STRUCTURE AND GROWTH OF INCISOR TEETH 81 
forming the gingival margin they acquire a flattened form. 
As a continuation of these flattened cells next the tooth is seen, 
extending out into the space between the erupted tip of the 
tooth and the epithelial gingival margin, a thin layer of tis- 
sue, which must be looked upon as the portion of the enamel- 
organ which has been carried out during eruption. At later 
stages this same appearance occurs—a thin layer of flattened 
cells continuous with the enamel-organ lying in the space be- 
tween the tooth and the epithelium of the gingival border. It 
may be that some of the cells are added to the epithelium of the 
gingival margin, but the majority appear to be continually car- 
ried out, and eventually detached. 
The mesenchymal tissues of the pulp at the anterior end are 
little affected by the mere act of eruption and not until some 
days later when attrition begins, do we see definite changes. 
At eruption the anterior conical extremity of the tooth is formed 
of osteodentine, containing within its matrix the remains of 
scattered cells and blood-vessels. Immediately posterior to 
this begins the true fine-tubed dentine with a central pulp-cham- 
ber. The cells at the anterior end of the pulp-chamber are 
irregularly arranged, but following backwards one soon sees 
the odontoblasts in parallel arrangement at the periphery of 
the chamber. At 10 days, when the apex of the tooth has 
pierced the epithelium and is easily seen from the outside, the 
measurements of the upper and lower teeth are 7 and 11 mm. 
respectively. At 12 days, they have increased to 7.5 and 11.8 mm. 
CHANGES IN APEX OF TOOTH BY USE 
Already at 12 days, when one examines the exposed ends of 
the teeth, they show little pits, which have been caused by the 
pressure of the opposing teeth. At 14 days, the ends are flat- 
tened, and at 16 days, because of the increased obliquity of this 
flattened surface due to the wearing away of the lingual side 
of the dentine, they are acquiring a cutting edge. The length 
of these occlusal surfaces continues to increase so that by 19 
or 21 days (fig. 24), they have nearly the appearance typically 
