Basic Occlusion

Chapter 6
Occlusion
Copyright © 2014 by Mosby, an imprint of Elsevier Inc.
Copyright © 2003 by Mosby, Inc., an affiliate of Elsevier Inc.
Previous editions copyrighted 1977, 1982, 1986, 1990, 1994, 1998.

 The eruption pattern, facial development, and
sequence in which tooth buds begin forming all
contribute to the eventual relationship of the
teeth and jaws.
Position and Sequence of Eruption
2

 The development of occlusion begins with the
eruption of the primary teeth.
 The mandibular central incisors are usually the
first to erupt followed by the maxillary central
incisors.
 The eruption of the lateral incisors, which occurs
next, follows the same sequence.
3

 The primary molars establish:
The vertical height of the primary occlusion.
Intercuspation; the mesial-distal and buccal-lingual
relationship determining how the upper teeth will
touch, hit, and interlock with the lower teeth.
4

 The upper primary molars also help establish
the anteroposterior (mesial-distal) relationship of
the remaining deciduous teeth because their
presence prompts the canines and second
deciduous molars to erupt around them.
5

 The primary dentition erupts in a more upright
position than secondary teeth replacements.
 The average overjet of primary teeth is 3.0 mm,
and the average overbite is 2.5 mm.
6

 Primary occlusion has three anteroposterior
molar relationships called steps or planes.
 Most children have a mesial step where the
mandibular molars are more mesial than their
maxillary counterparts (A).
 A smaller group of children exhibit a flush
terminal plane where the distal of the deciduous
second molars are even with each other (B).
 A still smaller minority has a distal step (C).
7

8

 Growth of the mandible and maxilla results in
horizontal and vertical growth of the dental
arches.
The teeth, however, remain the same size, creating
spaces called diastemas.
 The largest spaces are often found mesial to the
maxillary primary canines and distal to the
mandibular canines.
 As growth continues, diastemas also develop
between the incisors.
9

 These spaces are called primate spaces, and
although not always present, they are
characteristic of all primates, including man.
10

 The permanent molars erupt and touch the distal
surfaces of the deciduous molars.
 They cause a chain reaction that pushes all of
the spaces between the teeth closed.
 A mesial step occurs because closing the
primary space allows room for the lower molars
to move mesially.
Development of the Mesial Step
11

 A mesial step is further enhanced as the
deciduous molars exfoliate and are replaced by
the narrower permanent premolars.
 Extra space, called leeway space, is gained from
this exchange of the second premolars.
12

 The earlier eruption of
the mandibular teeth
before the maxillary
teeth further helps
establish the mesial
step.
13

 The heads of the condyles of the mandible continue
to grow later than the maxilla.
This mesial advancement heads the patient toward a
class I relationship.
 If further growth of the condyle head occurs, an
extreme mesial step results in a class III relationship.
 A class II relationship results if the mandible does not
continue to grow or if the maxilla outgrows the
mandible.
 It is possible for this type of relationship to occur on
just one side.
14

 A deep bite could result if the:
Condyle head is displaced distally in the glenoid
fossa.
Posterior teeth do not erupt enough.
Muscles of mastication are so hyperactive that they
prevent the eruption of the posterior teeth.
The condyle grows at an angle that causes the jaw to
develop in a less mesial direction.
15

 The development of occlusion is further
influenced by hereditary factors such as
congenitally missing teeth, impacted teeth, or
the size and shape of muscle and bone.
 Controllable factors that also affect occlusal
development include the premature loss of
deciduous teeth, decayed teeth that were not
restored, and harmful habits.
16

 The balance or equilibrium between the tongue
and the facial muscles allows the teeth to be
brought into proper alignment and to be
maintained in their proper positions once they
have erupted.
 If this balance is disturbed, a malocclusion, or an
abnormal alignment of the teeth within the dental
arches, can result.
Horizontal Alignment
17

 Abnormal forward
thrusting of the
tongue against the
anterior teeth can
cause such an
imbalanced state.
 Tongue thrusting
causes the maxillary
anterior teeth to
protrude labially.
18

 An opposite situation can occur if the lower lip is
constantly tightening against the lower anterior
teeth.
The lower teeth will be pushed back into the mouth by
this overdeveloped lower lip.
19

 The intercuspation of the teeth helps prevent
tooth deviations in a buccal or lingual direction.
When the jaws are closed, the buccal cusps of the
mandibular posterior teeth are interlocked between
the buccal and lingual cusps of the maxillary teeth.
20

 Alignment of previously erupted teeth affects the
alignment of successive teeth.
 Adequate space is needed between teeth to
allow for complete eruption of more teeth.
 If a tooth does not have room enough it will erupt
out of alignment.
It could also be blocked entirely and never erupt.
21

 Other factors that influence the alignment of
teeth:
Mesial drift.
Size and shape of the jaws.
Shape of the teeth.
22

 The buccal cusp tips of posterior teeth have a
fairly even curve in an anterior to posterior
direction known as the curve of Spee.
The curve of Spee deepens with age.
Curve of Spee, Curve of Wilson, and
Sphere of Monson
23

Sphere of Monson
 An occlusal curve exists for posterior teeth in a
direction from right to left called the curve of
Wilson.
24

Sphere of Monson
 The curves of Wilson
and Spee, in three-
dimensional alignment,
demonstrate an
illusion of the cusp tips
of the mandibular
posterior teeth resting
on a sphere known as
the sphere of Monson.
25

Vertical Alignment
 Teeth are not
positioned straight up
and down in the
mouth.
 The mandibular
posterior teeth have a
tendency to tip their
crowns lingually and
their roots laterally.
26

Vertical Alignment
 The maxillary
posterior teeth keep
the crown with a slight
buccal inclination and
a lingual inclination of
the root.
27

 From a lateral view all the teeth show a slight
mesial inclination, with the possible exception of
the maxillary third molar.
 Anterior teeth have a slight labial protrusion and
their crowns seem to incline laterally.
In other words, the anterior teeth tip out to the side
and toward the front.
Vertical Alignment
28

Vertical Alignment
29

 Occlusion describes the relationship of the
mandibular and maxillary teeth when the teeth
are closed together or during excursive
movements when the teeth are touching.
Occlusion
30

 When the jaws are closed, two possible
relationships occur:
1. A relationship of the upper jaw to the lower jaw
(centric relation).
2. A relationship of the upper teeth to the lower teeth
(centric occlusion).
Occlusion
31

Centric Relation
 Centric relation is defined as the most retruded
relationship of the mandible to the maxillae when
the condyles of the temporal mandibular joint are in
their most upward, backward, and unstrained
position in the glenoid fossae.
Occlusion
32

Centric Occlusion
 Centric occlusion is determined by the way the teeth
fit together.
 It is sometimes called acquired centric occlusion,
habitual occlusion, convenience occlusion, or
intercuspal position (ICP).
Occlusion
33

Occlusion
 With the jaws closed, the occlusal surfaces of
the maxillary teeth touch the occlusal surfaces of
the mandibular teeth.
34

Occlusion
 Lingual cusps of
upper posterior teeth
rest in the occlusal
surfaces of lower
posterior teeth.
 Buccal cusps of lower
posterior teeth rest in
the occlusal surfaces
of upper posterior
teeth.
35

 When the jaws are closed in centric occlusion,
the cusps of the maxillary teeth overlap the
cusps of the mandibular teeth.
 The amount of horizontal overlap of the
maxillary teeth is called an overjet.
Occlusion
36

Occlusion
 Line A represents the amount of horizontal
overlap, or overjet.
37

Occlusion
 Line A indicates the amount of vertical overlap,
or overbite.
38

Occlusion
 Overbite is the extension of the incisal edges of
the maxillary anterior teeth below the incisal
edges of the mandibular anterior teeth in a
vertical direction.
39

Occlusion
 If one or more teeth in the mandibular arch are
located facial to their maxillary counterparts, a
condition known as crossbite occurs.
 Shown here is a mandibular right first molar in
crossbite.
40

 A crossbite can exist between any number of
teeth.
 Acromegaly is a condition where a crossbite of
all the mandibular teeth occurs.
In this disease, growth hormone causes the mandible
to grow faster than the maxilla.
Occlusion
41

 Crossbite can also occur if the maxillae bones
do not grow in proportion to the mandible.
When this happens the maxillary teeth are edge to
edge with the mandibular teeth.
Occlusion
42

Open Bite
 If the anterior teeth are widely separated in
centric occlusion, the condition is known as an
open bite.
The anterior teeth of the maxillary arch do not overlap
the mandibular teeth in a vertical direction.
43

 An open bite can be caused by either a thumb-
sucking or a tongue-thrusting habit.
In either situation a powerful force is exerted against
the anterior teeth when the jaws close.
Open Bite
44

 There are two basic classifications of occlusion:
1. Skeletal; based on the relationship of the bone of
the maxilla to the bone of the mandible.
• Referred to as skeletal classification.
2. Dental; based on the relationship of the teeth of the
mandible to the teeth of the maxilla.
• Referred to as dental classification.
Occlusal Classification
45

 Skeletal classification is divided into three
classes of relationship:
Class I: The maxilla and mandible are in normal
relationship to each other.
Class II: The mandible is retruded.
• Retrognathic.
Class III: The mandible is protruded.
• Prognathic.
46

47

 Angle’s classification system is the most popular
dental classification system in use today.
 It is based primarily on the relationship of the
permanent first molars to each other and, to a
lesser degree, on the relationship of the
permanent canines to each other.
 It is possible for classification to be different on
different sides.
48

 Class I relationship (neutroclusion) is the normal
occlusal relationship.
The mesiobuccal cusp of the maxillary first molar is in
line with the buccal groove of the mandibular first
molar.
49

 A class II occlusal relationship exists when the
buccal groove of the mandibular first molar is
posterior to the mesiobuccal cusp of the
maxillary first molar.
50

 Class II contains two separate divisions.
1. Class II, division I
a. First molars are in class II with maxillary central incisors in
their normal position.
2. Class II, division II
a. First molars are in class II with the maxillary central incisors
retruded and inclined lingually.
51

 A class II, division II relationship often occurs
when there:
is a deep overbite.
are crowded maxillary anteriors.
is normal overjet.
is excessive masseter muscle development.
52

 A class III occlusal relationship exists when the
buccal groove of the mandibular first molar is
more anterior than normal to the mesiobuccal
cusp of the maxillary first molar.
53

 Canine classification:
Class I: the distal of the mandibular canine is within a
premolar’s width of the mesial of the maxillary canine.
Class II: the distal of the mandibular canine is distal to
the mesial of the maxillary canine by at least the width
of a premolar.
Class III: the distal of the mandibular canine is mesial
to the mesial of a maxillary canine by at least the
width of a premolar.
54

 Incisor relationships.
Class I: Mandibular incisors occlude with or lie directly
below the middle of the lingual surfaces of the
maxillary incisors (A).
55

Class II: Mandibular incisors lie behind the middle of
the lingual surfaces of the maxillary incisors.
• Division I - maxillary centrals are protruded (B).
• Division II - maxillary centrals are tipped lingually (C).
56

Class III: The mandibular incisors lie in front of the
middle of the lingual surface of the maxillary incisors
(D).
57

Lateral Mandibular Glide (Lateral
Excursion)
 In lateral excursion the mandible moves toward
the right or left side.
The side to which the mandible moves is referred to
as the working side, and the other side is referred to
as the nonworking side.
58

 In lateral mandibular glide, only a few pairs of
cusps make occlusal contact.
The canines carry the bulk of the contact.
• This is referred to as a canine rise because the mandibular
canine opens the bite by gliding down the lingual surface of
the maxillary canine.
Excursion)
59

 It is not uncommon to have the premolars
occluding in lateral excursion.
 When the premolars also occlude it is called
group function.
Excursion)
60

 Protrusion is when the mandible moves forward
from centric occlusion.
 The only teeth that should touch are the anterior
teeth.
Protrusion
61

 When the jaw closes, all of the posterior teeth
should come into contact at the same time.
 If one tooth hits more than the others, it becomes
an interference and bears more force than the
others, becoming a premature contact area.
 The anterior incisors may also hit but not harder
than the posteriors.
 If the anteriors do hit it is called anterior coupling.
Premature Contact
62

 A premature contact causes the jaw to deflect
before allowing the rest of the teeth to occlude.
 This deflection puts the temporomandibular jaw
joint into a stretched or abnormal position.
Premature Contact
63

 The following may result from a premature
contact:
Damage to the ligaments or muscles of the
temporomandibular joint.
Tired, sore, and tender muscles.
The tooth hitting prematurely becomes sensitive.
The responsible tooth may become cracked or
broken.
Premature Contact
64

Fundamentals of Ideal Occlusion in
Permanent Dentition
Stolarized Molar
 The upper first molar is
tipped forward so its
distal marginal ridge
touches the mesial
marginal ridge of the
lower second molar and
the middle of the
mandibular first molar.
65

Permanent Dentition
 Incisal wear such as
that seen in
prehistoric human’s
class II, division II
malocclusion may
cause exposure and
death of the tooth
pulp.
66

Permanent Dentition
 Incisal wear such as
that seen in
prehistoric human’s
class III malocclusion
may cause pulp
exposure.
67

 Ideal occlusion is the result of the maxillary
bones and the mandibular bone in proper
harmony with each other, with the condyles of
the mandible in their most favorable location
within the glenoid fossae and the muscles of the
face and jaws in balance with each other.
 The occlusion of the teeth is most stable when
all of the bones, muscles, and joints are
synchronized in balance and harmony with one
another.
Permanent Dentition
68

Basic Occlusion

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