Page 35 - My FlipBook

THE BICUSPIDS. 33
noiinced cingules. The buccal maro;inal rida^es de?^cend from the
points of the cusp to the points of the lateral lobes. The distal ridge
is usually longer than the mesial. The cervical border is rounded and
oval from side to side.
The lingual face (/) is full and rounded, more or less straight perpen-
dicularly and rounded mesio-distally. It is convex in both directions.
The lingual cusp rises over it full, but is blunt and round ; the mar-
ginal ridges are rounded, not angular, and curve sharply round to meet
the mesial and distal marginal ridges.
The mesial face (Fig. 18, g) is wide and flat transversely, full at
the morsal surface at the marginal ridge, which is prominent, and de-
scending flat to the cervix, where
a depression (h) occurs which ex- ^^^'- ^'^-
tends well up the face.
The distal face is of similar
form, but is rather more convex
and the portion at the marginal
ridge more prominent. The de-
pression from the root does not
"^
extend so far up on the face. „, , • -^
i The upper bicuspids.
The morsal sioface shows an
abrupt change from that of the canine next to it, as it presents two
distinct cusps or points instead of one. One cusp is on the buccal
margin {j) of the crown, and one on the lingual (k), and they are named
the buccal and lingual cusps. The buccal cusp is sharp and prominent,
and is not unlike the single canine cusp. The lingual cusp is broader
and more rounded—indeed it is preferable to term it a tubercle.
The outline of the morsal surface is imperfectly quadrate and is bor-
dered by Avell-marked mari>:inal ridy-es, named as follows :
The mesial marginal ridge {I), bordering the mesial face of the crown
;
the distal marginal ridge on the distal side {m), the buccal marginal
ridges (n) descending from the point of the buccal cusp to meet the buc-
cal terminations of the distal and mesial marginal ridges at the angle
formed by the junction with the buccal lateral lobes (o), and the lingual
marginal ridges (p), descending from the lingual tubercle to meet the
lingual termination of the mesial and distal marginal ridges.
The triangular ridges descend from the cusps toward the centre of
the tooth and unite at the central groove. In defective teeth they do
not fuse, leaving a fault or Assure which becomes the seat of caries.
This groove or sulcus extends from one lateral marginal ridge to the
other mesio-distally (r) and Avidens into the mesial and distal sulci at
each end. The triangular grooves (.s) run from the mesial and distal
sulci toward the mesial and distal angles, dividing the marginal ridges
3