Development of dentition

DEVELOPMENT OF
DENTITION AND
OCCLUSION.
DR. TAHER MANASAWALA
DEPT OF ORTHODONTICS AND DENTOFACIAL
ORTHOPEDICS

CONTENTS
A. Odontogenesis:
I. Initiation stage
II. Cap stage
III.Bell stage
IV.Advanced bell stage
B . Mouth of the neo-nate:
I. Gum pads
II. Neo-natal jaw relationship
III.Pre-deciduous dentition

• Development of primary
dentition
I. Eruption and emergence
II. Theories and types of
eruption
III.Phases of eruption
IV.Adult and juvenile
occlusal equilibrium
V. Characteristics of primary
dentition
• Mixed dentition phase
I. 1st transitional phase
II. Inter transitional phase
III. 2nd transitional phase
IV. Self correcting anomalies

• Development of
permanent dentition
I. Chronology of eruption
II. Butlers field theory
• Development of occlusion
I. History
II. Andrews keys to
occlusion
III. Curves of occlusion
IV. Centric and eccentric
relation
• Conclusion
• References

• After the rupture of the buccopharyngeal membrane, when
the embryo is about 6 weeks old, certain areas of basal cells
of the oral ectoderm proliferate more rapidly than do the
cells of the adjacent areas.
• This leads to the formation of the Primary epithelial band
which is a band of epithelium that has invaded the
underlying ecto-mesenchyme .
INTRODUCTION

• At about 7th week the primary epithelial
band divides into an inner lingual
process called Dental lamina and an
outer buccal process called Vestibular
lamina.
Orbans: Oral Histology and Embryology , 13th Edition

DENTALAND VESTIBULAR
LAMINA
• The dental laminae serve as the primordium for the
ectodermal portion of the deciduous teeth.
• The total activity of the dental lamina extends over a period
of at least 5 years

• As the teeth continue to develop, they lose their connection
with the dental lamina. They later break up by
mesenchymal invasion, which is at first incomplete and
does not perforate the total thickness of the lamina .
• Remnants of the dental lamina persist as epithelial pearls or
islands within the jaw as well as in the gingiva. These are
referred to as cell rest of Serres.

• Labial and buccal to the dental lamina, another epithelial
thickening develops independently which is the vestibular
lamina, also termed the lip furrow band.
• It subsequently hollows and forms the oral vestibule
between the alveolar portion of the jaws and the lips and
cheeks

The embryonic development of both deciduous and permanent
teeth proceeds in four stages which are named for the
characteristic features of the stage:
1. Initiation stage
2. Bud stage
3. Cap stage
4. Bell stage and Advanced bell stage.

INITIATION STAGE
• The first sign of tooth development appears late in the third
embryonic week when the epithelial lining of the oral cavity
begins to thicken in broad zones
• The epithelial thickenings occur on the inferolateral
borders of the maxillary and on the superolateral borders of
the mandibular arches where the two join to form the lateral
margins of the mouth.

• The teeth begin with invagination of the dental lamina into
the underlying mesenchyme at specific locations along the
free border of each arch.
• Morphologic changes in the dental lamina begin at about 6
weeks in utero and continue beyond birth to the fourth or
fifth year.

• This occurs in three main phases:
1. Initiation of the entire deciduous dentition occurs during the
second month in utero.
2. Initiation of the permanent teeth that will be the successors of
the deciduous teeth occurs by the growth into surrounding
connective tissues of the free distal end of the dental lamina,
giving rise to the successional lamina. Its continuing growth
lingual to the enamel organ of each deciduous tooth occurs from
about the fifth month in utero (second premolars).

3. The dental lamina elongates distal to the second
deciduous molar and gives rise to the permanent molar tooth
germs.

BUD STAGE
• Soon after the dental lamina formation, the dental lamina
shows specific sites of increased mitotic activity which
produce knob-like tooth buds corresponding to the ten
deciduous teeth in each jaw.
• The first buds to form (at about the seventh week) are of
the mandibular anterior teeth.

CAP STAGE
• The growth rate throughout the bud is not uniform, being
more active peripherally.
• By the end of the eighth week, there appears a concavity on
the deep surface of the bud. The tooth is now in its cap
stage

• As the epithelium of the cap shaped tooth organ enlarges and
proliferates into deeper specialized connective tissues (ecto-
mesenchyme), there is increased activity in cells contiguous
with the ectodermal tooth bud
• Areas of increased cellular density eventually give rise to the
non -enamel portions of the tooth and its periodontal matrix.

• At this time the essential parts of the tooth-enamel organ,
dental papilla, and dental follicle-are identifiable.
• Collectively they are called the tooth germ.

BELL STAGE
• The bell stage represents enlargement of the overall size of
the tooth germ and deepening of its undersurface.
• With deep invagination of the epithelium and its margins
which continue to grow, the enamel organ assumes a bell
shape ,during which the shape of the crown is determined.

• The determination of crown shape (tooth morphogenesis) is
under the control of genes and their signaling molecules and
growth factors.
• Four different types of epithelial cells can be distinguished
on light microscopic examination of the bell stage of the
enamel organ.
1. Inner enamel epithelium
2. Stratum intermedium
3. Stellate reticulum
4. Outer enamel epithelium

• Epithelial cells next to the papilla develops into an enamel-producing
layer of cells, the inner dental epithelium
• Epithelial cells along the leading edge of the germ forms the outer
dental epithelium, which eventually gives rise to the dental cuticle.
• Stellate reticulum cells secrete an acid muco -polysaccharide into the
extracellular space between the epithelial cells covering the germ,
which results in a drawing in of the water into the tooth germ.

ADVANCED BELL STAGE
• This stage is characterized by the commencement of
mineralization and root formation.
• The differentiation of dentin-producing odontoblasts in the
dental papilla is initiated by the neighboring cells of the
inner dental epithelium.

• After the first layer of dentin is formed, the ameloblast
which has already differentiated from inner enamel
epithelial cells lay down enamel over the dentin
• In the cervical loop area, neighboring cells of the two
epithelia progressively constrict around the dental papilla to
leave only a small opening, which will become the apical
foramen and lead to the formation of the root.

MOUTH OF THE NEONATE
1. Gum pads
2. Neo natal jaw relationship
3. Pre-deciduous dentition
Robert E. Moyers: Handbook Of Orthodontics; 4th Edition

GUM PADS
• At birth, the alveolar processes are covered by gum pads,
which soon are segmented to indicate the sites of the
developing teeth.
• The basic form of the arches is determined during the intra-
uterine life.

• The maxillary arch is horse shoe shaped while the
mandibular arch is U –shaped
• Neonatal gum pads may be considered as developing in 2
distinct parts,
1. LABIOBUCCAL
2. LINGUAL
• These portions are separated by the dental groove,which is
the site of origin of the dental lamina.

• The gum pads are divided by the transverse groove into ten
segments,each corresponding to a primary tooth sac.
• Grooves between the canine and the 1st deciduous molar is
known as the lateral sulci.
• The lateral sulci of the lower gum pad is usually more
posterior to that of the upper

• The size of the gum pads at birth might be determined by
anyone of the following factors:
1. the state of maturity of the infant at birth
2. the size at birth as expressed by birth weight
3. the size of the developing primary teeth
4. purely genetic factors.

NEO NATAL JAW RELATIONSHIP
• The maxillary and mandibular gum pads have been
frequently illustrated to describe an anterior open bite
relationship while the posterior segments are touching.
• The maxillary gum pad slightly overlaps the mandibular
gum pad both horizontally and vertically

• It is well recognized that what is a normal occlusion for the
deciduous dentition may become abnormal for the
permanent and in the same way abnormal occlusion may,
in rare cases, be followed by normal occlusion.
• The variability of the neo natal relationship of the upper and
the lower gum pads cannot be used as a diagnostic criteria
for predicting the future occlusal relationship

• The space between the anterior segments of the gum pads
varies in form which has been classified as follows:
• Class A. The maxillary and mandibular anterior segments
are in parallel planes.
• Class B. In the maxillary, the incisal segments are higher
than the canine segments while in the mandibular, the
anterior segments are in the same plane.
Relationship of maxillary and mandibular gum pads in the
newborn infant, J.H Sillman , AJODO, Volume 24 , Issue 5 , May
1938

• Class C. In the maxillary, the incisal segments are higher
than the canine segments while in the mandibular the canine
segments are higher.
• Class D. In the maxillary, the anterior segments are in the
same plane, while in the mandibular the canine segments
are higher
Relationship of maxillary and mandibular gum pads in the
newborn infant, J.H Sillman , AJODO, Volume 24 , Issue 5 , May
1938

PRE DECIDUOUS DENTITION
• The pre deciduous dentition include:
1. Natal teeth – erupted during birth.
2. Neo natal teeth – erupted within 30 days after birth
3. Pre erupted – erupted within the 2nd or 3rd month of life
Shobha Tandon: Textbook of Pedodontics; 2nd Edition

• The pre deciduous teeth are decribed as hornified epithelial
structures without roots,occurring on the gingiva over the
crest of the ridge,which may be easily removed.
• Usually only one or two teeth erupt early,mostly being the
deciduous and mandibular central incisors.

SELF CORRECTING ANOMALIES
• Retrognathic mandible- differential forward and
downward growth of the mandible
• Anterior open bite – eruption of the primary incisors
• Infantile swallow- weaning of liquid to solid food

DEVELOPMENT OF PRIMARY
DENTITION
• The sequence of initial calcification of the primary teeth is,
1. central incisors (14 weeks),
2. first molars (15weeks),
3. lateral incisors (16 weeks),
4. canines (17 weeks),and
5. second molars (18 weeks)

Wheeler’s: Dental Anatomy, Physiology, and Occlusion; 9th edition

ERUPTION & EMERGENCE OF
PRIMARY TEETH
• Eruption refers to the movement of teeth toward the
occlusal plane, from their initial location in the jaws to their
functional position in the mouth.
• The term emergence applies to the piercing of the surface
and may be distinguished as the penetration of either the
alveolar occlusal bone or the gingiva.

• The primary dentition stage extends from the time of
eruption of the primary teeth until the eruption of the first
permanent tooth around 6 years of age.

CHRONOLOGY OF ERUPTION

THEORIES OF TOOTH ERUPTION
1. bone remodeling theory,
2. root formation theory,
3. vascular pressure theory and
4. periodontal ligament traction theory.

AJO-DO Volume 27,Issue 10, Pages 552–576

• The bone remodeling theory supposes that selective
deposition and resorption of bone brings about eruption.
• The root growth theory supposes that the proliferating root
impinges on a fixed case ,thus converting an apically
directed force into occlusal movement.
Studies in tooth development : theories of eruption , Maury
Massler , AJO-DO Volume 27,Issue 10, Pages 552–576

• The vascular pressure theory supposes that a local increase
in tissue fluid pressure in the periapical region is sufficient
to move the tooth
• The ligament traction theory proposes that the cells and
fibers of the ligament pull the tooth into occlusion.
Studies in tooth development : theories of eruption , Maury
Massler , AJO-DO Volume 27,Issue 10, Pages 552–576

PHASES OF ERUPTION
1. Pre –emergent eruption
2. Post-emergent eruption
William R. Profitt: Contemporary Orthodontics; 5th Edition

PRE –EMERGENT ERUPTION
• During the period when the crown of the tooth is being
formed , there is little buccal or labial drift of the tooth
follicle within the bone , however there is no eruptive
movement
• Two processes are necessary for pre emergent eruption
1. Resorption of bone and primary tooth roots
2. Propulsive mechanism that moves the tooth in the occlusal
direction

POST EMERGENT ERUPTION
• The stage of relatively rapid eruption from the time a tooth
first penetrates the gingiva until it reaches the occlusal level
is called the post –emergent eruption
• The post-emergence phase can be differentiated further into
a period of rapid eruption (pre-functional spurt) and a
subsequent period of slow eruption.

JUVENILE OCCLUSAL
EQUILIBRIUM
• In humans ,after the teeth reach the occlusal level , eruption
becomes imperceptibly slow . This is known as juvenile
occlusal equilibrium.
• During this phase , teeth that are in function erupt at a rate
that parallels the vertical growth of the ramus
• Thus , a pubertal growth spurt in eruption would coincide
with the pubertal growth spurt of the jaw

ADULT OCCLUSAL EQUILIBRIUM
• During adult life ,teeth continue to erupt at an extremely
slow rate
• If its antagonist is lost at any stage , the tooth can again
erupt rapidly indicating that eruptive mechanism is still
active
• Wear of the teeth also plays an important role in the
eruption of the teeth.

• In most of the individuals , any wear of the teeth is
compensated by additional eruption by keeping the facial
height constant.
• However extreme loss of tooth structure is not
compensated, so the vertical height of the face decreases

CHARACTERISTICS OF PRIMARY
DENTITION

1. Spacing
2. Flush terminal plane
3. Deep overbite
4. No curve of spee
5. Overjet of 0-2mm
6. Shallow cuspal interdigitation
7. Ovoid arches

SPACING
• Spacing is normal throughout the anterior part of the
primary dentition but is most noticeable in two locations,
called the primate spaces
• In the maxillary arch, the primate space is located between
the lateral incisors and canines, whereas in the mandibular
arch, the space is between the canines and first molars
Bishara : Text book of orthodontics

• Developmental spaces between the incisors are often
present from the beginning, but become somewhat larger as
the child grows and the alveolar processes expand
• Generalized spacing of the primary teeth is a requirement
for proper alignment of the permanent incisors

PRIMARY MOLAR RELATIONSHIP
• In the primary dentition stage the anteroposterior molar
relationship is described in terms of the relationship
between terminal planes.
• The terminal planes are the distal surfaces of the maxillary
and mandibular second primary molars.

• Determining the terminal plane relationships in the primary
dentition stage is of great importance to the clinician
because the erupting first permanent molars are guided by
the distal surfaces of the second primary molars as they
erupt into occlusion.
• Primary molar relationships have been described by Moyers
as the,
1. flush terminal plane,
2. mesial step, and
3. distal step

• In the flush terminal plane relationship, both the maxillary
and mandibular planes are at the same level antero-
posteriorly .
• In the mesial step relationship, the maxillary terminal plane
is relatively more posterior than the mandibular terminal
plane.

• Lastly, in the distal step relationship, the maxillary
terminal plane is relatively more anterior than the
mandibular terminal plane

• In a study on 121 Iowa children at age 5 years, the
distribution of the terminal plane relationships of the
primary second molars were found to be as follows
• 10% Flush terminal plane
• 19%Distal step
• 29% Mesial step of 1.0 mm
• 42% Mesial step >1.0 mm

• Anterior deep bite – attrition of the incisal edges and
forward and downward growth of mandible
• Primary spacing – eruption of the permanent teeth
• Flush terminal plane – early mesial shift of the molars

DEVELOPMENT OF MIXED
DENTITION PERIOD
• The mixed dentition period is characterized by significant
changes in the dentition as a result of the loss of 20 primary
teeth and the eruption of their succadaneous permanent
teeth
• The timing of the shedding of the primary teeth has an
effect on the emergence of the permanent teeth (i.e., early
shedding of primary teeth advances the emergence of the
permanent teeth)

• Phases of transitional dentition can be divided into 3
phases:
1. First transitional phase
2. Inter transitional phase
3. Second transitional phase

FIRST TRANSITIONAL PHASE
• The two important events which occur during this phase:
a) Eruption of the first permanent molars
b) Eruption and exchange of incisors
c) Establishment of occlusion
Van der Linden: Development of the Human Dentition

EMERGENCE OF PERMANENT
FIRST MOLAR
• The first permanent molars are the largest teeth and provide
important support to the occlusion
• The large disto - palatal cusp of the maxillary first molar
has to coincide with the central fossa of the mandibular first
molar.
• Angle has called the maxillary first permanent molar the
“key to occlusion

• The preceding continuous increase in the size of the jaw
regions posterior to the primary molars provides space
needed for the addition of the 1st permanent molars.
• After the eruption of the 1st permanent molars ,they do not
attain maximal contact
• The correct transverse relationship is established by guiding
the mesio-palatal cusp of the upper molar against the buccal
and lingual cusp of the lower molar by means of a cone
funnel mechanism

EARLY MESIAL SHIFT
• Occurs during the early mixed dentition period
• Generally utilizes the primate spaces available in the oral
cavity
• The eruptive force of the 1st permanent molar is sufficient
enough to push the deciduous 1st and the 2nd molar forward
in the arch to close the primate spaces

• As this drift occurs in the early mixed dentition period ,this
is called as early shift

LATE MESIAL SHIFT
• In children who lack the primate spaces,the erupting
permanent 1st molar is unable to move forward to establish
a class I molar relationship
• In such cases once the deciduous 2nd molar will exfoliate
and the molar will then move forward by utilizing the lee
way spaces available

• As this mesial drifting of the 1st permanent molar occurs
during the late mixed dentition this is called as late mesial
shift

ERUPTION AND EXCHANGE OF
INCISORS
• The transition of the incisors lasts almost 3 years, measured
from the first associated changes in the deciduous dental
arch until the complete eruption of all permanent incisors.

• The important aspects during the 1st transitional phase,
1. Leeway space
2. Incisor liability
3. Change in the inter-canine width
4. Change of tooth axis of incisors

LEEWAY SPACE
• In general, the sum of the mesiodistal width of the primary
canine and the primary first and second molars is larger
than the sum of their succedaneous teeth, namely, the
permanent canine and first and second premolars.
• This difference is called the leeway space and is present in
both the maxillary and mandibular arches

E-SPACE
• It is the difference between the mesio-distal dimension of
the 2nd primary molar and the 2nd premolar considering that
the combined mesio - distal width of the permanent canine
and the 1st premolar and the mesio- distal width of the
primary canine and the primary first molar is the same .

• The aim of this study was to determine whether the E space
can be used instead of the Leeway space in the mixed
dentition analysis
• Many orthodontists use the E space instead of the Leeway
space because E space is easier to calculate and because
they believe that both these spaces are similar

• The result of this study concluded that E space predicts a
larger space than lee way space and this difference was
more than 1 mm .
• The clinician should be very careful of not over estimating
this measurement .

INCISOR LIABILITY
Maxillary arch-7mm
Mandibular arch-5mm

• The permanent incisors are much larger in mesio-distal
width than their corresponding primary incisors.
• This difference in the amount of space needed for the
incisors and the amount of space available is called incisor
liability.
• A period when the mandibular incisors are slightly crowded
is a normal developmental stage.

• The maxillary arch, on the average, has just enough space
to accommodate the permanent lateral incisors when they
erupt.
• In the mandibular arch, however, when the lateral incisors
erupt, there is on the average 1.6 mm less space available
for the four mandibular incisors than would be required to
perfectly align them

• Incisal liability is overcome by the following:
1. A slight increase in the inter canine width
2. Labial positioning of the permanent incisors in relation
with the deciduous incisors
3. Repositioning of the canines distally

CHANGE IN THE ARCH LENGTH
AND ARCH WIDTH
• Forward rotation of the maxillomandibular complex, which
is the more usual pattern, influences the magnitude of tooth
eruption as well as the ultimate anteroposterior position of
the incisors
• Lingual positioning of the mandibular incisors relative to
the mandible often accompanies forward rotation during
growth.

• Arch breadth, does not change materially in the deciduous
dentition from the ages of 4 to 6 years but arch length
decreases slightly, owing to the closure of interdental spaces
between the deciduous posterior teeth.
• However, arch breadth increases markedly (3 mm.) during
emergence of the permanent maxillary and mandibular
incisors.
Changes in the maxillary and mandibular tooth size-arch length
relationship from early adolescence to early adulthood A
longitudinal study , Samir E. Bishara, Jane R. Jakobsen

• Arch length also increases in the maxilla at this time because
of the greater labial inclination of the maxillary incisors
relationship from early adolescence to early adulthood A longitudinal study
, Samir E. Bishara, Jane R. Jakobsen

• The inter-canine diameter increases only slightly in the
mandible, and some of this increase is the result of the
distal tipping of the primary canines into the primate space,
since the mandibular incisors are not normally moved
labially through time .

• The changes in arch length, in terms of average trends, may
be summarized as follows :
• 1. Slight decrease initiated before the emergence of the
permanent first molars, owing to closure of the spaces
between deciduous molars.
• 2. Small increase during the eruption of permanent incisors
in the maxilla but negligible in the mandible.
• 3. Decrease following the shedding of deciduous molars,
especially the second molar.

INTER-TRANSITIONAL PHASE
• During the inter-transitional period, the dental arches
consist of the permanent incisors, deciduous canines,
deciduous molars, and first permanent molars .
• In the maxilla, the incisors are labially inclined

• Rotations of mandibular incisors are partially or fully
corrected through pressure of the tongue and lips, provided
that space was available.
• In both jaws, the crowns of the not-yet-emerged permanent
canines limit space for the roots of the incisors.
• The space for the elongation is created by vertical growth
of the jaws and an increase in height of the alveolar
processes.

Dentition during the inter –transitional phase

SECOND TRANSITIONAL PHASE
• The second transitional period lasts 1 to 1.5 years.
• It is characterized by:
1. Transition of the canines and molars/premolars
2. Emergence of the second permanent molars

• The most common sequence of emergence
• in the mandible is: canine, first premolar, second premolar,
• in the maxilla is: first premolar, second premolar, canine
• Here ,the late mesial shift will occur by utilizing the lee
way space of Nance to attain a stable class I molar
relationship.

UGLY DUCKLING STAGE
• One of the most common finding
during the late mixed dentition period
is the UGLY DUCKLING STAGE
• It is a transient /self correcting
malocclusion which is seen in the
maxillary incisor region between 8-9
years of age
• Shobha Tandon: Textbook of Pedodontics; 2nd Edition

• As the permanent canines erupt , they transmit their forces
to the roots of the lateral incisors which tends to move their
roots mesially.
• This also causes the divergence of the roots of the central
incisors mesially which then leads to a midline spacing
• This is also termed as BROADBENT PHENOMENON.

• Once the permanent canines will erupt , the forces will be
transferred from the roots to the coronal portion of the
crown.

• UGLY DUCKLING STAGE-eruption of the permanent
maxillary canines
• ANTERIOR DEEP BITE-
• eruption of the 1st permanent molar
• Forward and downward growth of the mandible
• Attrition of the incisal edges

• MANDIBULAR ANTERIOR CROWDING-tongue
pressure & increase in the inter-canine width
• END ON RELATION-late mesial shift in non-spaced
dentition

DEVELOPMENT OF PERMANENT
DENTITION
• The permanent dentition stage of dental development starts
after the shedding of the last primary tooth and the eruption
of all the permanent teeth excluding third molars
• Wheeler’s: Dental Anatomy, Physiology, and Occlusion; 9th edition

The eruption sequence of permanent dentition

BUTLER’S FIELD THEORY
• The theory is developed that teeth are repeated organs that
occupy different positions in a continuous morphogenetic
field.
• Butler divided the mammalian dentition into different
morphological fields.
• This includes the molar , premolar ,canine and incisor field.
Studies of the Mammalian Dentition.-Differentiation of the Postcanine Dentition.
By P. M. BUTLER, B.A., B.Sc., Commonwealth Fund Fellow at Columbia
University.

• Among the fields , the maximum variability is seen in
the distal direction and the least in the mesial direction
• The field can undergo changes in structure and position
in the course of evolution, and thus changes in the
differentiation of the dentition may be explained.
• So the highest amount of variability is seen in the third
molars among the posteriors and the lateral incisors
among the incisors
Studies of the Mammalian Dentition.-Differentiation of the Postcanine Dentition.
By P. M. BUTLER, B.A., B.Sc., Commonwealth Fund Fellow at Columbia
University.

DEVELOPMENT OF THE CONCEPT OF
OCCLUSION

• The study and practice of most branches of dentistry should
be based on a strong knowledge of occlusion
• Orthodontics is no exception to this as great many changes
occur in the occlusion during orthodontic therapy
• T.M. Graber: Orthodontics Principles and Practice; 4th Edition

• The development of concept of occlusion can be traced
through fiction and hypothesis to fact
• The fictional approach was a convenient arrangement of a
series of observation and thoughts more or less logically
arranged .

• The hypothetical approach was based on provisional
acceptance of certain logical entities.
• Fact is a truth known by actual experiences or observation

• The fictional period - prior to 1900
• The hypothetical period – from 1900 to 1930
• The factual period – from 1930 to present

FICTIONAL PERIOD
• Pioneers like Fuller , Clark , and Imrie talked of
ANTAGONISM, GLIDING or MEETING of teeth
• The creation of normal standard ,a basis on which to
compare conclusions from normal was lacking.

HYPOTHETICAL PERIOD
• Edward . H. Angle
• It was him , who channelized orthodontic thinking on
occlusion and brought the real concept out of fiction
• In 1907,he summarized his views as ‘occlusion shall be
defined as being the normal relation to the occlusal inclined
planes of the teeth when the jaws are closed.

• Angle furnished his ‘key to occlusion’ and emphasized the
upper first permanent molar and considers them to be most
constant in taking normal position
• From the hypothesis of constancy of first molar and the
‘line of occlusion’, he developed the concept that all teeth
should be present if normal occlusion is to be achieved.

MATHEW CRYER AND CALVIN
CASE
• On Angle’s illustration of old glory, Cryer questioned that
How could one mix prognathic denture with an orthognathic
profile?
• Case accepted Angles hypothesis of constancy of first
molar.

• He proposed the concept of apical base and divided
dentofacial area into 4 segments or zones of movement.
• Case proposed the concept of normal and ideal occlusion

LISCHER AND PAUL SIMON
• They broadened the concept of occlusion by relating the
teeth to the rest of the face and cranium .
• They related teeth in occlusal contact to cranial and facial
planes outside the denture proper

MILO HELLMAN
• Hellman showed the racial variation in so called normal
occlusion through anthropological studies
• Hellman and others studied the prognathism of the human
dentition in relation to a cranial base

FACTUAL PERIOD
• In 1930,HOLLY BROADBENT and HANS PLANER
introduced an accurate technique of roento-genographic
cephalometry .
• Investigators were able to follow longitudinally the
orofacial developmental pattern and the intricacies of tooth
formation ,eruption and adjustment.

• Planar laid emphasis of efficiency of masticating
mechanism . He explained physiological rest position and
vertical dimension.

ANDREWS SIX KEYS TO NORMAL
OCCLUSION
1. Molar relationship
The distal surface of the disto-buccal cusp of the upper first
permanent molar made contact and occluded with the mesial
surface of the mesio-buccal cusp of the lower second molar.
The mesio-buccal cusp of the upper first molar to occlude in
the groove between the mesial and middle cusps of the lower
first permanent molar
• Lawrence F. Andrews: The six keys to normal occlusion ;Am J Orthod.1972
Sep;62(3):296-309

Sep;62(3):296-309

2.Crown angulation
The gingival portion of the long axis of all crowns was more
distal than the incisal portion.
• “Plus reading” Gingival portion of the long
axis of the crown is distal to
the incisal portion.
Sep;62(3):296-309

• “Minus reading” Gingival portion of the long
axis of the crown is mesial
to the incisal portion.
Sep;62(3):296-309

3. Crown inclination
Plus reading- gingival portion of the
tangent line lying lingual to the incisal
portion
Minus reading-gingival portion of the
tangent line lying labial to the incisal
portion
Sep;62(3):296-309

4. Absence of rotations-The fourth key to normal occlusion is
that the teeth should be free of undesirable rotations.
5. Tight contacts-the contacts should be tight
6. Occlusal plane-there should be slight or flat curve of spee
Sep;62(3):296-309

• 7.Tooth size.
• Andrews non-orthodontic normal models had balanced
tooth size.
• Tooth size discrepancy may be corrected either by reducing
tooth mass in one arch with inter-proximal enamel
reduction (usually the lower incisors) and/or by addition of
tooth mass with restorative materials in the opposing arch
(usually the upper lateral incisors)
Sep;62(3):296-309

CURVE OF SPEE
• It refers to the antero-posterior curvature of the occlusal
surfaces beginning at the mandibular cuspid and following
the buccal cusp tips of bicuspid and molar continuing as an
arch through the condyle.
• There is a purpose behind the curve of spee as well as its
location in relation to the condyle.

• The maximum depth of the curve of Spee was measured as
the maximum of the perpendicular distances between the
buccal cusp tips of the mandibular teeth and a measurement
plane described by the central incisors and the distal cusp
tip of the most posterior tooth in the mandibular arch
Peter E. Dawson: Functional occlusion from TMJ to smile design

CURVE OF WILSON
• The curve of Wilson is the medio lateral curve that contacts
the buccal and the lingual cusp tips on each side of the arch.
• It results due to inward inclination of the lower posterior
teeth and outward inclination of upper posterior teeth

• There are 2 reasons for this type of inclination of posterior
teeth:
1. Resistance to functional loading
2. The elevated buccal cusp prevent the food going past the
occlusal table

CURVE OF MONSOON
• The curve of occlusion in which each cusp and incisal edge
touches the surface of an imaginary sphere 8 inches in
diameter.
• It is a combination of curve of spee and curve of wilson.
• concave-mandibular arch
• convex- maxillary arch

CENTRIC RELATION
• Centric relation is generally
defined as the “most retruded
relation of the mandible to the
maxillae when the condyles are in
their most posterior unstrained
positions in the glenoid fossae
from which lateral movement can
be made, at any given degree of
jaw separation

• Centric relation should not be confused with the term
centric occlusion which denotes maximum intercuspation .
• Centric relation is not about the teeth but about the position
of the condyles.

TYPES OF CUSPS
• Centric holding cusps (stamp cusps) :
• The facial cusp of the mandibular teeth and the palatal cusp
of the maxillary posterior teeth
• They occlude in the central fossae and the marginal ridges
of the opposing teeth.
• They are also called as supporting cusps.

• Non supporting cusps (shearing or guiding
cusps ) :
• The facial cusps of the maxillary and the
lingual cusps of the mandibular posterior teeth
are called the non supporting cusps .
• They contact and guide the mandible during
lateral movements .

TYPES OF CENTRIC HOLDING
CONTACTS
• Centric relation contact is usually established in of the 3
ways:
1. Surface to surface contact
2. Tripod contact
3. Cusp tip to fossa contact

• Surface to surface contact:
• It is the form that results if the articulator is
simply closed together when the wax on the dies
is soft.
• Tripod contact
• In this contact,the tip of the cusp never touches
the opposing tooth but instead the contact is
made on the side of the cusp that are convexly
placed

• Cusp tip to fossa contact:
• Here the cusp tips occlude in the most
advantageous fossa and this type of
occlusion offers excellent function and
stability with the flexibility to choose
any degree of distribution of lateral
forces that is warranted.

ECCENTRIC JAW RELATION
• It is defined as any relationship of the mandible to the
maxilla other than centric relation
• It includes protrusive and lateral movements of the
mandible.

• The contact relationship of the
lower teeth to the upper teeth on
the side towards which the
mandible moves is the working
side .
• The tooth contact which occurs
away from which the mandible
moves is called the non-
functional or balancing side

• Working side occlusion includes :
1. Group function occlusion
• It refers to the distribution of the lateral forces to a group of
teeth rather than assigning all the forces to one particular
tooth.

ADVANTAGES
• Lateral pressure is exerted towards the working side of the
teeth .
• Long centric relation thus allows some freedom of
movement in the anteroposterior direction

2. Partial group function occlusion
• It refers to allowing some of the posterior teeth to share the
load in excursive movements whereas others contact only
during centric relation
3. Posterior disclusion
• In posterior disclusion there is no contact on any posterior
teeth in any position but centric relation

4. Canine protected occlusion
• Refers to the disclusion of all the
other teeth by the canines
• During lateral mandibular
movement, the opposing upper and
lower canines of the working side
contact thereby causing disclusion of
all posterior teeth on working side
and balancing side.

ADVANTAGES
• Minimum amount of tooth contact is involved and this
makes for a better penetration of food .
• Force is directed along the long axis of all the teeth
• The arrangement of the marginal , transverse, and oblique
ridges so they have a shearing action which makes it a
better chewing apparatus .

CONCLUSION
• Because of the increasing number of adults seeking
orthodontic care, an understanding of the changes that
normally take place in the adult craniofacial structures
becomes critical
• The development of the dentition is complex and differs
from that of other structures and parts of the body.

• The goal of occlusal treatment is not just to maintain the
structures but to provide an easily continuing functional
homeostasis .

• References :
• Orbans: Oral Histology and Embryology , 13th Edition
• Van der Linden: Development of the Human Dentition
• Robert E. Moyers: Handbook Of Orthodontics; 4th Edition

• T.M. Graber: Orthodontics Principles and Practice; 4th
Edition
• William R. Profitt: Contemporary Orthodontics; 5th Edition
• Peter E. Dawson: Functional occlusion from TMJ to smile
design

• Wheeler’s: Dental Anatomy, Physiology, and Occlusion;
9th edition
• Lawrence F. Andrews: The six keys to normal occlusion
;Am J Orthod.1972 Sep;62(3):296-309
• Frans P.G.M Van der linden; Development of human
dentition

• Changes in the maxillary and mandibular tooth size-arch
length relationship from early adolescence to early adulthood
A longitudinal study , Samir E. Bishara, Jane R. Jakobsen.
• Relationship of maxillary and mandibular gum pads in the
newborn infant, J.H Sillman , AJODO, Volume 24 , Issue 5
, May 1938
• Studies of the Mammalian Dentition.-Differentiation of the
Postcanine Dentition. By P. M. BUTLER, B.A., B.Sc.,
Commonwealth Fund Fellow at Columbia University

• Studies in tooth development : theories of eruption ,
Maury massler , AJO-DO Volume 27,Issue 10, Pages 552–
576
• Bishara : Text book of orthodontics
• Tooth size discrepancy . Is the E space similar to Leeway
space? Fernandes et al. Journal of the World Federation of
Orthodontists 2013

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