development of occlusion

DEVELOPMENT OF OCCLUSION
• Development of occlusion is a genetically and
environmentally conditioned process which show a
great deal of individual variations.
• The term occlusion is derived from the Latin word
“Occlusio”.
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Defined as the relationship between all the
components of the masticatory system in normal
function, dysfunction and parafunction.
* An ideal occlusion is the perfect interdigitation at
the upper and lower teeth which is a result of
developmental process consisting of the main
three events :-
I. Jaw growth
II. Tooth formation
III. Eruption

• Although the interrelation between the
teeth essentially becomes established
in childhood but it continues to change
to some extent throughout life.
• Thus the occlusion is regarded as a
dynamic rather than a static
interrelation between the facial
structures.

PERIODS OF OCCLUSION
DEVELOPMENT
• The development of occlusion can be
divided into the following developmental
periods :-
1. Pre-dental period
2. The deciduous dentition period
3. The mixed dentition period
4. The permanent dentition period

1. PRE-DENTAL PERIOD
• This is the period after birth during
which the neonate does not have any
teeth.
• It usually lasts for 6 months after birth.
• At birth the alveolar arches called gum
pads.

GUM PADS
• The gum pad of maxila is
horseshoe shape and the
gum pad of mandible is U-
shaped.
• They are firm and pink in
colour.
• These gum pads develop in
two parts :-
* Labial portion
(Differentiate first)
* Lingual portion
(Differentiate later)

• These two portions of gum pads are separated
from each other by a groove called the dental
groove.
• The gum pads are divided into ten segments by
certain grooves called transverse grooves.
• Each of these segments consist of one
developing deciduos tooth sac.
• The gingival groove separates the gum pad from
the palate and the floor of mouth.
• The transverse groove between the canine & I
deciduous molar segment is called lateral
sulcus.

• The lateral sulcii are useful in judging
the inter-arch relationship at a very early
stage. The lateral sulcus of the
mandibular arch is normally more distal
to that of the maxillary arch.
• The upper gum pad is both wider as well
as longer than the mandibular gum pad.
• Thus when the upper and lower gum
pad are approximated there is a
complete overjet all around.

• Contact occurs between the upper and lower
gum pads in the first molar region and a space
exists between them in the anterior region.
• This infantile open bite is considered normal and
it helps in suckling.

THE DENTITION AT BIRTH
• No any tooth erupt in the oral cavity.
• The neonate is without teeth for about 6 months of
life.
• At birth the gum pads are not sufficiently wide to
accommodate the developing incisors which are
crowded in their crypts.www.indiandentalacademy.com

• During the first year of life the gum pads grow
rapidly permitting the incisors to erupt in good
aligment.
• Some times the neonate have Natal, Neonatal and
Premature teeth.
Natal teeth :- Those teeth which are present at birth.
Neonatal teeth :- The teeth which erupts within 30
days of birth.
Premature teeth :- If these teeth erupts within 3
months of life. www.indiandentalacademy.com

2. DECIDUOUS DENTITION PERIOD
• The initiation of primary tooth buds occurs
during the first six weeks of intra-uterine life.
• The primary teeth begin to erupt at the age of
about 6 months.
• The eruption of all primary teeth is
completed by 21/2 to 31/2 years of age.
• During this period there is increased anterior
positioning of the lower Jaw with relation to
the upper Jaw.

ERUPTION AGE AND SEQUENCE OF
DECIDUOUS DENTITION
• Mandibular
Tooth Eruption (In months)
Central incisor 6
Lateral incisor 7
Cuspid 16
I Molar 12
II Molar 20

• Maxillary
Tooth Eruption (in months)
Central incisor 71
/2
Lateral incisor 9
Cuspid 18
I Molar 14
II Molar 24
• The timing of tooth eruption is highly variable. A
variation of 3 months from the mean age has been
accepted as normal.
• The sequence of eruption of the deciduous dentition
is :
A -> B -> D-> C -> E
• It is last for 6 years.

• During the first year of life the infant
does not seem to have a definite centric
occlusal relationship and there is a
limited antirio-posterior movement of the
mandible but no lateral movements.
• The primary incisors erupt into the
anterior space of the gum pads. Thus
accounting for the apparent overbite.
• This overbite gets reduced as the
posterior deciduous teeth come into
occlusion.

DEVELOPMENT OF HUMAN DENTITION FROM
BIRTH TO 6TH
YEAR

CLINICAL FEATURES OF DECIDUOUS
DENTITION
1. General characterstics :-
I. Both dental arches are half round
in shape.
II. Almost no curve of spee is
present.
III. Shallow cuspal interdigitation.
IV. Slight overjet and overbite.
V. Vertical inclination of the
incisors.
VI. Little or no crowding.

2. Spacing :- According to space there are
two types of dentition.
(A) Spaced Dentition (B) Non Spaced Dentition
(A). Spaced Dentition :-
• Spaced deciduous dentition is good for
permanent dentition because permanent teeth is
always larger than deciduous teeth.
• These spaces are two types :-
(a) Primate Spaces
(b) Physiologic / Developmental Spaces

(a) Primate Spaces :-
• These spaces are very prominent and primate species
so called primate spaces.
• These primate spaces exist in human between the upper
lateral incisor and the canine and lower canine and first
molar.
• These spaces also called Anthropoid or Simian Spaces.
• These spaces help in placement of the canine cusp of
the opposing arch.

(b) Physiologic /
Developmental Spaces :-
• These spaces are present in between the primary
teeth and play an important role in normal
development of the permanent dentition.
•The total space present may vary from 0 to 8 mm
with the average 4 mm in the maxillary arch and 1 to
7 mm with the average of 3 mm in the mandibular
arch.

(B) Non Spaced Dentition :-
• Primary teeth are present without spaces
between the teeth.
• This lack of space may be due to the
narrowness of the dental arches or teeth
are wider than usual.
• This type of dentition usually indicates
crowding in permanent dentition but it is
not always the case. It may depend on the
individual’s growth of the Jaws.

3. Occlusal Relationship :-
• Primary dentition develops quite independantly of other
morphologic process i.e. there is little relationship
between primary tooth development and skeletal
maturation.
• This dentition is complete after the eruption of II
deciduous molars.
(a) Primary Molar Relationship :-
• The relationship of the distal surface of the maxillary
and mandiblar second primary molars is one of the
key factors that influence the future occlusion of the
permanent dentition.
• The posterior primary teeth occlude so that the
mandibular cusp articulates just ahead of its
corresponding maxillary cusp.

• The maxillary canine occludes distal to the mandibular
canine and mesial to the I molar.
• The maxillary I molar occludes between the disto-occlusal
aspect of the I Primary Molar and the mesio-occlusal
aspect of the II Molar in mandible.
• The mesiolingual cusp of maxillary molars occludes in the
central fossa of the lower molars.
• The mandibular second molar being somewhat wider
mesiodistaly give rise to a flush terminal plane at the end of
the primary dentition.
• The distal surface of the second primary molars guides the
I Permanent molars into occlusion.
• The mesiodistal relationship between the distal surfaces of
the upper and lower II Primary Molars can be classified into
three types :-

• The distal surface of the upper & lower teeth are
in a straight plane and therfore situated on the
same vertical plane.
• Usually it is favourable relationship to guide the
permanent molars.
(i) Flush Terminal / Vertical Plane

(ii) Mesial Step Type :-
• The distal surface of the lower molar is more
mesial to that of the upper. Invariably it is
favourable to guide the permanent molars into a
class I relationship.

(iii) Distal Step Type :-
• The distal surface of the lower molar is more
distal to that of the upper. This relationship is
prognastically unfavourable. It guides the
permanent molars into distal occlusion.

(b) Anterior teeth relationship
Overbite :- The average overbite is primary dentition is 2 mm.
Overjet :- The average overjet is 1-2 mm with normal
range of 2-6 mm.
Changes in incisor relation during deciduous dentition:-
• The changes in anterior relationship is reduction in overjet
and overbite.
• Reduction in overbite is due to the attrition of teeth and the
differential growth of alveolar processes of Jaws.
• Changes in overbite was variable :-
52% showing decreasing
44% showing increasing
4% showing no change

• Reduction overjet is due to the forward
growth of the mandible because there
is attrision of teeth to the dental arches
are free to move.
• The incisors may assume an edge to
edge interrelationship by the age of 6
years.

(c) Canine Relationship
• The relationship of the maxillary and
mandibular deciduous canines is most
stable
• It is classified as
Class I :- When mandibular Canine
interdigitate in embrasure between the
maxillary lateral and canine.
Class II :- When mandibular Canine
interdigitates distal to embrasure.

(d) Arch Dimensions
Arch Width :- Can be measured by width between
the primary canine & width between the second
primary molars.
Arch Length :- Can be measured from the most
labial surface of the primary central incisors to the
canines and to the second primary molars.

Arch perimeter :- Arch perimeter is
determined by measuring the length of the
curbed line passing over the buccal cusps
or the incisor edges of the teeth from distal
surface of primary second molar to distal
surface of other side primary second
molar.
• There is no change from 3 to 6 year until
the eruption of permanent teeth.

(e) Arch Height
Arch Height :- increase in the height of
alveolar bone take place as it grown with
time.
There is little or no increase in the arch
height during the period of primary
dentition.
It is difficult to measure and it is theoretical
value.

(f) Spaces
• Space dentition does not have any
change in the spaces present until the
eruption of permanent molars.
• Non space dentition does not show any
dovelopment of spaces in the primary
dentition.

development of occlusion

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