Journal of the Royal Society of New Zealand abstracts

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Tooth-sharpening behaviour (thegosis) and other causes of wear on sheep teeth in relation to mastication and grazing mechanisms

D. Every¹ , G. A. Tunnicliffe² , and R. G. Every³

Four types of wear can be defined in sheep teeth: thegotic, abrasive, interproximal and corrosive. Thegosis in sheep is the innate grinding of mandibular cheek teeth against maxillary teeth which produces characteristic flat facets on the enamel. The freshly thegosed facets characteristically have clearly defined edges and fine parallel striations on the surface. Thegosis maintains sharp enamel blade systems that allow efficient cutting of food during mastication while eating and ruminating. Interproximal wear results from adjacent teeth rubbing together, and, with mesial drift, helps prevent impaction of food between them. Abrasive wear is caused by the movement of food or other exogenous materials over the surfaces of these teeth. On the cheek teeth abrasion hollows out dentine between the enamel ridges and wears away the sharp edges and parallel striations of the thegotic facets on the enamel, replacing them with randomly placed scores of uneven depth. Hollowing out serves the useful function of exposing sharp enamel blades at the occlusal surface. Abrasion on the incisors results in characteristic wear areas on the enamel and dentine surfaces. These abrasive areas are bounded by relatively sharp edges to the labial enamel because of the particular morphology of the incisors and the grazing mechanism of sheep, which are described in this paper. Corrosive wear is caused by chemicals from herbage corroding the hard calcium phosphates from the teeth.

The main anatomical and functional features of the cheek teeth are described using R. G. Every's thegotic terminology for mammalian teeth. The thegotic nomenclature uses functional concepts not implicit in the more conventional Cope-Osborn terminology traditionally used to describe teeth. Sheep teeth, as generally for placental herbivores, are classed as beta dentition. The main feature is the triakididrepanoid blade system. The mechanism is described by which these blade systems interrelate during mastication to achieve efficient cutting up of food material.

The incidence of thegosis, rumination and eating was recorded during a continuous 24h cycle and showed that there is a major period of thegosis during the dark morning hours. The results provided unequivocal evidence for a tooth-to-tooth wearing behaviour (thegosis) that always occurred at a separate time from mastication. The advantage of night-time and stress-induced thegosis is discussed.

Keywords: sheep; dentition; thegosis; tooth sharpening; tooth wear; grazing; mastication.

(c) Journal of The Royal Society of New Zealand,

Volume 28, Number 1, March 1998, pp 169-184

PDF file of entire paper: medium quality (1238K); (scanned from paper original: notes about this process)

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