USED IN DENTAL SUEGERY. 115 



2nd. Those cases where the pulp is exposed, and 

 is either to be entirely destroyed or brought into 

 a condition to bear further operations. 



1st. As regards the action upon, sensitive den- 

 tine or cementum. 



For this purpose the most appropriate caustics 

 are either chloride of zinc or arsenious acid, in 

 accordance with the locality of the tender tissue, 

 or other circumstances. 



If the cementum be exposed by the receding 

 of the gums, from constitutional or mechanical 

 causes, or if there be a very sensitive surface of 

 exposed dentine after filing or cutting operations, 

 or from accidents to the teeth, the apphcation of 

 chloride of zinc seems peculiarly efiectual. The 

 surface of the tissue to be acted upon should be 

 thoroughly dried (for this salt, though under the 

 second class of caustic substances, somewhat re- 

 sembles the first in its attraction for water, being 

 highly deliquescent), and precautions taken to 

 prevent the chloride from spreading about the 

 mouth. A small crystal is to be placed in contact 

 with the bone, and immediately covered over with 

 firmly-compacted wool, or some other substance, 

 to exclude all excess of moist air. In most cases, 

 considerable pain comes on, lasting from five to 

 twenty minutes : when this has ceased, the tooth 

 may be exposed again by the removal of the wool, 

 «&c., and probably the tenderness will be found to 

 luive disa])pcarcd, or at least to be materially 



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