The document summarizes key stages in the development of oral functions from infancy to adulthood. It discusses: 1) How an infant's oral functions (respiration, suckling, swallowing) develop in the early stages to allow for feeding and breathing. 2) The transition from juvenile to adult swallowing patterns that occurs around age 12 with the eruption of permanent canines. 3) The chronology of primary and permanent tooth development including eruption times and replacement of teeth. 4) Factors involved in the pre-emergent and post-emergent eruption of teeth and maintenance of occlusal equilibrium.

1. EARLY STAGES OF
DEVELOPMENT
FINAL YEAR BDS
ORTHODONTICS

2. MATURATION OF ORAL
FUNCTION

3. • The principal physiologic functions of the oral cavity are: respiration, swallowing,
mastication and speech
• RESPIRATION:
• Important for survival of newborn infant
• Mandible is positioned downward and tongue positioned forward away from posterior pharyngeal
wall
• Allows air to move through nose, across pharynx and into lungs
• Newborn infants are obligatory nasal breathers
• SUCKLING:
• Suckling consists of small nibbling movements of lips, a reflex action
• The infant grooves their tongue so that the milk flows posteriorly into oesophagus and pharynx
• Tongue is placed anteriorly in contact with lower lip so that milk is deposited on the tongue
• Defined as “infantile swallow pattern”

4. • SWALLOWING:
• As infant matures, there is increasing activation of the elevator muscle
of mandible
• Tongue gathers bolus, positions it along the middle and transports it
posteriorly
• Juvenile chewing pattern: Mandible opens laterally on mouth opening,
then bringing it back toward the midline and closing to bring teeth into
contact with food. Established by the time primary molars erupt
• SPEECH:
Bilabial /m/, /p/, /b/
Tongue tip consonants /t/, /d/
Sibilants(tongue tip
close to but not against
palate)
/s/, /z/
Posterior tongue ( age
4-5)
/r/

5. • ADULT SWALLOW PATTERN:
• Characterised by cessation of lip activity
• Lips relaxed
• Tongue tip placed against alveolar process behind the upper incisors
• Posterior teeth brought into occlusion during swallowing
• Transition from juvenile to adult develops at age 12, with eruption of permanent
canines

6. ERUPTION OF PRIMARY
TEETH

7. • Natal teeth: aberration of dental lamina. Supernumerary tooth
present at time of birth. Most common in anterior Md. Interferes with
breast feeding, risk of inhalation if mobile
CHRONOLOGY OF TOOTH DEVELOPMENT; PRIMARY DENTITION
Calcification
Begins
Crown
Completed
Eruption
Root
Completed
Tooth Mx Md Mx Md Mx Md Mx Md
Centra
l
14 wk
IUL
14 wk
IUL
1½ mo 2½ mo 10 mo 8 mo 1½ yr 1½ yr
Lateral
16 wk
IUL
16 wk
IUL
2½ mo 3 mo 11 mo 13 mo 2 yr 1½ yr
Canin
e
17 wk
IUL
17 wk
IUL
9 mo 9 mo 19 mo 20 mo 3¼ yr 3¼ yr
1st
Molar
15 wk
IUL
15 wk
IUL
6 mo 5½ mo 16 mo 16 mo 2½ yr 2¼ yr
2nd
Molar
19 wk
IUL
18 wk
IUL
11 mo 10 mo 29 mo 27 mo 3 yr 3 yr

8. • Tooth eruption starts at 6 months and ends by 24 to 30
months
• Teeth erupt at interval of 3- 4 months
• Primate spacing- Spacing in anterior part of primary
dentition. In Mx, it is mesial to canine. In Md, it is distal to
canine

9. ERUPTION OF THE
PERMANENT TEETH

10. PRE-EMERGENT ERUPTION
• Labial or buccal drift of the tooth follicle within bone during
crown formation
• Two processes necessary for pre emergent eruption:
• Bone and root resorption overlying the crown
• Propulsive mechanism to move the tooth
• Resorption is rate limiting factor
• Signal for resorption of bone over the crown activated by crown
completion
• Dilaceration- occurs due to mechanical blockage of eruption. It
causes the apical area to move in opposite direction

11. THEORIES FOR PRE EMERGENT
ERUPTION
• Resorption of overlying bone
• Root elongation
• Cross-linking of maturing collagen in PDL
• Localised variation in blood pressure or flow
• Forces derived from contraction of fibroblasts
• Alterations in extra-cellular ground substance

12. POST-EMERGENT ERUPTION
• Post emergent spurt- stage of rapid eruption of tooth after it
penetrates the gingiva and reaches the occlusal level
• Juvenile occlusal equilibrium- period of slow eruption after
tooth reaches occlusal level. Teeth erupt at a rate that parallels
the rate of vertical growth of mandibular ramus. Experiences
pubertal growth spurt
• Adult occlusal equilibrium- occurs during adult life when
teeth erupt at extremely slow rate. However, eruption speeds
up when antagonist is lost

13. CHRONOLOGY OF TOOTH DEVELOPMENT; PRIMARY DENTITION
Calcification
Begins
Crown
Completed
Eruption
Root
Completed
Tooth Mx Md Mx Md Mx Md Mx Md
Central 3 mo 3 mo 4½ yr 3½ yr 7¼ yr 6 ¼ yr 10½ yr 9½ yr
Lateral 11 mo 3 mo 5½ yr 4 yr 8¼ yr 7½ yr 11 yr 10 yr
Canine 4 mo 4 mo 6 yr 5¾ yr 11½ yr 10½ yr 13½ yr 12¾ yr
1st PM 20 mo 22 mo 7 yr 6¾ yr 10¼ yr 10½ yr 13½ yr 13½ yr
2nd PM 27 mo 28 mo 7¾ yr 7½ yr 11 yr 11¼ yr 14½ yr 15 yr
1st M 32 wk
IUL
32 wk
IUL
4¼ yr 3¾ yr 6¼ yr 6 yr 10½ yr 10½ yr
2nd M 27 mo 27 mo 7¾ yr 7½ yr 12½ yr 12 yr 15¾ yr 16 yr
3rd M 8 yr 9 yr 14 yr 14 yr 20 yr 20 yr 22 yr 22 yr

14. SPACE RELATIONSHIP IN
REPLACEMENT OF INCISORS

15. • Permanent incisor tooth buds lie lingual and apical to primary incisors
• Mandibular permanent incisors erupt lingually and somewhat crowded
• In maxilla, permanent lateral incisor is lingually positioned at the time of its
emergence and it remains in that position
• Incisor liability- Permanent incisors are larger than the primary teeth which they
replace. This is the difference in amount of space needed and the amount
available
• Problems in eruption can displace teeth lingually or labially, however they are
displaced labially if there is crowding

16. • Overcoming incisor liability:
• Interdental spacing between primary incisors
• Slight increase in intercanine width (about 2 mm)
• Labial positioning of permanent incisors ( about 1-2
mm)
• Repositioning of mandibular canines

17. • Diastema- space between permanent maxillary incisors.
It closes when lateral incisors erupt.
• “Ugly duckling stage”- occurs during mixed dentition
stage due to flared and spaced permanent maxillary
incisors. It closes when canines erupt

18. SPACE RELATIONSHIP IN
REPLACEMENT OF CANINES
AND PREMOLARS

19. • E Space- difference is size between primary second
molar and second premolar. It is 2 mm in mandible and
1.5 mm in maxilla
• Leeway space- it is the combined size difference between
primary canines and molars and permanent canines and
premolars. It is 2.5 mm in mandible and 1.5 mm in
maxilla. Mesial migration of molars occurs here, reducing
arch length

20. Flush Terminal
Plane
Mesial Step Distal Step

21. Questions ??