2. DEFINITION
The period during
which both primary & permanent
teeth are in the
mouth together is known as the
mixed dentition period.
3. Successional teeth : Those permanent
teeth that follow into a place in the arch
once held by primary tooth
E.g.-Incisors, Canines, Premolars
Accessional teeth : Those permanent
teeth that erupt posteriorly to the primary
teeth
E.g.-Molars
4. Phases of Mixed Dentition
# First transitional period
# Inter transitional period
# Second transitional period
5. First Transitional Period
It is characterized by :
The emergence of first permanent
molars
The exchange of primary incisors
with permanent incisors
6. Emergence of first permanent
molars
The location & relationship of first
permanent molar depends much upon
the distal surface relationship
between the upper & lower second
primary molars.
7. “Changes in Occlusion”
• Flush terminal plane may lead to:
- Class I [ with late mesial shift ]
- Class II
- End-to-end
• Mesial step may lead to:
- Class I [ normally ]
- Class III
• Distal step leads to:
- Class II
11. Early Mesial shift
If the primary dentition is spaced dentition with flush
terminal relationship of second primary molars, the
eruptive forces of the permanent molar causes closing
of any existing spaces between the primary molars
(primate spaces) effectively causing a decrease in
arch length.
12. Late Mesial shift
When no spaces exist, the erupting first permanent
molar is not able to close spaces. In these cases when
the primary molars exfoliate the permanent molars
migrate mesially to use up the Leeway space.
14. Exchange of incisors
The permanent incisors are larger
than the primary teeth they replace.
This difference between the amount
of space needed for the
accommodation of the incisors & the
amount of space available for this is
called INCISAL LIABILITY.
7 mm 6 mm
(maxillary arch) (mandibular arch)
15. “Overcoming Incisal Liability”
1) Interdental spacing of primary incisors
2) Intercanine arch width growth
3) Labial positioning of permanent incisors
4) Favorable size ratio between primary &
permanent incisors
16. 1) Interdental spacing of primary
incisors
Good interdental spacing of primary incisors
allows for better alignment of the larger
permanent incisors.
Proper alignment Crowding
17. 2) Intercanine arch width growth
- Increased intercanine width creates more
room for the permanent incisors.
- Mandibular intercanine width increases
mostly during permanent incisor eruption.
- Maxillary intercanine growth occurs during
incisor eruption & continues unpredictable.
18. 3) Labial positioning of the permanent
incisors
Permanent incisors erupt to a more labial
position & are angled more labially, thereby
increasing the arch length.
130*
160*
PRIMARY PERMANENT
19. 4) Favorable size ratio between the
primary & permanent incisors
Size ratio may be favorable or unfavorable.
• Favorable : large primary, small permanent
• Unfavorable : small primary, large permanent
20. UGLY DUCKLING STAGE
(Broadbent phenomenon)
It is a transient/self-correcting malocclusion
seen in the maxillary incisor region between
8-9 yrs of age.
Erupting permanent canines displace the
roots of lateral incisors mesially, resulting in
transmission of force on to the roots of
central incisors which also get displaced
mesially.
21. A resultant distal divergence of crowns of
two central incisors causes a midline
spacing. This situation has been described
by Broadbent as the UGLY DUCKLING
STAGE as children tend to look ugly during
this phase of development.
22. Inter-transitional Period
In this period the maxillary & mandibular
arches consists of sets of primary &
permanent teeth i.e.
- permanent incisors
- primary canines & molars
- first permanent molars
23. Features of Inter-transitional period
• Under the influence of tongue, the
mandibular lateral incisors assume their
proper position in the arch & its initial lingual
location is eliminated.
• Small discrepancies are corrected by
pressure exerted by tongue & lips.
• No fixed intercusp relation is present, this
helps in mesial drift of mandibular teeth.
24. Second Transitional Period
It is characterized by the replacement of the
primary molars & canines by the premolars &
permanent canines respectively.
The combined mesiodistal width of the
permanent canines & premolars is usually less
than that of the primary canines & molars.
This surplus space is called LEEWAY SPACE .
It is - 1.8 mm in Maxilla (0.9 mm each side)
- 3.4 mm in Mandible (1.7 mm each side)
26. Features of Second Transitional Period
• Early Duckling stage is corrected.
• Arch loses its roundness.
• Most common sequence of eruption is :
4-3-5 in maxilla
3-4-5 in mandible
• This sequence is essential to prevent
crowding & utilization of Leeway space.
• The dental arch length & arch
circumference decreases with mesial
force.
