CHAPTER 13: DYNAMICS OF CHANGE

sas + ppt

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

0-14 days

fertilization to implantation

period of embryo

2-8 weeks, all major organs appear

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

period of fetus

8-40 weeks

maturation of the newly formed organs

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 → growth rate slows

• age 2 → good motor skills to run, climb, walk up, down steps

• birth-3y.o → the nervous system of the child grows dramatically

5 mesenchymal elevations 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 may cause cleft

medial nasal process

failure to fuse may cause medial nasal cleft (hair lip)

maxillary process + mandibular process

the fusion forms the cheek

failure to fuse may cause oblique facial cleft

maxillary process + lateral nasal process

failure to fuse may cause 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

11 weeks of leapfrog pattern

mandible surges, equaling the maxilla in size

13-20 weeks 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

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

fontanels

close by ossification within 2 years after birth

refer to the gaps that separate the bones that compose the cranium bc these are not fused

face of the newborn

tiny mouths

face appears broad and flat

underdeveloped and receded lower jaw

total face height is only 40% of adult face height

dental changes

teeth are formed by tissues originating from both ectoderm and mesoderm

• ectoderm responsible for the future enamel

• mesoderm responsible for the future pulp-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

aka: bud stage

first noticed in the 6-week old fetus

expansion of the basal layer above the basement membrane

proliferation

aka: cap stage

9-10 weeks in utero

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

this stage is characterized as the tooth germs continues to proliferate it produces as caplike appearance

histodifferentiation

11-12 weeks in utero, cells begin to specialize

this occurs for primary dentition between the 11th-12th week of prenatal development

it is characterized by the continuation of the process of proliferation, differentiation, morphogenesis

the cap continues to grow and begins to look like a bell (hence the name bell stage)

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

concave part

defines the shape of the crown

becomes ameloblasts (enamel producing) → bell stage

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

collapse → reduced enamel epithelium

cervical loop of HERS → defines the shape/form of root

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

• 1 → mn-mx anterior ; mn 1PM ; mn-mx 2PM

• 2 → mx 1PM ; mn molars

• 3 → mx molars

clinical anomalies in morphodifferentiation

morphological failure → peg teeth, microdontia

amelogenesis imperfecta → failure of ameloblasts to differentiate properly

dentinogenesis imperfecta → failure of odontoblasts to differentiate properly

morphodifferentiation

aka: advanced bell stage

stage at which the cells find an arrangement that ultimately dictates the final size and shape of the tooth

disturbances in this stage will result in abnormal forms & sizes of teeth (ex: peg teeth, microdontia & macrodontia)

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.

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

4% organic material and water

96% inorganic( calcium, phosphorus)

influx of mineral salts within the previously developed tissue matrix

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

HERS → responsible for the size and shape of the root and eruption of tooth

tooth root is approximately 1⁄2-2/3 of its final length at the time of gingival emergence

• mn incisors → are the first primary tooth to erupt

• 2 ½ - 3 y.o → 20 primary teeth are completed

• permanent 1st 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)

eruption heatmap of primary dentition

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

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

6-7 y.o → 1st permanent molars (the only permanent teeth that show a trace of hard tissue formation at the exact moment of birth)

sequence highlights:

• 6-7 y.o: mn central incisor & first molars

• 9-12 y.o: canines & premolars

• 11-13 y.o: 2nd molars

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

growth of the jaw

proliferation of HERS

pressure from muscular action

apposition and resorption of bone

pressure at the apical part of the tooth

proliferation of the connective tissue of the dental papillae

attrition

wearing of teeth during function

normal physiologic process when teeth occlude

exfoliation

eruptive pressure stimulates the osteoclasts (bone destroying cells)

caused by eruptive pressure of the permanent successor at the apex of the primary tooth and its surroundings

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

age 3 1⁄2 to 4 months in utero → 1st permanent molars (the only permanent teeth that show a trace of hard tissue formation)

6 weeks in utero → primary teeth begin to form

at birth → 1st molar (first tooth to show tooth germ formation)

6 mos. → primary mn incisors erupts (first primary tooth to erupt)

1 y.o → the enamel of all the primary teeth is usually completed

age 2 → all primary teeth erupted

eruption age of primary dentition

eruption age of permanent dentition

4 areas of cognitive development by Mussen&coworkers

area of perception → young infants only perceive movements, facial relationships, 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 → 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

note:

• macro → body & cognitive

• meso → craniofacial architectures

• micro → dental genesis

by the end of year 2:

• 75% adult brain capacity

• brain achieves three-quarters of its adult weight

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

tracks objects

primary circular reactions

cognitive development of a 9-12 mo

first real words

object permanence

finds hidden objects

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

close at 1-2 mo

sphenoidal / pterion

thiniest part of the skull

affects MMA → causes hematoma

parietal-occipital fontanelles

close at 2 mo

triangular-shaped

posterior / lambda

parietal-occipital-temporal fontanelles

close at 1-2 mo

mastoidal / asterion

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