DEVELOPMENT OF DENTITION & OCCLUSION. Spacing in mixed Dentition.ppt

DEVELOPMENT OF
DENTITION AND
OCCLUSION

DEVELOPMENT OF DENTITION
INTRODUCTION
 Embryonic cavity is lined by
oral ectoderm
 6th
week of intra uterine
life(IUL) local proliferation
→
of oral ectoderm formation
→
of dental lamina
 Deciduous teeth direct
→
proliferation of dental lamina
 Permanent teeth lingual
→
extension of dental lamina
 Permanent molars distal
→
proliferation of dental lamina

DEVELOPMENT OF TEETH
Bud stage
Cap stage
Bell stage
Root formation

PERIODS OF OCCLUSAL DEVELOPMENT
1. Pre-dental period
2. Deciduous dentition period
3. Mixed dentition
4. Permanent dentition period

PRE-DENTAL PERIOD
 Period after birth during which neonate does
not have teeth
 Lasts 6 months after birth

Gum pads
 Alveolar processes at the time of
birth
 Firm,pink,horse shoe
shaped,covered by fibrous
periosteum
 Develops in two parts
1. Labiobuccal portion
2. Lingual portion
 Both portions separated by dental
groove
 Gum pads are divided into 10
segments by transverse grooves
 Each segment has one developing
deciduous tooth sac

 lateral sulcus: transverse groove
between canine and first deciduous molar
segment.
 Useful in judging inter arch relationship at
a very early stage.
 Lateral sulcus of mandibular arch is more
distal to that of maxillary arch

 birth
At birth, no teeth are
visible. Primary teeth
are at least partially
formed and
development of
permanent teeth has
begun.

Infantile open bite
 Upper and lower gum pads are similar to each
other
 Upper gum pad is longer and wider
 When both are approximated, there is a complete
overjet all around
 Contact occurs between upper and lower gum
pads in first molar region and space exists in
anterior region
 This infantile open bite is considered normal and
helps in suckling

STATUS OF DENTITION
 Neonate is without teeth for 6 months of
life.
 Gum pads insufficient to accommodate
developing incisors that are crowded in
crypts
 1st
yr of life gum pads grow rapidly
→
permitting incisors to erupt in good
alignment.

NATAL TEETH
 Teeth erupted at the
time of birth natal
→
teeth
 Teeth erupted during
1st
month of life
neonatal teeth
→

 Natal and neonatal
teeth mostly in
mandibular incisor
region and show
familial tendencies

DECIDUOUS DENTITION PERIOD
 1st
6 weeks of IUL initiation of tooth buds
→
 Primary teeth erupt at about 6 months
 Eruption completed by 2 ½-3 ½ yrs
 Sequence of eruption A-B-D-C-E
→

 6 months
At six months, the
four central incisors
are visible, usually
appearing two at a
time and appearing in
the lower jaw first

 7-8 months
At seven or eight
months, the four
lateral incisors appear
next to the central
incisors. The primary
teeth are bluish white.

 12 months
At around twelve
months, the primary
first molars appear,
leaving temporary
spaces between them
and the lateral
incisors

 16 months
At sixteen months, the
primary canines erupt
between the lateral
incisors and first
molars.

 2 years
At two years, the
second primary
molars begin to
appear, completing
the primary teeth. By
age three, they
appear completely

SPACING IN DECIDUOUS DENTITION
 Spaces usually exist between deciduous
teeth physiological or developmental
→
spaces
 Important for normal development of
2°dentition
 Absence of spaces is an indication that
crowding of teeth may occur in 2°dentition

Primate spaces
 Also called as simian or
anthropoid spaces
 Seen mesial to
maxillary canines and
distal to mandibular
canines
 Helps in placement of
canine cusps of
opposing arch

Deep bite
 May occur in initial developing stages
 Accentuated by the fact that deciduous incisors
are more upright
 Lower incisal edges often contact cingulum area
of maxillary incisors
 Later reduced by
1. Eruption of deciduous molars
2. Attrition of incisors
3. Forward growth of mandible

Flush terminal plane
 Mesiodistal relation between distal
surfaces of upper and lower 2nd
deciduous
molars is called as flush terminal plane
 Normal feature of deciduous dentition
where second deciduous molars are in
same vertical plane

MIXED DENTITION PERIOD
 Begins at approximately 6yrs.Classified
into:
1. 1st
transitional period
2. Inter transitional period
3. 2nd
transitional period

FIRST TRANSITIONAL PERIOD
FIRST TRANSITIONAL PERIOD
 Emergence of 1st
permanent molars and exchange
of deciduous incisors with permanent incisors
 1st
permanent molar erupts at 6yrs-guided into the
dental arch by distal surface of 2nd
deciduous molar
 Mesiodistal relation between distal surfaces of
upper and lower deciduous molars are of 3 types
1. Flush terminal plane
2. Mesial step terminal plane
3. Distal step terminal plane

FLUSH TERMINAL PLANE
 Mesiodistal relation between distal
surfaces of upper and lower 2nd
deciduous
molars is called as flush terminal plane.
 Normal feature of deciduous dentition
where second deciduous molars are in
same vertical plane.

 Erupting first molars may be in a flush or
end on relation
 For transition of such an end on molar to a
Class I molar relation, lower molar has to
move forward by about 3-5mm relative to
upper molar
 This can occur in 2 ways. By early shift or
late shift

EARLY SHIFT
 Occurs during early
mixed dentition period
 Eruptive force of
permanent molar
pushes deciduous 1st
and 2nd
molars in the
arch to close primate
space and establishing
Class I
LATE SHIFT
 Occurs during late
mixed dentition period
 In children who lack
primate space, when
the deciduous molars
exfoliate the
permanent 1st
molars
drift mesialy utilizing
leeway space.

MESIAL STEP TERMINAL PLANE
 Distal surface of lower 2nd
deciduous molar
is more mesial than that of upper. Thus
permanent molars directly erupt into
Angles Class I occlusion
 Occurs due to early forward growth of
mandible

DISTAL STEP TERMINAL PLANE
 Distal surface of lower 2nd
deciduous molar
lies more distal to that of upper. Thus
erupting permanent molars maybe in
Class II relation

INCISAL LIABILITY
 The exchange of lower incisors take place.
The difference between the amount of
space needed for the accomodation of
incisors and the space available for this
incisal liability
→
 It is roughly 7mm in upper arch and 5 mm
in lower arch

Incisal liability
Overcome by the following factors:
1. Utilization of interdental spaces seen in
primary dentition
2. Increase in inter- canine width
3. Change in incisor inclination

INTER TRANSITIONAL PERIOD
 Maxillary and mandibular arches consists of
sets of deciduous and permanent teeth
 Between permanent incisors and permanent
1st
molars are deciduous canines and molars
 This phase during mixed dentition stage is
relatively stable and no change occurs

SECOND TRANSITIONAL PERIOD
 Replacement of deciduous molars and
canines by premolars and permanent
cuspids respectively

Leeway space of Nance
 Combined mesiodistal
width of permanent
canines and premolars
is usually less than that
of deciduous canines
and molars, this is
Leeway space of
Leeway space of
Nance
Nance

 Greater in mandibular
arch [3.4mm] than in
maxillary arch [1.8mm]
 This excess space is
utilized for mesial drift
of mandibular molars to
establish Class I molar
relation

Ugly duckling stage
 Transient or self
correcting malocclusion
seen in maxillary incisor
region b/w 8-9yrs seen
during eruption of
permanent canines

 As developing
permanent canines
erupt, they displace
roots of lateral incisors
mesially,in turn
transmitting force to
roots of central incisors
which gets displaced
mesially. Resultant
divergence of crown
causes midline spacing

 18 years
Last teeth to appear,
the third molars, or the
wisdom teeth, erupt at
about age 18

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