630 THE TEETH. 



substance of the dentine, after the bifurcation of the dentinal fibers, near the 

 boundary between dentine and enamel. 



In preparing specimens, on several portions of the crown it happened that 

 a larger portion of the enamel was ground away than was intended so much 

 so that only shreds of enamel in connection with the dentine were left. On 

 one of these places delicate beaded fibers were seen isolated on their upper 

 ends, while their lower ends could be traced into interstices between the 

 enamel-rods, and in connection with the ends of the dentinal fibers. No doubt 

 here the mechanical injury done to the enamel has luckily led to a tearing out 

 of a few enamel-fibers, which accident plainly illustrates their presence. 



That enamel is not a crystal, but a tissue, alive so long as the pulp of 

 the tooth is alive, no one, I think, will doubt who has studied caries and 

 seen the pigmentation of enamel and its reaction during that process. 



SECONDARY DENTINE. BY C. F. W. BODECKER, D. D. S., M. D. S.* 



It is generally acknowledged that the main portion of a tooth is composed 

 of dentine, which, on the crown, is covered by enamel. The latter is thickest 

 around the cusps, and becomes thinner the nearer to the neck. On the root 

 the dentine is covered by cementum, which is thinnest about the neck, and 

 thickest on the apex of the root. 



Exceptionally the relations between the three hard tissues of a tooth may 

 be found to deviate considerably from the general rule, whereby an anoma- 

 lous, though not strictly pathological, formation is produced. I extracted the 

 canine teeth from the upper jaw of a lady forty years of age, one of which I 

 split to obtain the pulp ; the other was ground thin immediately after its 

 extraction, for the purpose of studying enamel. The results were as follows : 



The crown was built up by dentine terminating in the ordinary pointed 

 way, and surrounded by a well-developed cap of enamel. A marked brown 

 discoloration in the usual fan-like arrangement was noticeable in the enamel, 

 mainly in the immediate neighborhood of the dentine, but without any decay. 

 The dentine, beginning at the neck and extending down into the root, was 

 divided into a broad inner portion, occupying four-fifths of the root, and a 

 narrow outer portion all around, corresponding in its thickness to that of the 

 cementum of normal teeth. The boundary between these two layers was 

 everywhere well defined by a scalloped line, the concavities of which look 

 outward. In some places several such scalloped marks ran perfectly parallel, 

 close to each other. The boundary line, however, was traversed by the den- 

 tinal canaliculi and their tenants without change of direction. The outermost 

 portion of the dentine of the root was surrounded by cementum, not thicker 

 than is seen on the necks of teeth of normal development. The cementum 

 was slightly thicker on one side of the apex of the root, exhibiting there a 

 scanty number of cement-corpuscles, which on all other portions were want- 

 ing. The boundary between dentine and cementum was sharply defined. 

 The former bore the characteristics of dentine in the vicinity of the neck, as 

 the canaliculi stopped short of its surface and were replaced by a coarsely 

 granular basis-substance. (See Fig. 271.) 



Nearest to the pulp-chamber there is a zone, with scanty and irregular 

 dentinal canaliculi formations which we are accustomed to call " secondary 

 dentine." Next to this is a broader layer of dentine, in which the dentinal can- 



* Abstract of the author's essay. Tlie Dental Cosmos, Philadelphia, 1879. 



