Development of occlusion

INTRODUCTION
 Term occlusion has both static and dynamic aspects.
 Statics refers to the form, alignment and articulation
of teeth within and between dental arches and
relationship of teeth to the supporting structure.
 It may be defined as the contact relationship of the
teeth in function or parafunction.

Periods of occlusal development
 Pre-dental period
 Deciduous dentition period
 Mixed dentition teeth
 Permanent dentition period

Pre dental period
 The period after birth during which the neonates does
not have teeth.
 Lasts for 6 months

Gum pads
 Alveolar processes at the time of birth.
 Pink, firm and are covered by a dense layer of fibrous
periosteum.
 Horse shoe shaped and develops in two parts.
 Labio-buccal portion and lingual portion.
 Two portions of gum pads are separated by dental
grooves.
 Gum pads are divided into 10 segments by certain
grooves called transverse grooves.

 Each of these segments consist of developing
deciduous tooth sac.
 Gingival grooves separate gum pads from palate and
the floor of mouth.
 Transverse groove between C and dec 1st molar
segment is called lateral sulcus.
 Lateral sulci are useful in judging the inter-arch
relationship at a early stages.
 The lateral sulcus of the mandibular arch is normally
more distal to that of maxillary arch

 The upper and lower gum pads are almost similar to
each other.
 The upper gum pad is both wider as well as longer
than the mandibular gum pad.
 Thus when upper and lower gum pads are
approximated, there is complete overjet all around.
 Contact occurs b/w upper and lower gum pads in first
molar region and a space exists between them in ant.
Region.
 Infantile open bite is considered to be normal and it
helps in suckling.

Status of dentition
 Neonate is without teeth for about 6 months of life.
 At birth gum pads are not sufficiently wide to
accommodate developing incisors, which are crowded
in their crypts.
 During 1st yr of life gum pads rapidly grow permitting
incisors to erupt in the good alignment.

 Teeth that are present at the time of birth are called
natal teeth.
 Teeth that erupts during the first month of age are
called neonatal teeth.
 The natal and neonatal teeth are mostly located in the
mandibular incisors region and shows a familial
tendency.

DECIDUOUS DENTITION PERIOD
 Initiation of primary tooth buds occurs during first six
weeks of intrauterine life.
 Primary teeth begin to erupt at the age of about 6
months.
 Eruption time for primary teeth : 2nd half year to 3 and
half yrs.

Eruption sequence
Tooth Emergence of
time(MONTH)
A 10 MONTHS (8-10)
B 11
C 19
D 16
E 29

TOOTH EMERGENE OF TEETH
(MONTH)
A 8 MONTH(6-10)
B 13
C 20
D 16
E 27

SEQUENCE
 MANDIBULAR CI (6-10)
 MAXILLARY CI (8-12)
 MAXILLARY LI (9-12)
 MANDIBULAR LI (10-16)
 MAX AND MAND IST MOLAR(13-19)
 MAXILLARY CANINE(16-22) APPRO 19 MONTH
 MANDIBULAR CANINE (17-23)
 MANDIBULAR 2ND MOLAR(27)
 MAX 2ND MOLAR(29)

SPACING IN DECIDOUS DENTITION
 Spacing usually present b/w deciduous teeth and called
physiological spaces or the developmental spaces
 Spaces in primary dentition is normal for the dev. Of
permanent dentition.
 Absence of spaces in primary dentition can cause crowding.
 Spacing invariably is seen mesial to max canine and distal
to mand canines.
 These spaces are called primate spaces or the simian spaces
or anthropoid spaces as they are seen commonly in
primates.

Deep bite
 A deep bite may occur initial stages of development.
 Deep bite is accentuated by fact that deciduous
incisors are more upright than their successors.
 Lower incisal edges often contact cingulum area of
maxillary incisors.
 This deep bite is later reduced due to following factors:
1. Eruption of deciduous molars.
2. Attrition of incisors
3. Forwards movement of mandible due to growth.

Mixed dentition teeth
 Mixed dentition period begins at approximately 6 yr of
age with eruption of 1st permanent molars.
 During mixed dentition period, deciduous teeth along
with some permanent teeth are present in oral cavity.
 Mixed dentition period classified into 3 phases:
1. 1st transitional period
2. Inter-transtional period
3. 2nd transitional period

1st transitional period
 Characterized by emergence of 1st permanent molars
and exchange of deciduous incisors with permanent
incisors.
 1st permanent molar erupts at 6 yrs guided into dental
arch by distal surface of 2nd deciduous molar.
 Mesio-distal relation b/w distal surface of upper and
lower 2nd deciduous molars can of 3 types:
1. Flush terminal plane
2. Distal step
3. Mesial step

FLUSH TERMINAL PLANE
 Distal surface of upper and lower 2nd deciduous molars are
in one vertical plane.
 Normal feature of deciduous dentition.
 Erupting 1st permanent molars may also be in a flush or end
on relationship.
 For transition of such an end on molar relation to a class 1
molar relation, lower molar has to move forward by about
3-5 mm relative to upper molar.
 Utilization of physiologic spaces and leeway spaces in lower
arch and by differential forward growth of mandible.
 Shift in lower from a flush terminal plane to class 1 relation
can occur in 2 ways- EARLY AND LATE SHIFT

EARLY SHIFT
 Early shift occurs during early mixed dentition period.
 Eruptive forces of 1st permanent molar is sufficient to
push deciduous 1st and 2nd molar forward in arch to
close primate space and establish a class 1 molar
relationship.
 Since this occur early in mixed dentition period it is
called early shift.

Late shift
 Many children lack primate spaces and thus erupting
permanent molars are unable to move forward to
establish class 1 relationship.
 In these cases, when deciduous second molars
exfoliate permanent 1st molar drift mesialy utilizing
leeway spaces
 This occur in late mixed dentition period and is thus
called late shift.

Mesial step terminal plane
 Distal surface of lower second deciduous molar is
more mesial than that of upper.
 Permanent molars erupts directly into class I
occlusion.
 Mesial step terminal plane most commonly occur due
to early forward growth of mandible.
 If differential growth of mandible in a forward
direction persists, it can lead to class III molar relation.
 If forward mandibular growth is minimal, it can
establish a class I relation.

Distal step terminal plane
 Distal surfaces of lower second deciduous molar being
more distal to that of the upper.
 Thus erupting permanent molars may be in Angle’s
class II occlusion.

Exchange of incisors
 During first transition period deciduous incisors are
replaced by permanent incisors.
 Mandibular CI : 1st to erupt
 Permanent incisors>deciduous incisors
 The difference b/w the amount of space needed for the
accomodation of incisors and the amount of space
available for this is called incisal liability.
 Incisal liability (maxillary arch)

The incisal liablity overcome by:
A. UTILIZATION OF INTERDENTAL SPACES SEEN IN
PRIMARY DENTITION:
Physiological spaces or developmental spaces
B. increase in INTERCANINE WIDTH
C. CHANGES IN INCISOR INCLINATION
Primary incisor more upright
Permanent labially inclined

INTER-TRANSITIONAL PERIOD
 In this period the maxillary and mandibular arches
consist of sets of deciduous and permanent teeth.
 Between the permanent incisors and the first
permanent molars are deciduous molars and canine.
 This phase during the mixed dentition period is
relatively stable and no change occurs.

2nd transitional period
 2nd transitional period is characterized by replacement
of deciduous molars and canines by premolars and
permanent cuspids respectively.
 Combined mesio-distal width of permanent canines
and premolars is usually less than that of deciduous
canines and molars and this surplus space is called
leeway space of nance.

 Leeway space in mandibular arch: about 3.4 mm
(1.7mm)
 Leeway space in maxillary arch: about 1.8mm
 Excess spaces available after exchange of deciduous
molar and canines are utilized for mesial drift of
mandibular molars to establish class I molar relation.

UGLY DUCKLING STAGE
 Sometimes a transient or self correcting malocclusion is seen in
maxillary incisor region b/w 8-9 yr of age.
 This is a particular situation seen during eruption of permanent
canines.
 As developing permanent C erupt, they displace roots of LI on to
toots of CI, which also get displaced mesialy.
 A resultant distal divergence of crowns of two central incisors
causes a midline spacing.
 Described by BROADBENT ( hence also known as broadbent
phenomenon) as ugly duckling stage as children tend to look
ugly during this phase of development.
 This usually corrects by itself when canines erupt and pressure
pressure is transferred from roots to coronal area of incisors.

PERMANENT DENTITION PERIOD
 Permanent dentition forms within jaws soon after
birth, except for cusps of first permanent molars,
which forms before birth.
 Permanent incisor develop lingual or palatal to
deciduous incisors and move labially as they erupt.
 Premolars develop below diverging roots of deciduous
molars.

 Eruption sequence of permanent dentition in maxilla
6-1-2-4-3-5-7 or 6-1-2-3-4-5-7
 In mandibular arch sequence is
6-1-2-3-4-5-7 or 6-1-2-4-3-5-7

Development of occlusion

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