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1. DEVELOPMENT OF DENTITION AND
OCCLUSION
INDIAN DENTAL ACADEMY
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2. Mixed dentition period:
This is the period where teeth of both deciduous
and permanent dentition are seen.
It extends from 6 to 12 years of age.
Most malocclusions make their appearance during
this period.
This period can be divided into two transitional
periods- first and second.
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3. First transitional period:
Emergence of first permanent molars and
transition of incisors are the events that take place
during this period.
Eruption of first permanent molars:
The first permanent molars erupts at 6 years of
age.
They play an important role in the establishment
and function of occlusion in the permanent
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dentition.

4. Factors influencing the antero posterior of
the permanent molars:
 Terminal plane relationship.
 Differential growth of maxilla ad mandible
Terminal plane relationship:
 When the deciduous second molars are in flush
terminal plane, the permanent first molars erupts
into a cusp to cusp relationship
Which later transforms into class I molar
relationship by early mesial shift or late mesial shift
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of the molars.

5. Early mesial shift:
In arches with physiologic spacing, the eruptive
forces of the permanent molars causes closing of
the spaces between the primary molars or the
primate spaces thus allowing the molars to shift
mesially (early) transforming into class I molar
relationship.
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6. Late mesial shift:
In arches with no physiologic spacing, the mesial
shift of the first permanent molars is delayed till
the exfoliation of the primary molars.
After the exfoliation of the primary molars the
mesial shift (late) of the permanent molars takes
place by making the use of Leeway space thus
transforming into class I molar relationship
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7. Leeway space:
The combined mesiodistal widths of deciduous
canine, first and second molars is more than that
of the combined mesiodistal width of permanent
canine, first and second premolar.
The difference between the two is called Leeway
Space.
Maxilla 0.9 / segment = 1.8 mm total
Mandible 1.7 / segment = 3.4 mm total
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8.  When the deciduous second molars are in
distal step, the permanent first molars will
erupt into a class II relationship
•This molar configuration is not self
correcting and will cause a class II
malocclusion despite leeway space and
differential growth
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9.  When the deciduous second molars are in
mesial step, the permanent first molars will
erupt into a class I relationship.
This may remain or progress to a half or
full cusp class III with continued
mandibular growth.
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10. Incisor eruption:
Permanent incisors develop lingual to the
primary incisors.
For incisors to erupt in normal alignment,
there is an obligate space requirement in the
anterior part of both the arches which is
termed as Incisor Liability.
i.e. the total sum of mesiodistal width of the
four permanent incisors is larger than the
primary incisors by 7.6 mm in the maxilla
and 6 mm in the mandible.
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11. The space required is provided by –
 interdental physiologic spacing in the primary
incisor region.
Increase in the inter canine arch width.
 permanent incisors erupt labially to the
primary incisors to obtain an added space of 2 to
3 mm. This is called Incisor Labiality.
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12. Ugly duckling stage: (Broadbent’s
Phenomenon)
Around the age of 9 to 10 years, a midline
diastema is commonly seen in the upper arch,
which is usually misinterpreted by the parents as
malocclusion.
crowns of canines in young jaws impinges on the
lateral incisor roots, driving them medially and
causing the crowns to flare laterally.
The roots of central incisors are also forced
together thus causing a maxillary midline
diastema.
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13. This period from eruption of lateral incisor to the
canine is termed as Ugly Duckling stage.
With the eruption of the canines, the impingement
from the roots shifts incisally thus driving the
incisor crown medially, effecting closure of the
diastema.
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14. Inter transitional period:
This is a stable phase where little changes take
place in the dentition.
Any asymmetry in emergence and corresponding
differences in the height levels or crown length
between the right and left side teeth are made up.
Root formation of the emerged incisors, canines
and molars continues, along with the concomitant
increase in alveolar process height.
Resorption of the roots of deciduous molars.
This phase prepares for the second transitional
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phase.

15. Second transitional period:
Following events take place.
1. Exfoliation of primary molars and canines at
around 10 years.
2. In this period the first posterior teeth to erupt are
the mandibular canine and the first premolar
around 9 – 10 yrs, followed by maxillary
premolars and canines around 11 – 12 yrs.
Most common eruption sequence is 4 – 5 – 3 in the
maxilla and 3 – 4 – 5 in the mandible
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16. Favorable occlusion in this region is
largely depend on –
Favorable eruption sequence.
 Satisfactory tooth size – available space
ratio.
 Attainment of normal molar relation with
minimum diminution of space available for
premolars.
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17. Permanent dentition:
The permanent dentition forms soon after birth
except for the first molar which starts before
birth.
Calcification begins after birth with the
calcification of first molar.
At approximately 13 years of age all permanent
teeth except third molars are fully erupted, thus
establishing the occlusion of the permanent
dentition.
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18. Features of permanent dentition:
Class I molar and canine relationship.
Vertical overbite of about one third the clinical
crown height of the mandibular central incisors.
Coinciding midlines.
Curve of Spee develops during transition and
stabilizes in adulthood.
The overjet and over bite decreases throughout
the second decade of life due to greater forward
growth pf the mandible
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