Mixed dent

INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

DEVELOPMENT OF MIXED DENTITION
 MIXED DENTITION PERIOD CONSISTS OF BOTH
DECIDUOUS & PERMANENT TEETH IN THE ORAL
CAVITY.
 EXTENDS FROM 6- 12 YEARS OF AGE
Department of orthodontics

MIXED DENTITION CONSISTS OF 3 PHASES:
1. FIRST TRANSITIONAL PERIOD
2. INTER-TRANSITIONAL PERIOD
3. SECOND TRANSITIONAL PERIOD

1. FIRST TRANSITIONAL PERIOD
A. EMERGENCE OF FIRST PERMANENT MOLARS
B. EXCHANGE OF DECIDUOUS INCISORS WITH
PERMANENT INCISORS

A. EMERGENCE OF FIRST PERMANENT
MOLARS
MANDIBULAR FIRST MOLAR IS THE FIRST
PERMANENT TOOTH TO ERUPT AT AROUND 6
YEARS OF AGE
ANTEROPOSTERIOR POSITIONING OF THE
PERMANENT MOLARS IS INFLUENCED BY
TERMINAL PLANE RELATION-SHIP OF DECIDUOUS
2ND
MOLARS WHICH IS OF 3 TYPES.

1. FLUSH TERMINAL PLANE
 THE DISTAL SURFACES OF THE UPPER AND
LOWER 2ND
DECIDUOUS MOLARS ARE IN
ONE VERTICAL PLANE.
 THIS IS A NORMAL FEATURE OF DECIDUOUS
DENTITION

 THE ERUPTING 1ST
PERMANENT MOLARS MAY
ALSO BE IN A FLUSH OR END-ON RELATION
 THE SHIFT IN PERMANENT LOWER MOLAR
FROM FLUSH TERMINAL PLANE TO CLASS 1
RELATION CAN OCCUR IN 2 WAYS:
1. EARLY SHIFT
2. LATE SHIFT

1. EARLY SHIFT
 ERUPTIVE FORCE OF 1ST
PERM MOLARS IS
SUFFICIENT TO PUSH THE DECI 1ST & 2ND
MOLARS FORWARD TO CLOSE THE PRIMATE
SPACES & ESTABLISH A CLASS I MOLAR
RELATIONSHIP
 SINCE THIS
OCCURS IN THE
EARLY MIXED
DENTITION PERIOD,
IT IS CALLED EARLY
SHIFT www.indiandentalacademy.com

2. LATE SHIFT
 When The Deciduous 2nd
Molars Exfoliate The
Permanent 1st
Molars Drift Mesially Utilizing
The LEEWAY SPACE OF NANCE.
 This Occurs In The Late
Mixed Dentition Period
& Is Called LATE SHIFT

LEEWAY SPACE OF NANCE
 THE COMBINED MESIODISTAL WIDTHS OF DECIDUOUS
CANINE, 1ST
& 2ND
MOLARS IS MORE THAN THAT OF THE
COMBINED MESIODISTAL WIDTHS OF PERMANENT
CANINE, IST & 2ND
PREMOLARS.
 THE DIFFERENCE BETWEEN THE TWO IS CALLED
LEEWAY SPACE
 MAXILLA : 0.9mm/ segment= 1.8mm total
 MANDIBLE : 1.7mm/ segment= 3.4mm total

2. MESIAL STEP TERMINAL PLANE
 DISTAL SURFACE OF LOWER 2ND
DECIDUOUS MOLAR IS MORE
MESIAL THAN THAT OF UPPER
 PERMANENT MOLARS MAY ERUPT IN CLASS I BUT IF
THE DIFFERENTIAL GROWTH OF MANDIBLE IN THE
FORWARD DIRECTION PERSISTS, IT CAN LEAD TO
ANGLE’S CLASS III MOLAR RELATION

3. DISTAL STEP TERMINAL PLANE
 DISTAL SURFACE OF LOWER 2ND
DECIDUOUS MOLAR IS MORE DISTAL
THAN THAT OF THE UPPER
 ERUPTING PERMANENT MOLARS MAY BE IN CLASS II
OR END-ON RELATION IF DIFFERENTIAL GROWTH
OF MANDIBLE PERSISTS

B. EXCHANGE OF INCISORS
• DECIDUOUS INCISORS ARE REPLACED BY PERMANENT
INCISORS
• MANDIBULAR CENTRAL INCISORS ARE USUALLY 1ST
TO ERUPT
INCISOR LIABILITY : The permanent incisors are larger than
the deciduous incisors they replace.This difference between the
amount of space needed for accommodation of incisors and the
amount of space available is called incisor liability.
MAXILLARY ARCH: 7mm
MANDIBULAR ARCH: 5mm

INCISOR LIABILITY IS OVERCOME BY :
a. UTILIZATION OF PHYSIOLOGICAL SPACES IN PRIMARY
DENTITION
b. INCREASE IN INTER-CANINE WIDTH:
During the transition from primary incisors to
permanent incisor there is an increase in inter-canine
width of both arches.
c. CHANGE IN INCISOR INCLINATION:
Permanent incisors erupt more labially inclined as
compared to primary incisors which are usually upright.
This causes increase in dental arch perimeter

INTER-INCISAL ANGLE :
PRIMARY INCISORS- 150O
PERMANENT INCISORS- 123O

2. INTER- TRANSITIONAL PERIOD
 LASTS FOR AROUND 1.5 YEARS
 RELATIVELY STABLE PHASE WITH NO CHANGES
OCCURING IN THE DENTITION
 TEETH PRESENT ARE PERMANENT INCISORS & 1ST
MOLARS ALONG WITH DECIDUOUS CANINES &
MOLARS

3. SECOND TRANSITIONAL PERIOD
CHARACTERIZED BY :
 REPLACEMENT OF DECIDUOUS MOLARS & CANINES
BY PERMANENT PREMOLARS & CUSPIDS
RESPECTIVELY
 BEGINS AT AROUND 10 YEARS OF AGE

UGLY DUCKLING STAGE
 This is a particular situation seen at around 8-9 years of
age during the eruption of Permanent canines. As the
developing permanent canines erupt, they displace the
roots of the lateral incisors Mesially.
 This results in transmitting of force on the roots of the
central incisors which also get displaced mesially.
 A resultant distal divergence of the crowns of the 2
central incisors causes a midline spacing.

 Ugly duckling stage has been described by BROADBENT
as during this stage children tend to look ugly
 This condition usually corrects by itself when canines erupt
& the pressure is transferred from the roots to the coronal
areas of the incisors

DEVELOPMENT OF PERMANENT DENTITION
 PERMANENT DENTITION FORMS WITHIN THE
JAWS SOON AFTER BIRTH EXCEPT FOR CUSPS
OF 1ST
PERMANENT MOLARS WHICH FORM
BEFORE BIRTH
 PERMANENT INCISORS DEVELOP LINGUAL OR
PALATAL TO DECIDUOUS INCISORS
 THE PREMOLARS DEVELOP BELOW THE
DIVERGING ROOTS OF DECIDUOUS MOLARS

 CALCIFICATION BEGINS AT BIRTH WITH THE
CALCIFICATION OF CUSPS OF 1ST
PERMANENT MOLARS & EXTENDS AS LATE AS
THE 25TH
YR OF LIFE
 COMPLETE CALCIFICATION OF INCISOR
CROWNS TAKES PLACE BY 4-5 YRS & OF
OTHER PERMANENT TEETH BY 6-8 YRS EXCEPT
FOR THE 3RD
MOLARS
 AT APPROXIMATELY 13 YRS OF AGE ALL
PERMANENT TEETH EXCEPT 3RD
MOLARS AREwww.indiandentalacademy.com

ERUPTION SEQUENCE OF PERMANENT DENTITION
MAXILLARY ARCH:
6 – 1 - 2 – 4 – 5 – 3 – 7 – 8
OR
6 – 1 – 2 - 4 – 3 – 5 – 7 – 8
MANDIBULAR ARCH:
6 – 1 – 2 – 3 – 4 – 5 – 7 - 8

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Mixed dent

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