ATTRITION OF THE IIYPSODONT TOOTH 109 



though such defects remain latent and even undetectable in sheep 

 of similar breeding grazing "unimproved" pasture. 



The hypsodont tooth lays down secondary dentine in the pulp 

 chamber as the tooth wears. The incisal surface of worn sheep's 

 teeth may eventually consist almost entirely of secondary dentine. 

 Caries has never been observed in sheep's teeth during this inves- 

 tigation. 



Results of extensive feeding trials, and considerations of chem- 

 ical analyses of the soil and the pastures, have, so far, given no 

 indication that the problem is nutritional in the generally accepted 

 sense. 



Constituents of actively metabolizing herbage which predispose 

 sheep's teeth to excessive wear appear to be: (1) enzymes (pro- 

 teinases) which attack the organic bonding material of the dentine; 

 (2) acids which chelate calcium of the apatite. By these agencies 

 tooth structure may become weakened and susceptible to attrition 

 by the tougher constituents of the herbage such as fiber and opal 

 phytoliths. 



References 



Baker, G., Jones, L. H. P., and Wardrop, I. D. 1959. Cause of wear in 



sheep's teeth. Nature, 184, 1583-1584. 

 Barnicoat, C. R. 1957. Wear in sheep's teeth. I-V. New Zealand }. Sci. 



and Technol, 38A, 583-632. 

 Barnicoat, C. R. 1959. Wear in sheep's teeth. VI. New Zealand J. Agr. 



Research, 2, 1025-1040. 

 Barnicoat, C. R., and Hall, D. M. 1960. Attrition of incisors of grazing 



sheep. Nature, 185, 179. 

 Franklin, M. C. 1950. Diet and dental development of sheep. Commonw. 



Sci. and hid. Research Organ., Melbourne, Bull. 252. 

 Gemmell, G. D. 1945. Fluorine content of New Zealand soils. New Zea- 

 land Inst. Chem. Conf., Paper 13. 

 Hall, D. M. 1959. Electron microscope studies of the submicroscopic 



structure of the dentinal matrix. /. Dental Research, 38, 386-391. 

 Hartley, W. J., and Grant, A. B. 1961. A review of selenium responsive 



diseases of New Zealand livestock. Federation Proc, 20, 679-688. 

 Leicester, H. M. 1949. Biochemistry of the Teeth. C. V. Mosby Co., St. 



Louis, Mo. 

 Manly, R. S., and Hodge, H. C. 1939. Dental hard tissues. I. Method for 



