NORMAL OCCLUSION

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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.


THANK YOU

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