiliation: Tribology Research Institute, Key Laboratory of Advanced Technologies of Materials, Ministry of Education of China, Southwest Jiaotong University, Chengdu 610031, People's Republic of China;
authors.forename: Jing
authors.initials: J
authors.lastname: Zheng
authors.affiliation: Tribology Research Institute, Key Laboratory of Advanced Technologies of Materials, Ministry of Education of China, Southwest Jiaotong University, Chengdu 610031, People's Republic of China;
authors.forename: Diaodiao
authors.initials: D
authors.lastname: Huang
authors.affiliation: Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701; Institute of Nanoscale Science and Engineering, University of Arkansas, Fayetteville, AR 72701;
authors.forename: Z Ryan
authors.initials: ZR
authors.lastname: Tian
authors.affiliation: Tribology Research Institute, Key Laboratory of Advanced Technologies of Materials, Ministry of Education of China, Southwest Jiaotong University, Chengdu 610031, People's Republic of China;
authors.forename: Lei
authors.initials: L
authors.lastname: Chen
authors.affiliation: Tribology Research Institute, Key Laboratory of Advanced Technologies of Materials, Ministry of Education of China, Southwest Jiaotong University, Chengdu 610031, People's Republic of China;
authors.forename: Zhongrong
authors.initials: Z
authors.lastname: Zhou
authors.affiliation: Department of Anthropology, University of Arkansas, Fayetteville, AR 72701 pungar@uark.edu linmao@home.swjtu.edu.cn.
authors.forename: Peter S
authors.initials: PS
authors.lastname: Ungar
authors.affiliation: Tribology Research Institute, Key Laboratory of Advanced Technologies of Materials, Ministry of Education of China, Southwest Jiaotong University, Chengdu 610031, People's Republic of China; pungar@uark.edu linmao@home.swjtu.edu.cn.
authors.forename: Linmao
authors.initials: L
authors.lastname: Qian
mesh_terms: D000535:Aluminum; D003300:Copper; D003743:Dental Enamel / Q000502:physiology / Q000648:ultrastructure; D003746:Dental Enamel Proteins / Q000502:physiology*; D004032:Diet; D005502:Food / Q000009:adverse effects*; D017276:Friction; D006244:Hardness; D006801:Humans; D066298:In Vitro Techniques; D018625:Microscopy, Atomic Force; D008855:Microscopy, Electron, Scanning; D008863:Microspheres; D008954:Models, Biological; D008963:Molar / Q000648:ultrastructure*; D054118:Nanospheres / Q000009:adverse effects; D010161:Paleodontology / Q000379:methods*; D010316:Particle Size; D011485:Protein Binding; D012822:Silicon Dioxide; D013052:Spectrometry, X-Ray Emission; D013499:Surface Properties; D014072:Tooth Abrasion / Q000209:etiology / Q000473:pathology*; D015032:Zinc
chemical_list: D003746:Dental Enamel Proteins; C048399:brass; D012822:Silicon Dioxide; D003300:Copper; D000535:Aluminum; D015032:Zinc
keywords: dental microwear; diet reconstruction; tooth wear