Maxillary Incisors Principal Identifying Features

The maxillary central incisor is the tooth in each maxillary

quadrant of the permanent dentition which is on each side of the

midline.

Normally, the max central incisors are the most prominent teeth

in the oral cavity and so they are most noticeable in the dental

arch, hence they contribute a focal point for the eye of the

observer. In general, the labial outline of the crown conform to

the general outline of the face.

The max central incisor (MCI) is the widest tooth mesio-distally

(MD), the labial surface is less convex than lateral incisor and

canine that give the tooth a rectangular appearance. It is the first

tooth from the midline. It has a slightly straight incisal edge.

Central Incisor Chronology

Appearance of enamel organ 5 m.i.u

First evidence of calcification 3 - 4 months.

Crown completed 4 - 5 years.

Eruption 7-8 y

Root completion 10-11 y

Labial aspect

Geometric out line

Trapezoid with the smallest side at the cervical line and the larger

side at the incisal ridge, where the central incisor

contacts its neighbors.

The mesial outline

The crown is slightly convex.

The distal outline

The crown is more convex than the mesial outline.

Contact areas

Mesially: approaching the mesio-incisal angle.

Distally: higher towards the cervical line near the

junction between middle and incisal thirds.

Incisal angles

The mesio- incisal angle is nearly a right angle “sharp”

disto-incisal angle is rounded.

The incisal outline

Incisal outline of newly erupted tooth usually reveals mamelons,

they are usually three in number, of which the central mamelon is

the smallest.

A time after eruption the incisal ridge undergoes attrition, the

incisal edge is straight and perpendicular to the longitudinal axis of

the tooth.

Cervical line

Semicircle with the curvature root-wise.

Surface description

The labial surface of this tooth is smoothly convex with the

maximum convexity at the cervical third, referred to as cervical

ridge. The labial surface is marked by 2 faint or shallow vertical

grooves which divide the labial surface into 3 portions or lobes.

The root

Root is cone shaped with blunt apex. A line drawn through the

center of the root and crown of the maxillary central incisor tends

to parallel the mesial outline of the crown and root.

Lingual Aspect

It represent elevations and depressions but the

general outline is the reverse picture of the labial

surface.

The proximal sides of the crown and root converge

lingually, making the lingual surface of the tooth

narrower than the labial surface to accommodate the

horse-shoe shaped alveolar ridge, where the outer

surface of the ridge is wider than the inner surface

that is called lingual convergence.

The root is generally triangular with rounded angles.

Cervical line is similar to that of labial.

Morphologically , lingual surface shows convexities and concavity:

The cingulum: smooth round large convexity present at the

cervical third immediately below the cervical line.

The mesial and distal marginal ridges: they extend from the

cingulum mesial and distally to the incisal ridge.

Incisal ridge (linguincisal edge): elevation (being on a level

with the marginal ridges) making the thickness of incisal

edge from the lingual surface.

Lingual fossa: lingual depression between the marginal

ridges and extend from the cingulum to the incisal ridge. It

has M-shape and occupying the incisal two third.

Mesial Aspect

The mesial surface of the crown is wedge-shaped or

triangular with the base of the triangular at the cervix and

the apex at the incisal ridge. This allows the tooth to be

forced easily through the food material.

The labial outline of the crown is slightly convex with the crest of

curvature at the cervical ridge.

The lingual outline is convex at the region of the cingulum. Then

it becomes concave as it outlines the mesial marginal ridge and

becomes slightly convex again as it outlines the linguo-incisal

ridge.

The cervical line is concave root-wise.

The incisal ridge is with the line bisecting the tooth.

The root is cone shaped with a blunt apex; the labial outline is

straighter than the lingual outline.

The mesial surface is smooth except for a concavity represents the

contact area.

Distal Aspect

It is similar in oultine to the mesial surface.

But the curvature of the cervical line is less in

curvature then from the mesial surface.

The distal contact area is more cervical than

mesial one.

Incisal edge distally is broader than mesially so the crown appear

thicker.

Incisal Aspect

The incisal ridge is seen to be centered over the root.

The crown superposes over the root entirely so that nothing of the

root is visible i.e. the crown and the root base on the same long

axis.

The crown outline is roughly triangular with somewhat curved

labial outline that form the base of the triangular while the

proximal sides converge toward the

cingulum.

Crown is wider MD than LL. Labial outline is broad, flat

compared with the lingual surface. Cingulum is located off center

toward the distal side. So, MMR is longer than DMR. Fossa is seen

as a concavity between the two MR and cingulum.

Note that

The incisal ridge is that portion of the crown which makes up the

complete incisal portion. When an incisor is newly erupted, the incisal

portion is rounded and merges with the mesioincisal and distoincisal

angles and the labial and lingual surfaces. This ridge portion of the

crown is called the incisal ridge. The term edge implies an angle

formed by the merging of two flat surfaces. Therefore, an incisal edge

does not exist on an incisor until occlusal wear has created a flattened

surface linguo-incisally, which surface forms an angle with the labial

surface. The incisal edge is formed by the junction of the linguoincisal

surface, (sometimes called the incisal surface), and the labial surface.

Variations and anomalies

a) Of all the crown surfaces, the lingual exhibits the greatest

variation. As previously mentioned, a pit may occasionally be

present, and the depth of the fossa has a considerable range.

b) When viewed from the labial or lingual aspects, a wide variation

occurs in the amount of convergence of the mesial and distal

surfaces toward the cervical. When there is little convergence, the

outline of the surface resembles a rectangle, but when great

convergence is present, it is more nearly triangular.

c) Root length may vary considerably, but deflections of the root are

relatively rare. When the root is exceptionally short, in conjunction

with an abnormal contour of the crown, this anomalous condition is

referred to as dwarfed root, and the lack of root support may

endanger the tooth's longevity in the mouth.

d) Hutchinson's incisors: Congenital syphilis sometimes manifests

itself in the central incisor by producing a screwdriver shaped

crown, when it is viewed from the labial aspect.

e) Talon cusp: A large accessory cusp on the lingual surface of

maxillary incisors characterizes this anomaly. Involved teeth often

bear a resemblance to a Phillips screwdriver.

f) The alveolar bone between the roots of the two central incisors is

occasionally the site of supernumerary teeth or extra teeth,

known as mesiodens. Cysts may also be found in this area.