ATTRITION OF THE HYPSODONT TOOTH 165 



ences except for silicon. The silicon content of dentine of the most 

 worn teeth was twice that of dentine from relatively unworn mouths. 



Fluorine is the only element showing wide variations. In 50 sam- 

 ples of mixed (whole) teeth from 21 farms, fluorine ranged from 

 28 to 320 parts per million, averaging 149 ppm, a value similar in 

 order to that for human teeth. It might be expected that teeth of 

 low fluorine content would be the most rapidly worn, since human 

 teeth of this type are susceptible to caries; or that teeth of high 

 fluorine content might appear bleached or mottled, with irregularities 

 in shape, as is typical of fluorosed sheep's teeth in Australia ( Peirce, 

 1938), although fluorine contents never approached those of even 

 the most mildly affected Australian samples. Such defects were not 

 observed, however, nor were there any indications that the propor- 

 tion of fluorine in New Zealand sheep's teeth influences their tend- 

 ency to wear. If there is any such tendency, it is obscured by other 

 factors. 



Since other constituents vary so little, the wide differences in 

 fluorine may seem surprising especially since the fluorine con- 

 tent of New Zealand soils shows little variation (Gemmell, 1945). 

 It. would appear that fluorine in sheep's teeth is derived from 

 that applied in phosphatic manures, which are reported to con- 

 tain about 1 per cent fluoride. For example, teeth from an experi- 

 mental area heavily top-dressed for 14 years contained on the aver- 

 age 290 ppm fluorine, whereas teeth from the neighboring farm on 

 the same type of soil, little top-dressed, contained only 123 ppm. 

 The lowest values for fluorine appear to be associated with farms 

 which have not been artificially manured. These values are low in 

 comparison with those reported overseas, both for sheep's and for 

 human teeth, but some of the best teeth came from these properties. 



Because of lack of chemical evidence of differences between diets, 

 or in the composition and histological appearance of teeth of widely 

 different types, it is concluded that the problem is not attrition of 

 nutritional origin in the usually accepted sense. 



Before discussing this investigation further, the peculiar aspects 

 of the New Zealand problem of excessive wear in sheep's teeth 

 should be restated: The wear occurs in teeth of sheep grazing luxuri- 

 ous, highly productive, "improved" pastures. The animals, judging 



