The bone has been removed to show the embedded parts of the teeth
_I^1_, _I^2_, _I^3_, Incisors; _C_, canines. The cheek teeth are
numbered.
]
The =upper= or =maxillary teeth= are embedded in the alveolar processes
of the maxilla. The exposed parts of the crowns are normally in close
contact, forming a continuous row which is slightly curved, with the
convexity toward the cheek. The embedded parts diverge in the manner
shown in the annexed figures (Figs. 251, 253). Thus the long axis of the
first is directed upward and a little forward, that of the second is
almost vertical, while in the remainder it is curved backward in an
increasing degree. The average =length= at six years of age is about
three to three and a half inches (ca. 7 to 9 cm.). The =buccal= (or
outer) =surface= presents a central ridge running lengthwise, and
separating two grooves; the first tooth has, in addition, a less
prominent ridge in front of the primary one. The =lingual= (or inner)
=surface= is marked by a wide, rounded ridge, the accessory pillar or
column, which separates two very shallow grooves. The =masticatory= or
=table surface= presents two infundibula, an anterior and a posterior.
It slopes obliquely downward and outward, so that the outer edge is
prominent and sharp. The first and last teeth have three roots, the
remainder four or three.
The position of the embedded crowns and roots of the last four varies at
different ages and in different subjects. Two factors in this variation
may be noted. All these teeth are developed in the maxillary sinus close
to the orbital fossa. As growth proceeds the teeth move forward, so that
commonly only the last three, but sometimes also the third, remain
(except as to their free crowns) in the sinus. The second cause of
variation is the fact that the anterior limit of the maxillary sinus may
be at the extremity of the facial ridge, or more than an inch beyond it.
In the latter case the third tooth projects into the sinus.[84]
[Illustration: