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
17-20
CROWN
FORMATION
1.5 months
2.5 months
9 months
6 months
11 months
ERUPTION
8 months 2
years
1.5
2.5
ROOT 3
3.5 4

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

12. Molar relation ship in deciduous dentition
Distal step
Flash terminal
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
Mesial step
Flash terminal
Distal step
Class I molar
If excess mandibular growth –class Ⅲ
Edge to edge
Class I
Class Ⅱ

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
1 2 C D E 6
6 E D C 2 1
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
years
CROWN
FORMATION
3.5
4.5
6.5
2.5-3 13
ERUPTION
7-8 10
10.5 12 18
ROOT
9-10
10-11
12.5
12-13
12-14
9.5
13-15
21.5

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