Landmarks of the teeth
Teeth landmarks can be divided into two main groups:
a) Elevated landmarks
b) Depresses landmarks
a) Elevated landmarks
Crown Elevations
b) Depresses landmarks
a) Elevated landmarks
Crown Elevations
Lobe: it is one of the primary centers of calcification and growth formed during the crown development - each tooth develops from four lobes or more: cusps, cingulum, and mamelons. There are four or more centers of formation for each tooth. The formation of each center proceeds until there is a coalescence of all of them. Each of these centers is called a lobe.
Mamelon: they are three small round projections of enamel present on the incisal ridge of newly erupted incisors and they represent the three labial lobes of anterior teeth.
Tubercle: is a smaller elevation
on some portion of the crown produced by an extra formation of enamel
(deviation from typical) tubercle differs from cusp as it is formed of enamel
only while cusp is formed of pulp horn covered by dentin and enamel. When
present, these tubercles are usually smaller than the major lobes (e.g., cusps
of Carabelli).
Cingulum: a rounded
elevation on t the cervical third of the lingual surface of an anterior tooth.
(incisors and canines) It represent the lingual lobe of anterior teeth, also
called lingo-cervical ridge as it represents the maximum convexity of the
lingual surface and it is present on the same line with cervical ridge
labially.
Cusp: is an
elevation found on the occlusal surfaces of premolars and molars teeth and the
incisal portion of the canines.
Ridge: Is a linear elevation on the different surfaces of the
crown. It can be further classified according to its location and shape.
Ridges
According to location:
a)
Proximal (marginal) ridges
Linear
elevations present on the mesial and distal boundaries of the lingual surfaces
of all anterior teeth and the occlusal surfaces of posterior teeth.
b) Labial ridge: linear elevation present on the labial surface of the
canines, and represents overdevelopment of the middle. It extends vertically
from the cervical line to the tip of the cusp.
c) Buccal
ridge: is a pronounced buccal elevation of the middle lobe of
premolars. It extends vertically from the cervical line to the tip of the
buccal cusp, and represents overdevelopment of the middle buccal lobe.
d) Lingual ridge: is a vertical elevation extending from the cingulum
to the cusp tip of the canine, thus, dividing the lingual surface to mesial and
distal depressions (Fossae).
e)
Cervical ridge: is a horizontal
elevation formed of enamel at the cervical third of the crown of all teeth
facially and some lingually, and represents the maximum convexity of these
surfaces.
f) Incisal ridge: is a linear
elevation present on the incisal one third of the lingual surfaces of all
anterior teeth above the incisal edge. The ridge is transformed into an edge as
attrition removes some of the incisal enamel.
g) Cusp
ridges: they are ridges that descend from each cusp tip mesially and
distally. They are called mesial cusp ridge or mesial slope and distal cusp
ridge or distal slope. They are present in the canines and cusps of the
posterior teeth.
Ridges
Ridges According
to Shape:
a) Triangular ridge: is the ridge that
descends from the tip of the cusp of molar and premolar toward the central part
of the occlusal surfaces. All posterior tooth cusps have a triangular ridge,
except the mesiolingual cusp on maxillary molars which has two triangular
ridges.
b) Transverse ridge: is a linear elevation present on the
occlusal surfaces of lower premolars and represents union between triangular
ridges of two transversally crossing the occlusal surface of posterior
teeth e.g., upper 1 and 2 premolars.
c) Oblique ridge: linear
elevation present on the occlusal surfaces of upper molars and represents union
between two triangular ridges obliquely crossing the occlusal surfaces of the
maxillary molar. (always mesiolingual cusp and distobuccal cusp).
b) Depresses landmarks
Crown Depressions:
Groove: Is a linear depression on the crown surfaces of the teeth.
Developmental groove: is a linear depression found on the occlusal surfaces of the posterior teeth and may extend to buccal or lingual surface. It denotes the union of the primary parts of the crown.
Supplemental groove: Is a shallow linear depression on the occlusal surface. Which does not denote union of lobes. It radiates from the developmental groove.
Fissure: is
a narrow linear depression-present at the depth of the developmental groove
during its development. It denotes incomplete union between lobes.
Sulcus: is a long valley on the occlusal surface running between the cusps and ridges, Its inclined surfaces meet centrally in the developmental groove.
Fossa: is
a small depression or concavity on the occlusal or lingual surfaces
of teeth. It has different shapes including:
- Triangular
fossa.
- Central fossa.
- Lingual fossa.
a)
Triangular fossa: it is found on the occlusal surface of posterior mesial and
distal to the marginal ridges. It is triangular in form and bounded by the
developmental grooves.
b) Central fossa: it is found on the
occlusal surfaces of molars. It may be circular or irregular in form. It
is formed at the point of termination of the triangular ridges of cusps.
c) Lingual fossa: is located in the
lingual surfaces of incisors and may be centrally divided by the lingual ridge
in canines.
Pit: it
is a pinpoint depression in enamel which may be true or false.
Miscellaneous structures
Contact area: the area on proximal surface of the crown that contacts the adjacent tooth in the same arch, and is thus named mesial and distal by location.
Embrasure: the
open space between the proximal surfaces of two adjacent teeth in the same
arch, where they diverge facially (buccally or labially) or lingually, and
incisally (occlusally) or cevically from the contact area (are named according
to their location) e.g., when viewing the teeth from the incisal or occlusal
aspect, the two embrasures which are visible are named labial (buccal) and
lingual embrasures.
