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1. DEVELOPMENT OF OCCLUSION
Introduction
Ideal occlusion is not easy to learn as it is not a static condition
but a changing function process, undergoing continued modifications
and adjustments during the whole life of deciduous and permanent
dentition.
The achievement of normal occlusion is the result of so many
interrelated variables starting from the prenatal developmental stages.
The multiplicity and complexity of these factors are such that often
malocclusion exists but occasionally there can be found a mouth without
orthodontic problems.
The active supervision of the developing dentition is a
responsibility of the pedodontists. Seeing things from the beginning is
the most advantageous. By making a detailed studies of dentition from
initiation through eruption till functional occlusion, we may be able to
obtain a clear concept of how occlusion develops and how its
development can be guided.
Occlusion is the approximation of upper and lower teeth, centric
occlusion is the maximum intercuspation between upper and lower
1

2. teeth. Centric relation is defined as the contact of teeth (U & L) in most
retruded position of the mandible so that condyle is in its most posterior
position with respect to glenoid fossa for the maximum comfort of the
patient.
The development of the concepts of occlusion:
There are various trends in the development of the concept of
occlusion. the trend ranges from static to dynamic.
The various periods in the development of concept of occlusion
are:
- Fictional period.
- Hypothetical period.
- Factual period.
Fictional period – 18th
century:
According to Talbot, concept of normal occlusion was that it was
a historical event and passed in the decline of the species this hardly
served as an inspirator for those to follow who were helpful of
preventing, intercepting and treating developing malocclusion.
2

3. Hypothetical period:
a. Edward H. Angle in 1899
Put a hypothesis stating that in the normal occlusion, it will be
seen that each dental arch describes a graceful curve, and that all the
teeth in the arches are so arranged as to be in harmony with their follows
int eh same arch, as well as with opposite arch. Each tooth helps to
maintain every other tooth in these harmonies relations for the cusps to
interlock and each inclined plane serves to prevent each tooth from
sliding out of position.
This basis created the impression of static relationship.
b. Mathew Cryer and Calvin Case: 1905
According to them occlusion refers to the closure of the teeth,
one upon the other, and normal dental relations, normal occlusion and
typical occlusion refers to the standard anatomical occlusion. He
rejected the first molar for the basis of normal occlusion. He told normal
occlusion and normal facial lines are inseparable. He used nose, chin
button areas in reference to the relative position of the teeth.
3

4. c. Lischer and Paul Simon:
They broadened the concept of occlusion by relating the teeth to
the rest of the face and cranium.
Lischer introduced the act of mastication as requisite part of the
definition.
Sinon made an approach to normal occlusion only through
biometry i.e. the anthropometric approach.
d. Milo Hellman
He showed a racial variations in normal occlusion. he studied the
number of skulls. But this still remained as static occlusion.
Factual period:
This concept divides the line between static and dynamic concept
of occlusion.
In 1930, Broadbent introduced an accurate technique of
roentgenographic cephalometry, which eliminated most of the
disadvantages of anthropologic measurements. He followed
longitudinally the orofacial developmental pattern, tooth formation,
eruption and adjustment.
4

5. In his concept, he considered the psychologic rest position, which
means that it is the position of mandible, where the muscles are in a
relaxed position. It is constant throughout life. On the other hand, it may
become smaller even disappear entirely. This is of utmost importance,
because once it reduces, patients often complains atleast the tiredness in
chewing muscles. The patients often complain of clicking of the joint
too.
This gives a concept of dynamic occlusion.
This shows the evolutionary changes of occlusion
Anthrolopithecus Ramapithicus
Evolutionary changes:
The primitive cartilage of the jawless fish developed into the jaws
of the palacoderm, and as evolution continued it developed into jaws of
modern mammals.
5

6. The mammalian dentition goes back to 75 million years. The
dental formula of the early primates consisted of 2 incisors, 1 canine, 4
premolars, 3 molars.
The theories behind this are:
a. Theory of concrescence
i.e. mammalian dentition was produced by the fusion of 2 or
more primitive conical teeth.
b. Theory of trituberculy
Each mammalian tooth was derived from single reptilian tooth by
a secondary differentiations of the tubercles and roots.
c. Theory of multituberculy:
The mammalian dentition is the result of reduction and
condensation of primitive multituberculate teeth.
Nolla C (1960) studied different stages of the permanent tooth
development. He arbitrarily divided the development of each tooth into
ten stages:
0  absence of crypt.
1  Presence of crypt.
6

7. 2  Initial calcification.
3  1/3rd
crown completion.
4  2/3rd
crown completion.
5  Crown almost completed.
6  Crown completed.
7  1/3rd
root formed.
8  2/3rd
root formed.
9  Root almost completed but open apex.
10  Root completed.
In stage 6  most teeth being eruptive movements and in stage 8 most
teeth pierce alveolar crest.
The humans have two sets of teeth:
a. Primary teeth.
b. Permanent teeth.
The dental formulae for primary dentition is 2102 and permanent
teeth is 2123.
Stages of occlusal development
According to Barnett 1978
a. Ist stage (3years) – primary dentition.
b. 2nd
stage (6 years) – eruption of first permanent molars.
c. 3rd
stage (6-9 years) – exchange of incisors.
7

8. d. 4th
stage (9-12 years) exchange of canine and premolars.
e. 5th
stage (12 years) – eruption of 2nd
molars.
Post natal development of occlusion:
Can be divided into (according to Vander Linden)
1. Birth to complete primary dentition.
2. First intertransitional period.
3. First transitional period.
4. Second intertransitional period.
5. Second transitional period.
6. Adult dentition.
Birth to Complete eruption of primary dentition
At birth the alveolar processes are covered by gumpads, which
are firm and pink. The basic form of the arches is determined in intra-
uterine life around 4 months.
Thus the gumpads are alveolar arches at the time of birth. They
develop in two distinct parts, a labio-buccal and a lingual portion of
these labiobuccal part is differentiated first and grows more rapidly and
gets divided into ten segments by transverse grooves. Lingual portion
which is differentiated later remains entirely smooth.
8

9. The buccal part is divided into ten segment by transverse
grooves, each corresponding to a deciduous tooth sac. It is
papillomatous at first. The groove between canine and first deciduous
molar crypts is important in assessing the relation of two pads. Their
groove is referred to as lateral sulcus.
The lingual groove portion which develops later is separated by
dental groove which is the site of origin of dental lamina. Lingual
portion is limited lingually by gingival groove. In the upper jaw,
gingival groove separates from the palate and is related to inner alveolar
plane. The grooves are more clear in upper arch than the lower arch.
9

10. The dental groove of the upper gum pad passes from the incisive
papilla and moves laterally and lingually, to join the gingival groove in
canine region and then continues distally and buccally across the
segment of the gum pads corresponding to the first deciduous molar
tooth crypt.
The lower gum pad is U-shaped and is limited on the lingual
aspect by a continuous groove. The gum pad is divided by transverse
grooves into ten segments not as clearly as upper anteriorly gum pad is
slightly everted. The lateral sulcus again passes at canine region.
The size of the gumpads at birth is determined by the following
factors:
- State of maturity of infant at birth.
- Size at birth as expressed by birth weight.
- Size of the developing primary teeth.
- Purely genetic factors.
The mandibular gum pad is distal to maxillary gum pad average
2.7mm in males and 2.5mm in females. The labial frenum varies in its
attachment at birth and may be found at the crest of gum pad, high
above the crest or even continuous with the incisive papilla.
10

11. During the first year, gumpads grow rapidly in the lateral
direction, with development of deciduous teeth, there is an increase in
labio-lingual dimensions of the gum pad.
Relationship of gumpads:
At rest gumpads are separated by the tongue and protrudes over
the lower gum pad to lie immediately behind lower lip. At this age,
upper lip appears very short. The gum pads do not have a definite
relationship when occluded. The antero-posterior movements vary and
there are no lateral movement. The upper gum pad is wider than lower
and when two are approximated, there is a complete overjet all around
the lower gum pad. The lateral sulcus of lower is usually posterior to
that of upper. The contact is only seen in first deciduous molar region.
It is common for a vertical space to exist between upper and
lower incisor segment even when they are pressed into occlusion. this
appears to be linked with the position of tongue.
At birth, the incisors are crowded and rotated in their crypts and
as the gumpads grow during first year of life now they are in good
alignment and spaced. Inspite of this incisors may erupt in irregular
relation to each other. But, this however is temporary and later gets
corrected by the tongue and lip pressure.
11

12. Clinch (1934) in Jr of Orthodontics demonstrated the increase in
the size of the alveolar arches from birth to the time just before the
eruption of the incisors. The arches increase in both length and breadth.
At birth no teeth are visible usually. The upper gum pad usually
overlaps the lower anterior pad by about 0.5mm.
At birth, the tooth buds of all primary teeth are present and in
various stages of development. The incisors are somewhat crowded at
this time for two reasons.
1. The arches have not yet complete rounded out anteriorly. Only
during the first 8-12 after the birth are the jaws are capable of
significant anterior apposition thereafter posterior growth and
anterior displacement accounts for the increase in jaw size.
2. The development of posterior teeth takes later hence follicles are
slower in achieving their complete size.
Usually, by the end of first year, sufficient jaw growth has
occurred that the primary teeth are seldom crowded or overlapped.
Infact a normal desirable dentition at this stage will exhibit spacing. The
extensive early transverse development of both jaws can be realized as
mainly because of the presence of mid-palatine suture in maxilla and in
mandible, the mandibular synchondroses. The mandibular
12

13. synchondrosis calcifies at around 1 year of life but maxilla maintain its
transverse growth potential till about 12 years of age.
The growth in the both arches is not coordinated till the occlusion
is established in the posterior region after which the development of
both dental arches are coordinated.
Characteristics of Primary dentition:
The cardinal feature of primary dentition in contrast to the
permanent teeth is that they drop almost vertically into the mouth
requiring very little mesiodistal or bucco-lingual adjustments in their
eruptive movement.
At this age, the roots of primary cuspids and molars are not yet
complete and the crowns of the permanent central incisors, lateral
incisors, cuspids and first molars are in various stages of formation.
By 30 months of age, 70% of all children have their primary
dentition fully erupted but a great deal of variation exists.
Eruption sequence of primary dentition according to ‘Bjork’.
13

14. CI, LI, Ist molars, canines, 2nd
molars.
CI
(mth)
LI
(mth)
C
(mth)
IM
(mth)
IIM
(mth)
According to Logen and
KronfeldUpper 71/2 9 18 14 24
Lower 6 7 16 12 20
Primary dentition can be broadly classified into two types:
a. Spaced arches.
b. Closed arches.
Spacing was first described by Dellabarre in the year 1819 in the
deciduous dentition between the ages of 4-6 years. The absence of
spacing in the primary dentition is an indication that crowding of teeth
can occur later when larger teeth erupt.
If 6mm of total space is there no crowding develops. If 3-6mm,
20% may develop crowding. If less than 5mm, 50% may develop
crowding. If no spaces, 70% may develop crowding. If crowding, 100%
develop crowding.
Spaces in primary dentition
It is very common to find the physiological spaces in the primary
dentition, with the most prevalent spaces mesial to the primary canines
in maxilla and distal to the primary canine in the mandible. These spaces
14

15. are called the primate spaces or simian spaces as they are commonly
seen in the primates and are characteristics of the primary dentition.
Boyko (1968) in American Jr. of Orthodontics found that 78%
had bilateral primate spaces in both upper and lower arches, 98% of
boys had bilateral primate spaces in the maxilla and 86% in the
mandible.
The primate (simian or primate) space is about 2mm and
generalized interdental spacing is seen between teeth which measures
about. These are also called as developmental or physiological spacs.
Occlusal relationships of the second primary molars:
The primary dentition is complete after the eruption of the 2nd
primary molars. This means that the location for the eruption of the
permanent teeth in the future has already been determined at this stage.
The relation of the distal surface of the maxillary and mandibular second
primary molar is, therefore, one of the most important factors that
influence the future occlusion of the permanent dentition. The mesio-
distal relation between the distal surface of the upper and lower second
primary molars is called the terminal plane when the primary teeth
contact in the centric occlusion. the terminal plane can be classified into
three types:
15

16. Flush or vertical plane type:
The distal surfaces of the upper and lower teeth are on the same
vertical plane. This plane would produce end-on relationship of the first
permanent molars. The change from a flush terminal plane to a mesial
step plane is desirable.
For the transition from end-on to Class I relation, the lower
molars have to move forward by 3-5mm. This is achieved by two
principles.
1. Early mesial shift : Occurs in children with spaced arches.
Eruptive force of the first permanent molar is sufficient to
mesialize the E and D in the arch to close the primate space. This
occur in the early mixed dentition stage.
2. Late mesial shift : Occurs in children with closed arches. The first
permanent molar drifts mesially by utilizing lee-way space of
nance. This occurs in the late mixed dentition stage.
Mesial step:
The distal surface of the lower molar is more mesial to that of the
upper. This is highly desirable as it would permit an immediate Class I
first permanent molar relationship upon eruption. The mesial step most
16

17. commonly occurs due to the early forward growth of the mandible, if
the differential growth of the mandible continues it can lead to Angle’s
Class II molar relation and if the forward mandibular growth is minimal
it can establish Angle’s Class I molar relationship.
Distal step:
The distal step of the lower molar is more distal to that of the
upper. The persistence of distal step would be consistent with
establishing an Angles Class II first permanent molar relationship.
Among Japanese children, the vertical type is the most prevalent
and also Caucasian children.
Alexander and Prabhu (1998), IJ of Ped. Dentistry, conducted a
study on 1026, 3-4 years old children to assess the profile, occlusal
relationships and presence of spacing or crowding of teeth in South
India males had a higher incidence of straight profiles, but it was not
statistically significant. 75% of both sexes had both physiologic and
primate spaces and 3% population were devoid of spacing. The convex
profiles were significantly correlated with flush and distal step terminal
planes in both sexes.
Foster T.D. and Hamilton in 1969 in Br. Dent. Jr. stated after the
completion of the primary dentition, the ideal features are the following:
17

18. - Spacing of incisor teeth.
- Anthropoidal spaces.
- Flush terminal plane.
- Deep bite and decreased overjet.
First intertransitional period:
This period is between the completion of primary dentition and
the emergence of first permanent teeth and is marked by little obvious
intraoral changes and multiple intrabony activities.
The arches by this time are capable of significant growth leading
to space for the first permanent molars, which is achieved posteriorly by
tuberosity apposition in the maxilla and ramal resorpting in the
mandible.
During the early part of this period, the tooth buds for 1st
and 2nd
premolar begin to form between furcations of the primary molar roots.
The first permanent molar crowns are fully developed and roots are
starting to form.
At the stage there is some indication of the future occlusion.
There may be excessive overbite and retrognathic tendency of the
mandible.
18

19. At 5-6 years of age, just before shedding of deciduous incisors,
there are more teeth in the jaws than any other time.
Description of occlusal contacts in primary dentition:
All the maxillary teeth except the maxillary second molars
occlude with two opposite teeth in the mandibular arch. The maxillary
second molar only occludes with the mandibular second molar. All
mandibular teeth except the central incisors occlude with two opposite
teeth in the maxillary arch. The lower central incisors only occlude with
the maxillary centrals.
Each mandibular tooth is one-half cusp mesial to the
corresponding maxillary tooth, there by establishing the following
dental relationship. The primary maxillary cuspid occludes distally to
the mandibular cuspid and mesially to the mandibular first primar molar.
The maxillary first primary molar occludes between the distal aspect of
the mandibular second primary molar.
The contacts between the upper and lower teeth can be described
as surface contact, or as cusp point contact with a fossa, groove or
embrasure, or ridge contact with embrasure, or ridge contact with
groove.
19

20. Factors guiding normal occlusion in primary:
The achievement of a normal occlusion is dependent upon a
number of factors.
Neuro-muscular considerations:
The action of the muscles of mastication on TMJ and also tongue
and cheek muscles are largely responsible for this relationship.
These masticatory muscles are controlled by a system of
complex-neuronal circuit consisting of sensory input to the CNS, and
formation, generation of appropriate motor responses.
Interdigitation occurs sequentially from the first teeth to erupt i.e.
central incisors. As other new teeth appear the muscles learn to effect
the necessary function occlusal movements. Since the primary occlusion
is established during periods of ready developmental adaptation, there is
less variability in occlusal relationship in primary when compared the
permanent. The primary teeth are guided into their occlusal position by
the functional matrix or muscles during very active growth of facial
skeleton. The low cuspal height and ease of occlusal wear also make the
primary occlusion more adaptable.
20

21. When teeth are erupted and muscles are functioning, the arch
formed by the crowns of the teeth is altered by muscular activities,
although original arch form is not probably determined by the muscles.
First transitional period:
The first exchange of teeth begins around six years of age and is
usually completed within two years. During this time span the
permanent first molars erupt posterior to the primary teeth and this
change usually goes unnoticed and the obvious exchange of eight
incisors occurs. The chronology of exfoliation can be determinant of
maturation in children and sequence of exfoliation can influence the
order of eruption of succedaneous teeth. There is bilateral symmetry of
tooth loss and the mandibular teeth exfoliate earlier than maxillary only
the 2nd
molars exfoliate at the same time.
In girls, teeth exfoliate earlier than boys. This difference is
greatest for canines especially. In the mandibular arch (10 months) and
least for maxillary incisors (1-3 months).
The rank of exfoliation of each tooth is the same for both sexes.
In the mandibular arch the teeth are lost in order from anterior to
posterior part of mouth but in maxillary, the posterior progression is
disrupted by the canines which exfoliate after the first deciduous molars
21

22. with the eruption of first permanent molars first of the three assaults on
the excessive overbite occurs. As the upper and lower first permanent
molars erupt, the pad of tissue overlying them creates a premature
contact. The proprioceptive response leads to the increased eruption of
deciduous teeth anterior to first permanent molar, thus reducing the
overbite.
The upper and lower first permanent molars display contrast
pathways of eruption. The tooth buds of the lower first permanent
molars are mesially and lingually inclined. The upper permanent first
molar bud develop with a buccal and distal orientation.
The mesiodistal relationship of the permanent molars is
determined by the alignment of distal surfaces of 2nd
primary molars.
The later mesial shift occurs because of Lee-way space of Nance.
The mesiodistal dimension of the primary molars is more than the
mesiodistal dimensions of premolars. This difference of 1.7mm
unilaterally in mandible and 0.9mm unilaterally in the maxilla.
According to Moyers 1.4mm mandible unilaterally.
The permanent incisors will start erupting in the early mixed
dentition period. At 4 ½ years the crowns of permanent central incisors
22

23. will be fully developed and located above and slightly lingual to the
roots of primary incisors.
Usually mandibular central incisors erupt first, followed by
maxillary permanent central incisors. The mandibular incisors erupt
lingual to the deciduous counterparts, while the maxillary permanent
incisors appear as large bulges in the muco-buccal vestibule above the
deciduous incisors before they erupt.
Since the permanent incisors are larger than the primary incisors,
inorder for the anterior tooth buds to fit within the jaws lingual to their
antecedents, they must overlap and assume different vertical levels.
In the maxilla, particularly the lateral incisors are situated behind
the centrals and cuspids in addition to their labial position are located
furthest from the occlusal plane. (The longer the root, the more away
from the occlusal plane is the tooth bud).
In the lower jaw, the cuspids are so inferior as to be almost at the
mandibular border. The labial movement of the anterior teeth effects on
the oblique resorption of the roots of the primary teeth.
Within few months of appearance of the first permanent molars,
the lower central incisors erupt. The upper centrals emerge a few months
23

24. late followed by lower lateral incisors. The upper centrals are the last
teeth to appear in the fist transitional phase.
Because of the discrepancy in the mesiodistal crown width
between the primary and permanent incisors, space available for the
permanent teeth after the exfoliation of the antecedents is barely
sufficient Mayne in 1969 has coined the term “Incisal liability” for this
difference. It is 7.18mm in the maxilla and 5.06mm in mandible. This
will be compensated by:
- The inter dental spacing of primary incisors.
- Increase in the intercanine width (3mm by eruption of LI in
maxilla and mandible and in maxilla further 1.5m by eruption of
canines).
- The average arch position of the maxillary central are 2.2mm
anterior to the primary incisors.
- Change of tooth axis of incisors. The interincisal angle is 150° in
the primary dentition 123° in permanent dentition.
When the mandibular lateral incisors emerge, not only they push
the primary lateral incisors labially but also more the primary cuspids
distally and laterally, closing the primate space or an unusual resorption
24

25. of the primary cuspid root. When the mandibular primary cuspids are
lost prematurely, the anterior arch loses its stability and incisors may tip
lingually by the hyperactivity of the mentalis muscle. This lingual
tipping of incisors permits the developing cuspid to slide labially where
it may erupt later in labioversion.
In maxilla, there is a diastema often found between central
incisors this may be because the central incisors often erupt with a slight
distal inclination. The maxillary lateral incisors on the other hand,
experience more difficulty in assuming their normal position, for as they
are erupting, the developing crown of the maxillary cuspids lies just
labial and distal to their roots. This position often causes the lateral
incisors to erupt more palatally than central incisors. After the erupting
cuspid has changed its course the lateral incisors correct itself and come
into position besides the central incisors.
Thus, as the end of first transitional phase the incisors are present
sometimes slightly crowded in the mandible and spaced in the maxilla
with more labial inclination than their antecedents.
The first permanent molars are erupted usually with an end on
relationship.
25

26. Gellin and Haley (1982) Int. J. Dent. Child conducted a clinical
study to determine if removal of the corresponding primary tooth is
necessary when the lingual eruption pattern of permanent incisor is
identified. They monitored 57 lingually positioned permanent central or
lateral incisors in 44 children. They concluded that the spontaneous
correction of lingually erupted mandibular incisor occurred in 95% of
cases by the age 8 years, 2 months to 4 months.
Ugly duckling stage:
Children tend to look ensued during the time of exchange of their
incisors, especially in the upper arch. Because of the presence of
diastema the parents become worried; and often frenum is sacrificed in
an effort to remove the cause of the space between the centrals. This
transitional malalignment during the exchange period of upper incisors
is called as ugly duckling stage, the term coined by Broadbent in 1937.
This is corrected later when the canines erupted and the pressure
is transferred from the roots to the crown of the incisors.
If diastema is very much abnormal (> 4mm) investigations has to
be carried out to rule out the presence of midline pathologies.
26

27. 2nd
intertransition period:
Almost 1 year gap between 1st
and 2nd
transitional period. During
this in space dentition the end-on will correct to the Class I molar
relation.
Lo and Moyers in 1953, American Jr. Of Orthodontics, studied
the sequence of eruption of maxillary and mandibular permanent teeth
on a sample of 236 children.
The most frequent in the maxilla was 6124537 appeared 48.72%
of the time. There were 18 possible sequences.
- 6124357  16.01%
- 6124573  11.87%
In mandible, 17 different sequences were noted:
- 6123457 was found in 45.77%
- 6123475 were found in 18.64%
- 6124357 were found in 8.47%
They reported the combination of eruption sequences of 6124537
in maxilla and 6123457 in mandible provides the greatest incidence of
normal molar relationship.
27

28. Nanda (1973) in Jr. of Dental Research, reported that most
common sequence of tooth emergence is 6124357 in maxillary arch and
6123457 in the mandibular arch:
The factors affecting the sequence of eruption:
- Endocrine (GH, TH).
- Familial tendency.
- Mental development.
Second transitional period:
The primary cuspids and molars are shed and permanent cuspids
and premolars erupt and 2nd
permanent molars erupt.
It is commonly occurs between the ages 10-12 years.
Occasionally maxillary cuspid and second premolar will erupt
simultaneously and mandibular cuspid and first premolar erupt
simultaneously.
The maxillary and mandibular 2nd
permanent molars are the last
teeth to erupt.
They start erupting at the age of 12-13 years and this delay may
be due to lack of space.
28

29. The maxillary 2nd
molar is tilled distally and buccally and
mandibular 2nd
molar is tilted mesially and lingually with the emergence
of teeth, they are guided into occlusion by the “cone funnel” mechanism
and not until contact is attained do these teeth start to upright.
If the 2nd
molar erupts before 2nd
premolar, there is tipping of first
molar thus reducing space for the erupting second premolar.
The eruptive force of the 2nd
molar helps in late mesial shift and it
also acts as bite-opener.
Adult dentition:
Although after the exfoliation of last primary tooth, the dentition
is considered as adult, it is only around the 20th
years when the 3rd
molars have erupted and finished root development, the adult dentition
is completed.
3rd
molars show more variability in calcification and eruption
than do any other teeth.
There is evidence of ethnic differences. The finnish aquire their
3rd
molars, later than middle American whites and south Indians show
eruption as early as 13-14 years.
29

30. Andrews – 6 keys to normal occlusion:
Andrew during 1970s put forward 6 keys to normal occlusion. He
considered the presence of these features essential to achieve an optimal
occlusion.
1. Molar inter arch relationship.
2. Mesio-distal crown angulation.
3. Labio-lingual crown inclination.
4. Absence of rotation.
5. Tight contacts.
6. Curve of spee.
Molar inter-arch relationship:
The mesio-buccal cusp of the upper first molar should occlude in
the groove between mesial and medial buccal cusp of the lower firt
molar. The mesio-lingual cusp of upper first molar must be angulated so
that the distal marginal ridge occludes with the mesial marginal ridge of
lower second molar.
Mesiodistal crown angulation:
It is the line that passes along the long axis of the crown through
the most prominent part in the center of labial or buccal surface. For the
normal occlusion, the gingival part of long axis of the crown must be
30

31. distal to the occlusal part of line. Different teeth exhibit different crown
angulation.
The labio-lingual crown inclination:
The crown inclination is determined from a mesial or distal view.
If the gingival area as the crown is more lingually placed from the
occlusal area, it is referred to as positive crown inclination and the
opposite is referred to as negative crown inclination.
The maxillary incisors exhibit a positive crown inclination, while
the mandibular incisors show a very mild negative crown inclination.
The maxillary and mandibular posterior have a negative crown
inclination.
Absence of rotation:
Normal occlusion is characterized by absence of any rotation.
Rotated posterior teeth occupy more space on the dental arch while
rotated incisors occupy less space in the arch.
Tight contacts:
To consider an occlusion as normal, should be light contact
between adjacent tooth.
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32. Curve of spee:
A normal occlusal plane according to Andrew should be flat, with
the curve of spee not exceeding 1.5mm.
Summary and Conclusion
Guidance of eruption and development of the primary and
permanent dentitions is an integral part of the speciality of pediatric
dentistry. Early diagnosis and successful treatment of developing
malocclusion can have both short term and long term benefits while
achieving the goal of occlusal harmony, function and dental facial
esthetics.
The understanding of the normal occlusion indicate whether
prevalence and interceptive orthodontic procedures can be applied or
not.
References
1. White & Gardner – Book of orthodontics.
2. Moyers.
3. Vander Lindon – Development of occlusion.
4. McDonald – Text book of children through adolescence.
5. Graber – Text book of orthodontics.
6. Wheeler – Text book of Dental anatomy.
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33. CONTENTS
INTRODUCTION
DEVELOPMENT OF CONCEPTS OF OCCLUSION
a. Fictional Period
b. Hypothetical Period
c. Factual Period
EVOLUTIONARY CHANGES
STAGES OF OCCLUSAL DEVELOPMENT
POST NATAL DEVELOPMENT OF OCCLUSION
BIRTH TO COMPLETE DEVELOPMENT OF PRIMARY DENTITION
RELATIONSHIP OF GUMPADS
CHARACTERISTICS OF PRIMARY DENTITION
SPACES IN PRIMARY DENTITION
OCCLUSAL RELATIONSHIP OF 2ND
PRIMARY MOLARS
a. Flush Or Vertical Plane Type
b. Mesial Step
c. Distal Step
FIRST INTERTRANSITIONAL PERIOD
DESCRIPTION OF OCCLUSAL CONTACTS IN PRIMARY DENTITION
FACTORS GUIDING NORMAL OCCLUSION IN PRIMARY DENTITION
a. Neuromuscular Co-ordinations
FIRST TRANSITIONAL PERIOD
UGLY DUCKLING STAGE
SECOND INTERTRANSITIONAL PERIOD
SECOND TRANSITIONAL PERIOD
ADULT DENTITION
ANDREW’S SIX KEYS ON NORMAL OCCLUSION
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