The document discusses the development of occlusion from birth through adulthood. It begins by describing the pre-dental gum pad period in infants and transitions to the deciduous dentition period where primary teeth begin to erupt around 6 months. Next is the mixed dentition period where permanent molars and incisors begin to erupt between ages 6-13 years. This involves two transitional phases as deciduous teeth are replaced. Finally, it describes the characteristics and development of the permanent dentition from formation to complete eruption in the late teens. Key factors for a smooth transition between dentitions include primate spaces, physiological spacing, and preservation of leeway space.

1. Development of
occlusion
Dr Lamis Elsharkasi

2. occlusion
• Occlusion simply means “contact between teeth”
The human dentition is in dynamic state constantly changing
throughout life.
Period of occlusion :
• Pre-dental period
• Deciduous dentition period
• Mixed dentition period
• Permanent dentition period

3. Pre-dental period
• The period after birth which the
neonate does not have teeth
• Lasts for 6 months
• The alveolar processes at the
time of birth are known as gum
pads

4. Gum pad
Gum pad are:
• Pink
• Firm
• Horse-shoe shaped
• Covered by a dense layer of fibrous periosteum
• Developed in two parts labio-buccal portion and lingual portion
• Dental groove separates the two portions

5. Gum pad
• The gum pad is divided into 10 segments by transverse grooves
• Each segment consists of one developing deciduous tooth sac
• Gum pad are separated from the palate and the floor of the mouth
by gingival grooves
• Lateral sulcus: present between the canine and 1st molar
Transverse groove
Gingival groove
Lateral sulcus

6. Gum pad
• The upper gum pad is larger and wider than the lower, so when
approximated there is a complete overjet all around.
• Contact between upper and lower gum pad occurs in the molar
region
• A space is exist in the anterior region (infantile open bite). It is
normal and helps in suckling

7. Gum pad
State of dentition:
• At birth the gum pad are not sufficiently wide to accommodate the
developing incisors
• During the first year of life a rapid growth happened which permits the
incisors to erupt in good alignment

8. Gum pad
• Natal teeth : presents at time
of birth
• Neonatal teeth: erupts during
the first month of age
• Both located in the mandibular
incisor region

9. Deciduous dentition period
• Initiation of primary tooth buds occurs during the first 6 weeks of
intra-uterine life
• Eruption of primary teeth begin around 6 months
• Establishment of primary dentition is usually by the age of 3years
• 3-5 years – no significant change
• Sequence of eruption: A-B-D-C-E

10. Decidous teeth development and
eruption time
MAXILLARY
TEETH
A B C D E
HARD TISSUE
FORMATION( months
intrauterine)
13-16 15-17 15-18 15-17 17-20
CROWN
FORMATION
1.5
months
2.5
months
9
months
6
months
11
months
ERUPTION 8
months
9
months
2
years
1.5
years
2.5
years
ROOT
FORMATION
3
years
3
years
3.5
years
3
years
4
years

11. MANDIBULAR
TEETH
A B C D E
HARD TISSUE
FORMATION( months
intrauterine)
13-16 15-17 16-18 15-17 17-20
CROWN
FORMATION
2
months
3
months
9
months
6
months
10
months
ERUPTION 6
months
10
months
2
years
1.5
years
2.5
years
ROOT
FORMATION
2.5-3
years
2.5
years
3.5
years
2.8
years
3.5
years
Variation in eruption of deciduous teeth +/- 6 months

12. Molar relation ship in
deciduous dentition
Flash terminal Distal step Mesial step

13. Characteristics of deciduous
dentition
• Flash terminal plane
• Deep bite: may occur in the initial stage of
deciduous dentition .
• This is later reduced by these factors:
Eruption of deciduous molars
Attrition of primary incisors
Forward movement of mandible
due to growth
• Upright inclination of incisors
• Spacing in deciduous teeth

14. Spacing in deciduous dentition
• 1. interdental spaces: also called physiological spaces and
developmental spaces
• These spaces are important for normal development of permanent
dentition
• Absence of spaces in deciduous dentition, leads to crowding in
permanent dentition

15. Spacing in deciduous dentition
• 2. primate space(arthropoid space):
• Spacing seen mesial to the maxillary deciduous canine (1.7 mm)
and distal to the Mandibular canine (1.5 mm).
• Importance: early mesial shift

16. Mixed dentition
• Begin around 6 years of age with the eruption of the first permanent
molars
• Mixed dentition = deciduous teeth + permanent teeth
• Divided into 3 phases:
1st transitional period
Inter-transitional period
2nd transitional period

17. 1st transitional period
• Characterized by the eruption of 1st permanent molar and
exchange of deciduous incisors with permanent incisors
• 1st permanent molar erupts at 6 yrs. and its location depends on the
deciduous molar relation ship
Class I molar
If excess mandibular
growth –class Ⅲ
Edge to edge
Class I
Class Ⅱ
Mesial step Flash terminal Distal step

18. Early mesial shift
• Early shift occurs during early mixed dentition period
• Eruption force of 1st permanent molar is sufficient to push deciduous
1st & 2nd molar forward to close the primate space

19. Exchange of incisors
• During the 1st transitional period the
deciduous incisors are replaced by the
permanent incisors
• Mandibular incisors erupt first
• The permanent incisors are larger than
the deciduous teeth they replace
• The amount needed for the
accommodation of the permanent
incisors and the amount available for
this is called Incisal liability
• 7mm in maxilla
• 5mm in mandible

20. Incisal liability
• The incisal liability is overcomed by the following factors:
• Interdental dental spaces
• Inter canine width
• Incisor inclination

21. Incisal liability
• 1. utilization of interdental spaces:
• Physiological spaces that exist in deciduous dentition are utilized to
account for incisal liability
• In spaced deciduous dentition, alignment of permanent teeth in arch
is easier than in closed dentition
•
• 2. intercanine width:
• Width growth creates more room for the permanent incisors
• 3. incisor inclination:
• Permanent incisors erupt more labially which tend to increase the
dental arch perimeter

22. Inter-transitional period
• this period started when 1st permanent molar & permanent incisors
are erupted
• Consists of set of deciduous and permanent teeth
• This period is relatively stable and no change occur
6 E D C 2 1
6 E D C 2 1
1 2 C D E 6
1 2 C D E 6

23. 2nd transitional period
• This period characterized by the replacement of deciduous molar
and canine by the premolars and permanent canine respectively
• Late shift of permanent molar occur in this period by utilizing leeway
space to establish class Ⅰmolar.

24. Late mesial shift
• In cases when the primate space is
absent, the permanent 1st molar shift drift
mesially utilizing the leeway space.
• Premolars are smaller than primary molar
teeth they replace
• The extra space is called leeway space
• C+D+E > 3+4+5
• Maxilla : 1.5mm
• Mandible: 2.5mm

25. Ugly duckling stage
• Characterized by spacing between
maxillary central incisors
• Parents often apprehensive during
this stage and consult the dentist
• It is a transient or self correcting
malocclusion which seen between 8-9
yrs. During the eruption of permanent
canine

26. Ugly duckling stage
• As the developing canines erupt, they
displace the roots of the lateral
incisors mesially
• This results in transmitting the force
on to the roots of central incisors
which also displaced mesially.

27. Permanent dentition
• Permanent dentition forms within the jaw soon after birth except the
cusps of the first permanent molar which forms before birth
• Permanent incisors develop lingual or palatal to the deciduous teeth
and move labially as they erupt
• Premolars develop below the diverging roots of deciduous molars

28. Permanent dentition
• Sequences of eruption of permanent teeth:
• Maxilla : 6 – 1 – 2 – 4 – 3 – 5 – 7
Or : 6 – 1 – 2 – 3 – 4 – 5 – 7
• Mandible: 6 – 1 – 2 – 3 – 4 – 5 – 7
or : 6 – 1 – 2 – 4 – 3 – 5 – 7

29. Permanent teeth development and
eruption time
MAXILLARY
TEETH
1 2 3 4 5 6 7 8
HARD TISSUE
FORMATION
4
months
11
months
5
months
20
months
26
months
7
months
intra-
uterine
3
years
8
years
CROWN
FORMATION
3.5
years
4.5
years
5
years
6.5
years
7
years
2.5-3
years
7
years
13
years
ERUPTION 7-8
years
8
years
11
years
10
years
10.5
years
6
years
12
years
18
years
ROOT
FORMATION
9-10
years
10-11
years
12.5
years
12-13
years
12-14
years
9.5
years
13-15
years
21.5
years

30. MANDIBULAR
TEETH
1 2 3 4 5 6 7 8
HARD TISSUE
FORMATION
4
months
4
months
5
months
20
months
26
months
7
months
intra-
uterine
8
years
9
years
CROWN
FORMATION
4.5
years
4.5
years
4.5
years
6.5
years
7
years
2.5
years
7
years
13
years
ERUPTION 6-7
years
7-8
years
10
years
10-11
years
11
years
6
years
12
years
18
years
ROOT
FORMATION
8-9
years
9-10
years
11-13
years
11-13
years
12-14
years
8-10
years
14-15
years
20
years
Variation in eruption of permanent teeth +/- 2 years

31. Characteristics of permanent
dentition
• Class i molar relationship ( mesiobuccal cusp of upper 1st molar
occludes with the mesiobuccal groove of lower 1st molar)
• No crowding
• No rotated teeth
• No spacing
• Appropriate inclination of teeth
• The occlusal plane should be flat or have only a mild curve of spee (
1.3mm)

32. Essential factors of smooth transition
from primary to permanent dentition
• Primate space
• Physiological spacing
• Preservation of leeway space
• Tooth size and jaw in harmony