Occlusal force Distribution...........

force distribution
I- Alignment of the teeth in the arch
- Dental arch design: Bownwill triangle, parabolic curves
- Compensatory occlusal curvature of dental arches: curve of spee, Wilson, Monsoon.
- Axial teeth angulation relative to median and horizontal plane: anterior and posterior teeth
- Compensatory axial curvature

II- Relation of teeth to centric occlusion

A- Functional form of crown at incisal and occlusal thirds
- Curved occlusal surface
- Occlusal embrasure
- Self-occluding design

B- Pattern of incisal and occlusal contact relation:
Ridge to fossa, cusp to fossa, cusp to ridge, cusp to sulcus, cusp to embrasure.

C- Facial relation of opposing teeth in centric occlusion:
Offset relation, overjet relation, overbite relation

D- Occlusal contact and inter-cusp relation of teeth in centric occlusion
Shearing or guiding cusp, stamp or supporting cusp, centric stops
Force acting on the teeth:
Occlusal force, growth, mastication, proximal contact muscle tonus
Types of force of occlusion:
Forward force, distal and lingual force, anterior resultant force

1. 1

Occlusal force distribution Dr. Mohammed Alruby











Occlusal
Force
Distribution









Prepared by:
Dr. Mohammed Alruby

2. 2

Occlusal force distribution Dr. Mohammed Alruby

Occlusal force distribution
I- Alignment of the teeth in the arch
- Dental arch design: Bownwill triangle, parabolic curves
- Compensatory occlusal curvature of dental arches: curve of spee, Wilson,
Monsoon.
- Axial teeth angulation relative to median and horizontal plane: anterior and
posterior teeth
- Compensatory axial curvature

II- Relation of teeth to centric occlusion

A- Functional form of crown at incisal and occlusal thirds
- Curved occlusal surface
- Occlusal embrasure
- Self-occluding design

B- Pattern of incisal and occlusal contact relation:
Ridge to fossa, cusp to fossa, cusp to ridge, cusp to sulcus, cusp to embrasure.

C- Facial relation of opposing teeth in centric occlusion:
Offset relation, overjet relation, overbite relation

D- Occlusal contact and inter-cusp relation of teeth in centric occlusion
Shearing or guiding cusp, stamp or supporting cusp, centric stops
Force acting on the teeth:
Occlusal force, growth, mastication, proximal contact muscle tonus
Types of force of occlusion:
Forward force, distal and lingual force, anterior resultant force

3. 3

Occlusal force distribution Dr. Mohammed Alruby
Occlusal force distribution

In latin oc: means, up ------- clusion: means, closing
Occlusion: the occlusal contact between maxillary and mandibular teeth
Centric occlusion: maximum intercuspation between maxillary and mandibular teeth

Static occlusion: when jaws are closed together and teeth are in contact
Dynamic occlusion: occlusion occurs during mandibular movement

The maxillary arch is larger than the mandibular arch giving horizontal space between upper
and lower teeth during occlusion called overjet
Also upper anterior teeth are overlap the lower teeth and the vertical distance between called
overbite

It should be made clear that both the form and functional activities of dental mechanism, as a
whole or in part, exhibit that curvature is the basic rule, this concept has been referred to as
(spherical congruency) by Maxwell and it generally means that:
- Tooth surface are curved
- Lines bisecting the tooth from any aspect exhibit some degree of curvature
- Teeth are aligned in either jaw to form arch
- Mandible operates in a curved path
- Occlusal and incisal surfaces adapt themselves to curved planes

Basic of ideal alignment and occlusion of permanent teeth:
I- Alignment of teeth in the arch:
a- Dental arch design
b- Compensatory occlusal curvatures of dental arches (curved occlusal planes)
c- Axial teeth angulation relative to median and horizontal planes (angulated tooth axis)
d- Compensatory axial curvature of individual teeth
II- Relation of teeth in centric occlusion:
a- Functional form and inter-occlusal relation at incisal and occlusal thirds
b- Occlusal contact and inter-cusp relation in centric occlusion
c- Facial relation of teeth in centric occlusion
d- Pattern of incisal and occlusal contact

I- Alignment of teeth in the dental arches:
A- Dental arch design:
a- Parabolic curve:
Upper and lower arches are horse – show shape from the occlusal view, the facial and lingual
outline of dental arch conform to a parabolic curve:
- Anterior segment: semicircular and equally bisected by midline include facial surface of
anterior teeth
- Middle segment: straight line, continuous with the anterior segment in buccal direction
include, 1
st
, 2
nd
premolars and mesial half of 1
st
molar
- Straight line parallel to the midline of jaw, slightly directed to the midline in maxillary
dental arch
Buccal outline of upper molar curves toward the midline more than the lower due to:
a- 2
nd
, 3
rd
molars upper located lingually to 1
st
molar

4. 4

Occlusal force distribution Dr. Mohammed Alruby
b- Distal convergence of 1
st
maxillary molar
b-Bownwill triangle:
it may also term mandibular triangle, as the mandible is seen occlusally it is adapted to
equilateral triangle, its angles are at the centers of both condyles and mesial contact area of
mandibular central incisors. Though most mandibles conform to 4 inches’ equilateral triangle,
however variables are always likely to be present, Bownwill claims that this triangle, with
double joint permits the largest number of teeth to antagonize at every movement for jaw
articulation















B- Compensating occlusal curvatures of dental arch (curved occlusal plane):
According to the principle of (spherical congruency), when the teeth are normally aligned in
the jaws, their occlusal and incisal surfaces adapt themselves to curved planes. The occlusal
surface of mandibular teeth is conforming to concave plane, while that of maxillary teeth
conform into convex plane therefore as the mandibular teeth are brought to contact the
maxillary one in centric occlusion, the concave mandibular occlusal plane identical to the
maxillary convex occlusal plane so that is why termed compensatory occlusal curvatures

Curve of Spee:
It describes that the incisal and occlusal surfaces of teeth in either dental arch when they are
seen buccally opposite to 1
st
molars, they follow a curve running anterior posterior parallel to
the sagittal plane and ending at the anterior surface of condyle

Curve of Wilson:
It describes that the occlusal surfaces of right and left posterior teeth conform to a transverse,
bilaterally extending curve that parallel
Wilson curve may be created since the mandibular buccal cusps push the maxillary buccal cusps
during the lateral chewing movements, the forces generated cause the buccal inclination of the
crown of maxillary posterior teeth while the mandibular posterior teeth crown incline lingually
This curve is parallel to coronal plane and perpendicular to curve of spee. Since, the teeth
inclination progress distally so the Wilson curve becomes deeper in the molar segment than
premolar segment
The occlusal surface of teeth in either dental arches are approximately conforming to sphere
of 8 inches in diameter that could rest on buccal cusps of mandibular posterior teeth

5. 5

Occlusal force distribution Dr. Mohammed Alruby
Curve of Monson:
Monsoon 1932, proposed that, the occlusal surfaces of teeth in normally developed mandibular
arch conform to the outer surface of a segment of sphere
The center of Monson sphere is in the Glabella point with radius of about 4 inches that is
equidistant from the occlusal surface of posterior teeth and from the centers of condyle




C- Axial teeth angulation to median plane and horizontal planes (angulated tooth axis):
The line of exerted force during occlusion should be parallel to the axial angulation of teeth, so
every tooth must position in the dental arch at advantageous angle that adequately withstand
the force brought against it during function
Anterior teeth:
Labially:
The axial inclination makes then crown of anterior teeth point toward median plane while their
roots are distally displaced away from the median plane
The significance of teeth angulation is the stabilization of proximal contact relation and the
promotion of mesial drift of teeth
The maxillary incisors are placed so that their long axis makes little less than right angles to
the horizontal plane but make more acute angles to median plane
Maxillary canine show more axial angulation, that is less acute angle to median plane than do
the incisors
Axial angulation of lower anterior teeth may approximate the right angles to the horizontal
plane than do the maxillary teeth

Proximally:
The maxillary incisors are placed with their long axes forming about 60 degree to horizontal
plane, while the long axis maxillary canine makes less acute angles than the incisors do with
the same plane
Mandibular anterior teeth have generally similar sequence of axial angulation but with less
extent than that occurring in their maxillary counterpart

6. 6

Occlusal force distribution Dr. Mohammed Alruby
Posterior teeth:
The general principle which controls the angulation of posterior teeth may be derived from the
sphere theory of Monson SO, the long axis of posterior teeth from extension of radius arising
from the center of sphere at Glabella to end with different angulations on occlusal surface of
posterior teeth.
Facial:
The long axis of the teeth upper and lower inclined at the crown end mesially while its apical
end points distally, the distal root inclination progress in distal direction
Proximally:
Long axis of maxillary posterior teeth inclines buccally at the crown end lingually at apical end
the reverse is true in respect to the mandibular posterior teeth, however this inclination becomes
progressively increased in anterior posterior direction, SO the molars angulation is greater
than of premolars

D- Compensating axial curvatures of teeth (curved tooth axis):
== the long axis of maxillary and mandibular teeth in centric occlusion from any aspect are not
perpendicular to the horizontal or occlusal plane
== any line bisecting the crown and the root of a tooth from any aspect when extended
Coronally or apically, it will draw a curve or arc
The axial arcs passing through the 1
st
molars and any tooth anterior to them, may form circles
of equal radius. The axes of these circles are on a line parallel with occlusal surface of
mandibular 1
st
molar. The long axis of teeth posterior to 1stThe long axis of teeth posterior to
1
st
molar described molar describe arcs of small circles

Significant of curved tooth axis:
- Occlusal balance: occluso-axial interdigitation: because the compensatory curvature not
establish the occlusal balance and there is individual curvature of the teeth
- Prevention of distal teeth drift: because the axis of 2
nd
, and 3
rd
molars are greater curve
than other so prevent distal drift
- Promotion of mesial teeth drift: because the axis of 2
nd
, and 3
rd
molars are greater so
make force when opposing with lower lead to mesial movement of teeth.
- Stability of normal occlusion: the curvature of the teeth axes allows the occlusal forces
to pass in curved path, this will not disturb the occlusion or teeth angulation, where:
a- The curved path of forces conforms better to the physical law than the forces
transmitted through the straight course
b- The accommodation of the curved tooth axes to the curved occlusal planes of dental
arch

II- Relation of teeth in centric occlusion:
A- Functional form of the crown at the incisal and occlusal third:

1- Curved occlusal surface:
the working part of tooth crown should have curved surfaces as those of ridges, cusps, fossa,
sulci. The curved surface may be concave or convex which are in contact with the convex or
concave surface of opposing tooth
Significant of curved crown surface:
i- Development of spillways around the contact of the opposed curved surface allowing
escapement of food between the teeth

7. 7

Occlusal force distribution Dr. Mohammed Alruby
ii- Considerable reduction of occlusal forces since they are produced at points rather
than great forces elaborated if forces are plane
iii- Teeth are used as cutters for food rather than to exert mashing effect produced if the
surface are plane
iv- Flexibility of occlusal adjustment since the curved surfaces secure occlusal contact
with minimal mandibular displacement and can keep this contact during various
mandibular movements

2- Occlusal embrasure (escapement spaces):
As the teeth come into centric occlusion or make contact during various mandibular movements,
the curved surfaces of the crown in one dental arch, contact similar crown surface in the other
dental arch.
While the curved surfaces of opposing crowns provide cutting food at their points of occlusal
contact, there is an escapement space developed around the point of occlusal contact during
centric occlusion
Significant of occlusal embrasure:
i- Provide escapement spaces for food between the occluding teeth during mastication
ii- Secure self-cleansing effect for the teeth and gingiva through the frictional flow of
saliva, fluids, and food during mastication

3- Self-occluding design:
The functional form at incisal and occlusal thirds of teeth is manifested with the presence of
elevations as cusps and ridges as well as depressions as fossa, sulci and embrasure
The depression of the crown in either dental arch interlock within the depression of crowns in
the opposing dental arch during centric occlusion. This is referred as (mortar and pestle
principle).
Significant of self-occluding design:
i- Establishment and maintenance of the proper functional alignment of teeth in either
dental arch which subsequently results in a normal relation of opposing teeth
ii- Determination of efficient masticatory function for teeth through the inter-cusp
relation during centric occlusion and the various mandibular movements

B- Patterns of the incisal and occlusal contact relations:
The curved surfaces of the opposing teeth may elaborate one or more of the following patterns
of incisal and occlusal contact relation when they are brought at centric occlusion:

1- Ridge to fossa:
This well seen when the incisal ridge of mandibular anterior teeth rests in the lingual fossa of
maxillary anterior teeth in centric occlusion

2- Cusp to fossa:
This occlusal contact is established when:
a- Lingual cusps of maxillary posterior teeth rest into fossa of mandibular opposing as:
= lingual cusps of maxillary premolars fits into the distal fossa of their mandibular namesakes
= mesio-lingual cusp of maxillary molar fits into the central fossa of their mandibular
namesakes which is important in:
Serving good masticatory function
Most effective in stabilizing the alignment teeth

8. 8

Occlusal force distribution Dr. Mohammed Alruby
b- Buccal cusps of mandibular posterior teeth rest into the fossa of their maxillary
opponents as:
= distobuccal cusp of mandibular molar rest into the central fossa of their maxillary namesakes
= buccal cusp of 2
nd
mandibular premolar rets into the mesial fossa of its maxillary namesakes

3- Cusp to ridge:
This relation is established when the tip of cusps contacts the opposing proximal ridges in
centric occlusion and occurs when:
= buccal cusp tip of mandibular premolars contacts the mesial ridges of their maxillary
namesakes
= mesiobuccal cusp tip of mandibular molars contacts the adjacent proximal ridges of their
maxillary namesakes and the tooth mesial to their namesakes
= disto-lingual cusp tip of maxillary molars contacts the mesial ridge of mandibular molars
distal to their namesakes

4- Cusp to sulcus:
This relation is established when triangular ridge of cusps become accommodated into the sulci
of the opposing teeth in centric occlusion it is occurs when:
= triangular ridge of buccal cusps of maxillary molars are accommodated into the sulci of
buccal groove of mandibular molars
= triangular ridge of disto-lingual cusps of mandibular molars are accommodated into sulci of
the lingual groove of maxillary molars
= triangular ridge of disto-buccal cusp of mandibular molar is accommodated into the sulcus
of buccal groove of maxillary molars.

5- Cusp to embrasure:
Which seen during centric occlusion occurs when:
= buccal cusp of maxillary canine and premolars and the disto-buccal cusp of maxillary molars
rest into the buccal embrasure between their namesakes and the teeth distal to them
= mesio-lingual cusp of mandibular molars and the lingual cusp of mandibular premolars
between their maxillary namesakes and teeth mesial to them

9. 9

Occlusal force distribution Dr. Mohammed Alruby
C- Facial relation of opposing teeth in centric occlusion:
There some fundamental characteristic features which can be seen facially between the
opposing teeth as they come into centric occlusion including:

1- Offset relation:
Definition: each tooth in either dental arch when seen facially, occludes with parts of two
adjacent teeth in opposite arch except the mandibular central incisor and maxillary 3
rd
molars
that only occlude with their namesakes
Etiology: the development of offset relation of opposing tooth due to:
- Less mesio-distal diameter of the mandibular anterior teeth than that of maxillary
anterior teeth, this pushes the mandibular teeth to be their maxillary opponents
- Less facial measurement of the mandibular jaw than that of the maxillary jaw pushes the
mandibular arch with its teeth to indirect teeth opposition
Significance:
- Maintenance of normal occlusion following tooth loss, since each tooth in either dental
arch occludes with two teeth in the opposing arch, so the loss of tooth in one arch does
not disturb the occlusion of opposing tooth
- Prevention of supra-eruption of teeth, the tooth opposing to the lost one is prevented from
supra-eruption since it is still partly controlled and occluding with the tooth adjacent to
the lost one
- Equalization and distribution of masticatory forces: the offset arrangement of teeth
allows shearing of masticatory load among them that subsequently reduces the forces
transmitted to jaw bone and the periodontium
- Mesial location of mandibular teeth relative to maxillary teeth, this occurs in all teeth
except mandibular central incisor.

2- Overjet relation:
Definition: is the horizontal relation between maxillary and mandibular teeth in centric
occlusion where the incisal edges and buccal cusps of maxillary teeth extended facial to their
corresponding in mandibular teeth
This relation results in:
- Lingual cusps of maxillary posterior teeth rests in occlusal fossa of mandibular posterior
teeth
- Buccal cusps of mandibular posterior teeth rest in the occlusal fossa of maxillary
posterior teeth
- Maxillary anterior teeth facially relate to mandibular anterior teeth
Etiology: overjet relation is developed due to:
- Smaller mandibular dental arch than the maxillary dental arch
- Lingual angulation of crowns of posterior teeth relative to crowns of maxillary posterior
teeth
Significance:
- Establishment of facio-lingual inter-cusp relation when mandibular teeth come into
centric occlusion with their maxillary opponents
- Protects the cheeks, lips, and tongue biting during mastication by preventing them from
being interposed between the maxillary and mandibular teeth

3- Overbite relation:

10. 10

Occlusal force distribution Dr. Mohammed Alruby
Definition: it is the vertical overlap between maxillary and mandibular anterior teeth in centric
occlusion
Etiology: occurs due to greater parabolic curvatures, particularly in anterior segment of
maxillary arch than that of mandibular arch
Significance:
- Permits functional mandibular movement against the maxillary arch without interference
with occlusal relation
- Proper overbite enables the guidance of mandibular canines to safety disengage the
occlusion of posterior teeth
- Proper overbite of incisors and canine enables the posterior maxillary and mandibular
teeth to only contact upon the centric occlusion
- Improper overbite causes traumatic injury to the adjacent gingiva as in severe overbite
which termed close or impinging overbite














D- Occlusal contact and inter-cusp relation of teeth in centric occlusion:
For perfect occlusal and functional contact of the opposing teeth to be established a satisfactory
cusp of fossa relation should mainly occur during centric occlusion
1- Shearing or guiding cusps:
They do not occlude in the inter-cusp relation since they are free of contact and not involved in
the opposing fossa, they include the lingual cusps of mandibular posterior teeth and buccal
cusps of maxillary teeth

2- Stamp or supporting cusps:
They do occlude in the inter-cusp relation into opposing fossa or proximal ridges as they come
into centric occlusion, they include:
- Lingual cusps of maxillary teeth
- Buccal cusps of mandibular teeth
- Incisal ridges of mandibular teeth

3- Centric stops:
They are the points or the circumscribed areas of occlusal contact made by the highest contour
of supporting cusps on the occlusal surface of the opposing teeth in centric occlusion

11. 11

Occlusal force distribution Dr. Mohammed Alruby

12. 12

Occlusal force distribution Dr. Mohammed Alruby
Forces acting on the teeth

The force acting on the teeth and cause them to move within their periodontal tissues vary in
magnitude, duration, frequency, and direction
The response of the teeth depends on:
- Shape and length of the roots
- Characteristic of the fluid content of periodontal space
- The composition and orientation of periodontal fibers
- Extent of alveolar bone
The displacement which tooth can make, divide into translator and rotational components, each
component can be divided into, apical, mesial, distal, buccal, lingual translation and rotational
component
Tooth can be displaced in one or more of these motion and the results is a directional movement
in response to force
These movements reach a limit when the periodontal receptors cause reflex stoppage of the
force or when an equal opposing force is reached
Muscle force:
The muscles of the tongue on one side of teeth and lips and cheeks (oro-facial muscle) maintain
the varying source of horizontal forces on the teeth. The activities of these muscles conform to
stable pattern throughout the life. Oro-facial muscle activity produces movement of the teeth

Occlusal force:
The position of each tooth within the jaw is maintained by curtained factors knowns as occlusal
forces, normally there is a balance between these forces which produce a harmonies
relationship of the teeth to each other
Any imbalance of these forces must affect the normal relationship of the teeth and / or arches
The occlusal forces may be due to: growth, muscle tonus, proximal contact, and mastication.

1- Growth:
Normal downward and forward growth of the face by harmonizing the size and form of jaw with
the teeth may produce effect on position of the teeth
Not only should the size of the jaw be adequate but also their relation should be correct. To
achieve this, it is necessary that:
- The growth of all those bones that contribute to the formation of the face should be
proportionate
- Growth of soft tissue particularly muscles should be harmonies

2- Muscle tonus:
It is continuous and passive partial contraction of the muscles force generated by the muscles
may be either:
a- Passive: due to muscle tonus which is continuous but very light
Certain muscle exerts a constant tension (muscle tonus) upon the jaws at rest a muscle is in
state of tonus, in this state small proportion of fibers are contracted but they are always the
same fibers
Muscles elevate the mandible: masseter, temporalis, medial pterygoid
Muscles depressed the mandible: lateral pterygoid

13. 13

Occlusal force distribution Dr. Mohammed Alruby
Muscles which have a direct effect on the jaw or dentoalveolar structures are those of
deglutition, expression, and mastication:
Deglutition: soft palate, pharynx, muscles of mouth
Expression: buccinator, orbicularis oris, mentalis
Mastication: masseter, temporalis, lateral pterygoid, medial pterygoid

Tongue applied force to the lingual surface of the teeth, hard and soft palate, lips and cheeks
applied force on the buccal surface of the teeth
= upper anterior teeth are prevented from moving labially by lip pressure and the lower incisors
by the overbite of upper
= there is a tension from the orbicularis oris muscle on upper anterior teeth and the buccinator
muscle limits buccal movements of upper third molars causing upper dental arch to assume in
horse shoe shaped
When an individual is at rest, the mandible is held in such a position that the upper and lower
teeth are normally separated by about 2 – 8mm in the premolar region which is called free-way
space or inter-occlusal clearance
The mandible position is maintained by the balance of muscle tonus, this balance effect not only
the vertical but also anterior posterior relation of teeth at rest

b- Active:
Fore exert pressure intermittently, the degree of force is larger than that of muscle tonus

3- Proximal contact:
This is continuous growth of bone at socket of teeth and at the crest of alveolar process

4- Mastication:
The force of mastication exerted on the teeth can be divided into: vertically, anterior posterior,
transversely

Force of occlusion can be divided into:
1- Forward force:
Designated as the anterior component force which become active with the eruption and
occlusion of 1
st
permanent molars, this forces produced by the relationship of the long axis of
the teeth to their occlusal surfaces and assisted by pressures of buccinator and masseter muscles

2- Distal and lingual forces:
Which act upon the incisors, the force is produced by orbicularis oris, zygomaticus, quadratus
labii superior and inferior, the mentalis and buccinator muscles. These forces keeping the
canines in their proper position in the arch

3- Anterior resultant force:
Guided by the proximal contact area of the teeth, each tooth in addition to its function in
mastication is an essential key in the dynamic balance of adjacent teeth and denture position