MORPHOLOGYOF

PERMANENT INCISORS

Dr. Firas Alsoleihat, BDS, PhDDepartment of Conservative Dentistry

Introduction

Human dentition is diphyodont Primary (deciduous/ predecessor) dentition

• Formula: I 2/2 C 1/1 M 2/2• Eruption: 6 months - 28±4 months

• Shedding: 6 to12 years Secondary (permanent/successor) dentition

• Formula: I 2/2 C 1/1 P 2/2 M 3/3• Eruption: 6 to (18-25) years

Stages of human dentition

Edentulous stage: 0 - 6 monthsEruption of primary dentition: 6 months-2.5

yearsFunctioning primary dentition: 2.5 – 6 yearsMixed dentition: 6 – 12 yearsPermanent dentition: 12+ yearsFull permanent dentition: (18-25)+ years

Dental terms

Dental arch: maxillary and mandibularTooth class

Incisor: incisal edge Canine: one pointed cusp Premolar (bicuspid): 2 cusps Molar: 3 or more flattened cusps

Identification traits Set traits Arch traits Class traits Type traits

Glossary

Terms related to anterior teeth Anterior teeth Surfaces Line angle Point angle Incisal edge Cusp Cingulum Fossa Ridge and marginal ridge Cervical line Lobe Mamelon Lingual pit Developmental groove Division into thirds Contact point

The permanent incisors Eruption sequence

41/31, 11/21, 42/32, 12/22

Functions Cutting Esthetics Speech

Class traits Incisal 2/3 flattened MD

& compressed LL Long horizontal

MD biting edge 2 or more mamelons Marginal ridges

parallel to long axis

Maxillary Lateral Incisor

First evidence of calcification:1yr

Enamel completed: 4-5yr

Eruption:8-9yr

Root completed:11yr

Maxillary Central incisor

First evidence of calcification:3-4mo

Enamel completed:4-5yr

Eruption: 7-8yr

Root completed:10yr

Chronology

The permanent maxillary incisors

Arch traits Crown

• Wider MD• Smaller height / width proportion• Greater MD / LL proportion

Root• Greater MD / LL proportion• Conical root in central incisors

Type traits Size Height / width proportion

in crown MD / LL proportion

in crown and root

The permanent maxillary central incisors

Labial aspect The widest MD of all incisors – type trait 3 mamelons

• Middle is the smallest in width• Mesial has a raised shoulder• Distal has a low shoulder

2 labial lobe grooves 90º mesioincisal line angle – type trait Rounded distoincisal line angle Mesial contour straight, distal is somewhat rounded

and both converge cervically Mesial height of contour (contact point) within incisal third Distal HOC at junction between incisal & middle thirds CEJ convex cervically Root is conical & inclined distally

The permanent maxillary central incisors

Lingual aspect Scoop-like surface Lingual fossa bordered by (all

more prominent in max.)• Mesial & distal marginal ridges• Cingulum

CEJ more convex than labial& summit toward distal

Root is narrower seen from lingual Mesial aspect

Chisel-shaped Labial HOC in the cervical third CEJ curved incisally (the most

pronounced) – type trait Incisal edge coincides with long

axis Root is conical

The permanent maxillary central incisors

Distal aspect CEJ is less curved than seen from mesial

Little differences exist between the mesial and distal aspects of this tooth.

The crown gives an illusion of being somewhat thicker toward the incisal third when viewed from this side due to the slope of the labial surface disto-lingually, more of that surface is seen from the distal aspect. Most teeth are turned a little on their root bases to adapt to the dental arch curvature.

The extent of curvature of the cervical line is less than on the mesial side “most teeth show this characteristic”

Incisal aspect Triangular outline Labial outline is slightly convex

• Meets M+L outlines at sharp line angles Mesial outline is longer than distal Labial lobe grooves

Maxillary central incisor

The crown closely resembles that of the central incisor.They supplement central incisors in function.Smaller than the central incisor in all dimensions except the

root length.They vary in form more than any other tooth in the mouth

except for the third molar.If the variation is too great it is considered a developmental

anomaly.Peg shaped lateral: a common anomaly where the tooth has a

pointed non descript form.

Permanent maxillary lateral incisor

In some individuals these teeth are missing.The presence of a palato-gingival groove ”palato-radicular

groove” in some individuals may be a predisposing factor to localized periodontal disease.

Some of the common malformations:1. The presence of a large pointed tubercle as part of the

cingulum2. A deep developmental groove that extend down on the

root lingually with a deep fold in the cingulum.3. Twisted root.4. Distorted crown…..

Permanent maxillary lateral incisor

The permanent maxillary lateral incisors

Labial aspect Narrower MD & shorter IC – type trait More rounded in general

• MI angle• DI angle more rounded• M & D outlines

HOCs are farther from incisal edge• Mesial HOC is between middle & incisal thrids• Distal HOC is at the center of middle third

Root is conical and slightly inclined distally

Labial aspect / Ctd.

The tooth is relatively narrow mesio-distally, about 2mm narrower than the central incisor.

The cervico-incisal measurement is 2-3mm shorter than the central incisor.

the root: is about 1.5 times the length of the crown. Tapers evenly from the cervical line to two thirds its

length apically. in most cases it curves sharply from this area apically in a distal direction and ends in a pointed apex.

Sometimes the root ends straight and sometimes curves mesially.

Lingual Aspect Marginal ridges & cingulum are

more pronounced Lingual fossa is deeper Developmental groove and pit?

Mesial and distal marginal ridges are marked.The cingulum is usually prominent with a tendency

to deep developmental grooves within the lingual fossa where it joins the cingulum.

The incisal ridge is more developed and the lingual fossa is more concave and circumscribed than the central incisor.

It tapers towards the lingual like the central incisor.A deep developmental groove is a common finding

at the distal side of the cingulum which may extend to the root.

Mesial Aspect

•Mesial aspect•Cingulum more convex

•CEJ less curved

Similar to a small central incisor except the root appears longer, the crown is shorter, the labio-lingual measurement of the tooth is less.The curvature of the cervical line is marked in an incisal direction though less than that of the central incisor.The incisal ridge appears somewhat thicker than that of the central due to the heavy development.The root appears tapered, cone shaped, with a blunt apex, again this is variable because sometimes it appears blunt, and other times it is pointed.A line drawn through the centre of the root bisects the incisal ridge of the crown.

Distal Aspect

The width of the crown distally appears thicker than mesially from the marginal ridge to the labial aspect due to the placement of the crown on the root.

The curvature of the cervical line is usually a mm or less than the mesial surface.

A developmental groove may be found on this aspect extending towards the root.

Incisal Aspect•Incisal aspect

•Ovoid outline

•Smaller MD than central

•Labial outline is rounded

•ML & DL line angles are more rounded

Sometimes it resembles that of a central incisor and sometimes it looks like a small canine.The cingulum may be large as well as the incisal ridge and the labio-lingul width may be greater than usual in comparison with the mesio-distal width. if these variations are present the tooth has a marked resemblance to a small canine.It exhibits more convexity labially and lingually from this aspect than the central incisor.

Maxillary lateral incisor

The permanent mandibular incisors

Arch traits Crown

• Narrower MD• Greater height / width proportion• Smaller MD / LL proportion

Root• Smaller MD / LL proportion• Generally oblong in x-section

Type traits (arch trait) Nearly equal in size &

dimensions

The permanent mandibular central incisors

Labial aspect The narrowest MD of all incisors Bilaterally symmetrical (type trait) 3 mamelons

• Mesail and distal mamelons are of equal prominence 90 º MI & DI angles and are at same level IC (type traits) Both HOCs are within the incisal third M & D outlines are almost straight lines CEJ convex cervically Root is narrow & conical

Lingual aspect Shallow fossa & less prominent cingulum

& marginal ridges CEJ summit in the center

The permanent mandibular central incisors

Mesial aspect Labial HOC within cervical third From HOC toward incisal edge labial

outline is straight Root

• Broad & flat• A shallow depression in the midportion• Ovoid in x-section

Distal aspect CEJ is less curved

Incisal aspect Triangular Labial surface is flat compared to max. incisors Seldom labial lobe groove Long axis of incisal edge is perpendicular to

LL line (type trait) Mesial outline = distal outline in length

Pulp Broad LL and narrow MD

Mandibular central incisor

The permanent mandibular lateral incisors

Labial surface Slightly wider than central Lack of bilateral symmetry MI angle is sharp while DI angle is

rounded & more cervically situated Lingual & mesial aspects

Nearly identical to that of central Distal aspect

More of the incisal edge is visible CEJ is less pronounced

Incisal aspect Incisal edge is not perpendicular to LL line DI angle is more toward lingual

Pulp Similar to that of central

Mandibular lateral incisor

Incisal relationship

Class IClass IIClass IIIOverjetReverse

overjetOverbite