NORMAL OCCLUSION

NORMAL
OCCLUSION
Prof Hanan Ismail

Normal versus ideal:
In humans Normal implies variation around an
average or a mean, therefore normal is always a range
and never a fixed value, for example one cannot state a
solid figure for normal men height, but it is accepted
to say that normal height could be between 150 cm to
190 cm for instance.

In addition normality changes with age
therefore it is dynamic and indicates
biological adaptability. For example
presence of a diastema is normal during the
ugly duckling stage but not in an adult
occlusion.

An occlusion is considered to be normal when all
the teeth are present and occlude in a healthy
stable and pleasing manner.
On the other hand ideal connotes a hypothetical
concept rarely found in clinical practice

DEFINITION
Dictionary definition: Occlusion by
dictionary definition refers to the act
of closure or being closed.
•

ANGLE DEFINITION
The normal relation of the occlusal
inclined planes of the teeth when the jaws
are closed. (According to Dr. Angle, normal
occlusion exists when the mesiobuccal
cusp of the upper first molar occludes with
the buccal groove of the lower first molar).

MODERN DEFINITION
Dental occlusion is the static and
dynamic inter-relationships of the
opposing surfaces of the maxillary and
mandibular teeth that occurs during
movements of the mandible and when
the maxillary and mandibular dental
arches are in terminal approximation.

FEATURES OF NORMAL ADULT OCCLUSION
1-The arch form varies from a parabolic to a
horse-shoe shape. Lower arch is U shaped.
2-The maxillary arch occupies a greater arch
of a circle than the mandibular arch hence,
overbite and overjet exist between the
upper and lower teeth.

3-The permanent upper central incisor occludes
on its palatal aspect with the incisal edge of the
lower central and the mesial half of the incisal
edge of the lower lateral incisor, so each tooth
occludes with its opposing number and the tooth
distal to it ,with the exeption of the upper third
molars which occludes with the distal twothirds of
the lower molars.
Both arches have a common midline.

4-The triangular ridge of the mesiobuccal
cusp of the maxillary first molar occludes in
the mesiobuccal groove of the mandibular
first molar. Class I molars and
Canines occlude in class I, mesial slope of
the upper canine cusp occludes with the
distal slope of the lower canine.

5-Both dental arches have a common
occlusal plane with maximum
intercuspation during closure.

ORGANIZATION OF OCCLUSION
There are three concepts that describe the
manner in which teeth should and should not
contact in various functional and excursive
positions of the mandible:
1- Balanced occlusion
2-Group function occlusion
3- Canine guidance occlusion
Both 2 and 3 are nonbalanced occlusions

BALANCED OCCLUSION
WHEN FUNCTIONAL AND NON -
FUNCTIONAL SIDES CONTACT
SIMULTANEOUSLY IN EXCURSIVE
MOVEMENTS

SUITABLE FOR
COMPLETE DENTURES
Balanced Dentures are
less likely to be
dislodged
causing Denture Sores

NOT SUITABLE FOR NATURAL
DENTITIONS
BALANCED NATURAL DENTITIONS
ARE LIKELY TO CAUSE HEADACHES
AND TEMPOROMANDIBLAR JOINT
PROBLEMS

NONE BALANCED OCCLUSION
Called(functional=organic=physiologic=
mutually protected) and is found in natural
teeth and fixed prosthodontics. Where
during protrusive movement there is an
incisal guidance that disengages posterior
teeth, and during lateral movement there
is a canine or group guidance that
disengages the teeth on the non working
side.

WHAT IS A MUTUALLY PROTECTED OCCLUSION?
Treatment should go beyond just straightening the
front teeth, but should establish an ideal bite,
which protects the teeth, muscles and joints. A
mutually protected occlusion includes :
1-A lower jaw that is comfortably seated in the
joint.
2-There is even simultaneous contact of the back
teeth and light contact of the front teeth during
max intercuspation.
3-There should also be anterior guidance, cuspid
disclussion, and the elimination of balancing side
interferences to maintain good health of the teeth,

Lawrence Andrews discussed six significant
characteristics of normal occlusion which he
observed in a study of 120 casts of
nonorthodontic patients with normal
occlusion.
Andrews noted that the lack of one of the six
characteristics[which he called the keys to
normal occlusion]was an indication of
incomplete end result in treated models.

THE SIX KEYS TO NORMAL OCCLUSION:
(Significant characteristics of normal occlusion)
1-MOLAR RELATION:
a.The distal surface of the distobuccal cusp of
the first permanent molar contact and
occluded with the mesial surface of the
mesiobuccal cusp of the lower second molar.

.The mesiobuccal cusp of the upper first
permanent molar fell within the groove
between the mesial and middle cusps of
the lower first permanent molar.
c.The mesiolingual cusp of the maxillary
first molar was seated in the central
fossa of the mandibular first molar.

2.Crown Angulation(mesiodistal tip):
This term refers to the long axis of the
crown not the long axis of the entire
tooth.
In normal occlusion the gingival
portion of the long axis of the crown
was distal to the incisal portion
varying with the individual tooth
type.

The degree of crown tip is the angle between the
long axis of the crown as viewed from the buccal
or labial surface and a line bearing 90 degrees
from the occlusal plane.
A +ve reading is given when the gingival portion of
the long axis of the crown is distal to the incisal
portion. A –ve reading is given when the gingival
portion is mesial to the incisal portion.

Normal occlusion is dependent upon the
proper distal crown tip especially the
upper anterior teeth, since they have the
longest crowns. Let us consider that a
rectangle occupies a wider space when
tipped than when upright.Thus, the
degree of tip of the incisors determines
the amount of mesiodistal space they
occupy and has a considerable effect on
posterior occlusion as well as anterior
esthetics.

3-CROWN INCLINATION (Torque):
The crown inclination is the faciolingual
torque of the long axis of the crown. It is the
angle formed between the facial long axis of
the crown and a perpendicular line erected
from the occlusal plane.

It is +ve when the gingival portion
of the long axis of the crown is
lingual to the incisal portion and
vice versa.
In normal occlusion it is negative
for all the teeth except the
maxillary central and lateral
incisors.

Upper and lower anterior crown
inclination affect overbite and
posterior occlusion. Properly inclined
anterior crowns contribute to normal
overbite and posterior occlusion.
When too straight they lose their
functional harmony and over-eruption
results.

When the upper anterior crowns are
insufficiently inclined , the upper posterior
crowns become forward to their position or
spaces open between posterior and
anterior teeth.
When the anterior crowns are properly
inclined the posterior teeth are encouraged
into their normal position.

4-ROTATIONS:
In normal occlusion the
teeth should be free of
undesirable rotations.

5-TIGHT CONTACT:
In normal occlusion contact
points should be tight.

6-OCCLUSAL PLANE:
It is the imaginary plane on which
teeth meet in occlusion. In normal
occlusion it should be flat or nearly flat.
Intercupationis best when the plane
of occlusion is relatively flat.

A deep curve of spee results in a more
contained area of the upper teeth making
normal occlusion impossible (only upper
first premolers are properly intercuspated,
the remaining upper teeth anteriorly and
posteriorly are in error).
A reverse curve of spee is an extreme form
of treatment allowing excessive space for
each tooth to be intercuspally placed.

LECTURE REFERENCE
Text book of Orthodontics
Second edition
G.Singh
Jaypee
Lecture Reference:
Peter E. Dawson. Evaluation,
Diagnosis, and Treatment of
Occlusal Problems, 2nd ed.. Mosby.

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