Chronology and morphology of primary and permanent teeth - PowerPoint Presentation

Slide1

Chronology and morphology of primary and permanent teeth Slide2

Outline

Tooth development phases

Pre-eruptive period

Period of eruption of the primary dentition

Static period of the primary dentitionSlide3

Tooth Development Phases

1- Initiation

The process of tooth development starts as early as 7 weeks in

utero

In this phase, the locations of teeth are established with the appearance of tooth germs

.Slide4

Tooth Development Phases

2- Morphogenesis

The shape of the teeth is determined in this phase.Slide5

Tooth Development Phases

3-

Histogenesis

Differentiation of cells takes place to produce the fully formed dental tissues.Slide6
Slide7

The primary epithelial bands divides into:

Vestibular lamina

(

buccally

).

Dental lamina

(

lingually

).

The dental lamina contributes to the formation of the teeth.

Underlying

MesenchymeSlide8

Tooth germ formation

Bud stage: (initiation)

The enamel organ appears as a simple ovoid epithelial

mass

Surrounded

by

mesenchyme

.

Mesenchyme

separated from the epithelium by a basement membrane.Slide9

Tooth germ formation

Cap stage (morphogenesis)

Invagination

of the deeper surface of the enamel organ.

Peripheral cells start to be arranged as

external and internal enamel epithelium

.Slide10

Cap stage Slide11

Tooth germ formation

Bell stage

The shape of the internal enamel epithelium decides the shape of the crown.Slide12

Bell stage Slide13

Bell stage

Cells of the inner enamel epithelium differentiate into

Ameloblasts

Adjacent cells from the dental papilla will differentiate into

Odontoblasts

Odontoblasts

produce pre-dentine and dentine.

The presence of dentine induces

Ameloblasts

to form enamel

Apposition of enamel and dentin will be followed by calcificationSlide14

Calcification

Starts between 14 and 16 weeks of intrauterine life for primary teeth

Begins in cusp tips and

incisal

edges of teeth and continues

cervically

Very sensitive process that takes place over a long period of time.Slide15

Calcification

Any severe systemic event during the development of teeth will result in some dental abnormality

Chronological enamel defects.Slide16

Calcification

Different teeth will show defects at different levels of the crown depending on the stage of crown formation.Slide17

Eruption

Eruption

is the movement of teeth within and through the bone of the jaws and the overlying mucosa to appear in the oral cavity and contact the opposing teeth.

Emergence of the tooth is the first sign of appearance in the oral cavity.Slide18

Pre-eruptive phase

: period during which the tooth root begins its formation and begins to move towards the surface of the oral cavity from its bony vault.Slide19

Eruptive phase (

prefunctional

):

period of gingival emergence until contact is achieved with the opposing tooth.

Functional eruptive phase:

after the tooth meets its antagonist. A dynamic unit throughout life. Slide20

Factors influencing tooth formation and eruption

Why is it difficult to study and understand the process of eruption?

T

ooth

structure and eruption vary from one species to another

Histological studies in humans are rarely possible because of the inaccessibility of tissue for sampling and ethical considerationsSlide21

Theories of eruption

1- Root formation

2- Hydrostatic pressure

3- Bone remodeling

4- Periodontal ligament Slide22

Root formation theory

The space for the growing root is accommodated by

occlusal

movement of the tooth crown

However;

Some teeth with extensive root development fail to erupt

A study using dogs, showed that the tooth itself played no part in the eruptive processSlide23

Hydrostatic pressure theory

Studies using dogs demonstrated that the tissue pressure apical to the erupting tooth was greater than

occlusally

, theoretically generating an eruptive force

However;

The study only compared pressure differentials but whether this pressure difference actually caused eruption is not proven Slide24

Bone remodeling theory

Bone remodeling around the tooth causes eruption

However;

Animal studies showed that bony remodeling occurs

around the dental follicle regardless

of the presence of a

toothSlide25

Periodontal ligament theory

Strong evidence exists to show that the periodontal ligament, which is derived from the dental follicle, provides the force required for eruption mainly by fibroblast contraction

However;

in vitro

tissue studies have limitations

Slide26

In conclusion

There is no evidence that one hypothesis fully explains tooth eruption, and that eruption is likely to be a

multifactorial

processSlide27

Basic biology of tooth eruption

1- Bone

resorption

Resorption

appears to be genetically controlled and

not mechanically

by the eruption of the

tooth

2- Role of the dental follicle

Removing

the follicle means the tooth will not erupt

while

leaving it and replacing the tooth with an artificial replica

means the tooth will erupt3- Cellular events and molecules

Certain molecules will recruit mononuclear cells into the dental follicle Slide28

Control of eruption

1- Hormonal control

2- Systemic conditions

3-

Physical

control mechanismSlide29

Hormonal control

Most eruption occurred in the late evening indicating that eruption was probably under hormonal control

Mainly due to the effects of the late evening secretion of

growth hormone and thyroid hormone.

Children with growth hormone deficiency had delayed tooth eruptionSlide30

Systemic conditions

Nutritional deficiency (extremes)

Preterm and low birth weight infants

Cerebral palsy

Anemia

Renal failure

Genetic disorders

Apert

syndrome

Cleidocranial

dysostosis

Down syndrome

Ectodermal

dysplasia

Gardner syndrome

OsteopetrosisSlide31

Physical control mechanism

According to the equilibrium theory teeth remained in a position within the jaws where forces acting in equal and opposite directions cancelled each other

Oral musculature, soft tissue pressures,

masticatory

forces, and eruptive force.Slide32

Pre-eruptive period

Upper anterior gum pad (

intercanine

width) is typically wider than the lower anterior gum pad

Upper anterior gum pad protrudes (

Overjet

) about 5mm

Overbite about 0.5mm.Slide33

Pre-eruptive period

Marked palatal width increase and a decrease in the

overjet

over the first 6 months of postnatal life.Slide34

Pre-eruptive period

Labial

frenum

is usually hypertrophic but it does not hinder suckling

Retro incisal papilla is hypertrophic.Slide35

Pre-eruptive period

Palate is straight at birth. Becomes concave under the effect of growth of the alveolar bone

Tongue is relatively large.Slide36

Oral mucosa

Epstein pearls.

Bohn nodules

Dental lamina cyst.Slide37

Epstein pearls

Small white or greyish white lesions

Present in about 80% of neonates.

Formed along the

midpalatine

raphe.Slide38

Epstein pearls

Considered remnants of epithelial tissue trapped along the raphe as the fetus grows.

Disappear within a few weeks of life.Slide39

Bohn nodules

Formed along the buccal and lingual aspects of the dental ridge and on the palate away from the raphe.Slide40

Bohn nodules

Considered remnants of mucous gland tissue and are histologically different from Epstein pearls.

Disappear spontaneously in the early months of life.Slide41

Dental lamina cysts

Found on the crest of the maxillary and mandibular dental ridges.

Are remnants of the dental lamina.

Slough within the first few months of life.Slide42

Dental lamina cysts

Differential diagnosis: natal teeth.

No treatment necessary.Slide43

Period of eruption of the primary dentition

Commences at 6 months and is well established by 30-36 months

Maximum growth of the jaws occurs during this period.Slide44

Deciduous Teeth

20 in number, 10 in each jaw.

There are no premolars in the deciduous dentition.

The primary molars are replaced by the permanent premolars.

The permanent molars erupt distal to the primary second molars.Slide45

Nomenclature

Beginning with the midline, the teeth are named as follows:

Central incisor.

Lateral incisor.

Canine.

First molar.

Second molar.Slide46

Tooth numbering

Palmer Notation Method

.

Children’s 20 primary teeth are lettered “A” through "E" in each quadrant.

Universal Numbering System.

FDI Two-Digit Notation

.

The currently accepted convention to view the FDI notation chart is from the perspective of the

patient's right

.Slide47

FDI Two-Digit Notation

1s are central incisors, 2s are laterals, 3s are canines, 4s are 1st premolars etc., up through 8s which are 3rd molars

The

permanent teeth

  quadrants are designated 1 to 4 such that 1 is upper right, 2 is upper left, 3 is lower left and 4 is lower right

In the

deciduous dentition

the numbering is correspondingly similar except that the quadrants are designated 5,6,7 and 8. Slide48

Chronology of eruption of primary teeth

1

st

tooth at approximately 6 months

Usually the lower central incisorSlide49

Chronology of eruption of primary teeth

All eruption schedules are

estimates

No two individuals are alike

.

Multiple parameters: race, gender, ethnicity, familial environment, heredity.Slide50

Chronology of eruption of primary teeth

Maxillary

Mandibular

Central incisors

6-10 months

5-8 months

Lateral incisors

8-12 months

7-10 months

Canines

16-20 months

16-20 months

First molars

11-18 months

11-18 months

Second molars

20-30 months

20-30 monthsSlide51

Sequence of eruption

A then B then D then C then E

Mandibular

precede maxillary most of the time.Slide52

Rhythm of eruption of primary teeth

Symmetrical groups of 4 teeth every 6 months

Teeth erupt symmetrically in both jaws, simultaneously and in pairs.Slide53

The ‘six/four’ rule for primary tooth emergence

Four teeth emerge for each 6 months of age.

6 months: 4 teeth (lower & upper As)

12 months: 8 teeth (1+upper & lower Bs)

18 months: 12 teeth (2+ upper & lower Ds)

24 months: 16 teeth (3+ upper & lower Cs)

30 months: 20 teeth (4+ upper & lower Es)Slide54

Static period of the primary dentition

Period of stability of the primary teeth

3-6 years of age

Child has 20 primary teeth in their final and functional position

Occlusion is well establishedSlide55

Static period of the primary dentition

Occlusal

features

Occlusion of the primary second molar

Inter-arch relationship of primary teethSlide56

Occlusal

features in the established primary dentition

Incisor teeth tend to be spaced

Primate spaces exist between upper B & C and between lower C and DSlide57

Occlusal

features in the established primary dentition

Upper incisors are upright

Incisor relationship is more towards edge to edge.Slide58

Occlusal

features in the established primary dentition

Long axis of primary teeth is parallel

Absence of the curve of

Spee

In general, teeth in the primary dentition tend to be well aligned.Slide59

Classification of occlusion of the primary second molar

Look at the distal aspect of the primary second molar

Flush terminal plane

Mesial

step

Distal stepSlide60

Flush terminal planeSlide61

Mesial stepSlide62

Distal stepSlide63

Inter-arch relationship of primary teeth

Each tooth occludes with two opposing teeth except for the lower central incisors and the upper second molars.

Canine is a key to occlusion in the primary dentition.

Look at the long axis of the canineSlide64

Canine relationship

Long axis of the canine should be placed in the midline between the lower D and C for a class I relationship.Slide65

Inter-arch relationship

Natural wearing away of the canines is an important physiologic process that facilitates movement of the mandible

In children raised on soft food the natural wearing process may be slowed down

May have to carry out selective grinding on primary canines, especially in the presence of a unilateral

crossbite

.