Normal and abnormal occlusion For general practitioners Prepared by Dr. M Alruby Normal occlusion it is the usual or accepted relationship for species of teeth in the same jaw and those in the opposing jaw when the teeth are approximated in terminal occlusion and mandibular condyles are in centric position in the glenoid fossa Normal occlusion in deciduous dentition 1= except the deciduous molars all other teeth are spaced and this spacing is rule or at least not abnormal. 2= curve of spee is less marked than the permanent teeth because: = Short arch length anteroposterior. = The cusps of posterior teeth are short and occlusal plane is flat. 3= the buccal cusps of maxillary deciduous molars and the incisal edge of maxillary deciduous incisors overlaps the mandibular one but the degree of overlaps differ because of short cusps. 4= the maxillary incisors and canines are larger than the mandibular one and the mandibular molars are larger than the maxillary one. 5= the long axis of the teeth are nearly parallel to each other. 6= the midline rule and arch symmetry similar to the permanent dentition. 7= all the maxillary teeth except 2nd deciduous molars occlude with two opposing teeth Occlusal relationship of primary molars: 1= flush terminal plane: occurs where the primary erupt in an end to end fashion 2= A mesial step: is where the distal surface of the mandibular second primary molars is mesial to the distal surface of the second primary maxillary molar, that leads to Class I molars relationship 3= A Distal step: is where the distal surface of the mandibular second primary molar is distal to the distal surface of the second primary maxillary molars leads to class II molar relationship Figure (1): flush terminal plane figure (2) mesial step figure (3) distal step Characteristics of normal occlusion in permanent dentition: 1= each arch is regular with the teeth at ideal mesiodistal and buccolingual inclination and the correct proximal contact relationship at each interdental contact area. 2= All teeth must be angulated mesially. 3- The buccal surfaces of incisors are labially inclined, but from the canines posteriorly, the buccal surfaces are progressively more lingually inclined. 4=the dental arch relationships are such that: = each lower tooth except central incisors contact the corresponding upper tooth and tooth anterior to it. = the upper arch overlaps the lower arch anteriorly and laterally Six keys to normal occlusion: (1) Molar relationship: *- The mesiobuccal cusp of the upper 1st permanent molar falls within the groove between the mesial and middle cusps of the 1st permanent molar. *- The mesiopalatal cusp of the upper 1st permanent molar seat in the central fossa of the lower 1st permanent molar. *- The distal surface of the distal marginal ridge of the upper 1st permanent molar contact and occlude with the mesial surface of the mesial marginal ridge o

1. 1
Dr. Mohammed Alruby
Orthodontics for G.P
Normal and abnormal occlusion
For general practitioners
Prepared by
Dr. M Alruby

2. 2
Dr. Mohammed Alruby
Orthodontics for G.P
Normal occlusion
it is the usual or accepted relationship for species of teeth in the same jaw and those in the
opposing jaw when the teeth are approximated in terminal occlusion and mandibular condyles
are in centric position in the glenoid fossa
Normal occlusion in deciduous dentition
1= except the deciduous molars all other teeth are spaced and this spacing is rule or at least not
abnormal.
2= curve of spee is less marked than the permanent teeth because:
= Short arch length anteroposterior.
= The cusps of posterior teeth are short and occlusal plane is flat.
3= the buccal cusps of maxillary deciduous molars and the incisal edge of maxillary deciduous
incisors overlaps the mandibular one but the degree of overlaps differ because of short cusps.
4= the maxillary incisors and canines are larger than the mandibular one and the mandibular
molars are larger than the maxillary one.
5= the long axis of the teeth are nearly parallel to each other.
6= the midline rule and arch symmetry similar to the permanent dentition.
clude with two opposing teeth
deciduous molars oc
nd
7= all the maxillary teeth except 2
Occlusal relationship of primary molars:
1= flush terminal plane: occurs where the primary erupt in an end to end fashion
2= A mesial step: is where the distal surface of the mandibular second primary molars is mesial
to the distal surface of the second primary maxillary molar, that leads to Class I molars
relationship
3= A Distal step: is where the distal surface of the mandibular second primary molar is distal to
the distal surface of the second primary maxillary molars leads to class II molar relationship
Figure (1): flush terminal plane figure (2) mesial step figure (3) distal step
dentition:
cclusion in permanent
Characteristics of normal o
1= each arch is regular with the teeth at ideal mesiodistal and buccolingual inclination and the
correct proximal contact relationship at each interdental contact area.
2= All teeth must be angulated mesially.
3- The buccal surfaces of incisors are labially inclined, but from the canines posteriorly, the
buccal surfaces are progressively more lingually inclined.

3. 3
Dr. Mohammed Alruby
Orthodontics for G.P
4=the dental arch relationships are such that:
= each lower tooth except central incisors contact the corresponding upper tooth and tooth
anterior to it.
= the upper arch overlaps the lower arch anteriorly and laterally
Six keys to normal occlusion:
(1) Molar relationship:
*- The mesiobuccal cusp of the upper 1st
permanent molar falls within the groove between the
mesial and middle cusps of the 1st
permanent molar.
*- The mesiopalatal cusp of the upper 1st
permanent molar seat in the central fossa of the lower
1st
permanent molar.
*- The distal surface of the distal marginal ridge of the upper 1st
permanent molar contact and
occlude with the mesial surface of the mesial marginal ridge of the lower second molar.
(2) Crown angulations: ( mesio- distal tip):
In normally occluded teeth, the gingival portion of the long axis of each crown is distal to the
occlusal portion of that axis. The degree of the tip varies with each tooth type.
lingual torque:
-
lingual or bucco
-
Crown inclination: labio
(3)
Is the angle between a line 90 degree to the occlusal plane and a line tangent to the middle of
the labial or buccal surface of the clinical crown.
Rotation:
(4)
*- Teeth must be free of undesirable rotation that affect contact area and occupy space different
than normal
*- Rotation of premolar teeth are occupies more space than normal
*- Rotation of anterior teeth is occupying space less than normal
- Rotation of teeth leads to loss of contact which leads to instability of treatment results
*
:
5) Tight contact
)
Contact point must be tight; the teeth in either arch are aligned into tight contact, which
maintained through:
1- Periodontal force (transeptal fibers)
2-anterior component of force
3- Physiologic mesial drifting
** newly erupted teeth have pointed contact, which later on transformed into an area of contact
due to interproximal wear
Significance of interproximal contact:
1- Stabilize the teeth against separating forces
2- Distribution of masticatory force and forces of occlusion between the adjacent teeth
3- Prevent food impaction and trumatization of interdental tissues.
4- Maintain the integrity of peridontium.
5- Together with the interdental embrasure form a spell way for food deflection, thus prevent
undue frictional trauma and allow a proper gingival massage.
6) Curve of spee:
It is imaginary curve in the horizontal dimension passing through the condyle and buccal cusps
of the teeth ending at the incisal edge of the mandibular central incisors.

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Dr. Mohammed Alruby
Orthodontics for G.P
It is measured from the most prominent cusp of the lower second molar to the incisal edge of the
most prominent central incisors.
Normal curve of spee lead to stability of the dental arch which decrease tendency to relapse
Figure (4) molar relationship Figure (5) crown angulations
Figure (6) crown inclination

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Dr. Mohammed Alruby
Orthodontics for G.P
Figure (7) tooth rotation
Figure (8) curve of spee
Centric relation and centric occlusion:
Centric relation is the relation of the mandible to the maxilla when the mandibular condyles are
in the most superior and retruded position in their glenoid fossa with the articular disc properly
interposed. At centric relation both the condyles are simultaneously seated most superiorly in
their glenoid fossa.
Centric occlusion is that position of the mandibular condyle when the teeth are in maximum
intercuspation.
Centric relation and centric occlusion should coincide in order to have perfect harmony between
the teeth, the teporomandibular joint and the neuromuscular system.
**- definition of classification: it is the description of dentofacial deviations according to a
common characteristic or norm.
**- purpose of classification:
1-for the traditional reasons and for ease of reference.
2-for purposes of comparisons and for ease in self communication
3-it indicates the proper procedures in treatment.
4-it facilitates more accurate conclusions about the etiology, progress, retention and
presentation of malocclusion.
Types of malocclusion:
Malocclusion can be broadly divided into:
a) Intra -arch malocclusions that include variations in individual tooth position and
malocclusion affecting a group of teeth within the arch.
b) Inter – arch malocclusion that comprise of malrelation of dental arches to one another
upon a skeletal bony bases, which may themselves be normally related.

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Dr. Mohammed Alruby
Orthodontics for G.P
c) Skeletal malocclusions that involve the underlying bony bases.
a) Intra arch malocclusion:
A tooth can be abnormally related to its neighboring teeth. Such abnormal variations are called
individual tooth malposition.
Some commonly seen individual teeth malpositions are:
*- Distal inclination or distal tipping: this refers to a condition where the crown of the tooth is
tilted or inclined distally.
*- Mesial inclination or mesial tipping: this is a condition where the crown of the tooth is tilted
or inclined mesially.
*- Lingual inclination or lingual tipping: this is an abnormal lingual or palatal tilting of the
tooth. This condition is also called retroclination.
*- Buccal inclination or buccal tipping: this refers to labial (in case of anterior) or buccal (in
case of posterior) tilting of the tooth. This condition is also called proclination.
*- Mesial displacement: this refers to a tooth that is bodily moved in a mesial direction toward
the midline.
*- Distal displacement: this refers to a tooth that is bodily moved in a distal direction away from
the midline.
*- Lingual displacement: This condition where the entire tooth is displaced in lingual direction.
*- Buccal displacement: this describes a condition where the tooth is displaced bodily in a
labial or buccal direction.
*- Infra occlusion or infraversion: this refers to a tooth that has not erupted enough compared
to the other teeth in the arch.
*- Supra version or supra occlusion: this refers to a tooth that has over-erupted as compared to
other teeth in the arch.
*- Rotation: referred to a tooth moved around its long axis.
*- Disto- lingual or mesio- buccal rotation: this described a tooth that has moved around its
long axis so that the distal aspect is more lingulaly placed.
*- Mesio- lingual or disto buccal rotation: this described a tooth that has moved around its long
axis so that the mesial aspect is more lingulaly placed.
*- Transposition: this term describes a condition where two teeth have exchanged places.
B) Inter- arch malocclusions:
1- Sagittal plane malocclusion: this includes conditions where the upper and lower arches are
abnormally related to each other in a sagittal plane. *-
Pre-normal occlusion: this term refers to a condition where the lower arch is more forwardly
placed when the patients bites in centric occlusion.
*- Post- normal occlusion: this is a condition where the lower arch is more distally placed when
the patient bites in centric occlusion.
2- Vertical plane malocclusion: This malocclusion includes deep bite and open bite where an
abnormal vertical relation exists between the teeth of the upper and lower arch.
*- deep bite or increased over bite: it is a condition where there is excessive vertical overlap
between the upper and lower anterior.
*- open bite: this is a condition where there is no vertical overlap between the upper and lower
teeth. Thus a space may exist between the upper and lower teeth when the patient bites in centric
occlusion. The open bite can be in the anterior or posterior region.

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Dr. Mohammed Alruby
Orthodontics for G.P
3- Transverse plane malocclusions: it is inter-arch malocclusions include various types of cross
bites. The term cross bite refers to abnormal transverse relationship between the upper and the
lower arches.
Figure (8) Diagrammatic representation of the possible skeletal relationship in the transverse
plane
Angle's system of classification:
Angle's classification was based on the mesio-distal relation of the teeth, dental arches and the
molar is the key to occlusion. He considered these
st
jaws. According to Angle the maxillary 1
permanent
st
teeth as fixed anatomical points within the jaws. Based on the relation of the lower 1
molar to the upper one, he classified malocclusion into three main classes designated by the
Roman numeral, I, II, III.
:
Angle's class I
The mandibular dental arch and the body of the mandible are in normal relation
st
buccal cusp of the upper 1
-
to the maxillary dental arch, with the mesio
anteroposterior
-
permanent molar, and the mesio
st
the lower 1
of
buccal groove
ermanent molar occludes in the
p
permanent molar occludes in the occlusal fossa, when the jaws are
st
palatal cusp of the upper 1
at rest and the teeth are approximated in centric occlusion. Malocclusion in Class I is localized
anterior to the first molars and fall one of the following:
1-lacal abnormalities:
*- crowding of anterior teeth.
*- labial inclination of upper anterior teeth.
*- anterior cross bite.
*-impaction of premolars or canines.

8. 8
Dr. Mohammed Alruby
Orthodontics for G.P
*- deep over bite.
*- anterior or posterior open bite.
*- local abnormalities due to premature loss of deciduous molars and forward tilting of
permanent molars with loss of space in the premolar region.
2- Disproportion in size between the teeth and basal bone resulting in crowding or spacing of
teeth.
Figure (9) Class I occlusion
Angle's Class II:
The mandibular dental arch and the body of the mandible are in distal relation to the maxillary
distal width of a premolar. The mesio
-
permanent molar or mesio
st
arch by half width of the 1
permanent molar occlude in the space between mesio buccal
st
buccal cusp of the maxillary 1
premolar.
nd
permanent molar and the distal aspect of buccal cusp of 2
st
cusp of the mandibular 1
permanent molar occludes mesial to the mesio lingual
st
e mesio palatal cusp of maxillary 1
Th
. Class II malocclusion divided into:
molar
st
cusp of the mandibular 1
that characterized by the following:
Class II division 1:
-
*
1- Maxillary incisors are in labio- version.
2- Excessive over jet and deep bite.
3-V shaped upper arch.
4-Short upper lip with failure of anterior lip seal.
5- Mandible may be deficient and the chin under developed.
6- Normal path of closure.
7- Increased mentalis and buccinators activity.
that characterized by the following:
Class II division 2:
-
*
1- Maxillary lateral incisors may over lap the central incisors which are in lingo version.
2- Deep over bite.
3- Normal upper lip with normal lip seal and deep mental groove.

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Dr. Mohammed Alruby
Orthodontics for G.P
4- Mandible is of good size.
5- Upper arch usually broad.
6- Backward path of closure.
7- Decreased lower facial height.
8- Normal muscle activity of mentalis and buccinator.
N:B: When a Class II molar exist in one side and a Class I relation on the other side, it is
referred to as Class II subdivision based on it is division 1 or division 2, it can be called Class II
division 1 subdivision or Class II division 2 subdivision.
Figure (10) A) Class II division 1 B) division 2
)
occlusion
(mesio
II:
I
Angle's Class
The mandibular dental arch and the body of the mandible present in bilateral mesial
relationship to the maxillary dental arch.
permanent molar occludes in the interdental space
st
The mesio buccal cusp of the maxillary 1
permanent molar and mesial aspect of mesial
st
l cusps of lower 1
between distal aspect of dista
permanent molar. The teeth are in centric occlusion and mandibular condyles
nd
cusps of lower 2
are within the glenoid fossa.
that can occur due to the
gin
this is class III malocclusion of genetic ori
true Class III:
-
*
following causes:
1. Excessively large mandible.
2. Forwardly placed mandible.
3. Smaller than normal maxilla.
4. Retro positioned maxilla.
5. Combination of the above causes.
normal occlusion:
-
postural pre
bite of accommodation,
pseudo Class III,
-
*
The lower dental arch is postured forward in relation to the upper dental arch while the
condyles are outside their normal position within the glenoid fossa.

10. 10
Dr. Mohammed Alruby
Orthodontics for G.P
deciduous molars as the child
d
n
It may be the result of premature loss of both upper and lower 2
will protrude the mandible to bring lower posterior part in contact with the upper to achieve bite
of comfort.
This can be differentiating from true Class III by:
1. The mandible can assume a normal mesio distal relationship by manual retrusion of
mandible.
2. The condyles are in forward position outside glenoid fossa with the teeth in occlusion.
3. There may be labial inclination of lower incisors due to pulling action of muscles to
retrude the mandible to its original position and also this may be cause some lingual
inclination of upper incisors.
: The molar relationship is Class III on one side and Class I on the
Class III subdivision
-
*
other side
Skeletal malocclusion:
They are malocclusions caused due to abnormalities in the maxilla or mandible. The defect
can be in size, position or relationship between the jaws. The skeletal malocclusions can also
occur in the three planes of space namely sagittal, vertical, and transverse plane.
In the sagittal plane, the forward placement of jaw is referred to as prognathism while
retrognathism refers to a more backward placement of jaw. These sagittal abnormalities can
occur in one or both the jaws and can occur in various combinations.
Skeletal malocclusions in the transverse plane are usually a result of narrowing or widening
of the jaws. They can be described as narrow maxilla, wide mandible etc. these transverse
malocclusions are usually referred to as cross bites.
In the vertical plane abnormal variations in the vertical measurements of the jaws can affect
the lower facial height.
Normal development of dentition and occlusion
:
Deciduous dentition stage
Eruption of deciduous teeth beings usually at 6 to 7 months and complete between 2, 5 to 3 years.
7 months), maxillary central incisors
-
mandibular central incisors (6
:
Sequence of eruption
molars (15months), canines (18months), and second
st
(8months), lateral incisors (9months), 1
molars (30months). By about 2.5 years the deciduous teeth is usually complete and in full
function, the jaw of the child contain the calcifying crowns of all the permanent teeth with the
molars.
rd
exception of the permanent 3

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Dr. Mohammed Alruby
Orthodontics for G.P
The deciduous teeth are usually spaced; the spaces in the incisor region are present to allow for
the difference in size between the deciduous incisor and their permanent successors. Two distinct
deciduous
st
spaces can be observed one between the mandibular deciduous canine and the 1
molar and the other between the maxillary lateral deciduous incisor and the deciduous canine,
these two spaces are termed primate spaces.
With the eruption of incisor teeth, the upper incisors overlap the lower incisor teeth (deep over
bite), and characterized by slight over jet. This deep overbite is reduced by the eruption o f the
deciduous molars, at the age of about 5 years, the occlusal surfaces of the primary teeth wear to
the extent that, the incisor relationship end with an edge to edge bite. This edge to edge bite
occurs among people whose diet includes coarse rough food. The removal of cuspal interferences
permits the mandible which is growing more at this age than the maxilla to assume a forward
position more easily.
Two types of occlusion considered normal, one in which the canine and the posterior teeth to it
are in a cusp to cusp relationship, and the other with cuspal relationship resemble that in the
permanent dentition, the maxillary canine occlude distal to the mandibular canine and mesial to
the deciduous first molar. The distal surfaces of the upper and lower second deciduous molars
may end of the same vertical plane, mesial step, distal step.
The occlusal relationship remains unchanged during development and the arches are
comparatively constant from 3.5 years until beginning of eruption of the permanent teeth.
nd
: this is the distance from the distal surface of the 2
Arch length or arch circumference
deciduous molar on the other side. It
nd
deciduous molar alongside to the distal surface of the 2
-
deciduous molars, inter
nd
diminishes with age from 3 to 6 years due to mesial migration of the 2
inter-proximal attrition and inter-proximal cavities.
Mixed dentition stage:
This stage start from 6years of age until all the deciduous teeth have been shed, the most
common sequence of eruption in the maxillary and mandibular teeth are the following:
permanent molars.
st
The mandibular 1
-
1
permanent molars.
st
The maxillary 1
-
2
3-the mandibular central incisors.
4-The maxillary central incisors.
5-The mandibular lateral incisors.
6-The maxillary lateral incisors.
premolars.
st
The maxillary 1
-
7
8-The mandibular canines.
premolars.
st
The mandibular 1
-
9
premolars.
nd
maxillary 2
The
-
10
11-The maxillary canines.
premolars.
nd
The mandibular 2
-
12
premolars, the mandibular permanent teeth erupt ahead
nd
the maxillary 2
With the exception of
of the maxillary teeth.

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Dr. Mohammed Alruby
Orthodontics for G.P
There are two different mechanisms of normal occlusal adjustment as the deciduous dentition
enters the mixed dentition until the permanent dentition is established.
nd
deciduous molars is distal to that of the lower 2
nd
When the distal surface of the maxillary 2
-
1
altering the
molars erupt directly in the proper position
st
the permanent 1
molars;
deciduous
position of deciduous teeth.
deciduous molars are in the same vertical
nd
2
When the distal surfaces of both upper and lower
-
2
sial shift of the
molars occlusion is affected by an early me
st
plane, normal permanent 1
deciduous molars closing the primate space distal to the mandibular deciduous canines. Or late
deciduous molars are shed and the eruption of
nd
molars after 2
st
mesial shift of the mandibular 1
distal dimensions of
-
e between the sum of the mesio
premolars. This because the differenc
nd
the 2
the deciduous canines and molars, and that of their permanent successors. The mesio-distal
dimension of the deciduous is greater than that of the permanent, by about 1.9 to 1.3mm in the
LEE WAY SPACE
in the mandible. The difference is known as
.7 to 3.1mm
maxilla and from 1
permanent molars.
st
that is most important in normal occlusal adjustment of the 1
The permanent maxillary incisors usually erupted fanning out and with median diastema, due to
-
UGLY
roots from the developing permanent canines, this is known as the
pressure on their
f the permanent
stage. The incisor position usually improved with the eruption o
UCKLING
D
canines.
The permanent mandibular incisors may show crowding at the time of their eruption and the
permanent lateral incisors may overlap the deciduous canines. This crowded condition can be
overcome by the lee way space thus provided in addition to the usual increase in the inter-canine
width, which is active during the eruption of the permanent incisors and canines. This increase is
about 2.5 to 3.5mm from the age 6 to 8 years.
Permanent dentition stage:
permanent molar are erupting. Thus space for these teeth is created
nd
At 14 years the 2
principally by the forward migration of the anterior two third of the facial mass and partially by
erupt
molars usually
permanent
nd
the backward growth of the posterior third of the face. The 2
premolars and the mandibular before the maxillary one.
nd
shortly after the 2
At 18 years the room of the third molars is now available and takes their way toward the occlusal
plane, to complete the permanent dentition.