Anatomy and dev of occlusion /orthodontic courses training by indian dental academy

ANATOMY AND
DEVELOPMENT OF
OCCLUSION
INDIAN DENTAL ACADEMY
Leader in continuing dental education
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DEFINITION OF OCCLUSION
SKELETAL COMPONENT
JOINTS, LIGAMENTS AND MUSCLES
DENTAL COMPONENT
Development of teeth
Anatomical features in brief of individual groups of teeth
DEVELOPMENT OF OCCLUSION
DETERMINANTS OF OCCLUSAL MORPHOLOGY


DEFINITION OF OCCLUSION

Dorland’s medical dictionary – act of
closure or state of being closed

In dentistry – Relationship of maxillary
and mandibular teeth when they are in
functional contact during activity of the
mandible.

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To have a good understanding of
occlusion and its development it is essential
to have a proper understanding of the
masticatory system.

The masticatory system comprises
a) Skeletal component
b) Joints, ligaments and muscles and
c) Dental component.

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SKELETAL
COMPONENT


Three major skeletal components make up the
masticatory system
MAXILLA
MANDIBLE
TEMPORAL BONE


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MAXILLA
 Develops from the 1st Branchial arch at
about the 4th week of intrauterine life.
 It is by intra membranous ossification of the
fronto-nasal and maxillary processes.
 Two maxillae are formed in this way which
are fused together in the mid-palatine suture.

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The growth takes place by two mechanism –
sutural growth and surface apposition.
 Growth sites in the maxilla
o Maxillary tuberosity
o Sutures
o Alveolar border
o Nasal septum
o Lateral walls

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 Superiorly it forms the floor of the nasal
cavity and the floor of each orbit
 Inferiorly it forms the palate and the
alveolar ridges which support the teeth.
 As the maxillary bones are intricately fused
to the skull, the maxillary teeth make up the
stationary components of the masticatory
system.


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MANDIBLE
 Develops from the 1st Branchial arch at
about the 4th week of intrauterine life.
 It is derived from the Meckel’s cartilage.
 The lower part of the body of the mandible
by membranous ossification
 The ramus and processes by cartilaginous
ossification.
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 The growth sites in the mandible
o Mandibular condyle
o Posterior border of Ramus
o Alveolar process
o Lower border of the mandible
o Suture {at the suture between the two
halves of the mandible fibrous connective
tissue (symphyseal cartilage) serves as a
growth site}

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 It is a U-shaped bone which supports the
lower teeth and makes up the lower facial
skeleton.
 It is suspended below the maxilla by muscles,
ligaments and other soft tissues.
 The condyle articulates with the cranium
around which movement occurs making it the
moveable component of the masticatory
system.

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TEMPORAL BONE
 The mandibular condyle articulates at the base of the
cranium with the squamous portion of the temporal
bone in the concave mandibular fossa called articular or
glenoid fossa.
 Immediately anterior to the mandibular fossa is a
convex bony prominence called the articular eminence.
 The posterior roof of the glenoid fossa is thin and not
suitable to sustain heavy forces, however, the articular
eminence consists of dense bone which can.

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JOINTS, LIGAMENTS
AND MUSCLES


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The joint which plays an important role
in the masticatory system is the Temporomandibular joint.
Formed by the articulating surface of
the condyles of the mandible and the articular
fossa (bilaterally) of the temporal bone.


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The ligaments in conjunction with the joint are
1. Collateral ligament
2. Capsular ligament
3. Temporo-mandibular ligament
4. Spheno-mandibular ligament
5. Stylo-mandibular ligament

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The skeletal components of the
masticatory system are supported and brought
into function with the help of four pairs of
muscles called the muscles of mastication;
masseter, temporalis, medial pterygoid and
lateral pterygoid muscles.


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Masseter


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Temporalis


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Lateral and medial
pterygoids


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The masseter, temporalis and medial
pterygoid are responsible for closure of the
mandible
The lateral pterygoid is responsible for
opening of the mandible.
Along with these muscles the digastric
muscle also acts in the functioning of the
masticatory system by depressing the
mandible.

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DENTAL
COMPONENT


The human dentition comprises of two
stages : a stage of deciduous dentition and a
stage of permanent dentition.
The deciduous dentition is made up of 20
teeth and the permanent dentition is made up
of 32 teeth.
Each tooth comprises of 2 basic parts –
the crown and the root
The root is attached to the alveolar bone
by numerous fibers of connective tissue called
the periodontal ligament.

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Deciduous dentition
 Comprises of 20 teeth equally distributed in
the upper and lower jaws
 Based on their morphology and function
they are classified as incisors, canines and
molars.
 Each arch is divided into two quadrants,
each comprising of 5 teeth in the grouping of
2 incisors, 1 canine and 2 molars.

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Permanent dentition
 Comprises of 32 teeth equally distributed in
the maxillary and mandibular jaws
 Based on their morphology and function they
are classified as incisors, canines, premolars and
molars.
 Each arch is divided into two quadrants, each
comprising of 8 teeth in the grouping of 2
incisors, 1 canine, 2 premolars and 3 molars.

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Development of teeth
Teeth are developed from the dental lamina
6 weeks intra uterine life – basal cells of oral
epithelium proliferate to form the dental lamina.
This serves as the primordium for the ectodermal
portion of the tooth.


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Bud stage
The epithelium of the dental lamina is separate from
the underlying ectomesenchyme by a basement membrane.
From this basement membrane, round or ovoid
swellings called tooth buds (primordia for enamel organ)
arise.
The enamel organ – peripheral low columnar cells
and central polygonal cells.
Several cells of the tooth bud and the surrounding
mesenchyme undergo mitosis leading to condensation

of the ectomesenchymal cells around the tooth bud.
The condensed ectomesenchyme subjacent to the
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enamel organ is the dental papilla

The dental papilla and the tooth bud
together is surrounded by the dental sac.
The dental papilla forms the tooth pulp
and dentin while the dental sac forms the
cementum and the periodontal ligament.


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Cap stage
The tooth bud continues to proliferate in an
unequal growth in different parts to form the
cap stage
1) Outer and inner enamel epithelium : outer cells
are cuboidal and inner cells are tall columnar.
2) Stellate reticulum : Polygonal cells situated in
the center of the enamel organ between the outer
and inner enamel organ form a network. The
inter-cellular spaces are filled with mucoid fluid
rich in albumin.

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3. Dental papilla : The ectomesenchyme (neural
crest cells) that is enclosed by the invaginated
portion of the inner enamel epithelium
proliferates to form the dental papilla, which is
the formative organ of the dentin and the
primordium of the pulp. The peripheral cells of
the dental papilla enlarge to and differentiate
into odontoblasts.
4. Dental sac : The ectomesenchyme surrounding
the enamel organ and the dental papilla
undergoes condensation. Here a denser and
more fibrous layer develops which forms the
primitive dental sac.
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Bell stage
As the invagination of the epithelium deepens
and its margins continue to grow, the enamel
organ assumes a bell shape. Four different types
of cells are seen in this stage:
1) Inner enamel epithelium: single layer of cells
that differentiate into tall columnar cells called
ameloblasts.
2) Stratum intermedium: formed from squamous
cells between the inner enamel epithelium and
the stellate reticulum.

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3) Stellate reticulum: increase in intercellular
fluid and it expands. Star shaped cells are
seen.
4) Outer enamel epithelium: cells flatten to a
low cuboidal form.


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Dental papilla
The dental papilla is enclosed in the invaginated
portion of the enamel organ. Prior to enamel formation
by the inner enamel epithelium, the peripheral cells of
the mesenchymal dental papilla differentiate into
odontoblasts.

Dental sac
Before formation of dental tissues commences the
dental sac shows a circular arrangement of fibers and
resembles a capsular structure. With the development of
the root, the fibers of the dental sac differentiate into the
periodontal ligament. www.indiandentalacademy.com
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Dentinogenesis and Amelogenesis
After the differentiation of the cells of the dental
papilla and the inner enamel epithelium into the
odontoblasts and ameloblasts, respectively, the dentin is
laid down first. After the first layer of dentin is laid, only
then does amelogenesis commence.


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Hertwig’s Epithelial Root Sheath
 Formation of root begins after enamel and dentin
formation has reached the future C.E junction
 HERS consists of the outer and inner enamel
epithelium only.
 The cells differentiate the radicular cells into
odontoblasts and the first layer of dentin is laid down.
The root sheath then loses its structural continuity.
 Single rooted and multi rooted teeth are formed by
tongue like projections from a horizontal diaphragm.

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Anatomical
features in brief of
individual groups
of teeth

Permanent Incisors
Human incisors have thin, blade-like crowns
which are adapted for the cutting and shearing of
food. There are two incisors per quadrant, four per
arch. The first incisor, the central incisor, is next to
the midline. The second incisor, the lateral incisor, is
distal to it.
Maxillary incisors by definition arise in the
premaxilla; mandibular incisors are the teeth that
articulate with them.


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Facial: It is the most
prominent tooth in the
mouth. It has a nearly
straight incisal edge
and a gracefully curved
cervical
line.
The
mesial aspect presents a
straight outline; the
distal aspect is more
rounded. Mamelons are
present
on
freshly
erupted,
unworn
central incisors.

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Lingual: The lingual
aspect presents a
distinctive
lingual
fossa that is bordered
by mesial and distal
marginal ridges, the
incisal edge, and the
prominent cingulum
at the gingival third.


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Proximal: Mesial and
distal aspects present
a
distinctive
triangular
outline.
This is true for all of
the
incisors.
The
incisal ridge of the
crown is aligned on
the long axis of the
tooth along with the
apex of the tooth.

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Incisal: The crown is
roughly triangular in
outline; the incisal
edge is nearly a
straight line, though
slightly
crescent
shaped.


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Contact Points: The mesial contact point is just about at the
incisal, owing to the very sharp mesial incisal angle. The distal
contact point is located at the junction of the incisal third and
the middle third.

Variation: The maxillary central incisor usually develops
normally. Variations include a short crown or, on occasion, and
unusually long crown. This tooth is rarely absent. The
Hutchinson incisor is a malformation due to congenital syphilis
in utero.


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Facial: The maxillary lateral
incisor resembles the central
incisor, but is narrower
mesio-distally. The mesial
outline
resembles
the
adjacent central incisor; the
distal
outline--and
particularly the distal incisal
angle is more rounded than
the mesial incisal angle
(which resembles that of the
adjacent central incisor. The
distal
incisal
angle
resembling the mesial of the
adjacent canine.

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Lingual: On the lingual
surface,
the
marginal
ridges
are
usually
prominent and terminate
into
a
prominent
cingulum. There is often a
deep
pit
where
the
marginal ridges converge
gingivally.
A
developmental
groove
often extends across the
distal of the cingulum
onto the root continuing
for part or all of its length.


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Proximal: In proximal
view, the maxillary
lateral
incisor
resembles the central
except that the root
appears longer--about
1 1/2 times longer
than the crown. A
line through the long
axis of the tooth
bisects the crown.


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Incisal: In incisal view,
this
tooth
can
resemble either the
central or the canine
to varying degrees.
The tooth is narrower
mesiodistally
than
the upper central
incisor; however, it is
nearly
as
thick
labiolingually.


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Contact Points: The mesial contact is at the junction of the
incisal third and the middle third. The distal contact is is
located at the center of the middle third of the distal surface.

Variation: This tooth is quite variable. Often the tooth is
narrow, conical, and peg-shaped. It is absent either singly or
bilaterally in 1-2% of individuals. Only the lower second
premolar is more frequently missing.
The lingual pit when present can be very deep and is prone to
early caries in many individuals.


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Facial: The mandibular
central incisor is the
smallest tooth in the
dental arch. It is a
long,
narrow,
symmetrical
tooth.
The incisal edge is
straight. Mesial and
distal
outlines
descend apically from
the sharp mesial and
distal incisal angles.

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surface
has
no
definate
marginal
ridges. The surface is
concave
and
the
cingulum is minimal
in size.


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Proximal: Both mesial
land distal surfaces
present a triangular
outline. The incisal
ridge of the crown is
aligned on the long
axis of the tooth
along with the apex
of the tooth.


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Incisal: The incisal edge
is at right angles to a
line
passing
labiolingually
through the tooth
reflecting its bilateral
symmetry.


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Contact Points: The mesial and distal contacts are at the
junction of the incisal third and the middle third.
Variation: This tooth is consistent in development and is is
rarely absent. The upper incisor region is a common site for
supernumerary teeth which may occasionally occur in the
midline; such a variant is called a mesodens.


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Facial:
This
tooth
resembles the central
incisor,
but
is
somewhat larger in
most proportions. It is a
more rounded tooth;
this
is
especially
evident in the distal
incisal angle in unworn
specimens. There is a
lack of the bilateral
symmetry seen in the
central.

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Lingual: Except for the
lack of symmetry,
this tooth resemble
the central.


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Proximal:
Like
the
central, the crown
presents a triangular
outline. When viewed
critically, the rotation
of the incisal edge
can be seen.


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Incisal: The incisal edge
'twisted' from the 90
degree angle with a
line
passing
labiolingually
through the tooth.


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Contact Points: The mesial and distal contacts are at the
junction of the incisal third and the middle third.

Variation: This tooth is stable, but variations in root length
and direction are occasionally seen.


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Permanent Canine
Human canines are the longest and most stable of
teeth in the dental arch. Only one tooth of this class is
present in each quadrant. In traditional dental literature,
canines are considered the cornerstones of the dental
arch. They are the only teeth in the dentition with a
single cusp. They are especially anchored as prehensile
teeth in the group from whence they get their name, the
Carnivora.
Maxillary canines by definition are the teeth in the
maxilla distal, but closest to the incisors. Mandibular
canines are those lower teeth that articulate with the
mesial aspect of the upper canine.
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Facial:
The
canine
is
approximately 1 mm narrower
than the central incisor. Its
mesial aspect resembles the
adjacent lateral incisor; the
distal aspect anticipates the
first premolar proximal to it.
The canine is slightly darker
and more yellow in the color
than the incisor teeth. The
labial surface is smooth, with a
well developed middle lobe
(labial ridge) extending the full
length of the crown cervically
from the cusp tip. The distal
cusp ridge is longer than the
mesial cusp ridge.

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Lingual: Distinct mesial
and distal marginal
ridges,
a
welldeveloped
cingulum,
and the cusp ridges
form the boundaries of
the lingual surface. The
prominent lingual ridge
extends from the cusp
tip to the cingulum,
dividing the lingual
surface into mesial and
distal fossae.


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Proximal: The mesial
and distal aspects
present a triangular
outline.
They
resemble the incisors,
but are more robust-especially
in
the
cingulum region.


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Incisal: The asymmetry
of this tooth is readily
apparent from this
aspect. It usually
thicker labiolingually
than
it
is
mesiodistally. The tip
of
the
cusp
is
displaced
labially
and mesial to the
central long axis of
this tooth.

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Contact point: The mesial contact point is at the
junction of the incisal and middle third. Distally, the
contact is situated more cervically. It is at the middle
of the middle third.

Variation: Each of the major features of this tooth are
'variations on a theme.' In some persons, a cusp-like
tubercle is found on the cingulum. Lingual pits occur
only infrequently. On occasion, the root is unusually
long or unusually short.


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Facial: The mandibular canine is
noticeably narrower mesiodistally
than the upper, but the root may be
as long as that of the upper canine.
In an individual person,the lower
canine is often shorter than that of
the upper canine. The mandibular
canine is wider mesiodistally than
either lower incisor. A distinctive
feature is the nearly straight
outline of the mesial aspect of the
crown and root. When the tooth is
unworn, the mesial cusp ridge
appears as a sort of 'shoulder' on
the tooth. The mesial cusp ridge is
much shorter than the distal cusp
ridge

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Lingual: The marginal
ridges and cingulum
are less prominent
than those of the
maxillary canine. The
lingual surface is
smooth and regular.
The lingual ridge, if
present, is usually
rather subtle in its
expression.

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Proximal: The mesial and
distal aspects present a
triangular outline. The
cingulum as noted is
less well developed.
When the crown and
root are viewed from
the proximal, this tooth
uniquely presents a
crescent-like
profile
similar to a cashew nut.


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Incisal: The mesiodistal
dimension is clearly less
than the labiolingual
dimension. The mesial
and distal 'halves' of the
tooth are more identical
than the upper canine
from this perspective.
You will recall that the
cusp tip of the maxillary
canine is facial to a ling
through the long axis. In
the mandibular canine,
the unworn incisal edge
is on the line through
the long axis of this
tooth.

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Contact point: The mesial contact point is at the
junction of the incisal and middle third. Distally, the
contact is situated more cervically. It is at the middle
of the middle third.

Variation: On occasion, the root is bifurcated near its
tip. The double root may, or may not be accompanied
by deep depressions in the root.


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Premolar
The premolar teeth are transitional teeth
located between the canine and molar teeth. There
are two premolars per quadrant and are identified
as first and second premolars. They have at least
two cusps.
Premolar teeth by definition are permanent
teeth distal to the canines preceded by deciduous
molars.
Utilized in the initial breakdown of food

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Facial:
The
buccal
surface
is
quite
rounded and this
tooth resembles the
maxillary canine. The
buccal cusp is long;
from that cusp tip, the
prominent
buccal
ridge descends to the
cervical line of the
tooth.

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cusp is smaller and
the tip of that cusp is
shifted toward the
mesial. The lingual
surface is rounded in
all aspects.


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Proximal: The mesial aspect
of this tooth has a
distinctive concavity in
the cervical third that
extends onto the root. It is
called
variously
the
mesial
developmental
depression,
mesial
concavity, or the 'canine
fossa'--a
misleading
description since it is on
the premolar. The distal
aspect of the maxillary
first permanent molar also
has
a
developmental
depression. The mesial
marginal developmental
groove is a distinctive

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Occlusal: There are two
well-defined
cusps
buccal and lingual. The
larger cusp is the buccal;
its cusp tip is located
midway mesiodistally.
The lingual cusp tip is
shifted mesially. The
occlusal outline presents
a hexagonal appearance.
On the mesial marginal
ridge is a distinctive
feature,
the
mesial
marginal developmental
groove.

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Contact Points; Height of Curvature: The distal contact
area is located more buccal than is the mesial contact area.
Both contact points are at the junction of the occlusal and
middle third of the tooth.

Variation: Most upper first premolars of people in our
society have two roots; however, a single root is found in
about 20% of teeth. Three rooted premolars are found
occasionally.


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Facial: This tooth closely
resembles
the
maxillary
first
premolar but is a less
defined copy of its
companion to the
mesial. The buccal
cusp is shorter, less
pointed, and more
rounded than the
first.

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Lingual: Again, this
tooth resembles the
first. The lingual
cusp, however, is
more nearly as large
as the buccal cusp.


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Proximal: Mesial and
distal surfaces are
rounded. The mesial
developmental
depression
and
mesial marginal ridge
are not present on the
second premolar.


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Occlusal: The crown
outline is rounded,
ovoid, and is less
clearly defined than
is the first.


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Contact Points; Height of Curvature: When viewed from
the facial, the distal contact area is located more cervically
than is the mesial contact area.

Variation: The occlusal anatomy is more variable in the
second than in the first. There is wide variability is root
size, curvature, and form.


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Facial: The outline is
very
nearly
symmetrical
bilaterally,
displaying a large,
pointed buccal cusp.
From it descends a
large, well developed
buccal ridge.


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Lingual: This tooth has
the smallest and most
ill-defined
lingual
cusp of any of the
premolars.
A
distinctive feature is
the
mesiolingual
developmental
groove. (Remember
the mesial marginal
developmental
groove in the upper
first premolar? That
one is mesial. The
one on the lower is
toward the lingual.)


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Proximal:
The
large
buccal cusp tip is
centered over the root
tip, about at the long
axis of this tooth. The
very large buccal cusp
and much reduced
lingual cusp are very
evident. You should
keep in mind that the
mesial marginal ridge
is more cervical than
the distal contact
ridge; each anticipate
the shape of their
respective
adjacent
teeth.

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Occlusal: The occlusal outline
is
diamond-shaped.
(Review
of
premolar
occlusal outlines: the upper
first is hexagonal, the upper
second is ovoid, the lower
first is diamond, and the
lower second is square.)
The large buccal cusp
dominates the occlusal
surface. Marginal ridges are
well developed and the
mesiolingual
developmental groove is
consistently present. There
are mesial and distal fossae
with pits, affectionately
known as 'snake eyes' when

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Contact Points; Height of Curvature: When viewed from the
facial, each contact area/height of curvature is at about the
same height.
Variation: This is a variable tooth in both crown and root. It
may, in some persons, more nearly resemble the lower
second premolar.


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Facial: From this aspect,
the tooth somewhat
resembles the first,
but the buccal cusp is
less pronounced. The
tooth is larger than
the first.


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Lingual: Two significant
variations are seen in
this view. The most
common is the threecusp form which has
two lingual cusps.
The mesial of those is
the larger of the two.
The other form is the
two-cusp for with a
single lingual cusp.
In that variant, the
lingual cusp tip is
shifted to the mesial.

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Proximal: The buccal
cusp is shorter than
the first. The lingual
cusp (or cusps) are
much
better
developed than the
first and give the
lingual a full, welldeveloped profile.


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Occlusal: The two or three
cusp versions become
clearly evident. In the
three-cusp version, the
developmental
grooves
present a distinctive 'Y'
shape and have a central
pit. In the two cusp
version,
a
single
developmental
groove
crosses
the
transverse
ridge from mesial to distal.
(Review: the lower second
premolar is larger than the
first, while the upper first
premolar is just slightly

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Contact Points; Height of Curvature: From the facial,
the mesial contact is more occlusal than the distal
contact. Why? The distal marginal ridge is lower than
the mesial marginal ridge.

Variation: There may be one or two lingual cusps. This
tooth is sometimes missing; only the third molars and
upper lateral incisors are missing more frequently than
this tooth.


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Permanent Molar Teeth
The permanent molars occupy the most
posterior portion of the dental arch. They have the
largest occlusal surfaces of any of the teeth and
have from three to five major cusps.
Molar teeth by definition are cheek teeth that
are NOT preceded by primary teeth. Permanent
molars are accessional teeth without primary
predecessors. In contrast to the molars, permanent
incisors, canines, and premolars are succedaneous
(successional teeth). These teeth are important in
chewing and maintaining the vertical dimension.

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Facial: The mesiobuccal
and distobuccal cusps
dominate the facial
outline. They are
separated
by
the
buccal developmental
groove. All three roots
are
visible.
The
buccal roots present a
'plier
handle'
appearance with the
large lingual root
centered
between
them.

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Lingual: Two cusps of
unequal size dominate the
occlusal profile. The cusps
are separated by the
lingual
developmental
groove
which
is
continuous
with
the
distolingual (or distal
oblique)
groove.
The
larger mesiolingual cusp
often
displays
the
Carabelli trait. It is a
variable feature. It appears
most often as a cusp of
variable size, but is
occasionally
expressed
merely as a pit. www.indiandentalacademy.com

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Proximal:
In
mesial
perspective
the
mesiolingual
cusp,
mesial marginal ridge,
and mesiobuccal cusp
comprise the occlusal
outline. When present,
the Carabelli trait is seen
in this view. In its distal
aspect, the two distal
cusps are clearly seen;
however,
the
distal
marginal
ridge
is
somewhat shorter than
the mesial one. A small
concavity on the distal
surface that continues
onto the distobuccal root

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Occlusal: The tooth outline is
somewhat rhomboidal with
four distinct cusps. The cusp
order according to size is:
mesiolingual,
mesiobuccal,
distobuccal, and distolingual.
The tips of the mesiolingual,
mesiobuccal, and distobuccal
cusps
form
the
trigon,
reflecting the evolutionary
origins of the maxillary
molar. The distolingual cusp
is called the talon (heel) and
is a more recent acquisition in
evolutionary
history.
A
frequent feature of maxillary
molars is the Carabelli trait
located on the mesiolingual

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Contact Points; Height of Curvature: The mesial
contact is above, but close to, the mesial marginal ridge.
It is somewhat buccal to the center of the crown
mesiodistally. The distal contact is similarly above the
distal marginal ridge but is centered buccolingually.

Variation: Deviation from the accepted normal is
infrequent. The Carabelli trait is a variable feature. It is
of special interest to the dental anthropologist in tracing
human evolutionary history.

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Facial: The crown is shorter
occluso-cervically and narrower
mesiodistally when compared
to the first molar. The
distobuccal cusp is visibly
smaller than the mesiobuccal
cusp. The two buccal roots are
more nearly parallel. The roots
are more parallel; the apex of
the mesial root is on line with
the
with
the
buccal
developmental groove. Mesial
and distal roots tend to be
about the same length.

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Lingual:
The
distolingual cusp is
smaller
than
the
mesiolingual
cusp.
The Carabelli trait is
absent.


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Proximal: The crown is
shorter than the first
molar and the palatal
root
has
less
divergence. The roots
tend to remain within
the crown profile.


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Occlusal: The distolingual
cusp is smaller on the
second than on the first
molar. When it is much
reduced in size, the crown
outline is described as
'heart-shaped.'
The
Carabelli trait is usually
absent. The order of cusp
size, largest to smallest, is
the same as the first but is
more
exaggerated:
mesiolingual,
mesiobuccal, distobuccal,
and distolingual.


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Contact Points: Height of Curvature: Both mesial and
distal contacts tend to be centered buccolingually below the
marginal ridges. Since the molars become shorter, moving
from first to this molar, the contacts tend to appear more
toward the center of the proximal surfaces.

Variation: The distolingual cusp is the most variable
feature of this tooth. When it is large, the occlusal is
somewhat rhomboidal; when reduced in size the crown is
described as triangular or 'heart-shaped.' At times, the
root may be fused.


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Facial: The crown is
usually shorter in
both
axial
and
mesiodistal
dimensions.
Two
buccal
roots
are
present, but in most
cases they are fused.
The mesial buccal
cusp is larger than the
distal buccal cusp.

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Lingual: In most thirds,
there is just one large
lingual cusp. In some
cases there is a poorly
developed
distolingual cusp and
a lingual groove. The
lingual root is often
fused to the to buccal
cusps.


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Proximal: The outline of
the crown is rounded;
it is often described
as bulbous in dental
literature.
Technically,
the
mesial surface is the
only
'proximal'
surface. The distal
surface
does
not
contact another tooth.

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Occlusal: The crown of
this tooth is the
smallest
of
the
maxillary molars. The
first molar is the
largest in the series.
The outline of the
occlusal surface can
be described as heartshaped. The mesial
lingual cusp is the
largest, the mesial
buccal is second in
size, and the distal
buccal cusp is the
smallest. www.indiandentalacademy.com

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Contact Points; Height of Curvature: This tooth is rounded
and variable in shape. The distal surface has no contact with
any other tooth.

Variation: They are the most variable teeth in the dentition.
Impaction occurs frequently. Some resemble the adjacent
second molar; others may have many cusps, small 'cusplets',
and many grooves.


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Facial: The lower first permanent molar has the
widest mesiodistal diameter of all of the
molar teeth. Three cusps cusps separated by
developmental grooves make up the occlusal
outline seen in this view. Moving from
mesial to distal, these features form the
occlusal outline as follows: mesiobuccal cusp,
mesiobuccal
developmental
groove,
distobuccal cusp, distobuccal developmental
groove, and the distal cusp. The mesiobuccal
cusp is usually the widest of the cusps and is
generally considered the largest of the five
cusps. The distal cusp is smaller than any of
the buccal cusps and it contributes little to
the buccal surface. The two roots of this tooth
are clearly seen. The distal root is usually less
curved than the mesial root.

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Lingual: Three cusps make
up the occlusal profile in
this
view:
the
mesiolingual,
the
distolingual, and the
distal cusp which is
somewhat
lower
in
profile. The mesiobuccal
cusp is usually the
widest and highest of the
three. A short lingual
developmental
groove
separates the two lingual
cusps

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Proximal: The distinctive height
of curvature seen in the
cervical third of the buccal
surface is called the cervical
ridge. The mesial surface may
be flat or concave in its
cervical third . It is highly
convex in its middle and
occlusal thirds. The occlusal
profile is marked by the
mesiobuccal
cusp,
mesiolingual cusp, and the
mesial marginal ridge that
connects them. The mesial
root
is
the
broadest
buccolingually of any of the
lower molar roots. The distal
surface of the crown is
narrower buccolingually than
the mesial surface. Three
cusps are seen from the distal

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Occlusal: This tooth
presents a pentagonal
occlusal outline that
is distinctive for this
tooth. There are five
cusps. Of them, the
mesiobuccal cusp is
the largest, the distal
cusp is the smallest.
The
two
buccal
grooves
and
the
single lingual groove
form the "Y5" pattern
distinctive for this
tooth. The five cusp
and "Y5" pattern is
important in www.indiandentalacademy.com
dental
anthropology.

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Contact Points; Height of Curvature: The mesial contact is
centered buccolingually just below the marginal ridge. The
distal contact is centered over the distal root, but is buccal to
the center point of the distal marginal ridge.

Variation: Most lower first molars have five cusps.
Occasionally the distal cusp is missing. More rarely, in large
molars, the distal cusp is joined by a sixth cusp, the 'cusp six'
or tuberculum sextum. Two mesial roots are seen on
occasion; this Sinodont feature is occasionally seen clinically,
particularly in persons of North American Indian heritage.


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Facial: When compared to
the first molar, the
second molar crown is
shorter
both
mesiodistally and from
the cervix to the occlusal
surface. The two welldeveloped buccal cusps
form the occlusal outline.
There is no distal cusp as
on the first molar. A
buccal
developmental
groove appears between
the buccal cusps and
passes midway down the
buccal surface www.indiandentalacademy.com
toward the

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Lingual: The crown is
shorter than that of
the first molar. The
occlusal outline is
formed
by
the
mesiolingual
and
distolingal cusps.


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Proximal: The mesial
profile resembles that
of the first molar. The
distal
profile
is
formed
by
the
distobuccal
cusp,
distal marginal ridge,
and the distolingual
cusp. Unlike the first
molar, there is no
distal fifth cusp.


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Occlusal: There are four
well developed cusps
with developmental
grooves that meet at a
right angle to form
the distinctive "+4"
pattern characteristic
of this tooth.


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Contact Points; Height of Curvature: When moving distally
from first to third molar, the proximal surfaces become
progressively more rounded. The net effect is to displace the
contact area cervically and away from the crest of the
marginal ridges.

Variation: Morphologically this is a stable tooth. Five-cusp
versions are seen on occasion, however root variability is
greater than in the first molar.


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Facial: The crown is
often short and has a
rounded outline.


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Lingual: Similarly, the
crown is short and
the crown is bulbous.


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Proximal: Mesially and
distally, this tooth
resembles the first and
second molars. The
crown of the third
molar, however, is
shorter than either of
the
other
molars.
Technically, only the
mesial surface is a
'proximal' surface.


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Occlusal: Four or five
cusps may be present.
This surface can be a
good copy of the first or
second molar, or poorly
developed with many
accessory grooves. The
occlusal outline is often
ovoid and the occlusal
surface is constricted.
Occasionally,
the
surface has so many
grooves that it is
described
as
crenulated--a condition
seen in the great apes.

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Contact Points; Height of Curvature: The rounded mesial
surface has its contact area more cervical than any other
lower molar. There is no tooth distal to the third molar.

Variation: This is an extremely variable tooth and on
occasion it is missing. While the most common anomaly of
upper third molars is that they are undersized, lower third
molars can be undersized or oversized. Lower third molars
fail to erupt in many persons.


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DEVELOPMENT
OF
OCCLUSION

SEQUENCE OF ERUPTION
TIME OF ERUPTION
PATH OF ERUPTION
STAGES OF DEVELOPMENT OF OCCLUSION


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SEQUENCE OF ERUPTION


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Primary dentition
Central incisor
Lateral incisor
First molar
Canine
Second molar


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Permament dentition
First molars
Central incisor
Lateral incisor
Mandibular canines
First premolars
Second premolars
Maxillary canines
Second molars
Third molars

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TIME OF ERUPTION


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Maxillary

Mandibular

Deciduous
Tooth

Eruption

Root
complete

Eruption

Root
complete

A

7½

10

6

8

B

9

11

7

13

C

18

19

16

20

D

14

16

12

16

E

24

29

20

27


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Maxillary

Mandibular

Permanent
Tooth

Eruption

Root
complete

Eruption

Root
complete

CI

7-8

10

6-7

9

LI

8-9

11

7-8

10

C

11-12

13-15

9-10

12-14

1ST PM

10-12

12-13

10-12

12-13

2ND PM

10-12

12-14

11-12

13-14

1ST M

6-7

9-10

6-7

9-10

2ND M

12-13

14-16

11-13

14-15

3RD M

17-21

18-25

17-21

18-25


PATH OF ERUPTION
(Permanent dentition)


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Mandibular Permanent Incisor
 Permanent central incisors develop lingually and apically
to the primary incisors
 Permanent lateral incisors occupy a position lingual to the
central incisors. The developing lateral incisor may be seen
in close proximity to the lingual cortical plate of the
mandibular symphysis
 Crowns of both central and lateral are lingually inclined
The incisal path of eruption of the teeth is oblique and
usually directed labially relative to primary incisors
 As the permanent incisors erupt they resorb the lingual
aspect of the primary incisor roots
 On completion of eruption they occupy a more labial
inclination
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Maxillary Permanent Incisor
 Eruption takes place after the mandibular lateral
has erupted
 Central incisor precedes lateral incisor
The path of eruption is more labial and oblique
than that of mandibular permanent incisors
(resulting in a more labial positioning of maxillary
incisors)
 There is a distal tilting of the crowns of the central
incisors on eruption causing a mild midline
diastema. This gets closed with the eruption of the
lateral incisors

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Mandibular Permanent Canines
 During the eruption, the axis is directed
mesially and lingually
 The permanent cuspids erupt along the
distal aspect of the roots of the permanent
lateral incisors
 Upon eruption, their final positioning,
relative to their predecessors, is labial with a
mesial inclination

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Maxillary Permanent Canines
 This is the last tooth to erupt anterior to the

molars in this arch
As they erupt, they are directed towards the
distal aspect of the maxillary permanent
lateral incisor roots and erupt in the dental
arch
 Their final position in the arch is labial in
their relation with the lateral incisors and 1st
premolar

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Mandibular and Maxillary First Premolars
 It develops beneath the first primary molar and is
enclosed by its roots
 The path of eruption is directly towards the
occlusal plane
 Resorbs the roots of the first primary molar to
weaken its support and pushes it out to occupy its
position in the arch

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Mandibular Second Premolars
 Last tooth to erupt anterior to the first molar
 There are three possible paths
 Distal path of eruption – This is considered the
best as there is no loss of space. As the 2 nd
premolar erupts distally, it resorbs the distal root
of the 2nd primary molar and glides along the
mesial surface of the 1st permanent molar. This is
considered the normal path of eruption.
 Occlusal path of eruption – Here there is a loss
of space owing to the mesial shifting of the 1 st
permanent molar at the time of exfoliation of the
2nd primary molar. www.indiandentalacademy.com
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 Mesial path of eruption – Least desirable path
of eruption. This occurs owing to the blocking out
of space for the 2nd premolar due to an increased
time lapse between the exfoliation of the 2nd
primary molar and the eruption of the 2nd
bicuspid.

Mandibular Second Premolars
Identical to the first premolar in its path of
eruption. Mostly follows an occlusal path of
eruption.

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Mandibular First Permanent Molar
 The first permanent teeth to erupt
 Prior to eruption, the crowns are canted mesially and
lingually, with their bony crypts positioned at the angle
formed by the junction of the body of the mandible and the
anterior border of the ramus
 Movement of the tooth occlusally, along with the
resorption of the anterior border of the ascending ramus,
facilitates the eruption of the tooth
 During the course of eruption, the molar undergoes a
rotation, re-orienting the crown with the occlusal plane
 Ultimately they are positioned with a slight mesial tilt and a
slight lingual inclination in the transverse axis
 Flush terminal plane later changes to Class I relationship
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Maxillary First Permanent Molar
 The Crowns are distally and buccally oriented in their
crypts.
 As the maxillary arch gets lengthened due to appositional
growth at the tuberosities, the maxillary 1St permanent molar
rotates mesially and the crowns are uprighted so that they
move vertically towards the occlusal plane
 On completion of eruption, they are inclined mesially on
their long axis and buccally in their transverse axis


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Mandibular Second Permanent Molar
 Crypts positioned at base of the ascending ramus
 Space for eruption is gained by resorption of the anterior
border of the ramus
 In the crypts, the crowns are pointed mesially, almost at
right angles to the occlusal plane
 The crown rotates in a distal direction and erupts against
the mandibular 1st permanent molar in and occlusal direction


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Maxillary Second Permanent Molar
 Position in crypt and pathway of eruption is similar to the
1st permanent molar
 Mesiobuccal inclination of the tooth in its final occlusal
position


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STAGES OF
DEVELOPMENT OF
OCCLUSION

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Stage

Age in years

Characteristics

First stage

3

Second stage

6

Eruption of 1st
permanent molar

Third stage

6–9

Exchange of incisors

Fourth stage

9 – 12

Exchange of lateral
teeth

Fifth stage

12

Eruption of 2nd molar

Primary dentition


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PRIMARY DENTITION


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Primary tooth buds form at 6 weeks IUL
Commence erupting at 6 months post birth and
goes upto 2 ½ years of age when the 2nd primary
molar occludes
At the age of 3 the primary dentition is established
From 3 – 5 years no activity
From 5 – 6 years, the size of the dental arch begins
to change due to eruptive forces from the first
permanent molar

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Spaces in primary dentition
Primate space – mesial to maxillary canine,
distal to mandibular canine

Developmental space – between the incisors

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Occlusal relationship of 2nd primary molars
 Eruption and root completion of the 2nd primary molar
marks the completion of the primary dentition development
 The relationship of the distal surfaces of the maxillary and
mandibular primary molars is one of the most important
factors to influence the future occlusion of the permanent
dentition
 Terminal plane – Mesiodistal relation of the max. and
mand. 2nd primary molars when in centric occlusion
Three types:
a) Flush terminal plane
b) Mesial step
c) Distal step


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Size of the dental arch
 Size can be measured by the dental arch width
between the primary canines and between the 2 nd
primary molars
 Length can be measured from the most labial
surface of the primary Central incisor to the canine
and to the 2nd primary molars
A.Inter canine width
B.Inter molar width
C.Anterior arch
length
D.Total arch length

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ERUPTION OF 1ST
PERMANENT MOLAR


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1st permanent molar is the key to the permanent
occlusion
The prediction of the occlusion of the 1st permanent
molars is known at the primary dentition stage
a) Flush terminal plane – If there are dental spaces
existing in the primary dental arch, the 1st molar will
erupt into CLASS I. If not, it becomes a cusp-tocusp occlusion
b) Mesial step – Erupts directly into CLASS I
occlusion
c) Distal step – Directly and definitely into CLASS II
occlusion
The physiologic spaces get closed due to mesially
directed eruptive forces of permanent molars HOME

Some cases of Flush terminal plane go in for
CLASS III when physiologic spaces are absent
in the mandible
The active growth of the mandible also
regulates the occlusion (forward and downward
growth of mandible)


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EXCHANGE OF INCISORS


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 This commences after the eruption of the 1st molar
begins
 Total sum of the mesiodistal widths of permanent
incisors is greater than that of primary incisors bye
about 7mm in maxilla and 5mm in mandible
 Moorress (1965) observed some degree of crowding of
anteriors during their eruption, which is transient


Regulating factors for arrangement of permanent
incisors are:
a) Interdental spaces between primary incisors
b) Increase of intercanine width
c) Increase of anterior length in dental arch
d) Change of tooth axis of incisors
e) Ugly duckling stage

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EXCHANGE OF
LATERAL TEETH
(Canines and Premolars)


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 Limited by the mesial surface of the 1st molar distally
and distal surface of the lateral incisor
 Two factors permit smooth eruptive pathways
a) Leeway space – The combined width of the
permanent lateral teeth is less than that of the
primary lateral teeth by about 1mm in the maxilla
and 3mm in the mandible


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b)Order of exchange – Eruption pattern sequences usually
seen are 3-4-5, 4-3-5, 4-5-3
In the mandible it is usually 3-4-5 and as the
permanent canine is larger than the primary canine,
crowding is very common immediately after the exchange
of canines.
If the pattern isn’t changed the crowding gets
alleviated after the exfoliation of the 2nd primary molar.
If the sequence changes to 4-3-5 or 4-5-3, there isn’t
efficient utilization of the Leeway space and teeth get
crowded


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ERUPTION OF 2ND
PERMANENT MOLARS


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 Occurs after the eruption of all the permanent teeth in
the dental arch upto the 1st permanent molar is complete
 Its eruptive pathway is guided by the destal surface of
the 1st permanent molar
 The dental arch length may be less than in primary
dentition owing to closure of Leeway space and this can
cause crowding of the 2nd molar. However, this gets
compensated by the growth of the mandible in a forward
downward direction.


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DETERMINANTS
OF OCCLUSAL
MORPHOLOGY

Posterior controlling factor (Condylar guidance)
Anterior controlling factor (Anterior
guidance)
Vertical determinants
1. Effect of condylar guidance on cusp height
2. Effect of anterior guidance on cusp height
3. Effect of plane of occlusion on cusp height
4. Effect of curve of spee on cusp height
5. Effect of mandibular lateral translation
movement on cusp height

Horizontal determinants
1. Effect of distance from the rotating condyle
2. Effect of distance from midsagittal plane
3. Effect of distance from rotating condyle and
fossa from midsagittal plane
4. Effect of mandibular lateral translation movement
5. Effect of intercondylar distance

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Posterior controlling factor
(Condylar guidance)


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 As the condyle moves out of centric relation it
descends along the articular eminence
 If the articular eminence is steep, the condyle
describes a steep vertically inclined path and if
flatter, the path is less vertically inclined
 The angle at which the condyle moves away
from a horizontal reference plane is referred to as
the condylar guidance angle


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 The CGA is steeper for the orbiting condyle in a
latero-trussive movement of the mandible as the
medial wall of the mandibular fossa is steeper
than the articular eminence in front
 The two TMJ’s provide the guidance for the
posterior portion of the mandible and are largely
responsible for determining the character of
mandibular movement posteriorly. Thus they
become the posterior controlling factor
 It is a fixed factor

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Anterior controlling factor
(Anterior guidance)


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 The anterior teeth guide the movement of the
anterior portion of the mandible
 As the mandible protrudes, the incisal edge of
the mandibular anterior teeth occlude with the
lingual surfaces of the maxillary anterior teeth
The steepness of the lingual surface determines
the amount of vertical movement of the mandible
 It is a variable factor


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Vertical determinants


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1. Effect of condylar guidance on cusp height

Steeper the articular
eminence, more is
the descent of the
condyle, resulting in
greater
vertical
movement.
Thus
allowing for steeper
posterior cusps


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2. Effect of anterior guidance on cusp height
Increased horizontal overlap decreases
the anterior guidance angle. There is less
vertical movement of the mandible leading to
flatter posterior cusps


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Increased vertical overlap increases the
anterior guidance angle. There is more vertical
movement of the mandible leading to steeper
posterior cusps


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3. Effect of plane of occlusion on cusp
height
 Plane of occlusion is an imaginary line touching
the incisal edges of the maxillary anterior teeth
and the cusps of the maxillary posterior teeth
 Depending on the angulation of the plane of
occlusion in relations to the horizontal plane, the
degree of movement of the tooth varies. If less
degree of movement is seen – flatter cusps; and if
more degree of movement is seen – taller cusps.

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4. Effect of curve of spee on cusp height
 Curve of spee is an antero - posterior curve
extending from the tip of the mandibular canine
along the buccal cusp tips of the mandibular
posterior teeth
 Its degree of curvature influences the height of the
posterior cusps. Flatter the curve of spee, greater is
the angle away from the maxillary posteriors – taller
cusp. More acute curve of spee, smaller the angle of
mandibular posterior tooth movement – flatter
cusps.

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 Orientation of the curve of spee also
influences cusp height
 Radius perpendicular to horizontal reference
plane
Posterior teeth located distal to the radius
need shorter cusps and those mesial to the
radius need taller teeth
Rotated posteriorly : Shorter cusps
Rotated anteriorly : Taller cusps

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5. Effect of mandibular lateral translation
movement on cusp height
 This is a bodily sideshift of the mandible where
the orbiting condyle moves downwards, forwards
and inwards. The degree of inward movement of the
orbiting condyle is determined by two factors
(1) Morphology of medial wall of mandibular
fossa
(2) Inner horiz. Portion of TM ligament, which
attaches to the lateral pole of the rotating condyle
 The lateral translation has three attributes:
amount, direction and timing

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 The amount of lateral translation depends on the
tightness of the inner horizontal portion of the TM
ligament attached to the lateral
 pole of the rotating condyle. Looser the ligament,
greater is the amount of lateral translation, posterior
cusps should be shorter to permit lateral translation
without contact
 The direction of shift of the rotating condyle is
determined by morphology and ligamentous attachment
of the rotating TMJ. Movement occurs within a 60˚ cone
permitting superior, inferior, anterior and posterior
movements in addition to the lateral translation. The
vertical movement of the rotating condyle during a
lateral translation helps determine cusp height.
Latero-superior movement – shorter posterior cusps
Latero inferior movement – longer posterior cusps HOME

 The time of lateral translation is of great influence on
occlusal morphology. If late, there is less influence as the
maxillary and mandibular cusps are beyond functional
range. If early, a shift is seen even before the condyle
begins to translate (immediate side shift). If it occurs along
with an eccentric movement, the movement is called
progressive side shift. The more immediate the side shift,
the shorter are the posterior teeth cusps to avoid
interference.


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Horizontal determinants


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1. Effect of distance from the rotating condyle
Increased distance – wider angle between
laterotrussive and mediotrussive pathways, flatter
centric cusps


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2. Effect of distance from midsagittal plane
Increased distance – wider angle between
laterotrussive and mediotrussive pathways, flatter
centric cusps


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3. Effect of distance from rotating condyle and
fossa from midsagittal plane
They generally counter act each other. The
combination of the two positional relationships is what
determines the exact pathways of the centric cusp tips.
Curvature of dental arch causes the two
components to counter act each other and negate their
effect


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4. Effect of mandibular lateral translation movement
Increased lateral movement, increases the angle
between laterotrussive and mediotrussive pathways
The direction of rotation of the rotating condyle also
plays a role
Lateral and anterior direction – Increased angle (flatter cusp)
Lateral and posterior direction – decreased angle (sharper
cusp)


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5. Effect of intercondylar distance
Increase in distance, reduces the angle
between laterotrussive and mediotrussive
pathways


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