MORPHOLOGYOF

PERMANENT INCISORS

Oral HistologyDent 201

Summer semester 2005/2006

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

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

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

Pulp Mirrors the external configuration Widest LL diameter at CEJ Line of division between pulp chamber

& canal is not marked Most incisally, pulp chamber is thin LL

with 2 horns Pulp canal is conical

Maxillary central incisor

The permanent maxillary lateral incisors

Labial aspect Narrower MD & shorter IC – type trait Root is of same length 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

Lingual aspect Marginal ridges & cingulum are more pronounced Lingual fossa is deeper Developmental groove and pit?

The permanent maxillary lateral incisors

Mesial aspect Cingulum more convex CEJ less curved

Distal aspect Incisal aspect

Ovoid outline Smaller MD than central Labial outline is rounded ML & DL line angles are more rounded

Pulp Similar to central

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