EARLT DESTRUCTION OF THE TEETH. 115 



places for the chemical agent — ^the work of destruc- 

 tion then begins and is speedily accomplished, 

 because at this early period the cavity within the 

 tooth is large, and the wall which protects the pulp 

 is thin, so that there is only this thin portion of 

 bone to penetrate ere the membrane becomes ex- 

 posed. In the middle and later periods of life the 

 bony partition becomes thickened, thus increasing 

 the distance between the surface of the bone and 

 the cavity of the tooth ; and, moreover, it is to be 

 assumed that those teeth which have escaped destruc- 

 tion up to the latter periods of life, had their enamel 

 more regularly distributed, and never did present 

 those pits and fissures already described. 



When an attack is made upon the teeth in the 

 after periods of life, it generally begins on their 

 lateral edges, occasioned by the receding of the 

 gums. For if the gums be not kept in a healthy con- 

 dition, they recede from the necks of the teeth, and to 

 whatever distance they may have receded they cannot 

 be restored to their original position ; -consequently 

 interstices — those resting-places for the chemical 

 agent — are produced for the first time, and then, at 

 this late period, the work of destruction begins. 



The rapidity of the chemical action upon the 

 teeth will depend upon the adaptation of the inter- 

 stices, pits, and fissures, to receive and retain more 

 or less of the destructive matter. A tooth may be 

 destroyed in one year after its appearance above the 

 gums ; in other cases it may be ten, twenty, or even 



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