Excerpt from Atlas and d104-Book of Human Anatomy, Vol. 2: The Viscera, Including the Heart
The cusps of the molar teeth are four, rarely five in number, two being lingual and two buccal. In the lower molars the four cusps are separated by a tolerably regular cruciform groove (fig. 3 and since the lingual cusps are higher than the buccal ones, the lower molars look as though they were composed of two fused premolars. The lower first molar usually has five cusps, three buccal and two lingual. In the upper molars the buccal cusps are higher than the lingual and the separating sulci have the form of a slanting H (fig. So that the lingual and buccal cusps hold an oblique relation to each other. Irregularities in the number and arrange ment Of the cusps are common, particularly in the third molar (wisdom tooth, see below), which may have from three to five cusps. As in the case of the premolars, the frontal surfaces of the crowns Of the molars are in relation with each other, so that an anterior and a posterior surface of contact may be recognized. Both the lingual and the buccal surfaces of the molar crowns are convex, and both surfaces of the upper molars (at least of the first) have a longitudinal sulcus, while in the lower molars only the buccal surface presents this marking.
The lower molars have two roots, an anterior and a posterior, which are sometimes grooved. They are of moderate length, compressed in the frontal plane, and their apices are usually bent backward. The grooves are an indication that each root is formed by the fusion of two halves, and in rare instances more than two roots may consequently be present.
The upper molars have three conical roots the ends of which are also bent backward. Two are buccal and one is lingual (or palatine, i. E., directed toward the palate, posterior). All three roots are well developed in almost all cases in the first upper molar, while they may be more or less fused in the second. The latter condition is the rule in the third.
The third molars do not make their appearance until from the twentieth to the twenty-fifth year, and have consequently been called the wisdom teeth (dentes serotini). They are only rudimentary structures in civilized nations, but in ancient skulls and in those of many savage races they are well developed and frequently but slightly Smaller than the second molars. The upper wisdom tooth is always much smaller than the lower, and its roots are usually fused together, although the original number is frequently indicated, particularly by the number Of the root canals. There are frequently only three cusps present. The lower wisdom tooth usually has two short roots and the crown seems better developed than that of the upper jaw.
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