EFFECT OF HIBERNATION ON TEETH %H7 



bedded in celloidin, sectioned, and prepared for examination his- 

 tologically in the routine manner. 



Observations 



The dentin of a nonhibernating Arctic ground squirrel presents a 

 wide, homogeneously calcified outer layer which extends from its 

 outer surface through the uncalcified predentin toward the odonto- 

 blastic laver ( Fig. 1 ) . After about 3 weeks in hibernation, however, 

 there is evidence of a disturbed calcification process (Fig. 2). One 

 may still see a thinner outer zone of dentin which is homogeneously 

 calcified. There is, however, an increase in the number of inter- 

 globular spaces in the deficient dentin extending toward the odonto- 

 blastic layer. 



In nonhibernating Arctic ground squirrels the interradicular and 

 the interseptal bone show a high degree of calcification and both 

 are compact and normal in histological configuration (Fig. 3). In 

 contrast, after an animal has been in hibernation for 3 months there 

 is a progressive loss or resorption of both interradicular and inter- 

 septal bone. Figure 4 shows a marked osteoporosis of the spongiosa 

 arid the presence of calculus in the interproximal gingivae. Even 

 though the alveolar bone proper and the attachment fibers are rela- 

 tively unaffected in this animal, alveolar bone frequently undergoes 

 degenerative changes during hibernation. 



Caries appears rather consistently in both the molar and premolar 

 teeth of squirrels kept in captivity for extended periods of time. As 

 field-caught wild animals do not show such a predisposition to caries, 

 it is believed that decay is not related so much to hibernation as to 

 conditions of captivity, including diet. However, as the effects of 

 hibernation on noncarious normal teeth are drastic, in carious teeth 

 these effects even further aggravate tooth destruction. 



All stages of caries, from early lesions to fracturing of the coronal 

 part of the tooth, accompany hibernation. Figure 5 shows early 

 carious lesions. Two plaques occur in the occlusal pits, and from 

 these plaques dark-staining lamellae project through the decalcified 

 enamel toward the dentin. Figure 6 shows a more advanced carious 

 lesion which involves an invasion of the dentinal tubules. The in- 



