Normal occlusion 1

Department of Orthodontics &
Dentofacial Orthopedics
NORMAL OCCLUSION
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

INTRODUCTION :
• The study and practice of most branches
of dentistry should be based on a strong
foundation of knowledge of occlusion.
• The orthodontist should know what
constitutes normal occlusion in order to be
able to recognize abnormal occlusion.
• Normal in physiology is always a range,
never a point.
• A balanced, stable, healthy and
esthetically attractive occlusion is also
conceivable normal even if minor rotation
are present.

• And yet, what may be abnormal for one
age may be normal for another.
• The curve of spee, compensatory curve,
cusp height and facial relation of each
tooth to its antagonist and other
characteristics of occlusion may all vary
within a broad range and still be
normal.
• It may be equally normal for one child
to have a marked overbite and overjet
and procumbent incisors and for
another to have little overbite or
overjet.

• Good examples of the time-linked nature of
normally are such transient malocclusion, as
crowding during, eruption of incisors, the „ugly
duckling‟ flaring of maxillary lateral incisors, the
Class II first molar relationship tendencies
before loss of second deciduous molars.
• Original concept of occlusion were those of a
complete act – literally an anatomic approach, a
description of how the teeth meet when the
jaws are closed.
• “clusion” means closing and “oc” means up thus
“occlusion” is closing up.

• DEVELOPMENT OF CONCEPT OF
OCCLUSION
• The development of the idea of occlusion
can be traced through fiction and hypothesis to
fact.
• The fictional approach, in a philosophical sense,
was convenient arrangement of series of
observed and thoughts more or, less logically
arrange.
• The hypothetical attack on the problem of
occlusion was based on a provisional acceptance
of certain logical entities. As Simon said, a
hypothesis can be maintained only if it does not
contradict the facts of experience. This is just
the opposite of fiction.

• Fact is reality, what has really happened.
Fact is a truth known by actual experience or
observation. Both the functional and
hypothetical approaches are necessary preludes
to the establishment fact but must given way
wherever contradiction arises.
• The development of concept of occlusion thus
can be divided into three periods:
• The fictional period, prior to 1900, the
hypothetical period, from 1900 to 1930, the
factual period, from 1930 to the present
development of concept of occlusion

• DEFINITIONS
• Occlusion
• Is defined as the anatomic alignment of teeth and
their relationship to the rest of the masticatory
system.
• BSSO in 1926 defined occlusion as the
relationship of the teeth in the maxilla and mandible
when the jaws are closed and the condyles are at rest
in the glenoid fossae.
• Normal occlusion
• This refers to an occlusion that deviates in one or
more ways from ideal yet it is well adopted to that
particular environment, is esthetic and shows no
pathologic manifestations or dysfunction.
• BSSO (1926) has defined normal occlusion as the
occlusion which is within the standard deviation from
the ideal. www.indiandentalacademy.com

• Ideal occlusion
• It is a preconceived theoretical concept of
occlusal structural and functional relationships
that includes idealized principles and
characteristics that an occlusion should have.
• BSSO (1926) has defined ideal occlusion as
„a hypothetical standard of occlusion based on
morphology of the teeth.

• COMPENSATORCURVES
OF THE DENTAL ARCHES
1) Curve of spee
• It refers to the antero-
posterior curvature of the
occlusal Surfaces, beginning
at the tip of the mandibular
cuspid and following the
buccal cusps of bicuspid and
molar continuing as an arc
through the condyle. If the
curve is extended, it would
form a circle of about 4 inch
diameter. This curvature is
within the sagittal plane only.
• The curve of spee given by
F. Graf Von Spee in
Germany in 1890.www.indiandentalacademy.com

2) Curve of Wilson
• This is a curve that
contacts the buccal and
lingual cusp tips of
mandibular buccal
teeth. The curve of Wilson
is medio-lateral on each
side of the arch. It results
from inward inclination of
the lower posterior teeth.
• Curve of Wilson helps in
two ways.
1. Teeth are aligned parallel to
the direction of medial
pterygoid for optimum
resistance to masticatory
forces.
2. The elevated buccal cusps
prevent food from going
past the occlusal table.www.indiandentalacademy.com

3) Curve of Monson
• Manson (1920), at a
later date, connected the curve
of spee and curve of
Wilson to all cusps and
incisal edges, and
suggested that the
mandibular arch adopted
itself to the curved
segment of a sphere of a
4 inch radius.

• POSITION OF TEETH IN THE DENTAL ARCH
1) Contact point
• The point of contact of teeth should be situated
at their greatest mesio-distal diameter.
2) Anteroposterior position
• The posterior teeth normally in contact with
each other mesiodistally
• The anterior teeth should have their incisal
edges along a smooth curve. This is usually the
case for the lower incisors because of their
relative equal size.
• The maxillary lateral and central incisors
however, do not have the same labiolingual
thickness, which causes the lateral incisors
edges to be slightly lingual to those of central.

• The canines serve as a corner stones between the anterior
and posterior. They are slightly more buccal than first
bicuspids and the lateral incisors. This is more accentuated
in the maxillary arch than in the mandibular arch
3) Vertical position
• The tips of cusps of all the teeth are situated
approximately on a segment of a sphere, the centre of which
is located about 10mm above the crista galli in the cranial
base. i.e. the curve of spee. In attritional dentition, when
reduction is confined to the cusp, the same curve is
maintained
4) Axial inclination
• The long axis of maxillary molars and bicuspids tends to
meet in the area of crista galli. The maxillary central and
lateral incisors are move inclined than the buccal teeth.
Their long axis convergent apically. The long axis of canine
fallows lateral walls of nose.

• The axis of mandibular posterior teeth are
relatively parallel antero-posteriorly and
divergent apically in the transverse direction.
This means that the apices are farther apart
than the buccal cusps. The axis of canines are
convergent apically in the transverse direction,
as are the axis of lower incisors, which in turn
are inclined labially, relative to the buccal teeth.

• ANDREWS SIX KEYS TO NORMAL
OCCLUSION
• - Andrews gathered data from 1960 to
1964 of non-orthodontic normal models.
• Key I – Molar relationship
• the distal surface of distobuccal cusp of upper
first permanent molar occluded with the mesial
surface of the mesiobuccal cusp of the lower
second molar.
• The closure the distal surface of buccal surface
of distobuccal cusp of upper first permanent
molar approaches the mesial surfaces of the M-B
cusp of lower second molar, the better the
opportunity for normal occlusion.

• Key II Crown angulation (Tip)
• The gingival portion of the long axis of
the all crowns was more distal than the
incisal portion.
• The degree of crown tip is the angle
between the long axis of crown and a line
bearing 90˚ from the occlusal plane.
• It varied with each tooth type, but within
each type tip patterns was consistent from
individual to individual.

• Key III Crown inclination
• crown inclination refers to the labiolingual or buccolingual
inclination of long axis of the crown, not to the inclination
of long axis of entire tooth.
• Crown inclination is expressed in plus or minus degrees. A
plus reading is given if the gingival portion of the crown is
lingual to the incisal portion. A minus reading is recorded
when the gingival portion of the crown is labial to the
incisal portion.
• a) Anterior crown inclination:
properly inclined anterior crowns contribute to normal
overbite and posterior occlusion, when too straight-up and
down they lose their functional hormony and overeruption
results. Inclination should be positive in this categary of
teeth.

• b)Posterior crown inclination (upper) :A
minus crown inclination should exist in
each crown from the upper canine
through the upper second premolar . A
slightly more negative crown inclination
exists in the upper first and second
molars.
• c) posterior crown inclination (lower): A
progressively greater minus crown
inclination exists from the lower canine
through lower second molar.

• Key IV – Rotations
• The fourth key to normal occlusion is that the teeth
should be free of undesirable rotations.
• Key V – Tight contacts
• The fifth key is that the contact points should be
tight (no spaces).
• Key VI – Occlusal plane or curve of spee
• The planus of occlusion found on normal models
ranged crown flat to slight curves of Spee.
• Even though not all of the non-orthodontic normal had
flat planes of occlusion, flat plane should be a treatment
goal as a form of over-treatment. There is a natural
tendency for curve of Spee to deepen with time.
• Intercuspation of teeth is best when the plane of
occlusion is relatively flat.

Thank you
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Normal occlusion 1

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