THE TEETH 



169 



the summits of the crowns of the upper and lower teeth are brought 

 together, the line of contact being known as the dental articulation. 

 A hne drawn through this articulation forms the best means of 

 determining the breadth of the crown of each tooth. 



The crowns of the upper eight anterior teeth — namely, the four 

 incisors, two canines, and the two first bicuspids — are broader than 

 the crowns of the corresponding lower eight anterior teeth, measured 

 according to the foregoing Hne. 



The crowns of the lower eight posterior teeth — namely, the six 

 molars and the two second bicuspids — similarly measured, are 

 broader than the crowns of the corresponding upper eight posterior 

 teeth. 



The difference in breadth between the crowns of the upper and 

 lower eight anterior teeth is equal to the difference in breadth 

 between the crowns of the lower and upper eight posterior teeth. 



Fig. 93. — The Superior and Inferior Maxillary Bones at the Seventh 

 Year, showing Most of the Temporary Teeth, and the Permanent 

 Teeth about to replace them. 



The First Permanent Molars and the Permanent Lower Central Incisors 

 are in position. 



The result is that, if the dental arches could be straightened out, 

 the crowns of the upper and lower sets of teeth would have the 

 same measurement as regards breadth. 



The crowns of the upper six anterior teeth — namely, the four 

 incisors and the two canines — overlap the crowns of the corre- 

 sponding lower six anterior teeth. 



The Temporary Teeth.—Proceeding from the median hne, these 

 are as follows on either side: two incisors, central and lateral, one 

 canine, and two molars, first and second. Their necks are more 

 constricted than in the permanent set. The incisors and canines 

 resemble, for the most part, those of the permanent set, but they 

 are smaller. The molars, which are replaced by the permanent 

 bicuspids, exceed them in size, the second molars being particularly 

 large. The first upper molar has three cusps — two labial and one 



