Development of occlusion (2)

DEVELOPMENT
OF
DENTITION
&
OCCLUSION
www.indiandentalacademy.com

Role of occlusion in maintaining
aesthetics and function of dentofacial
complex:
Term occlusion is derived from Latin word
occlusio defined as the relationship between
all the components of the masticatory
system in the normal function dysfunction
and parafunction

Occlusion is an anatomic and physiologic complex
present when the opposing teeth are in contact.
It consists of positional relations , the stresses
directed to the supporting structures their resistance
to the stresses , the form and arrangement of the
teeth , the influencing parts of the components of
the TMJ & the neuromuscular mechanism
responsible for mandibular movements.

The development of dentition is closely
associated with the morphology & growth
of the face & the way in which the
functions of the orofacial region are
exercised.
The size of the two jaws , their
anteroposterior relationship , the vertical
dimension as well as the changes occurring
during growth in these components play an
essential role in the development of the
dentition

Why 2 sets of teeth?
The possession of 2 sets of teeth in
mammals imparts the advantage of
equipping the young in a short time , with
the teeth capable of cutting crushing &
grinding , while the much larger , more
durable & slowly formed permanent teeth
are being constructed & erupted.

The deciduous or temporary dentition is
gradually shed & followed by a permanent
or succedaneous dentition . This is a
mechanism that adjusts the size of dental
battery to the growing face and jaws.
Since teeth once formed cannot increase in
size a second dentition consisting of larger
& more teeth is required for the larger jaws
of the adult

Factors that cause the resorption of
deciduous dentition:
The physiologic process resulting in the
elimination of the deciduous dentition is
called shedding or exfoliation.
The pressure generated by the growing and
erupting permanent tooth dictates the
pattern of deciduous tooth resorption.

Cells responsible - odontoclasts.
Histochemically characteristic
feature - alkaline phosphatase.
Alk phosphatase activity occurs
with in the vacuoles.

found - on surfaces of roots in relation to
advancing permanent teeth. Also found in
root canals & pulp chambers of resorbing
teeth lying against the predentin
origin - same as osteoclasts.( monocytes
circulating in the blood originally gives rise
to all the different tissue macrophages.)

Sequence of events in resorption of
dental lamina:
pressure
osteoclast
Alk phosphatase
activity
Initial removal
of mineral
Followed by
extracellular
dissolution of
organic matrix
If succesional
tooth germ
is missing , shedding
of deciduous teeth
is delayed

Experimental removal of permanent tooth
germ delays but not prevents shedding of
deciduous teeth
Forces of mastication applied to the deciduous
teeth are capable of initiating the resorption.
As the individual grows , the muscles of
mastication increase in size & exert forces on
the deciduous teeth greater than its periodontal
ligament can with stand. This leads to trauma
to the ligament & the initiation of resorption

Stages of dental
development
The first local changes occurring in
tooth development occurs as early as
the 6th
week of prenatal life.
The oral epithelium in the upper &
lower jaw thickens , forming the dental
lamina from which local buds arise at
each point where a tooth will form.

Individual tooth formation proceeds by means of
mitotic activity ,particularly in the inner enamel
epithelium , until the ameloblasts & odontoblasts
are differentiated.
The stages of dental development are bud stage,
cap stage, bell stage
The tooth is an example of typical vertebrate organ
starting as an epithelial bud & undergoing
complex morphogenesis , regulated by interactions
between cells & tissues

Heritability of malocclusion:
genetic basis of tooth development & dental defects
,Irma theslef, Acta odontol scan 2000
Tooth dev under genetic control
Dev regulatory genes identified in genetic
& biological studies
Analysis on dorsophila & mouse
Conclusion drawn –unforeseen
conservation of genes regulating dev.

Same genes regulate the dev of all animals.
Hence studies in any animal are highly
relevant in all other animals.
Same genes control numerous
developmental processes in the same animal.
They are used through out development in
all parts of embryo & their effects depend on
tissue & time they act.

Similar sets of genes govern the dev of all
organs in all animals including teeth which
are present only in vertebrates.
Majority of regulatory genes are associated
with interactions between the cells.such
interactions are central regulators of
development.
All cells have same genes.

But information from outside the cells
affects the decisions of the cell to turn
on & off the expression of genes.
Several families which transmit
information between the cells are
present.

SM Bind to specific
cell receptors
Activation of trans
cription factors
Through
molecular
cascades in
cytoplasm
Enter the
nucleus
Regulate the
Expression
of genes
Results in
production
of new signals,
receptors, transcription
Factors, proteins.
Change in
behavior of
target cell

Signaling net work:
Each signaling path way includes numerous
diff molecules.
Path ways of diff molecules interact with
each other & so the development is
regulated by complex signaling networks.

Signaling network in tooth dev:
Depends on inductive interaction between
the epithelial & mesenchymal tissues.few
signals act with in the same tissue.
Signaling interactions which determine the
location , identity, size & shape of teeth
take place during early stages of tooth dev.

Most of the signals belong to the families:
FGF(fibroblast growth factor)
BMPs ( bone morphogenic protein)
TGFbeta( transforming growth factors)
Hh ( hedge hog)
Wnt
Each family consists of several signals
encoded by several genes . They are used
reiteratively. www.indiandentalacademy.com

1st
signals
Oral ectoderm
Initiates odontogenic
programme in
underlying neural
crest derived mesenchyme
Growth &
folding of the
epithelium
Induce
signaling
centers in E
Regulate the
advancing dev
including cusp
dev in molarswww.indiandentalacademy.com

Mutations in genes:
Mutations in diff genes can cause
disruption to the dev of tooth.
Functions of these genes are found out
by genetic manipulation of mouse
development.
In knock – out mice the function of a
specific gene is inhibited & its
importance for development can be
analyzed. www.indiandentalacademy.com

1st
gene demonstrated to be essential for
tooth dev in mice was msx1
Later mutations in humans MSX1 gene
was shown to cause autosomal
dominant oligodontia.
Msx1 knock outs – tooth dev is arrested
at bud stage.

MSX1 is expressed in dental mesenchyme.
Its deletion results in inhibition of expression
of BMP 4 & FGF 3 which act as reciprocal
signals to the epithelium.
It was shown recently that BMP4 when
added to cultures of msx1 mutant tooth germ
could rescue their dev.
This ex shows how understanding of
molecular hierarchies involved in the
reciprocal signaling path ways offers the
possibility to rescue defective dev.

Deletion of one component of the path
way (msx1) arrests dev but this can be
compensated by the introduction of its
down stream target BMP4.
Gene defects causing dental defects
usually affect other tissues also.
Infact there is no regul;atory gene
which is solely responsible for tooth
dev.

Dental defects are most commonly
seen in syndromes affecting
various derivatives of skin.
Epithelial – mesenhymal
interactions usually affects hair
tooth, glands.

Path of eruption of permanent
dentition:
The word eruption refers to cutting of the
tooth through the gum.( in Latin erumpere
means “to break out”.)
permanent incisors & canines first develop
lingual to the deciduous tooth germs at the
level of their occlusal surfaces & in the
same bony crypt.

As their deciduous predecessors erupt they
move to a more apical position & occupy
their own bony crypts.
Premolars begin their development lingual
to the predecessors at the level of their
occlusal surfaces & in the same bony crypt.
They also shift so that they are eventually
situated in their own crypts beneath the
divergent roots of the deciduous molars.

The permanent molars which have no
deciduous predecessors also move
considerably from the site of their initial
differentiation.
For ex the upper permanent molars which
develop in the tuberosity of the maxilla , at
first have their occlusal surfaces facing
distally & swing around only when the
maxilla has grown sufficiently to provide
the necessary space.

Mandibular molars develop with their occlusal
surfaces inclined mesially & only become upright
as room becomes available .
All these movements are related to jaw growth and
may be considered as movements positioning the
tooth & its crypts with in the jaws preparatory to
tooth eruption

Occlusal homeostasis is dependent on the
elaborate & sophisticated sensory feedback
mechanisms from the periodontal
membrane, tmj & other parts of the
masticatory system.
Such sensory feedback serves as a
regulating mechanism helping to regulate
the strength of muscle contractions.
The neuromuscular & osseous
movements influencing the
eruption of teeth:

A number of physiologic forces determine
the tooth position occlusally ,including
eruption, the occlusal force during
swallowing , the forces of mastication,
occlusal wear of the crown of the tooth, &
so forth.

Pre-emergent eruption
Post-emergent eruption
juvenile occlusal equilibrium
adult occlusal equilibrium.
Eruption :

Pre emergent eruption:
Labial or buccal drift
Eruptive movement begins soon after root begins
to form
Processes necessary for pre-emergent eruption
resorption of bone & primary tooth
overlying the crown of erupting tooth.
eruption mechanism.
Ex: cleidocranial dysplasia.

Rate of bone resorption & the rate of
tooth eruption are not controlled
physiologically by the same
mechanism.
Ex : expts on dog & child
Follicle of erupting tooth signals
bone resorption
Nature of signal – unknown .

Mechanism of eruption:
Cross linking of collagen fibers
contribute to elasticity of periodontal
ligament.
Contractions & relaxations of these
fibers leads eruption force.
Proved by animal expts.

Other possibilities:
Localized variations in BP
Forces delivered from contraction
of fibroblasts.
Alterations in the extra cellular
ground substances of the PL similar
to those that occur in thixotropic
gels.

Post emergent eruption:
Once tooth emerges into oral
cavity it continues till it
approaches the occlusal level & is
subjected to the forces of
mastication.
Post emergent spurt.

Juvenile occlusal equilibrium:
Phase of very slow eruption
Rate of eruption parallels rate of jaw
growth.
Disturbance in coordination between these
two leads to orthodontic problems.
Since the rate of eruption parallels the rate
of jaw growth pubertal spurt in eruption of
teeth accompanies the spurt in jaw growth.

Adult occlusal equilibrium
When pubertal growth spurt ends , a final
phase in tooth eruption called the adult
occlusal equilibrium is achieved.
During adult life , teeth continue to erupt at
a n extremely slow rate.

If its antagonist is lost at any age , a tooth
can again erupt at more rapidly ,
demonstrating that eruption mechanism
remains active and capable of producing
significant tooth movement even late in life.
Occlusal wear of teeth is compensated by
eruption of teeth.

If severe occlusal wear occurs – cannot be
compensated by eruption hence lower facial
height decreases.
In few cases any wear of teeth is
compensated by additional eruption &
facial height remains constant or even
increases slightly in 4th
5th
& 6th
decades of
life

Neonatal line:
Despite the physical adaptations
that facilitate it, birth is a traumatic
process.
For a short period growth ceases &
there may be a small decrease in
weight during first 7 – 10 days of
life.

Such an interruption in growth
produces a physical effect in skeletal
tissues that are forming at that time,
because the orderly sequence of
calcification is disturbed – noticeable
line across bones & teeth that are
forming at that time.

Natal tooth:
First primary teeth do not erupt until
approximately 6 months of age.
The natal tooth may be a supernumerary
one formed by an aberration in the
development of the dental lamina, but
usually is merely a very early but otherwise
normal central incisor.

Eruption of primary teeth:
Development of incisors & canines
precedes that of the structures that contain
them – this explains the overlapping of
incisors & canines before birth. This extra
space needed is provided by the jaw growth
after birth in first 6- 8 months after birth.
The extensive early transverse development
of both jaws can be realized mainly because
of the presence of suture in the median
plane of the maxilla & of a synchondrosis in
the mandible. www.indiandentalacademy.com

As synchondrosis in the mandible calcifies
at about 6 months of age , the potency for
transversal growth in the lower jaw is
eliminated . In contrast with the situation
of the mandible maxilla maintains its rapid
median growth potency.
Maxillary median suture remains until the
development of the two dental arches
become coordinated.

The first vertical support associated
with interdigitation – the interlocking of
maxillary & mandibular posterior teeth
occurs when the first deciduous molar
attains contact.
As rule , those teeth are not centered
over each other in such a position that
no transverse or sagittal translation will
be required to reach correct
interdigitation.

In most instances , the large palatal
cusp of the maxillary 1st
molar arrives
with its cone shape with in the crater
formed by the occlusal anatomy of the
mandibular one.
The crater will function as a funnel by
which both teeth are directed towards
each other in the proper position.

 A required movement of the teeth will
be involved will be derived more from a
displacement of the maxilla than of the
mandibular molar as the structures in the
mandible favor such a movement less
than those in the maxilla.
 The occlusion in the posterior region is
established when the deciduous 1st
molars have settled.

There after the relation between the two
dental arches will stabilize in the transverse
& sagittal direction.
The deciduous dentition is complete after
all the 2nd
deciduous molars have attained
occlusion, usually at around 2.5 years of
age.
Diastemata is present between all teeth
particularly in the anterior region.

Mandibular teeth occlude slightly lingual
with the maxillary ones. The terminal plane
of deciduous dentition will be flush.
Little changes take place in the deciduous
dentition from 2.5 to 5 years.
Superiorly & lingually to the deciduous
teeth the formation of their successors
continues in the maxilla.
The permanent molars are formed posterior
to the dental arches.

MIXED
DENTITION

First transitional period:
Emergence of 1st
permanent molar & the
transition of the incisors.
The anteroposterior relation between the
two opposing molars after emergence
depends on their positions previously
occupied with in the jaws, the sagittal
relation between the mandible & maxilla &
the ratio of mesiodistal crown dimensions of
the mandibular & maxillary deciduous 2nd
molars

If the crown dimensions of the max & mand
deciduous second molars are same , the sagittal
relation between corresponding M & D surfaces
will be similar.
A mesial shoulder will be present anteriorly at the
mesial surfaces & posteriorly at the D surfaces of
the teeth. The terminal plane will have a M step.
Baume (journal of dental research, 1950 ) classified
the relationships of primary teeth into straight
terminal plane, mesial step & distal step.

If the mand 2nd
deciduous molar is
considerably larger than the maxillary one
then the distal surfaces will lie in one plane.
Under these occlusal conditions a flush
terminal plane is present.
One month or more may pass between the
emergence of corresponding left & right
incisors in one jaw.

Early mesial shift
In pts with spaced primary dentition & st terminal
plane relationship of molars , the permanent
molars will erupt at around 6 yrs of age & move
the primary molars mesially , close the space
distal to the primary canines, convert the st
terminal plane to mesial step , reduce the arch
length in mand dentition & allow the permanent
molars to emerge in class I relationship.

Late mesial shift:
In pts with closed primary dentition & st terminal
plane the permanent max &mand 1st molars
emerge into a cusp to cusp relationship as no
space exists. At approximately 11 yrs the primary
mand 2nd molars are exfoliated & the permanent
mand 1st molars migrate mesially into the excess
leeway space provided by the diffs in the mesio-
distal dimensions of the primary second molars &
the permanent second premolar teeth. Again this
reduces arch length ,converts the st terminal plane
into a mesial step & provides for a class I
relationship of 1st molars. It has been referred to
as the late mesial shift.www.indiandentalacademy.com

JCO 1995 Feb The Pseudo-Class I: A
Newly Defined Type of Malocclusion JAN
DE BAETS
Observation of the development of the P-
Cl.I showed that the following
characteristics are present in the mixed
dentition
• Mesial rotation of the upper first molars
• Crowding of the lower incisors
• Lack of space for the lower canines to
erupt

Pseudo class I

Incisor liability:(Warren Mayne 1969)
Mesiodistal width of permanent incisors are
more compared to deciduous incisors.
This space is gained by the labial & distal
movement of canines thus enhancing the
intercanine distance(secondary spacing).
The incisor liability is about 1.6 mm on
each side. www.indiandentalacademy.com

Inclination of incisors

Safety valve mechanism:
During the period of permanent incisor eruption
notable amounts of intercanine arch width
development occur in both the max & mand
dentition.
In mand the increase occurs between 6 &9 years
for boys & between 6&8 yrs for girls.
In maxilla it increases longer to 16 yrs in boys &
12 yrs in girls. This is called safety valve
mechanism.

According to Moorrees ( J dent res 1965) the
average increase in the mandibular dentition of
boys & girls is approximately 3mm ,in maxilla it
is approximately 4.5 mm.
according to Mayne ( current orthodontic concepts
& techniques 1969) permanent incisors erupt
labial to the deciduous incisors.Baume estimated
that the permanent incisors are 2.2 mm forward of
primary incisors in maxilla & 1.3 mm in the
mandible.

A small opening in the bony alveolar
process is present on the lingual aspect of
each deciduous incisor in the upper & lower
jaws. This opening forms the oral aspect of
gubernacular canal which runs to the crypt
of the successor.
Gubernacular canal contains the
gubernacular cord which which consists of
epithelium of the dental lamina. The
epithelium dissolves & a C.T strand
remains ,which subsequently disintegrates
further

The opening of the gubernacular canal on
the oral side increases in size with the
approach of the associated permanent tooth.
The gubernacular canal probably plays a
role in the guidance of the direction of
eruption of incisors through the bone & in
the determination of the spot of emergence.

Inter transitional period:
The inter transitional period presents itself
in a growing child as a rather stable phase
with little changes in the dentition.when
only the intraoral picture is considered.
However with in the jaws resorption of the
deciduous roots & reduction in the
cervically surrounding bone takes place.

Root formation of the already emerged
incisors & molars continues. The roots of
permanent canines, premolars, & 2nd
molars
gradually increase in length. The space
needed for that purpose is is provided by the
concomitantly increase in height of the
alveolar processes in both jaws.
In the inter transitional period the mandible
& maxillary dental arches consists of sets of
deciduous & permanent teeth.

Between the 4 permanent incisors & right &
left first permanent molars , the deciduous
canines & & 1st
& 2nd
deciduous molars are
located on each side of the dental arch.
Maxillary incisors are labially inclined . A
central diastema is present. Frequently no
contact exists between centrals & laterals.
Like wise a diastema is often present in the
maxillary dental arch mesial to the deciduous
canine.

Ugly duckling stage:( 9 - 12 yrs
Broad bent)
During the eruption of permanent canines,
the crowns of permanent canines hit the
roots of lateral incisors leading to their
mesial tipping .
It is a self correcting anomaly. Once the
permanent canine erupts, the diastema will
be closed as the erupting canines apply a
mesial force on the incisors.

In mandible the incisors are less
labially inclined than in the maxilla. A
diastema is seldom present between the
mandibular central incisors. All incisor
crowns are usually in contact with each
other & laterals touch the deciduous
canines.

Second transitional period:
At approximately 10 yrs of age the 1st
deciduous tooth in the post region usually a
mand canine sheds.
This happens more than 1.5 years after the
maxillary LI has emerged & about 1 yr after
it has reached the level of the occlusal
plane.

During formation maxillary canine & 1st
premolar are in close proximity of with
each other& overlap vertically. The already
calcified distal corner of the permanent
canine is directly adjacent to the forming
mesial cervical region of the 1st
PM.
Accordingly max 1st
PM shows a concavity
on the M surface at the cementoenamel
junction.(fossa canina). The premolar erupts
first.

A comparable M concavity is absent or
present only in reduced form at the maxillary
2nd
premolar whose crown morphology
strongly resembles that of the maxillary 1st
premolar.
Sequence of emergence of posterior
permanent teeth in mandible – canine,1st
PM,
2nd
PM.
Maxilla – 1st
PM,2nd
PM,canine.

Variations may occur in the sequence of
emergence with a restriction that as a rule
the 1st
PM precedes the permanent canine in
eruption.
In majority of cases the 2nd
permanent molar
emerges after all the deciduous teeth have
been lost& replaced.
The transition in lower jaw usually runs
ahead of that in the upper

During the replacement of deciduous
canines & molars by premolars, leeway
space is utilized.
The deciduous 1st
& 2nd
molars are wider in
mesiodistal dimension compared to
premolars.
This leeway space is around 2.5 mm in
upper arch & 1.5 mm in lower arch.

Abnormalities in dental arches
The most frequently occuring abnormality
in the dental arches is a discrepancy
between the needed & the available dental
arch perimeter.
Concerning the individual teeth ,
abnormalities in size shape number &
position.

Deviation in the number of teeth in the
deciduous dentition is rare.they are regularly
encountered in the permanent dentition.
Agenensis occurs quite often. The sequence
of diminishing frequency in agenesis is
3rd
molars , max lateral incisor, mand 2nd
PM,
mand incisor, max 2nd
PM.

Supernumerary teeth can be encountered
in the dental arches & particularly in the
mand & max incisor region.
most frequently a supernumerary tooth
occurs between two max central
incisors.
May form at any time before birth or at
10 –12 years of age.
Most commonly found in maxilla.

Anomalies in size
MD width is more in males compared to
females & it is more pronounced in
permanent teeth.
Anomalies are more common in mand 2nd
PM region.
One or more teeth fuse with neighbouring
teeth.

Anomalies in shape:
Peg shaped lateral
Cingulum quite prominent
Sharp marginal ridges (particularly
Japanese)
Extra lingual cusp on mand 2nd
PM

Developmental defects like
amelogenesis imperfecrta,
hypoplasia, gemination, dens in
dente, odontomas, fusion,
congenital syphilitic aberrations
such as hutchinsons incisors &
mulberry molars

Diastema:
Midline diastema & presence of fibrous
tissue attachment provides excellent
chicken & egg routine for controversy.
Faustin weber noted the following as
causative factors. They are
Microdontia, Macrognathia, Supernumerary
teeth(mesiodens), peg shaped lateral,
missing laterals.

Heavy occlusion against the
lingual surface of the maxillary
incisors, habits such as thumb
sucking, tongue thrusting, lip
biting, lip sucking, midline cysts.

Premature loss of deciduous teeth
Primary teeth are organs of mastication,
space savers, maintain opposing teeth at
occlusal level.
When there is generalized lack of space,
primary canines exfoliate faster to give
space for erupting incisors. This is often a
clue for guided extraction of deciduous
teeth & possible removal of 1st
PM.

If primary second molar exfoliates early _ 2nd
PM is blocked out.
If maxillary molar drifts mesially, the
mesiobuccal cusp rotates lingually.
If mandibular molar drifts rotation is less but
it tips mesially.
Permanent 1st
molar is lost in many children
due to caries. It leads to shortening of arch
length on that side ,tipping of contiguous
teeth, over eruption of opposing teeth,
periodontal implications

Prolonged retention & abnormal
resorption of deciduous tooth:
Dentist should maintain the tooth
shedding timetable at about the same
level for each of the 4 buccal segments.
If dental developmental age is
abnormally advanced or retarded a
check into endocrine history should be
made.

Hypo thyroidism – delayed developmental
pattern, prolonged retention of deciduous
teeth
Increased gonadotropic harmone – dental
dev markedly accelerated because
maturation occurs early ,crowding is
mandatory.
Cortisone & other steroids are frequently
used in treatment of a variety of general
diseases.dental dev pattern may become
abnormal.
Hence medication may be the ultimate cause.

Retained root fragments of
deciduous tooth:
Deflect permanent tooth
Prevent proper contact between permanent
teeth
Serve as foci for cysts ocassionally
Rupture of periodontal membrane at one or
more points establishing a bony bridge
between tooth and lamina dura preventing
normal eruption

Delayed eruption of permanent
teeth:
Endocrine disorders – hypothyroidism
Congenital absence
Supernumerary tooth
Deciduous root
Mucosal barrier – if erupting force is not
vigorous , the mucosa can effectively stop
the erupting tooth for a considerable period
of time

Bony crypt occasionally forms in
line of eruption of permanent
teeth .
A check of timetable in other
segments should be made before
deciding to curette bone barrier.

Abnormal eruptive path
Secondary manifestation of primary
disturbance.
Early ortho intervention of class II cases
trying to move maxillary dentition back can
cause maxillary 2nd
molar to erupt in cross
bite or can impact 3rd
molar.

Coronal cyst
3rd
molars are impacted due to
abnormal path of eruption
Ectopic eruption.
Sign of arch length deficiency
indicate the need of surgical or
guided extraction.

Ankylosis :
6 – 12 years
May be due to injury
Part of PL is perforated & bony bridge is
formed joining the laminadura & cementum
Accidents or trauma
Endocrine conditions
Congenital conditions like cleidocranial
dysostosis

Dental caries:
Premature loss of teeth both primary &
secondary
Abnormal axial inclination
Over eruption
Bone loss
Not only to prevent infection & loss of teeth
but to maintain integrity of dental arches

Improper dental restorations:
Over extended proximal restorations
cause irregular mandibular incisors .
Loose contact permits easy packing of
food in the interdental area leading to
caries.

SELF CORRECTING
ANOMALIES:
Predentate period:
Retrognathic mandible
Anterior open bite
Infantile swallowing pattern

Primary dentition:
Anterior deep bite
Flush terminal plane
Spacing
Edge to edge

Mixed dentition
Anterior deep bite
Mandibular anterior crowding
Ugly duckling stage
End on relation

Occlusion of permanent dentition
Any definition of normal occlusion should
no longer be static & descriptive merely of
tooth relationships. A dynamic definition is
essential.
Not only the teeth themselves , but the
investing tissues, the contiguous &
motivating masticatory musculature , the
curve of spee, the interocclusal clearance &
the tmj morphology & action are essential
considerations in the modern concept of
occlusion.

Development of the
concept of occlusion:
Fictional period
Hypothetical period
Factual period

Factual period:
Broadbent introduced an accurate technique
of roentgenographic cephalometry which
eliminated the disadvantages of
anthropologic cephalometry.
They were able to follow longitudinally the
orofacial developmental pattern & the
intricacies of tooth formation, eruption &
adjustment.

JCO 1979 Occlusion with particular
emphasis on the functional and
parafunctional role of anterior teeth
Good occlusions, if to be preserved, must
also have disocclusions (disclusions),
otherwise excessive contacts of the tooth
surfaces would result in abrasions and wear
of their parts. Disclusion, as defined by Dr.
Harvey Stallard26, "is a separation of the
teeth from occlusion; the opposite of
occlusion". Chewing is a reciprocal motion
consisting of occluding and discluding

The proposed ideal arrangement of the
teeth was described geometrically by
Angle as the line of occlusion.
The buccal cusps & the incisal edges of
the mand teeth should coincide with the
central fossae and cingula of the maxilla
when the teeth are normallyn occluded.
The line of occlusion is a smooth ,
continuous , symmetric curve .(catenery
curve)

Brader demonstrated that the total arch
form is better fitted with a trifocal ellipse,
a curve that is mathematically complex but
easily constructed geometrically.
The trifocal ellipse is patterned after the
shape of an egg.
Because an egg is extremely resistant to
collapse under pressure ,the elliptical arch
form should in theory produce a stable
arch form.

Mutually protected occlusion:
The six anterior maxillary teeth together
with 6 anterior mandibular teeth, guide
excursive movements of the mandible, & no
posterior occlusal contacts occurred during
any lateral or protrusive excursions which
minimizes the horizontal loading on the
teeth.
Rosensteil

Canine guided occlusion:
A form of mutually protected
occlusion in which the vertical and
horizontal overlap of the canine teeth
disengage the posterior teeth in the
excursive movements of the mandible

The six keys to normal occlusion -
Andrews 1972 AJO
Molar relationship
Crown angulation ( MD tip )
Crown inclination ( torque )
No rotations
Tieght contacts
Flat or slight curve of spee.

Crown inclination

JCO Leveling The Curve of Spee: Its
Effect On Mandibular Arch Length -
DOYLE W.
In 1890, Graf Spee30 was the first one to
state that a definite relationship existed
between the curvature of the occlusal
surfaces of the teeth, the condylar path, and
the slant of the articular eminence. He
found that anterior and posterior
movements of the condyle around the
articular eminence described a curve.

Due to Spee's original work of describing
the concave curve that exists in the
mandibular arch, this curve has become
known as the curve of Spee. It is also
known, and often referred to, as the
compensating curve.

Conclusion :
Orthodontist should have a
thorough knowledge of dentition
regarding what is normal?& what is
abnormal?for the particular age to
know when to intervene or attempt
correction of malocclusion.

Development of occlusion (2)

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