CHAPTER 13: DYNAMICS OF CHANGE

sas +

ectoderm origin

formative tissue: dental organ (epithelial)

final structure: enamel

mesoderm origin

formative tissue 1: dental papilla

final structure: dentin & pulp

formative tissue 2: dental sac

final structure: cementum and PDL

3 phases of gestation (lasts for 9mo)

period of ovum

period of embryo

period of fetus

period of ovum

fertilization to implantation

0-14 days

period of embryo

most important because of the cell differentiation that occurs during this time

-all major organs appear

-2-8 weeks

period of fetus

maturation of the newly formed organs

- 8-40 weeks

Body Changes

No year is more dramatic in terms of growth than the first year of life. - Most children undergo 50% increase in length
- 200% increase in weight
Toward the end of the first year of life, the growth rate slows.

By age 2, a child has the gorss motor skills to run, climb, walk up and down steps.

The nervous system of the child grows dramatically from birth until 3 years.

5 Mesenchymal elevations that constitute the initial feature of the face:

Frontonasal process -2 Maxillary process -2 Mandibular process

[happens during 4th week in utero}

frontnasal + lateral nasal process

the fusion forms upper lip

failure to fuse → cleft

failure to fuse of medial nasal process

results to medial nasal cleft (hair lip)

maxillary process + mandibular process

the fusion forms the cheek

failure to fuse oblique facial cleft

maxillary process + lateral nasal process

failure to fuse transverse facial cleft

embryonic stage of leapfrog pattern

mandible is considerably larger than the maxilla

early fetal stage of leapfrog pattern

maxilla accelerates, outgrowing the mandible

week 11 of leapfrog pattern

mandible surges, equaling the maxilla in size

week 13-20 of leapfrog pattern

mandible lags again

at birth of leapfrog pattern

the infant is born with a mandible that is retrognathic (receded) relative to the maxilla

cranial vault

closer to adult size than any other part of the head

the 6 membrane-filled fontanel gaps allow compression during birth and close by ossification within 2 years

face

extremely underdeveloped

total face height is only 40% of adult size

remodelling

driven by cellular mechanics Osteoblast (bone forming) build up tissue while osteoclast (bone destroying) resorb it, expanding the jaw to accommodate teeth and sinuses

Growth and Development after Birth

At birth, the bones that compose the cranium are not fused and are separated by gaps, called FONTANELS
Gaps close by ossification within 2 years after birth

Face of the Newborn

Tiny mouths
Underdeveloped and receded lower jaw
Face appears broad and flat
Total face height is only 40% of adult face height

Dental Changes

Teeth are formed by tissues originating from both ECTODERMand MESODERM. Ectoderm responsible for the future ENAMEL
Mesoderm responsible for the future PULP AND DENTIN

3 formative tissues:

Dental Organ → forms the Enamel

Dental Papilla → forms the Dentin and pulp

Dental Sac → forms the periodontium (cementum, alveolar bone, PDL)

Initiation

First noticed in the 6-week old fetus -Also recognized as the BUD STAGE.

expansion of the basal layer above the basement membrane

Proliferation

9-10 weeks in utero

The multiplication of the cells of the initiation stage and an expansion of the tooth bud-----tooth germ.

-This occurs for the primary dentition between the ninth and

the tenth week of prenatal development during the fetal

period. This stage is characterized by the continuation of the

As the tooth germs continues to proliferate it produces as caplike appearance. This stage is called the CAP STAGE.

Histodifferentiation

11-12 weeks in utero

Cells begin to specialize
-The cap continues to grow and begins to look like a bell(BELL STAGE)
This occurs for primary dentition between the eleventh and

the twelfth week of prenatal development. It is characterized

by the continuation of the process of proliferation, differentiation and morphogenesis

6 odontogenic steps

elongation of iee → reciprocal induction

differentiation of odontoblasts → reciprocal induction

deposition of dentin → bulk of tooth

deposition of enamel

root formation

cementum, pdl formation

4 types of cells within the enamel/dental organ produced by Differentiation

Inner enamel epithelium

Outer enamel epithelium

Stellate reticulum

Stratum intermedium

Inner enamel epithelium

becomes ameloblasts (enamel producing) → bell stage

concave part

defines the shape of the crown

Outer enamel epithelium

convex part

Stellate reticulum

bulk of dental organ

network of star-shaped central core

Stratum intermedium

nourishes IEE

main structure for enamel formation

fuse of OEE-IEE

root development

cervical loop → hertwig’s epithelial root sheath (defines the shape/form of root)

total # of roots → epithelial diaphragm (most apical segment of HERS) (defines the # of roots)

collapse → reduced enamel epithelium

1 = MN maxillary anterior ; MN 1 PM ; MN maxillary 2PM

2 = MX 1PM ; MN molars

3 = MX molars

clinical anomalies in morphodifferentiation

Amelogenesis imperfecta - failure of ameloblasts to differentiate properly Dentinogenesis imperfecta- failure of odontoblasts to differentiate properly

morphological failure → peg teeth, microdontia

Morphodifferentiation

-Stage at which the cells find an arrangement that ultimately dictates the final size and shape of the tooth.
-AKA ADVANCED BELL STAGE
Korff’s fibers- irregular spiraling fibers from deep in the pulp that entangle with the reticular fibrils from the mesenchyme of the pulp. These long spiraling fibers assist in the structural support of the developing dentin.

Disturbances in morphodifferentition stage will result in abnormal forms & sizes of teeth like peg teeth, microdontia & macrodontia

Apposition

Occurs when the network or the tissue matrix of the tooth is formed.
-The organized special tissues now deposit incremental layers of enamel and dentin matrix

Calcification

Influx of mineral salts within the previously developed tissue matrix -96% inorganic( calcium, phosphorus, etc)
-4% organic material and water

Eruption

The process of elimination of primary teeth is caused by the eruptive pressure of the permanent successor at the apex of the primary tooth and its surroundings.
-Hertwig Epithelial Root Sheath- responsible for the size and shape of the root and eruption of tooth

-Tooth root is approx. 1⁄2 to 2/3 of its final length at the time of gingival emergence. -Mandibular incisors- are the first primary tooth to erupt
-20 primary teeth are completed at the age of 2 and a half to 3 year old.
-Permanent first molars- the only teeth that show a trace of hard tissue formation at birth.

3 phases of eruption:

Preeruptive phase

Eruptive phase(prefunctional)

Eruptive phase(functional)

engine of eruption

HERS

root formation

bone remodelling

cellular proliferation

HERS

dictates the size/shape of root and drives eruption

root formation

pushes against the base of the crypt (root is only ½ - 2/3 final length at emergence

bone remodelling

simultaneously apposition (building) and resorption (destroying by osteoclasts) clears the path

eruption heatmap of primary dentition

6-month start → eruption sequence beings with the primary mn central incisor

3-year finish → by age 2.5-3yrs, all 20 primary teeth have fully erupted into the oral cavity

first PM molars (6-7 yrs) → the only permanent teeth that show a trace of hard tissue formation at the exact moment of birth

sequence highlights:

mn central incisor & first molars: 6-7 yrs

canines & premolars: 9-12yrs

second molars: 11-13 yrs

delays in this sequence can be tied to: genetics, low birth weight, nutritional deficiencies, specific syndromes (down syndromes, regional odontoplasia)

cellular proliferation

connective tissue of the dental papillae expands

Causes of Tooth Eruption

Root formation
Proliferation of HERS
Proliferation of the connective tissue of the dental papillae Growth of the Jaw
Pressure from muscular action
pressure at the apical part of the tooth
Apposition and resorption of bone

Attrition

Wearing of teeth during function
-Normal physiologic process when teeth occlude

Exfoliation

Caused by eruptive pressure of the permanent successor at the apex of the primary tooth and its surroundings. Eruptive pressure stimulates the bone destroying cells, osteoclasts.

nolla’s stages of tooth calcification

nolla’s 6 stage

crown completed

eruptive movement begins

nolla’s 7 stage

1/3 root completed

alveolar crest pierced

nolla’s 8 stage

2/3 root completed

gingival margin pierced

Primary Dentition Development Up to Age 3

Primary teeth begin to form @6 weeks in utero
-The enamel of all the primary teeth is usually completed by the first year of age.
-First primary tooth to erupt-Primary mandibular incisors at 6 months
-All primary teeth erupted at age 2.
1st Molar- first tooth to show tooth germ formation which occurs at age 3 1⁄2 to 4 months in utero At birth, the only permanent teeth that show a trace of hard tissue formation are the FIRST PERMANENT MOLARS.

eruption age of primary dentition

eruption age of permanent dentition

4 areas of cognitive development(by Mussen and coworkers)

Area of perception → young infants only perceive movements, facial relationships, and color

Recognition of information → infants have the ability to recognize the similarity of new objects compared with old ones

Ability to categorize → ability to group things together by shape, color and use as early as 1 year of age

Enhancement of memory → Even young infants have been shown to have some memory and recall past experiences

the developmental triad

the first 3 years of human life represent the most dramatic biological remodelling an individual will ever undergo

this atlas examines that transformation by zooming inward; from staggering mathematics of whole-body growth into the intricate assembly of the face and finally down to the precise cellular choreography of tooth formation

by the end of year 2, there is 75% adult brain capacity and the brain achieves three-quarters of its adult weight

macro → body & cognitive

meso → craniofacial architectures

micro → dental genesis

motor skills of a 6.0 mo

sits alone for 30+ seconds

motor skills of a 8.9 mo

neat pincer grasp

motor skills of a 11.7 mo

walks alone

motor skills of a 24 mo

runs, climbs stairs with both feet, kicks a ball

cognitive development of a 0-4 mo

primary circular reactions, tracks objects

cognitive development of a 9-12 mo

object permanence

finds hidden objects

first real words

cognitive development of a 12-18 mo

tertiary circular reactions

categorizes objects by shape/color

cognitive development of a 24 mo

telegraphic two-word sentences, symbolic play

cephalocaudal growth gradient

frontal-parietal fontanelles

anterior / bregma

close at 12-24 mos / 18 mos

last to close

diamond-shape

intersect of coronal & sagittal suture

frontal-parietal-sphenoidal-temporal fontanelles

sphenoidal / pterion

close at 1-2 mo

thiniest part of the skull

affects MMA → causes hematoma

parietal-occipital fontanelles

posterior / lambda

close at 2 mo

triangular-shaped

parietal-occipital-temporal fontanelles

mastoidal / asterion

close at 1-2 mo

intersect of sagittal and lambdoid suture

2 frontal suture

metopic

frontal-parietal suture

coronal

2 parietal suture

sagittal

parietal-temporal suture

squamosal

parietal-occipital suture

lambdoid

korff’s fibers

long spiraling fibers from deep pulp mesenchyme

entangle to support the developing dentin

practice question in sas